GLIDER FLYINGHANDBOOK

2003

U.S. DEPARTMENT OF TRANSPORTATIONFEDERAL AVIATION ADMINISTRATION

Flight Standards Service

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PREFACE

The Glider Flying Handbook is designed as a technical manual for applicants who are preparing for glidercategory rating and for currently certificated glider pilots who wish to improve their knowledge. Certificatedflight instructors will find this handbook a valuable training aid, since detailed coverage of aeronauticaldecision making, components and systems, aerodynamics, flight instruments, performance limitations,ground operations, flight maneuvers, traffic patterns, emergencies, soaring weather, soaring techniques,and cross-country is included. Topics, such as radio navigation and communication, use of flight informa-tion publications, and regulations are available in other Federal Aviation Administration (FAA) publications.

This handbook conforms to pilot training and certification concepts established by the FAA. There are dif-ferent ways of teaching, as well as performing flight procedures and maneuvers, and many variations inthe explanations of aerodynamic theories and principles. This handbook adopts a selective method andconcept to flying gliders. The discussion and explanations reflect the most commonly used practices andprinciples. Occasionally, the word “must” or similar language is used where the desired action is deemedcritical. The use of such language is not intended to add to, interpret, or relieve a duty imposed by Title 14of the Code of Federal Regulations (14 CFR).

It is essential for persons using this handbook to also become familiar with and apply the pertinent partsof 14 CFR and the Aeronautical Information Manual (AIM). Performance standards for demonstrating com-petence required for pilot certification are prescribed in the appropriate glider practical test standard.

This handbook contains all or part of the information found in AC 61-94, Pilot Transition Course for Self-Launching or Powered Sailplanes (Motorgliders). This publication may be purchased from theSuperintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9325, orfrom U.S. Government Bookstores located in major cities throughout the United States.

The current Flight Standards Service airman training and testing material and subject matter knowledgecodes for all airman certificates and ratings can be obtained from the Flight Standards Services web siteat http://av-info.faa.gov.

The FAA gratefully acknolwedges the valuable assistance provided by many individuals and organizationsthroughout the aviation community who contributed their time and talent in publishing this handbook.

Comments regarding this handbook should be sent to U.S. Department of Transportation, Federal AviationAdministration, Airman Testing Standards Branch, AFS-630, P.O. Box 25082, Oklahoma City, OK 73125.

AC 00-2, Advisory Circular Checklist, transmits the current status of FAA advisory circulars andother flight information publications. This checklist is free of charge and may be obtained bysending a request to U.S. Department of Transportation, Subsequent Distribution Office, SVC-121.23, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785. The check -list also is available on the Internet at: http://www.faa.gov/aba/html_policies/ac00_2.html

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Chapter 3—Aerodynamics of FlightAirfoil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

Angle of Attack . . . . . . . . . . . . . . . . . . . . . . 3-1Angle of Incidence . . . . . . . . . . . . . . . . . . . 3-1Center of Pressure . . . . . . . . . . . . . . . . . . . 3-1

Forces of Flight . . . . . . . . . . . . . . . . . . . . . . . . 3-1Lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

Magnus Effect . . . . . . . . . . . . . . . . . . . . 3-2Bernoulli’s Principle . . . . . . . . . . . . . . . . 3-3Newton’s Third Law of Motion . . . . . . . . 3-3

Drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4Parasite Drag . . . . . . . . . . . . . . . . . . . . . 3-4

Form Drag. . . . . . . . . . . . . . . . . . . . . . 3-4Interference Drag . . . . . . . . . . . . . . . . 3-4Skin Friction Drag . . . . . . . . . . . . . . . . 3-4

Induced Drag . . . . . . . . . . . . . . . . . . . . . 3-4Total Drag . . . . . . . . . . . . . . . . . . . . . . . . 3-5Drag Equation . . . . . . . . . . . . . . . . . . . . 3-6Wing Planform . . . . . . . . . . . . . . . . . . . . 3-6Aspect Ratio . . . . . . . . . . . . . . . . . . . . . . 3-7

Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8Thrust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8

Three Axes of Rotation . . . . . . . . . . . . . . . . . . 3-8Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-8

Flutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10Lateral Stability . . . . . . . . . . . . . . . . . . . . . 3-10Directional Stability . . . . . . . . . . . . . . . . . . 3-10

Turning Flight . . . . . . . . . . . . . . . . . . . . . . . . 3-11Rate of Turn . . . . . . . . . . . . . . . . . . . . . . . 3-12Radius of Turn . . . . . . . . . . . . . . . . . . . . . 3-12Turn Coordination. . . . . . . . . . . . . . . . . . . 3-12Slips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12Forward Slip . . . . . . . . . . . . . . . . . . . . . . . 3-13Side Slip . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13Stalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14Spins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

Ground Effect . . . . . . . . . . . . . . . . . . . . . . . . 3-14

Chapter 4—Flight InstrumentsPitot-Static Instruments . . . . . . . . . . . . . . . . . . 4-1

Impact and Static Pressure Lines. . . . . . . . 4-1Airspeed Indicator . . . . . . . . . . . . . . . . . 4-1Indicated Airspeed . . . . . . . . . . . . . . . . . 4-2Calibrated Airspeed . . . . . . . . . . . . . . . . 4-2True Airspeed . . . . . . . . . . . . . . . . . . . . . 4-2Airspeed Indicator Markings. . . . . . . . . . 4-2Other Airspeed Limitations . . . . . . . . . . . 4-3Altimeter . . . . . . . . . . . . . . . . . . . . . . . . . 4-4Principle of Operation . . . . . . . . . . . . . . . 4-4Effect of Nonstandard Pressure And

Temperature . . . . . . . . . . . . . . . . . . . . 4-4

Chapter 1—Introduction to Glider FlyingGliders–The Early Years . . . . . . . . . . . . . . . . . 1-1Glider or Sailplane? . . . . . . . . . . . . . . . . . . . . 1-1Glider Certificate Eligibility Requirements. . . . 1-2Aeronautical Decision Making. . . . . . . . . . . . . 1-2Origins of ADM Training . . . . . . . . . . . . . . . . . 1-2The Decision-Making Process . . . . . . . . . . . . 1-3

Defining the Problem . . . . . . . . . . . . . . . . . 1-4Choosing a Course of Action . . . . . . . . . . . 1-4Implementing the Decision and Evaluating

the Outcome . . . . . . . . . . . . . . . . . . . . . . 1-4Risk Management . . . . . . . . . . . . . . . . . . . . . . 1-4

Assessing Risk . . . . . . . . . . . . . . . . . . . . . . 1-5Factors Affecting Decision Making . . . . . . . . . 1-6

Pilot Self-Assessment. . . . . . . . . . . . . . . . . 1-6Recognizing Hazardous Attitudes . . . . . . . 1-6Stress Management . . . . . . . . . . . . . . . . . . 1-7Use of Resources. . . . . . . . . . . . . . . . . . . . 1-7

Internal Resources . . . . . . . . . . . . . . . . . 1-8External Resources . . . . . . . . . . . . . . . . 1-8

Workload Management . . . . . . . . . . . . . . . 1-8Situational Awareness . . . . . . . . . . . . . . . . 1-9

Obstacles to Maintaining Situational Awareness . . . . . . . . . . . . . . . . . . . . . 1-9

Operational Pitfalls . . . . . . . . . . . . . . . . . . . . . 1-9Medical Factors Associated with Glider Flying1-10

Hypoxia. . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10Hypoxic Hypoxia. . . . . . . . . . . . . . . . . . 1-10Hypemic Hypoxia . . . . . . . . . . . . . . . . . 1-10Stagnant Hypoxia . . . . . . . . . . . . . . . . . 1-10Histotoxic Hypoxia . . . . . . . . . . . . . . . . 1-10

Hyperventilation . . . . . . . . . . . . . . . . . . . . 1-11Middle Ear and Sinus Problems . . . . . . . . 1-11Spatial Disorientation . . . . . . . . . . . . . . . . 1-12Motion Sickness . . . . . . . . . . . . . . . . . . . . 1-13Carbon Monoxide Poisoning . . . . . . . . . . 1-13Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14Dehydration and Heatstroke . . . . . . . . . . . 1-14Alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-15Scuba Diving . . . . . . . . . . . . . . . . . . . . . . 1-16

Chapter 2—Components and SystemsThe Fuselage . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Wings and Components . . . . . . . . . . . . . . . 2-1Lift/Drag Devices. . . . . . . . . . . . . . . . . . . . . . . 2-2The Empennage . . . . . . . . . . . . . . . . . . . . . . . 2-3

Tow Hook Devices . . . . . . . . . . . . . . . . . . . 2-4Powerplant . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4Landing Gear . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Wheel Brakes . . . . . . . . . . . . . . . . . . . . . . . 2-4

CONTENTS

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Setting the Altimeter . . . . . . . . . . . . . . . . 4-5Types of Altitude . . . . . . . . . . . . . . . . . . . . . 4-7Variometer . . . . . . . . . . . . . . . . . . . . . . . . . 4-7Total Energy System . . . . . . . . . . . . . . . . . 4-8Netto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9Electronic Flight Computers . . . . . . . . . . . . 4-9

Magnetic Compass . . . . . . . . . . . . . . . . . . . . 4-11Magnetic Variation . . . . . . . . . . . . . . . . . . 4-12Magnetic Deviation . . . . . . . . . . . . . . . . . . 4-12Compass Errors . . . . . . . . . . . . . . . . . . . . 4-12Acceleration Error. . . . . . . . . . . . . . . . . . . 4-13Turning Error . . . . . . . . . . . . . . . . . . . . . . 4-13Yaw String. . . . . . . . . . . . . . . . . . . . . . . . . 4-14Inclinometer . . . . . . . . . . . . . . . . . . . . . . . 4-14

Gyroscopic Instruments . . . . . . . . . . . . . . . . 4-15Rigidity in Space. . . . . . . . . . . . . . . . . . . . 4-15Precession . . . . . . . . . . . . . . . . . . . . . . . . 4-15Attitude Indicator. . . . . . . . . . . . . . . . . . . . 4-16Heading Indicator . . . . . . . . . . . . . . . . . . . 4-16

G-Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17Outside Air Temperature Gauge . . . . . . . . . . 4-17

Chapter 5—Glider PerformanceFactors Affecting Performance . . . . . . . . . . . . 5-1

Density Altitude. . . . . . . . . . . . . . . . . . . . . . 5-1Pressure Altitude . . . . . . . . . . . . . . . . . . . . 5-1Atmospheric Pressure . . . . . . . . . . . . . . . . 5-1Altitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1Temperature . . . . . . . . . . . . . . . . . . . . . . . . 5-2Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2High and Low Density Altitude Condition . . 5-2Winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

Rate of Climb . . . . . . . . . . . . . . . . . . . . . . . . . 5-5Flight Manuals and Placards . . . . . . . . . . . 5-5

Areas of the Manual . . . . . . . . . . . . . . . . 5-5Placards . . . . . . . . . . . . . . . . . . . . . . . . . 5-6Performance Information . . . . . . . . . . . . 5-6Glider Polars . . . . . . . . . . . . . . . . . . . . . . 5-6Weight and Balance Information . . . . . . 5-8Limitations . . . . . . . . . . . . . . . . . . . . . . . 5-8Terms and Definitions. . . . . . . . . . . . . . 5-10

Center of Gravity . . . . . . . . . . . . . . . . . . . . . . 5-11Problems Associated with CG Forward of

Forward Limit . . . . . . . . . . . . . . . . . . . . 5-11Problems Associated with CG Aft of

the Aft Limit. . . . . . . . . . . . . . . . . . . . . . 5-11Sample Weight and Balance Problems . . . . 5-12

Determining CG Without Loading Charts. 5-12Ballast Weight . . . . . . . . . . . . . . . . . . . . . . . . 5-13Effects of Water Ballast . . . . . . . . . . . . . . . . . 5-13

Chapter 6—Preflight and Ground OperationsAssembly Techniques . . . . . . . . . . . . . . . . . . . 6-1

Trailering. . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

TieDown and Securing . . . . . . . . . . . . . . . . 6-2Ground Handling . . . . . . . . . . . . . . . . . . . . 6-2Launch Equipment Inspection . . . . . . . . . . 6-2Glider Preflight Inspection . . . . . . . . . . . . . 6-4Cockpit Management . . . . . . . . . . . . . . . . . 6-4Personal Equipment . . . . . . . . . . . . . . . . . . 6-4Prelaunch Checklist . . . . . . . . . . . . . . . . . . 6-4

Chapter 7—Launch and Recovery Procedures andFlight Maneuvers

Aerotow Launch Signals . . . . . . . . . . . . . . . . . . . 7-1Pre-Launch Signals for Aerotow Launches 7-1In-Flight Aerotow Visual Signals. . . . . . . . . 7-2

Takeoff Procedures and Techniques. . . . . . . . 7-2Aerotow Takeoffs . . . . . . . . . . . . . . . . . . . . 7-2Normal Takeoffs . . . . . . . . . . . . . . . . . . . . . 7-3Crosswind Aerotow Takeoffs . . . . . . . . . . . 7-3Common Errors . . . . . . . . . . . . . . . . . . . . . 7-4

Takeoff Emergency Procedures . . . . . . . . . . . 7-4Aerotow Climbout and Release Procedures. . 7-6

Common Errors . . . . . . . . . . . . . . . . . . . . . 7-8Aerotow Abnormal Procedures . . . . . . . . . . . . 7-8Slack Line . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10

Common Errors . . . . . . . . . . . . . . . . . . . . 7-10Boxing the Wake . . . . . . . . . . . . . . . . . . . . . . 7-10

Common Errors . . . . . . . . . . . . . . . . . . . . 7-11Ground Launch Takeoff . . . . . . . . . . . . . . . . . 7-11

Ground Launch Signals . . . . . . . . . . . . . . 7-12Pre-launch Signals for Ground Launches 7-

12In-flight Signals for Ground Launches . 7-12

Tow Speeds. . . . . . . . . . . . . . . . . . . . . . . . . . 7-12Automobile Launch. . . . . . . . . . . . . . . . 7-14

Normal Into-the-Wind Ground Launch . . . . . 7-14Crosswind Takeoff and Climb–Ground Launch 7-15Ground Tow Launch–Climbout and Release

Procedures . . . . . . . . . . . . . . . . . . . . . . . . 7-16Common Errors . . . . . . . . . . . . . . . . . . . . 7-16

Abnormal Procedures, Ground Launch . . . . 7-16Emergency Procedures, Ground Launch . . . 7-16Self-Launch Takeoff Procedures . . . . . . . . . . 7-18

Preparation and Engine Start . . . . . . . . . . 7-18Common Errors . . . . . . . . . . . . . . . . . . . . 7-18

Taxiing the Self-Launching Glider . . . . . . . . . 7-18Common Errors . . . . . . . . . . . . . . . . . . . . 7-18

Before Takeoff Check–Self-Launching Glider7-18Common Errors . . . . . . . . . . . . . . . . . . . . 7-18

Normal Takeoff–Self-Launching Glider . . . . . 7-18Crosswind Takeoff–Self-Launching Glider . . 7-19

Common Errors . . . . . . . . . . . . . . . . . . . . 7-19Self-Launch—Climb-Out and ShutDown

Procedures . . . . . . . . . . . . . . . . . . . . . . . 7-20Common Errors . . . . . . . . . . . . . . . . . . . . 7-21

Landings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-21

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Common Errors . . . . . . . . . . . . . . . . . . . . 7-21Emergency Procedures, Self-Launching Glider 7-22Performance Maneuvers, Straight Glides . . . 7-22

Common Errors . . . . . . . . . . . . . . . . . . . . 7-22Turns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-22

Common Errors . . . . . . . . . . . . . . . . . . . . 7-24Steep Turns . . . . . . . . . . . . . . . . . . . . . . . . . . 7-25

Common Errors . . . . . . . . . . . . . . . . . . . . 7-25Spiral Dive . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-25

Common Errors . . . . . . . . . . . . . . . . . . . . 7-26Maneuvering at Minimum Control Airspeed,

Stalls, and Spins . . . . . . . . . . . . . . . . . . . . 7-26Maneuvering at Minimum Controllable Airspeed7-26

Common Errors . . . . . . . . . . . . . . . . . . . . 7-26Stall Recognition and Recovery . . . . . . . . . . 7-26

Advanced Stalls . . . . . . . . . . . . . . . . . . . . 7-28Secondary Stall. . . . . . . . . . . . . . . . . . . . . 7-28Accelerated Stalls . . . . . . . . . . . . . . . . . . . 7-29Crossed-Control Stall . . . . . . . . . . . . . . . . 7-30Common Errors . . . . . . . . . . . . . . . . . . . . 7-31

Spins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-31Entry Phase . . . . . . . . . . . . . . . . . . . . . . . 7-32Incipient Phase. . . . . . . . . . . . . . . . . . . . . 7-32Developed Phase . . . . . . . . . . . . . . . . . . . 7-32Recovery Phase . . . . . . . . . . . . . . . . . . . . 7-32Common Errors . . . . . . . . . . . . . . . . . . . . 7-33

Minimum Sink Airspeed . . . . . . . . . . . . . . . . 7-33Common Errors . . . . . . . . . . . . . . . . . . . . 7-34

Best Glide Airspeed . . . . . . . . . . . . . . . . . . . 7-34Common Errors . . . . . . . . . . . . . . . . . . . . 7-34

Speed-To-Fly . . . . . . . . . . . . . . . . . . . . . . . . . 7-34Common Errors . . . . . . . . . . . . . . . . . . . . 7-34

Traffic Patterns . . . . . . . . . . . . . . . . . . . . . . . 7-34Crosswind Landings . . . . . . . . . . . . . . . . . . . 7-36

Common Errors . . . . . . . . . . . . . . . . . . . . 7-36Slips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-36

Common Errors . . . . . . . . . . . . . . . . . . . . 7-38Downwind Landings . . . . . . . . . . . . . . . . . . . 7-38

Common Errors . . . . . . . . . . . . . . . . . . . . 7-38After-Landing and Securing . . . . . . . . . . . . . 7-38

Chapter 8—Abnormal and Emergency Procedures Porpoising . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1Pilot-Induced Oscillations . . . . . . . . . . . . . . . . 8-1

Pilot-Induced Pitch Oscillations During Launch8-1Factors Influencing PIOS . . . . . . . . . . . . 8-1Improper Elevator Trim Setting . . . . . . . 8-2Improper Wing Flaps Setting . . . . . . . . . 8-2

Pilot-Induced Roll Oscillations During Launch8-3Pilot-Induced Yaw Oscillations During Launch8-3

Gust-Induced Oscillations . . . . . . . . . . . . . . . . 8-4Vertical Gusts During High-Speed Cruise . 8-5Pilot-Induced Pitch Oscillations During Landing8-

5Glider Induced Oscillations . . . . . . . . . . . . . . . 8-5

Pitch Influence of the Glider Towhook Position8-5Self-Launch Glider Oscillations During

Powered Flight . . . . . . . . . . . . . . . . . . . . 8-6Nosewheel Glider Oscillations During

Launches and Landings . . . . . . . . . . . . 8-6Tailwheel/Tailskid Equipped Glider Oscillations

During Launches and Landings . . . . . . . . 8-7Off-Field Landing Procedures . . . . . . . . . . . . . 8-7

After Landing Off-Field . . . . . . . . . . . . . . . . 8-9Off-Field Landing Without Injury. . . . . . . 8-9Off-Field Landing With Injury . . . . . . . . 8-10

Systems and Equipment Malfunctions . . . . . 8-10Flight Instrument Malfunctions . . . . . . . . . 8-10

Airspeed Indicator Malfunctions . . . . . . 8-10Altimeter Malfunctions . . . . . . . . . . . . . 8-10Variometer Malfunctions . . . . . . . . . . . . 8-11Compass Malfunctions . . . . . . . . . . . . . 8-11

Glider Canopy Malfunctions . . . . . . . . . . . 8-11Glider Canopy Open Unexpectedly . . . 8-11Broken Glider Canopy . . . . . . . . . . . . . 8-11Frosted Glider Canopy . . . . . . . . . . . . . 8-11

Water Ballast Malfunctions . . . . . . . . . . . . 8-11Retractable Landing Gear Malfunction . . . 8-11Primary Flight Controls. . . . . . . . . . . . . . . 8-12

Elevator Malfunctions . . . . . . . . . . . . . . 8-12Aileron Malfunctions . . . . . . . . . . . . . . . 8-12Rudder Malfunctions . . . . . . . . . . . . . . 8-13

Secondary Flight Control Systems. . . . . . 8-14Elevator Trim Malfunctions . . . . . . . . . . 8-14Spoiler/Dive Break Malfunctions . . . . . 8-14

Miscellaneous Flight System Malfunctions8-14Towhook Malfunctions . . . . . . . . . . . . . 8-14Oxygen System Malfunctions . . . . . . . . 8-15Drogue Chute Malfunctions . . . . . . . . . 8-15

Self-Launch Gliders . . . . . . . . . . . . . . . . . . . 8-15Self-Launch Glider Engine Failure During

Takeoff or Climb . . . . . . . . . . . . . . . . . . 8-15Inability to Re-start a Self-Launch Glider

Engine While Airborne . . . . . . . . . . . . . 8-16Self-Launch Glider Propeller Malfunctions8-16Self-Launch Glider Electrical System

Malfunctions . . . . . . . . . . . . . . . . . . . . . 8-17In-Flight Fire . . . . . . . . . . . . . . . . . . . . . . . 8-17

Emergency Equipment and Survival Gear . . 8-17Survival Gear Item Checklists . . . . . . . . . 8-17Food and Water . . . . . . . . . . . . . . . . . . . . 8-18Clothing . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18Communication . . . . . . . . . . . . . . . . . . . . . 8-18Navigation Equipment . . . . . . . . . . . . . . . 8-18Medical Equipment . . . . . . . . . . . . . . . . . . 8-18Stowage . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18Oxygen System . . . . . . . . . . . . . . . . . . . . 8-18Parachute . . . . . . . . . . . . . . . . . . . . . . . . . 8-18

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Chapter 9—Soaring WeatherThe Atmosphere . . . . . . . . . . . . . . . . . . . . . . . 9-1

Composition . . . . . . . . . . . . . . . . . . . . . . . . 9-1Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2Temperature . . . . . . . . . . . . . . . . . . . . . . . . 9-2Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2Standard Atmosphere . . . . . . . . . . . . . . . . . 9-3Layers of the Atmosphere . . . . . . . . . . . . . 9-3Scale of Weather Events . . . . . . . . . . . . . . 9-4Thermal Soaring Weather . . . . . . . . . . . . . 9-4Thermal Shape and Structure . . . . . . . . . . 9-5Atmospheric Stability . . . . . . . . . . . . . . . . . 9-6Understanding Soundings . . . . . . . . . . . . . 9-8Air Masses Conducive to Thermal Soaring9-11Cloud Streets . . . . . . . . . . . . . . . . . . . . . . 9-11Thermal Waves . . . . . . . . . . . . . . . . . . . . 9-12Thunderstorms . . . . . . . . . . . . . . . . . . . . . 9-13Weather for Slope Soaring . . . . . . . . . . . . 9-18Wave Soaring Weather . . . . . . . . . . . . . . 9-20Mechanism for Wave Formation . . . . . . . 9-20Lift Due to Convergence. . . . . . . . . . . . . . 9-23Obtaining Weather Information. . . . . . . . . 9-25

Automated Flight Service Stations . . . . 9-25Preflight Weather Briefing . . . . . . . . . . 9-25Direct User Access Terminal System. . 9-26On the Internet . . . . . . . . . . . . . . . . . . . 9-26

Interpreting Weather Charts, Reports, AndForecasts . . . . . . . . . . . . . . . . . . . . . . . 9-27Graphic Weather Charts. . . . . . . . . . . . 9-27Surface Analysis Chart. . . . . . . . . . . . . 9-27Weather Depiction Chart . . . . . . . . . . . 9-27Radar Summary Chart . . . . . . . . . . . . . 9-28US Low-Level Significant Weather

Prognostic Chart . . . . . . . . . . . . . . . . 9-28Winds and Temperatures Aloft . . . . . . . 9-30Composite Moisture Stability Chart . . . 9-30

Printed Reports and Forecasts. . . . . . . . . 9-33Printed Weather Reports . . . . . . . . . . . . . 9-33

Aviation Routine Weather Report . . . . . 9-33Pilot Reports . . . . . . . . . . . . . . . . . . . . . 9-34Radar Weather Reports . . . . . . . . . . . . 9-34

Printed Forecasts . . . . . . . . . . . . . . . . . . . 9-34Terminal Aerodrome Forecast . . . . . . . 9-34Aviation Area Forecast . . . . . . . . . . . . . 9-36Communications and Product Headers 9-36Precautionary Statements . . . . . . . . . . 9-37Synopsis. . . . . . . . . . . . . . . . . . . . . . . . 9-37VFR Clouds and Weather . . . . . . . . . . 9-37

Convective Outlook Chart . . . . . . . . . . . . 9-37Winds and Temperatures Aloft Forecast . 9-38Transcribed Weather Broadcasts . . . . . . . 9-39

Chapter 10—Soaring TechniquesThermal Soaring . . . . . . . . . . . . . . . . . . . . . . 10-1Ridge and Slope Soaring . . . . . . . . . . . . . . . 10-9Wave Soaring . . . . . . . . . . . . . . . . . . . . . . . 10-12

Preflight Preparation. . . . . . . . . . . . . . . . 10-12Getting into the Wave. . . . . . . . . . . . . . . 10-13Flying in the Wave . . . . . . . . . . . . . . . . . 10-15

Soaring Convergence Zones . . . . . . . . . . . 10-18Combined Sources of Updrafts. . . . . . . . . . 10-18

Chapter 11—Cross-Country SoaringFlight Preparation and Planning . . . . . . . . . . 11-1Personal and Special Equipment . . . . . . . . . 11-2Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-4

Using the Plotter . . . . . . . . . . . . . . . . . . . . 11-4A Sample Cross–Country Flight . . . . . . . . . . 11-6Navigation Using GPS . . . . . . . . . . . . . . . . . 11-8Cross-Country Techniques . . . . . . . . . . . . . . 11-8Soaring Faster and Farther . . . . . . . . . . . . . 11-10Special Situations . . . . . . . . . . . . . . . . . . . . 11-13Course Deviations . . . . . . . . . . . . . . . . . . . . 11-13Lost Procedures . . . . . . . . . . . . . . . . . . . . . 11-14Cross-Country Using a Self-Launching Glider11-14High-Performance Glider Operations and

Considerations . . . . . . . . . . . . . . . . . . . . 11-15Cross-Country Using Other Lift Sources . . . 11-16

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Welcome to the world of soaring. The GliderFlying Handbook is designed to help you achieveyour goals in aviation and to provide you with theknowledge and practical information needed toattain private, commercial, and flight instructorcategory ratings in gliders.

GLIDERS — THE EARLY YEARSThe fantasy of flight led people to dream up intri-cate designs in an attempt to imitate the flight ofbirds. Leonardo da Vinci sketched a vision of fly-ing machines in his 15th century manuscripts. Hiswork consisted of a number of wing designsincluding a human-powered ornithopter, derivedfrom the Greek word for bird. Centuries later,when others began to experiment with hisdesigns, it became apparent that the human bodycould not sustain flight by flapping wings likebirds. [Figure 1-1]

GLIDER OR SAILPLANE?The Federal Aviation Administration (FAA)defines a glider as a heavier-than-air aircraftthat is supported in flight by the dynamic reac-tion of the air against its lifting surfaces, andwhose free flight does not depend on an

engine. The term glider is used to designate therating that can be placed on a pilot certificateonce a person successfully completes requiredglider knowledge and practical tests.

Another widely accepted term used in the industryis sailplane. Soaring refers to the sport of flyingsailplanes, which usually includes traveling longdistances and remaining aloft for extended periodsof time. Gliders were designed and built to provideshort flights off a hill down to a landing area. Sincetheir wings provided relatively low lift and high drag,these simple gliders were generally unsuitable forsustained flight using atmospheric lifting forces.The most well known example of a glider is the space shuttle, which liter-ally glides back to earth. The space shuttle, likeg l i d e r s ,cannot sustain flight for long periods of time. Early gliders were easy and inexpensive to build, andthey played an important role in flight training.

Self-launch gliders are equipped with engines, but with the engine shut down, they display the sameflight characteristics as non-powered gliders. Theengine allows them to be launched under their

Figure 1-1. A human-powered ornithopter is virtually incapable of flight due to the dramatic difference in the strength-to-weight ratio ofbirds compared to humans.

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own power. Once aloft, pilots of self-launch gliderscan shut down the engine and fly with the poweroff. The additional training and proceduresrequired to earn a self-launch endorsement arecovered later in this handbook.

GLIDER CERTIFICATE ELIGIBILITY REQUIREMENTSTo be eligible to fly a glider solo, you must be atleast 14 years of age and demonstrate satisfactoryaeronautical knowledge on a test developed byyour instructor. You also must have received andlogged flight training for the maneuvers and pro-cedures in Title 14 of the Code of Federal AviationRegulations (14 CFR) part 61 that are appropriateto the make and model of aircraft to be flown, aswell as demonstrate satisfactory proficiency andsafety. Only after all of these requirements aremet, can your instructor endorse your student cer-tificate and logbook for solo flight.

To be eligible for a private pilot certificate with aglider rating, you must be at least 16 years ofage, complete the specific training and flight timerequirements described in 14 CFR part 61, passa knowledge test, and successfully complete apractical test.

To be eligible for a commercial or flight instructorglider certificate, you must be 18 years of age, complete the specific training requirementsdescribed in 14 CFR part 61, pass the requiredknowledge tests, and pass another practical test.If you currently hold a pilot certificate for a pow-ered aircraft and are adding a glider category rat-ing on that certificate, you are exempt from theknowledge test but must satisfactorily completethe practical test. Certificated glider pilots are notrequired to hold an airman medical certificate tooperate a glider.

AERONAUTICAL DECISION MAKINGAeronautical decision making (ADM) is a system-atic approach to the mental process used by pilotst oconsistently determine the best course of actionin response to a given set of circumstances. Theimportance of learning effective ADM skills cannotbe overemphasized. While progress is continuallybeing made in the advancement of pilot trainingm e t h o d s ,aircraft equipment and systems, and services forpilots, accidents still occur. Despite all the changesin technology to improve flight safety, one factorremains the same—the human factor. It is estimated that 65percent of the total glider accidents are humanfactors related.

Historically, the term “pilot error” has been usedto describe the causes of these accidents. Piloterror means that an action or decision made bythe pilot was the cause of, or a contributing factorthat lead to, the accident. This definition alsoincludes the pilot’s failure to make a decision or take action. From abroader perspective, the phrase “human factorsrelated” more aptly describes these accidentssince it is usually not a single decision that leadsto an accident, but a chain of events triggered bya number of factors.

The poor judgment chain, sometimes referred toas the “error chain,” is a term used to describethis concept of contributing factors in a humanfactors related accident. Breaking one link in the chain normallyis all that is necessary to change the outcome ofthe sequence of events. The following is anexample of the type of scenario illustrating thepoor judgment chain.

An experienced glider pilot returning from across-country flight is approaching a jaggedmountain ridge that lies between him and hishome airport located in the valley below. As henears the ridge he sees people on the top wavingto him in excitement. Overjoyed with having flownover 400 kilometers, he decides to do a low pass over the peak. He is flying into a 30knot headwind that is blowing across the peak.Holding what he feels is adequate airspeed as henears the lee side of the peak, he realizes his alti-tude is not very high in relation to the peak of theridge. As he nears the peak he finds himself in astrong downdraft created by the strong wind blow-ing over the ridge. In an attempt to make a 180°turn to avoid contacting the ridge, the pilot puts hisglider into a steep right turn and pulls back hardon the control stick resulting in an acceleratedstall/spin. In the ensuing crash, the pilot is fatallyinjured and the glider is completely destroyed.

By discussing the events that led to this accident,we can understand how a series of judgmentale r r o r scontributed to the final outcome of this flight. Forexample, one of the first elements that affected the pilot’s flight was his inability to realize that hisdecision-making skills were probably dulled by thelong distance flight, which preceded the accident.The pilot had flown over this ridge a number oftimes and was aware that downdrafts are oftenpresent on the lee side of the peak but had neverhad problems in the past.

Next, he let his desire to show-off for the people onthe mountain peak override his concern for arriving

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events unfolded, each poor decision left him withfewer and fewer options.

ORIGINS OF ADM TRAININGThe airlines developed some of the first training programs that focused on improving ADM.H u m a nfactors-related accidents motivated the airlineindustry to implement crew resource management( C R M )training for flight crews. The focus of CRM pro-grams is the effective use of all availableresources—human resources, hardware, andinformation. Human resources include all groupsroutinely working with the cockpit crew (or pilot)who are involved in decisions required to operatea flight safely. These groups include, but are not

safely at his home airport, and he failed to recog-nize the threat posed by the strong wind blowingover the ridge. Rather than heading straight for theairport, he decided to make a low pass over theridge with insufficient altitude to maintain the FAAmandatory minimums in dangerous wind condi-tions. Next, rather than aborting his attempt to makethe pass over the peak when he realized his alti-tude was not sufficient, he continued to fly towardthe peak rather than making a 180° turn away fromit.

On numerous occasions during the flight, the pilotcould have made effective decisions that mayh a v eprevented this accident. However, as the chain of

Figure 1-2. These terms are used in AC 60-22 to explain concepts used in ADM training.

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limited to: ground, maintenance, and flight per-sonnel. Although the CRM concept originated asairlines developed ways of facilitating crew coop-eration to improve decision making in the cockpit,CRM principles, such as workload management,situational awareness, communication, the lead-ership role of the captain, and crewmember coor-dination have direct application to the generalaviation cockpit. This also includes single pilotoperations, since pilots of small aircraft, as wellas crews of larger aircraft, must make effectiveuse of all available resources—human resources,hardware, and information. You can also refer toAC 60-22, Aeronautical Decision Making, whichprovides background references, definitions, andother pertinent information about ADM training inthe general aviation environment. [Figure 1-2]

THE DECISION-MAKING PROCESSAn understanding of the decision-making process provides you with a foundation for developingADM skills. Some situations, such as towropebreaks, require you to respond immediately, usingestablished procedures, with little time for detailedanalysis. Traditionally, pilots have been welltrained to react to emergencies, but are not aswell prepared to make decisions that require amore reflective response. Typically during a flight,you have time to examine any changes that occur,gather information, and assess risk before reach-ing a decision. The steps leading to this conclu-sion constitute the decision-making process.

DEFINING THE PROBLEMProblem definition is the first step in the decision-making process. Defining the problem begins withrecognizing that a change has occurred or that anexpected change did not occur. A problem is per-ceived first by the senses, then is distinguishedthrough insight and experience. These same abili-ties, as well as an objective analysis of all availableinformation, are used to determine the exact natureand severity of the problem.

While going through your pre-landing checklist,you discover that your landing gear is stuck inthe retracted position.

CHOOSING A COURSE OF ACTIONAfter the problem has been identified, you mustevaluate the need to react to it and determine theactions that need to be taken to resolve the situa-tion in the time available. The expected outcomeof each possible action should be considered andthe risks assessed before you decide on aresponse to the situation.

Your first thought was to try to thermal back up tobuy yourself some time and see if you could get

the landing gear freed. After weighing the conse-quences of not finding lift and not focusing on fly-ing the glider, you realize your only course is tomake a gear-up landing. You plan to land on thegrass runway to the east of the paved runway toavoid causing extensive damage to your gliderand allow for a softer touchdown.

IMPLEMENTING THE DECISION ANDEVALUATING THE OUTCOMEAlthough a decision may be reached and acourse of action implemented, the decision-mak-ing process is not complete. It is important to thinkahead and determine how the decision couldaffect other phases of the flight. As the flight pro-gresses, you must continue to evaluate the out-come of the decision to ensure that it is producingthe desired result.

As you make your turn to downwind, you realize atractor mowing the field is in the middle of thegrass runway. At this point you make the decisionto land on the paved runway with as smooth a touchdownas possible. You make a normal pattern andapproach to landing and perform a minimumenergy touchdown, at which point the glider’s bellycontacts the pavement and grinds to a stop wingslevel, causing only minor damage to the glider’sunderside.

The decision making process normally consistso fseveral steps before you choose a course ofaction. To help you remember the elements of thedecision-making process, a six-step model hasbeen developed using the acronym “DECIDE.”[Figure 1-3]

RISK MANAGEMENTDuring each flight, decisions must be maderegarding events that involve interactionsbetween the four risk elements—the pilot in com-mand, the aircraft, the environment, and the oper-

Figure 1-3. The DECIDE model can provide a framework foreffective decision making.

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ation. The decision-making process involves anevaluation of each of these risk elements to achieve an accurate perception of theflight situation. [Figure 1-4]

One of the most important decisions that a pilot incommand must make is the go/no-go decision.Evaluating each of these risk elements can help you decide whether a flight should be conductedor continued. Let us evaluate the four risk ele-ments and how they affect our decision makingregarding the following situations.

Pilot—As a pilot, you must continually make deci-sions about your own competency, condition ofhealth, mental and emotional state, level of fatigue,and many other variables. For example, you planfor an extended cross-country flight. You have hadonly a few hours of sleep, and you are concernedthat the congestion you feel could be the onset of acold. Are you safe to fly?

Aircraft—You will frequently base decisions on yourevaluations of the aircraft, such as performance,equipment, or airworthiness. Picture yourself in thefollowing situation. You are on a cross-country flightand have begun to fly over extremely rugged ter-rain, which covers the next 20 miles of your plannedroute and will not allow you to land safely should theneed arise. The thermals are beginning to dissipateand your altitude is 3,000 feet above ground level(AGL). Should you continue to fly over this terrain?

Environment—This encompasses many elementsnot pilot or aircraft related. It can include such fac-tors as weather, air traffic control, navaids, terrain,takeoff and landing areas, and surrounding obsta-cles. Weather is one element that can change dras-tically over time and distance. Imagine you areflying on a cross-country flight when you encounterunexpected snow squalls and declining visibility inan area of rising terrain. Do you try to stay aloft andstay clear of the snow or land at the airport locatedin the valley below as soon as possible?

Operation—The interaction between you as the pilot,your aircraft, and the environment is greatly influ-

Figure 1-4. When situationally aware, you have an overview of the total operation and are not fixated on one perceived significant factor.

Figure 1-5. Statistical data can identify operations that have the highest risk.

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enced by the purpose of each flight operation. Youm u s tevaluate the three previous areas to decide on the desirability of undertaking or continuing the flight asplanned. It is worth asking yourself why the flight isbeing made, how critical is it to maintain theschedule, and is the trip worth the risks? Forinstance, you are giving glider rides at a busy commercial glider operation located near a mountain range on anextremely windy and turbulent day with strongdowndrafts. Would it be better to wait for better conditions to ensure safe flight? How would your priorities change if your boss told you he only wantedyou to take one more flight and then you could call ita day?

ASSESSING RISKExamining National Transportation Safety Board(NTSB) reports and other accident research canhelp you to assess risk more effectively. Fore x a m p l e ,studies indicate the types of flight activities thatare most likely to result in the most serious acci-dents. For gliders, takeoff and landing accidentsconsistently account for over 90 percent of thetotal number of accidents in any given year.

Causal factors for takeoff accidents are evenlydivided between loss of directional control, collisionwith obstructions during takeoff, mechanical factors,and a premature termination of the tow. Accidentsoccurring during the landing phase of flight consis-tently account for an overwhelming majority of injuryto pilots and damage to aircraft. This has proven tobe especially true during recent years in whichapproximately 80 percent of all glider accidentsoccurred during the landing phase

of flight. Accidents are more likely during takeoffand landing because the tolerance for error isg r e a t l ydiminished and opportunities for pilots to overcomeerrors in judgment and decision-making becomeincreasingly limited. The most common causal fac-tors for landing accidents include collision withobstructions in the intended landing area. [Figure1-5]

FACTORS AFFECTING DECISION MAKINGIt is important to point out the fact that beingfamiliar with the decision-making process doesnot ensure that you will have the good judgmentto be a safe pilot. The ability to make effectivedecisions as pilot in command depends on a number of factors.S o m ecircumstances, such as the time available to

Figure 1-7. You must be able to identify hazardous attitudes andapply the appropriate antidote when needed.

Figure 1-6. Prior to flight, you should assess your fitness, just asyou evaluate the aircraft’s airworthiness.

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make a decision, may be beyond your control.However, you can learn to recognize those fac-tors that can be managed and learn skills toimprove decision-making ability and judgment.

PILOT SELF-ASSESSMENTThe pilot in command of an aircraft is directlyresponsible for, and is the final authority as to, theo p e r a t i o nof that aircraft. In order to effectively exercise thatresponsibility and make effective decisionsregarding the outcome of a flight, you must havean understanding of your limitations. Your per-formance during a flight is affected by many fac-tors, such as health, recency of experience,knowledge, skill level, and attitude.

Exercising good judgment begins prior to takingthe controls of an aircraft. Often, pilots thoroughlycheck their aircraft to determine airworthiness,

yet do not evaluate their own fitness for flight. Justas a checklist is used when preflighting an aircraft,a personal checklist based on such factors asexperience, currency, and comfort level can helpdetermine if you are prepared for a particularflight. Specifying when refresher training shouldbe accomplished and designating weather mini-mums, which may be higher than those listed inTitle 14 of the Code of Federal Regulations (14CFR) part 91, are elements that may be includedon a personal checklist. In addition to a review ofpersonal limitations, you should use the I’MSAFE Checklist to further evaluate your fitnessfor flight. [Figure 1-6]

RECOGNIZING HAZARDOUS ATTITUDESBeing fit to fly depends on more than just yourphysical condition and recency of experience.For example, attitude affects the quality of yourdecisions. Attitude can be defined as a personal

Figure 1-8. You should examine your decisions carefully to ensure that your choices have not been influenced by a hazardous attitude.

Figure 1-9. The three types of stressors that can affect a pilot’s performance.

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motivational predisposition to respond to per-sons, situations, or events in a given manner.Studies have identified five hazardous attitudesthat can interfere with your ability to make sounddecisions and exercise authority properly. [Figure 1-7]

Hazardous attitudes can lead to poor decisionmaking and actions that involve unnecessary risk.You must examine your decisions carefully toensure your choices have not been influenced byh a z a r d o u sattitudes, and you must be familiar with positivealternatives to counteract the hazardous attitudes.These substitute attitudes are referred to as anti-dotes. During a flight operation, it is important tobe able to recognize a hazardous attitude, cor-rectly label the thought, and then recall its anti-dote. [Figure 1-8]

STRESS MANAGEMENTEveryone is stressed to some degree all the time.A certain amount of stress is good since it keeps aperson alert and prevents complacency.However, effects of stress are cumulative and, ifnot coped with adequately, eventually add up toan intolerable burden. Performance generallyincreases with the onset of stress, peaks, andthen begins to fall off rapidly as stress levelsexceed a person’s ability to cope. The ability tomake effective decisions during flight can beimpaired by stress. Factors, referred to as stres-sors, can increase a pilot’s risk of error in the cock-pit. [Figure 1-9]

There are several techniques to help manage theaccumulation of life stresses and prevent stressoverload. For example, including relaxation time ina busy schedule and maintaining a program ofphysical fitness can help reduce stress levels.Learning to manage time more effectively can helpyou avoid heavy pressures imposed by gettingbehind schedule and not meeting deadlines. Takean assessment of yourself to determine yourcapabilities and limitations and then set realisticgoals. In addition, avoiding stressful situationsand encounters can help you cope with stress.

USE OF RESOURCESTo make informed decisions during flight opera-tions, you must be aware of the resources foundboth inside and outside the cockpit. Since usefultools and sources of information may not alwaysbe readily apparent, learning to recognize theseresources is an essential part of ADM training.Resources must not only be identified, but youmust develop the skills to evaluate whether you

have the time to use a particular resource and theimpact that its use will have upon the safety offlight. For example, the assistance of air trafficcontrol (ATC) may be very useful if you are notsure of your location. However, in an emergencysituation when action needs be taken quickly,time may not be available to contact ATC immedi-ately.

INTERNAL RESOURCESInternal resources are found in the cockpit duringflight. Since some of the most valuable internalresources are ingenuity, knowledge, and skill,you can expand cockpit resources immensely byimproving these capabilities. This can be accom-plished by frequently reviewing flight informationpublications, such as the CFRs and theAeronautical Information Manual (AIM), as wellas by pursuing additional training.

A thorough understanding of all the equipmentand systems in the aircraft is necessary to fullyutilize all resources. For example, satellite navi-gation systems are valuable resources. However,if pilots do not fully understand how to use thisequipment, or they rely on it so much that theybecome complacent, it can become a detrimentto safe flight.

Checklists are essential cockpit resources for ver-ifying that the aircraft instruments and systemsare checked, set, and operating properly, as wellas ensuring that the proper procedures are per-formed if there is a system malfunction or in-flightemergency. Other valuable cockpit resourcesinclude current aeronautical charts, and publica-tions, such as the Airport/Facility Directory(A/FD).

Passengers can also be a valuable resource.Passengers can help watch for traffic and maybe able to provide information in an irregular sit-uation, especially if they are familiar with flying. Astrange smell or sound may alert a passenger to

Figure 1-10. Task requirements vs. pilot capabilities.

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a potential problem. As pilot in command, youshould brief passengers before the flight to makesure they are comfortable voicing any concerns.

EXTERNAL RESOURCESPossibly the greatest external resources duringflight are air traffic controllers and flight servicespecialists. ATC can help decrease pilot workloadby providing traffic advisories, radar vectors,and assistance in emergency situations. Flightservice stations can provide updates onweather, answer questions about airport condi-tions, and may offer direction-finding assis-tance. The services provided by ATC can beinvaluable in enabling you to make informed in-flight decisions.

WORKLOAD MANAGEMENTEffective workload management ensures thatessential operations are accomplished by plan-ning, prioritizing, and sequencing tasks to avoidwork overload. As experience is gained, youlearn to recognize future workload requirementsand can prepare for high workload periods duringtimes of low workload. Reviewing the appropriatechart and setting radio frequencies well in advance of when they areneeded helps reduce workload as your flightnears the airport. In addition, you should listento the Automatic Terminal Information Service(ATIS), Automated Surface Observing System(ASOS), or Automated Weather ObservingSystem (AWOS), if available, and then monitorthe tower frequency or the Common TrafficAdvisory Frequency (CTAF) to get a good ideaof what traffic conditions to expect. Checklistsshould be performed well in advance so there istime to focus on traffic and ATC instructions.These procedures are especially important priorto entering a high-density traffic area, such asClass B airspace.

To manage workload, items should be prioritized.For example, during any situation, and especiallyin an emergency, you should remember thephrase “aviate, navigate, and communicate.” Thismeans that the first thing you should do is makesure the glider is under control. Then begin flyingto an acceptable landing area. Only after the firsttwo items are assured, should you try to commu-nicate with anyone.

Another important part of managing workload isrecognizing a work overload situation. The firsteffect of high workload is that you begin to workfaster. As workload increases, attention cannot bedevoted to several tasks at one time, and youmay begin to focus on one item. When you

become task saturated, there is no awareness ofinputs from various sources, so decisions may bemade on incomplete information, and the possi-bility of error increases.

Accidents often occur when flying task require-ments exceed pilot capabilities. The differencebetween these two factors is called the margin ofsafety. Note that in this example, the margin ofsafety is minimal during the approach and land-ing. At this point, an emergency or distractioncould overtax pilot capabilities, causing an acci-dent. [Figure 1-10]

Figure 1-11. All experienced pilots have fallen prey to, or havebeen tempted by, one or more of these tendencies in their flyingcareers.

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When becoming overloaded, you should stop,think, slow down, and prioritize. It is important thatyou understand options that may be available todecrease workload.

SITUATIONAL AWARENESSSituational awareness is the accurate percep-tion of the operational and environmental fac-tors that affect the aircraft, pilot, andpassengers during a specific period of time.Maintaining situational awareness requires anunderstanding of the relative significance ofthese factors and their future impact on theflight. When situationally aware, you have anoverview of the total operation and are not fix-ated on one perceived significant factor. Someof the elements inside the aircraft to be consid-ered are the status of aircraft systems, you asthe pilot, and passengers. In addition, an aware-ness of the environmental conditions of theflight, such as spatial orientation of the glider,and its relationship to terrain, traffic, weather,and airspace must be maintained.

To maintain situational awareness, all of the skillsinvolved in aeronautical decision making areused. For example, an accurate perception ofyour fitness can be achieved through self-assess-ment and recognition of hazardous attitudes. Aclear assessment of the status of navigationequipment can be obtained through workloadmanagement, and establishing a productive relationship with ATC can be accomplished byeffective resource use.

OBSTACLES TO MAINTAINING SITUATIONAL AWARENESSFatigue, stress, and work overload can cause youto fixate on a single perceived important itemrather than maintaining an overall awareness ofthe flight situation. A contributing factor in manyaccidents is a distraction that diverts the pilot’s attention frommonitoring the instruments or scanning outsidet h eaircraft. Many cockpit distractions begin as aminor problem, such as a gauge that is not read-ing correctly, but result in accidents as the pilotdiverts attention to the perceived problem andneglects to properly control the aircraft.

Complacency presents another obstacle to main-taining situational awareness. When activitiesbecome routine, you may have a tendency torelax and not put as much effort into performance.Like fatigue, complacency reduces your effective-ness in the cockpit. However, complacency is

harder to recognize than fatigue, since everythingis perceived to be progressing smoothly. Forexample, you have been flying multiple gliderrides out of an uncontrolled airport. The wind hasbeen calm, and you have been using the samerunway all day. Without thinking, you enter down-wind without taking the wind direction intoaccount. As you make your turn to final, you real-ize that your groundspeed is extremely fast. Youovershoot the runway and collide with a fence,causing extensive damage to the glider and injur-ing your passenger.

OPERATIONAL PITFALLSThere are a number of classic behavioral trapsinto which pilots have been known to fall. Pilots,particularly those with considerable experience,as a rule, always try to complete a flight asplanned, please passengers, and meet sched-ules. The basic drive to meet or exceed goalscan have an adverse effect on safety, and canimpose an unrealistic assessment of pilotingskills under stressful conditions. These tenden-cies ultimately may bring about practices that aredangerous and often illegal, and may lead to amishap. You will develop awareness and learn toavoid many of these operational pitfalls througheffective ADM training. [Figure 1-11]

MEDICAL FACTORS ASSOCIATEDWITH GLIDER FLYINGA number of physiological effects can be linkedto flying. Some are minor, while others are impor-tant enough to require special attention to ensuresafety of flight. In some cases, physiological fac-tors can lead to in-flight emergencies. Someimportant medical factors that you should beaware of as a glider pilot include hypoxia, hyper-ventilation, middle ear and sinus problems, spa-tial disorientation, motion sickness, carbonmonoxide poisoning, stress and fatigue, dehy-dration, and heatstroke. Other subjects includethe effects of alcohol and drugs, and excessnitrogen in the blood after scuba diving.

HYPOXIAHypoxia occurs when the tissues in the body donot receive enough oxygen. The symptoms ofhypoxia vary with the individual. Hypoxia can becaused by several factors, including an insuffi-cient supply of oxygen, inadequate transportationof oxygen, or the inability of the body tissues touse oxygen. The forms of hypoxia are divided intofour major groups based on their causes; hypoxichypoxia, hypemic hypoxia, stagnant hypoxia, andhistotoxic hypoxia.

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HYPOXIC HYPOXIAAlthough the percentage of oxygen in the atmos-phere is constant, its partial pressure decreasesproportionately as atmospheric pressuredecreases. As you ascend during flight, the per-centage of each gas in the atmosphere remainsthe same, but there are fewer molecules avail-

able at the pressure required for them to passbetween the membranes in your respiratorysystem. This decrease of oxygen molecules atsufficient pressure can lead to hypoxic hypoxia.

HYPEMIC HYPOXIAWhen your blood is not able to carry a sufficientamount of oxygen to the cells in your body, a con-dition called hypemic hypoxia occurs. This type ofhypoxia is a result of a deficiency in the blood,rather than a lack of inhaled oxygen, and can becaused by a variety of factors. For example, if youhave anemia, or a reduced number of healthyfunctioning blood cells for any reason, your bloodhas a decreased capacity for carrying oxygen. Inaddition, any factor that interferes or displacesoxygen that is attached to the blood’s hemoglobincan cause hypemic hypoxia. The most commonform of hypemic hypoxia is carbon monoxide poi-soning, which is discussed later. Hypemic hypoxiaalso can be caused by the loss of blood thatoccurs during a blood donation. Your blood cantake several weeks to return to normal following adonation. Although the effects of the blood lossare slight at ground level, there are risks when fly-ing during this time.

STAGNANT HYPOXIAStagnant hypoxia is an oxygen deficiency in thebody due to the poor circulation of the blood.Several different situations can lead to stagnanthypoxia, such as shock, the heart failing to pumpblood effectively, or a constricted artery. Duringflight, stagnant hypoxia can be the result of pullingexcessive positive Gs. Cold temperatures also

can reduce circulation and decrease the bloodsupplied to extremities.

HISTOTOXIC HYPOXIAThe inability of the cells to effectively use oxygenis defined as histotoxic hypoxia. The oxygen maybe inhaled and reach the cell in adequateamounts, but the cell is unable to accept the oxy-gen once it is there. This impairment of cellularrespiration can be caused by alcohol and otherdrugs, such as narcotics and poisons. Researchhas shown that drinking one ounce of alcohol canequate to about an additional 2,000 feet of physiological altitude.

High-altitude flying, which glider pilots encounterwhen mountain wave soaring or thermal soaringat high elevations, can place you in danger ofbecoming hypoxic. Oxygen starvation causes thebrain and other vital organs to become impaired.One particularly noteworthy attribute of the onsetof hypoxia is the fact that the first symptoms areeuphoria and a carefree feeling. With increasedoxygen starvation, your extremities become lessresponsive, and your flying becomes less coordi-nated. The following are common symptoms ofhypoxia.

• Headache• Decreased Reaction Time• Impaired Judgment• Euphoria• Visual Impairment• Drowsiness• Lightheaded or Dizzy Sensation• Tingling in Fingers and Toes• Numbness• Blue Fingernails and Lips (Cyanosis)• Limp Muscles

As hypoxia worsens, your field of vision begins tonarrow, and instruments can start to look fuzzy.Even with all these symptoms, the intoxicatingeffects of hypoxia can cause you to have a falsesense of security and deceive you into believingyou are flying as well as ever. The treatment forhypoxia includes flying at lower altitudes and/orusing supplemental oxygen.

All pilots are susceptible to the effects of oxygenstarvation, regardless of your physicalendurance or acclimatization. When flying athigh altitudes, it is paramount that you carry avi-ator’s breathing oxygen in your glider and haveit readily accessible. The term “time of usefulconsciousness” is used to describe the maxi -mum time you have to make rational, life-savingdecisions and carry them out at a given altitude

Figure1-12. This illustration shows the symptoms of hypoxia andtime of useful consciousness as altitude increases.

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without supplemental oxygen. As altitudeincreases above 10,000 feet, the symptoms ofhypoxia increase in severity, while the time ofuseful consciousness rapidly decreases.[Figure 1-12]

Since symptoms of hypoxia vary in an individ-ual, the ability to recognize hypoxia can begreatly improved by experiencing and witness-ing the effects of it during an altitude chamber“flight.” The FAA provides this opportunitythrough aviation physiology training, which isconducted at the FAA Civil Aerospace MedicalInstitute (CAMI) and at many military facilitiesacross the United States. To attend thePhysiological Training Program at CAMI tele-phone (405) 954-6212 or write:

FAA/AAM-400Aerospace Medical Education DivisionP.O. Box 25082Oklahoma City, OK 73125

HYPERVENTILATIONHyperventilation occurs when you are experiencingemotional stress, fright, or pain, and your breathingrate and depth increase although the carbon diox-ide is already at a reduced level in the blood. Theresult is an excessive loss of carbon dioxide fromyour body, which can lead to unconsciousness dueto the respiratory system’s overriding mechanism toregain control of breathing.

Glider pilots encountering extreme, unexpectedturbulence, or strong areas of sink over roughterrain or water, may unconsciously increasetheir breathing rate. If you are flying at higher

altitudes, either with or without oxygen, you mayhave a tendency to breathe more rapidly thannormal, which often leads to hyperventilation.

Since many of the symptoms of hyperventilationare similar to those of hypoxia, it is important tocorrectly diagnose and treat the proper condition.If you are using supplemental oxygen, check theequipment and flow rate to ensure you are not suf-fering from hypoxia. The following are commonsymptoms of hyperventilation.

• Headache• Decreased Reaction Time• Impaired Judgment• Euphoria• Visual Impairment• Drowsiness• Lightheaded or Dizzy Sensation• Tingling in Fingers and Toes• Numbness• Pale, Clammy Appearance• Muscle Spasms

Hyperventilation may produce a pale, clammyappearance and muscle spasms compared to thecyanosis and limp muscles associated withhypoxia. The treatment for hyperventilationinvolves restoring the proper carbon dioxide levelin the body. Breathing normally is both the bestprevention and the best cure for hyperventilation.In addition to slowing the breathing rate, you alsocan breathe into a paper bag or talk aloud to over-come hyperventilation. Recovery is usually rapidonce the breathing rate is returned to normal.

Figure 1-13. The semicircular canals lie in three planes, and sense the motions of roll, pitch, and yaw.

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MIDDLE EAR AND SINUS PROBLEMSSince gliders are not pressurized, pressurechanges affect glider pilots flying to high altitudes.Inner ear pain and a temporary reduction in yourability to hear is caused by the ascents anddescents of the glider. The physiological explana-tion for this discomfort is a difference between thepressure of the air outside your body and that ofthe air inside your middle ear. The middle ear cav-ity is a small cavity located in the bone of the skull.While the external ear canal is always at the samepressure as the outside air, the pressure in themiddle ear often changes more slowly. Even aslight difference between external pressure andmiddle ear pressure can cause discomfort.

During a climb, as the glider ascends, middle earair pressure may exceed the pressure of the air inthe external ear canal, causing the eardrum tobulge outward. You become aware of this pres-sure change when you experience alternate sen-sations of “fullness” and “clearing.” Duringdescent, the reverse happens. While the pressureof the air in the external ear canal increases, themiddle ear cavity, which equalized with the lowerpressure at altitude, is at lower pressure than theexternal ear canal. This results in the higher out-side pressure, causing the eardrum to bulgeinward.

This condition can be more difficult to relieve dueto the fact that air must be introduced into the mid-dle ear through the eustachian tube to equalizethe pressure. The fact that the inner ear is a par-tial vacuum tends to constrict the walls of theeustachian tube. To remedy this often painful con-dition, which causes temporary reduction in hear-ing sensitivity, pinch your nostrils shut, close yourmouth and lips, and blow slowly and gently in themouth and nose.

This procedure, which is called the Valsalvamaneuver, forces air up the eustachian tube intothe middle ear. If you have a cold, an ear infection,or sore throat, you may not be able to equalize thepressure in your ears. A flight in this condition canbe extremely painful, as well as damaging to youreardrums. If you are experiencing minor conges-tion, nose drops or nasal sprays may reduce thechance of a painful ear blockage. Before you useany medication, check with an aviation medicalexaminer to ensure that it will not affect your abilityto fly.

During ascent and descent, air pressure in thesinuses equalizes with the pressure in the cockpitthrough small openings that connect the sinusesto the nasal passages. Either an upper respira-

tory infection, such as a cold or sinusitis, or anasal allergic condition can produce enough con-gestion around an opening to slow equalizationand, as the difference in pressure between thesinus and the cockpit mounts, eventually plug theopening. This “sinus block” occurs most fre-quently during descent. Slow descent rates canreduce the associated pain. A sinus block canoccur in the frontal sinuses, located above eacheyebrow, or in the maxillary sinuses, located in eachupper cheek. It will usually produce excruciatingpain over the sinus area. A maxillary sinus block canalso make the upper teeth ache. Bloody mucus maydischarge from the nasal passages.

You can prevent a sinus block by not flying withan upper respiratory infection or nasal allergiccondition. Adequate protection is usually not pro-vided by decongestant sprays or drops to reducecongestion around the sinus openings. Oraldecongestants have side effects that can impairpilot performance. If a sinus block does not clearshortly after landing, a physician should be con-sulted.

SPATIAL DISORIENTATIONSpatial disorientation specifically refers to the lackof orientation with regard to position in space andto other objects. Orientation is maintained throughthe body’s sensory organs in three areas: visual,vestibular, and postural. The eyes maintain visualorientation; the motion sensing system in theinner ear maintains vestibular orientation; and thenerves in the skin, joints, and muscles of the bodymaintain postural orientation.

During flight in visual meteorological conditions(VMC), the eyes are the major orientation sourceand usually prevail over false sensations fromo t h e rsensory systems. When these visual cues aretaken away, as they are in instrument meteorolog-ical conditions (IMC), false sensations can causethe pilot to quickly become disoriented.

The vestibular system in the inner ear allows youto sense movement and determine your orienta-tion in the surrounding environment. In both theleft and right inner ear, three semi-circular canalsare positioned at approximate right angles toeach other. Each canal is filled with fluid and hasa section full of fine hairs. Acceleration of theinner ear in any direction causes the tiny hairs todeflect, which in turn stimulates nerve impulses,sending messages to the brain. The vestibularnerve transmits the impulses from the utricle,saccule, and semicircular canals to the brain tointerpret motion. [Figure 1-13]

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The postural system sends signals from the skin,joints, and muscles to the brain that are inter-preted in relation to the Earth’s gravitational pull.These signals determine posture. Inputs fromeach movement update the body’s position to thebrain on a constant basis. “Seat of the pants” fly-ing is largely dependent upon these signals. Usedin conjunction with visual and vestibular clues,these sensations can be fairly reliable. However,because of the forces acting upon the body in cer-tain flight situations, many false sensations canoccur due to acceleration forces overpoweringgravity.

Under normal flight conditions, when you have reference to the horizon and ground, these sen-sitive hairs allow you to identify the pitch, roll,and yaw movement of the glider. When youbecome disoriented and lose visual reference tothe horizon and ground, the sensory system inyour inner ear is no longer reliable. Lackingvisual reference to the ground, your vestibularsystem may lead you to believe you are in levelflight, when, in reality, you are in a turn. As the airspeed increases, youmay experience a postural sensation of a leveldive and pull back on the stick. This increasedback-pressure on the control stick tightens theturn and creates ever-increasing g-loads. If recovery is not initi-ated, a steep spiral will develop. This is some-times called the graveyard spiral, because if thepilot fails to recognize that the aircraft is in a spi-ral and fails to return the aircraft to wings-levelflight, the aircraft will eventually strike theground. If the horizon becomes visible again,you will have an opportunity to return the gliderto straight-and-level flight. Continued visual con-tact with the horizon will allow you to maintainstraight-and-level flight. However, if you losecontact with the horizon again, your inner earmay fool you into thinking you have started abank in the other direction, causing the grave-yard spiral to begin all over again.

For glider pilots, prevention is the best remedyfor spatial disorientation. If the glider you are fly-ing is not equipped for instrument flight, and youdo not have many hours of training in controllingthe glider by reference to instruments, youshould avoid flight in reduced visibility or at nightwhen the horizon is not visible. You can reduceyour susceptibility to disorienting illusions through training and aware-ness, and learning to rely totally on your flightinstruments.

MOTION SICKNESSMotion sickness, or airsickness, is caused by thebrain receiving conflicting messages about thestate of the body. You may experience motionsickness during initial flights, but it generally goes away within thefirst 10 lessons. Anxiety and stress, which youmay feel as you begin flight training, can con-tribute to motion sickness. Symptoms of motionsickness include general discomfort, nausea, dizzi-ness, paleness, sweating, and vomiting.

It is important to remember that experiencing air sickness is no reflection on your ability as a pilot.Let your flight instructor know if you are prone tomotion sickness since there are techniques thatcan be used to overcome this problem. For exam-ple, you may want to avoid lessons in turbulentconditions until you are more comfortable in theglider, or start with shorter flights and graduate tolonger instruction periods. If you experiencesymptoms of motion sickness during a lesson, you can alleviate some of the discomfortby opening fresh air vents or by focusing ono b j e c t soutside the glider. Although medication likeDramamine can prevent airsickness in passen-gers, it is not recommended while you are flyingsince it can cause drowsiness.

CARBON MONOXIDE POISONINGOne factor that can affect your vision and conscious-n e s sin flight and poses a danger to self-launch glider pilotsis carbon monoxide poisoning. Since it attaches itselfto the hemoglobin about 200 times more easily thandoes oxygen, carbon monoxide (CO) prevents thehemoglobin from carrying oxygen to the cells. Itcan take up to 48 hours for the body to dispose ofcarbon monoxide. If the poisoning is severe enough, it can result in death.Carbon monoxide, produced by all internal com-bustion engines, is colorless and odorless. Aircraftheater vents and defrost vents may provide carbonmonoxide a passageway into the cabin, particu-larly if the engine exhaust system is leaky or dam-aged. If you detect a strong odor of exhaust gases,you can assume that carbon monoxide is present.However, carbon monoxide may be present in dan-gerous amounts even if you cannot detect exhaustodor. Disposable, inexpensive carbon monoxidedetectors are widely available. In the presence ofcarbon monoxide, these detectors change color toalert you to the presence of carbon monoxide.Some effects of carbon monoxide poisoninginclude headache, blurred vision, dizziness,drowsiness, and/or loss of muscle power. Anytime

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you smell exhaust odor, or any time you experi-ence these symptoms, immediate correctiveactions should be taken. These include turning offthe heater, opening fresh air vents, windows andusing supplemental oxygen, if available.

STRESSStress can be defined as the body’s response tophysical and psychological demands placed uponit. Reactions of your body to stress include therelease of chemical hormones (such as adrenaline) into the blood andthe speeding of the metabolism to provide energyto the muscles. In addition, blood sugar, heart rate,respiration, blood pressure, and perspiration allincrease. The term stressor is used to describe anelement that causes you to experience stress.

Stress falls into two categories: acute stress(short-term) and chronic stress (long-term). Acutestress involves an immediate threat that is per-ceived as danger. This is the type of stress thatoften involves a “fight or flight” response in anindividual, whether the threat is real or imagined.Stressors are categorized on page 1-7 within thestress management discussion. Examplesinclude noise (physical stress), fatigue (physio-logical stress), and difficult work or personal situ-ations (psychological stress). Normally, a healthyperson can cope with acute stress and preventstress overload. However, on-going acute stresscan develop into chronic stress.

Chronic stress can be defined as a level of stressthat presents an intolerable burden, exceeds theability of an individual to cope, and causes per-formance to fall sharply. Unrelenting psychologi-cal pressures such as loneliness, financialworries, and relationship or work problems, canproduce a cumulative level of stress that exceedsa person’s ability to cope with the situation. Whenstress reaches these levels, performance falls offrapidly. Pilots experiencing this level of stress arenot safe and should not exercise their airman priv-ileges. The stress management discussion onpage 1-7 contains several recommendations forcoping with stress. If you suspect you are suffer-ing from chronic stress, consult your doctor.

FATIGUEFatigue is frequently associated with pilot error.Some of the effects of fatigue include degradationof attention and concentration, impaired coordi-nation, and decreased ability to communicate.These factors can seriously influence your abilityto make effective decisions. Physical fatigue canresult from sleep loss, exercise, or physical work.Factors, such as stress and prolonged perform-

ance of cognitive work, can result in mentalfatigue.

Fatigue falls into two broad categories; acutefatigue (short-term) and chronic fatigue (long-term). Acute fatigue is short-lived and is a normaloccurrence in everyday living. It is the kind oftiredness people feel after a period of strenuouseffort, excitement, or lack of sleep. Rest afterexertion and eight hours of sound sleep ordinarilycures this condition.

A special type of acute fatigue, skill fatigue hastwo main effects on performance:

• Timing disruption—You appear to performa task as usual, but the timing of eachcomponent is slightly off. This makes thepattern of the operation less smooth,because you perform each component asthough it were separate, instead of part ofan integrated activity.

• Disruption of the perceptual field—Youconcentrate your attention upon move-ments or objects in the center of your visionand neglect those in the periphery. Thismay be accompanied by loss of accuracyand smoothness in control movements.

Acute fatigue has many causes, but the followingare among the most important for the pilot.

• Mild hypoxia (oxygen deficiency)• Physical stress• Psychological stress• Depletion of physical energy resulting

from psychological stress

Acute fatigue can be prevented by a proper dietand adequate rest and sleep. A well-balanced dietprevents the body from having to consume itsown tissues as an energy source. Adequate restmaintains the body’s store of vital energy.

Sustained psychological stress accelerates theglandular secretions that prepare the body for quickreactions during an emergency. These secretionsmake the circulatory and respiratory systems workharder, and the liver releases energy to provide theextra fuel needed for brain and muscle work. Whenthis reserve energy supply is depleted, the bodylapses into chronic fatigue.

Chronic fatigue, extending over a long period oftime, usually has psychological roots, although anunderlying disease is sometimes responsible.Continuous high stress levels, for example, canproduce chronic fatigue. Chronic fatigue is notrelieved by proper diet and adequate rest and sleep, and usually requires

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treatment from your doctor. You may experiencethis condition in the form of weakness, tiredness,palpitations of the heart, breathlessness,headaches, or irritability. Sometimes chronicfatigue even creates stomach or intestinal prob-lems and generalized aches and pains through-out the body. When the condition becomes serious enough, it can lead to emotional illness.

If you find yourself suffering from acute fatigue,stay on the ground. If you become fatigued in thecockpit, no amount of training or experience canovercome the detrimental effects. Getting ade-quate rest is the only way to prevent fatigue fromoccurring. You should avoid flying when you havenot had a full night’s rest, when you have beenworking excessive hours, or have had an espe-cially exhausting or stressful day. If you suspectyou are suffering from chronic fatigue, consultyour doctor.

DEHYDRATION AND HEATSTROKEDehydration is the term given to a critical loss ofwater from the body. The first noticeable effect ofdehydration is fatigue, which in turn makes topphysical and mental performance difficult, if notimpossible. As a glider pilot, you often fly for along period of time in hot summer temperaturesor at high altitudes. This makes you particularlysusceptible to dehydration for two reasons: theclear canopy offers no protection from the sunand, at high altitude, there are fewer air pollutantsto diffuse the sun’s rays. The result is that youare continually exposed to heat that your bodyattempts to regulate by perspiration. If this fluid isnot replaced, fatigue progresses to dizziness,weakness, nausea, tingling of hands and feet,abdominal cramps, and extreme thirst.

Heatstroke is a condition caused by any inabilityof the body to control its temperature. Onset ofthis condition may be recognized by the symp-toms of dehydration, but also has been known tobe recognized only by complete collapse. To prevent these symptoms, itis recommended that you carry an ample supplyof water and use it at frequent intervals on anylong flight, whether you are thirsty or not. Wearinglight colored, porous clothing and a hat providesprotection from the sun, and keeping the cockpitwell ventilated aids in dispelling excess heat.

ALCOHOLEveryone knows that alcohol impairs the effi-ciency of the human mechanism. Studies havepositively proven that drinking and performancedeterioration are closely linked. Pilots must makehundreds of decisions, some of them time-criti-cal, during the course of a flight. The safe out-come of any flight depends on your ability tomake the correct decisions and take the appropri-ate actions during routine occurrences, as well asabnormal situations. The influence of alcoholdrastically reduces the chances of completingyour flight without incident. Even in smallamounts, alcohol can impair your judgement,decrease your sense of responsibility, affect yourcoordination, constrict your visual field, diminishyour memory, reduce your reasoning power, andlower your attention span. As little as one ounceof alcohol can decrease the speed and strengthof your muscular reflexes, lessen the efficiency ofyour eye movements while reading, and increasethe frequency at which you commit errors.Impairments in vision and hearing occur at alco-hol blood levels as low as .01 percent.

The alcohol consumed in beer and mixed drinks is simply ethyl alcohol, a central nervous systemdepressant. From a medical point of view, it acts on

Figure 1-14. Scuba divers must not fly for specific time periodsfollowing dives to avoid the bends.

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your body much like a general anesthetic. The“dose” is generally much lower and more slowly con-sumed in the case of alcohol, but the basic effectson the system are similar. Alcohol is easily andquickly absorbed by the digestive tract. The blood-stream absorbs about 80 to 90 percent of the alco-hol in a drink within 30 minutes on an emptystomach. The body requires about three hours to riditself of all the alcohol contained in one mixed drinkor one beer.

When you have a hangover, you are still under the influence of alcohol. Although you may think thatyou are functioning normally, the impairment ofmotor and mental responses still remains.Considerable amounts of alcohol can remain in thebody for over 16 hours, so you should be cautiousabout flying too soon after drinking.

The effect of alcohol is greatly multiplied when a person is exposed to altitude. Two drinks on theground are equivalent to three or four at altitude.The reason for this is that, chemically, alcoholinterferes with the brain’s ability to utilize oxygen.The effects are rapid because alcohol passes soquickly into the bloodstream. In addition, the brainis a highly vascular organ that is immediately sen-sitive to changes in the blood’s composition. For apilot, the lower oxygen availability at altitude, along with the lower capability of the brainto use what oxygen is there, adds up to a deadlycombination.

Intoxication is determined by the amount of alco-hol in the bloodstream. This is usually measuredas a percentage by weight in the blood. 14 CFRpart 91 requires that your blood alcohol level beless than .04 percent and that eight hours passbetween drinking alcohol and piloting an aircraft. Ifyou have a blood alcohol level of .04 percent orgreater after eight hours, you cannot fly until yourblood alcohol falls below that amount. Eventhough your blood alcohol may be well below .04 percent, you cannot fly sooner than eight hoursafter drinking alcohol. Although the regulations are

quite specific, it is a good idea to be more conser-vative than the regulations.

DRUGSPilot performance can be seriously degraded byboth prescribed and over-the-counter medica-tions, as well as by the medical conditions forwhich they are taken. Many medications, such astranquilizers, sedatives, strong pain relievers, andcough-suppressants, have primary effects thatmay impair judgment, memory, alertness, coordi-nation, vision, and the ability to make calculations.Others, such as antihistamines, blood pressuredrugs, muscle relaxants, and agents to controldiarrhea and motion sickness, have side effectsthat may impair the same critical functions. Anymedication that depresses the nervous system,such as a sedative, tranquilizer, or antihistamine,can make a pilot much more susceptible tohypoxia.

Pain killers can be grouped into two broad cate-gories: analgesics and anesthetics. Over-the-counter analgesics, such as aspirin and codeine,are drugs that decrease pain. The majority of thedrugs that contain acetylsalicylic acid (Aspirin),acetaminophen (Tylenol), and ibuprofen (Advil)have few side effects when taken in the correctdosage. Although some people are allergic to cer-tain analgesics or may suffer from stomach irrita-tion, flying usually is not restricted when takingthese drugs. However, flying is almost always pre-cluded while using prescription analgesics, suchas Darvon, Percodan, Demerol, and codeine,since these drugs may cause side effects such asmental confusion, dizziness, headaches, nausea,and vision problems.

Anesthetics are drugs that deaden pain or cause aloss of consciousness. These drugs are commonlyused for dental and surgical procedures. Most local anes-thetics used for minor dental and outpatient proce-dures wear off within a relatively short period oftime. The

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anesthetic itself may not limit flying so much asthe actual procedure and subsequent pain.

Stimulants are drugs that excite the central nerv-o u ssystem and produce an increase in alertness andactivity. Amphetamines, caffeine, and nicotine areall forms of stimulants. Common uses of thesedrugs include appetite suppression, fatiguereduction, and mood elevation. Some of these drugs may cause a stim-ulant reaction, even though this reaction is nottheir primary function. In some cases, stimulantscan produce anxiety and mood swings, both of which are dan-gerous when you fly.

Depressants are drugs that reduce the body’s func-tioning in many areas. These drugs lower bloodpressure, reduce mental processing, and slowmotor and reaction responses. There are severaltypes of drugs that can cause a depressing effecton the body, including tranquilizers, motion sickness medication, sometypes of stomach medication, decongestants, andantihistamines. The most common depressant isalcohol.

Some drugs, which can neither be classified asstimulants nor depressants, have adverseeffects on flying. For example, some forms ofantibiotics can produce dangerous side effects,such as balance disorders, hearing loss, nausea, and vomiting. While manyantibiotics are safe for use while flying, the infec-tion requiring the antibiotic may prohibit flying. Inaddition, unless specifically prescribed by aphysician, you should not take more than onedrug at a time, and you should never mix drugswith alcohol, because the effects are oftenunpredictable.

The danger of illegal drugs also are well docu-mented. Certain illegal drugs can have hallucina-tory effects that occur days or weeks after thedrug is taken. Obviously, these drugs have noplace in the aviation community.

Federal Aviation Regulations prohibit pilots from performing crewmember duties while using anymedication that affects the faculties in any waycontrary to safety. The safest rule is not to fly as acrewmember while taking any medication, unlessapproved to do so by the FAA. If there is any doubtregarding the effects of any medication, consult anAviation Medical Examiner (AME) before flying.

SCUBA DIVINGThe reduction of atmospheric pressure thataccompanies flying can produce physical prob-lems for scuba divers. This is because theincreased pressure of the water during a divecauses excess nitrogen to be absorbed into thebody tissues and bloodstream. When flying,reduced atmospheric pressures at altitude allowthis nitrogen to come out of solution in the blood-stream and body tissues at a rapid rate. Thisrapid outgassing of nitrogen is called the bendsand is painful and incapacitating. The bends canbe experienced from as low as 8,000 feet meansea level (MSL), with increasing severity as alti-tude increases. As noted in the AIM, the mini-mum recommended time between scuba divingon nondecompression stop dives and flying is 12hours, while the minimum time recommendedbetween decompression stop diving and flying is24 hours. [Figure 1-14]

2-1

Although gliders come in an array of shapes and sizes,the basic design features of most gliders are fundamen-tally the same. All gliders conform to the aerodynamicprinciples that make flight possible. When air flowsover the wings of a glider, the wings produce a forcecalled lift that allows the aircraft to stay aloft. Gliderwings are designed to produce maximum lift with min-imum drag.

Glider airframes are designed with a fuselage, wings,and empennage or tail section. Self-launch gliders areequipped with an engine that enables them to launchwithout assistance and return to an airport underengine power if soaring conditions deteriorate.

THE FUSELAGEThe fuselage is the portion of the airframe to which thewings and empennage are attached. The fuselagehouses the cockpit and contains the controls for theglider, as well as a seat for each occupant. Glider fuse-lages can be formed from wood, fabric over steel tub-ing, aluminum, fiberglass, kevlar or carbon fibercomposites, or a combination of these materials.[Figure 2-1]

WINGS AND COMPONENTSGlider wings incorporate several components, whichhelp the pilot in maintaining the attitude of the glider

Figure 2-1. Components of a glider.

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and changes the wing’s chord line. Both of these factors increase the lifting capacity of the wing. Theslotted flap is similar to the plain flap. In addition tochanging the wing’s camber and chord line, it alsoallows a portion of the higher pressure air beneath the wing to travel through a slot. This increases the velocity of the airflow over the flap and providesadditional lift.

Another type of flap is the Fowler flap. When extended,it moves rearward as well as down. This rearward motionincreases the total wing area, as well as the camber andchord line. Negative flap is used at high speeds wherewing lift reduction is desired to reduce drag.

When the flaps are extended in an upward direction, ornegative setting, the camber of the wing is reduced,resulting in a reduction of lift produced by the wing at afixed angle of attack and airspeed.

and controlling lift and drag. These include ailerons,as well as lift and drag devices, such as spoilers, divebrakes, and flaps.

The ailerons control movement around the longitudi -nal axis. This is known as roll. The ailerons areattached to the outboard tailing edge of each wing andmove in the opposite direction from each other.

Moving the control stick to the right causes the rightaileron to deflect upward and the left aileron to deflectdownward. The upward deflection of the right ailerondecreases the camber resulting in decreased lift on theright wing. The corresponding downward deflectionof the left aileron increases the camber resulting inincreased lift on the left wing. Thus, the increased lifton the left wing and decreased lift on the right wingcauses the glider to roll to the right.

LIFT/DRAG DEVICESGliders are equipped with devices that modify the liftand drag of the wing. High drag devices include spoil-ers, dive brakes, and flaps. Spoilers extend from theupper surface of the wing interrupting or spoiling the airflow over the wings. This action causes the glider todescend more rapidly. Dive brakes extend from both theupper and lower surfaces of the wing and help to increasedrag. [Figure 2-2]

Flaps are located on the trailing edge of the wing, inboardof the ailerons, and can be used to increase lift, drag, anddescent rate. When the glider is cruising at moderate air-speeds in wings-level flight, the flaps are set to zerodegree deflection and are in trail with the wing. When theflap is extended downward, wing camber is increased,and the lift and the drag of the wing increase.

There are several different types of flaps. [Figure 2-3]The plain flap is the simplest of the four types. Whendeflected downward, it increases the effective camber

Figure 2-2. Types of lift/drag devices.

Figure 2-3. The four different types of flaps.

THE EMPENNAGEThe empennage includes the entire tail section, con-sisting of fixed surfaces, such as the horizontal stabi-lizer and the vertical fin, or stabilizer. These two fixedsurfaces act like the feathers on an arrow to steady theglider and help maintain a straight path through the air.The movable surfaces include the elevator and the rud-der. [Figure 2-4]

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The elevator is attached to the back of the horizontalstabilizer. The elevator controls movement around thelateral axis. This is known as pitch. During flight, theelevator is used to move the nose up and down, whichcontrols the pitch attitude of the glider. The trim tabnormally located on the elevator of the glider lessensthe resistance you feel on the flight controls due to theairflow over the associated control surface.

The rudder is attached to the back of the vertical stabilizer. The rudder controls movement about the vertical axis. This is known as yaw. The rudder is usedin combination with the ailerons and elevator to coor-dinate turns during flight.

Some gliders use a stabilator , which is a one-piece horizontal stabilizer used in lieu of an elevator. Thestabilator pivots up and down on a central hinge point.When you pull back on the control stick, the nose of the glider moves up; when you push forward, thenose moves down. Stabilators sometimes employ an anti-servo trim tab to achieve pitch trim. The anti-servotab provides a control feel comparable to that of an elevator. [Figure 2-5]

Trim devices reduce pilot workload by relieving thepressure required on the controls to maintain a desiredairspeed. One type of trim device found on gliders iscalled an elevator trim tab. The elevator trim tab is asmall, hinged, cockpit-adjustable tab on the trailingedge of the elevator. Other types of elevator trimdevices include bungee spring systems and ratchet trim systems. In these systems, fore and aft controlstick pressure is applied by an adjustable spring orbungee cord.

Figure 2-4. The empennage components.

Figure 2-5. Empennage components and trim tabs.

the soaring conditions deteriorate. Self-launch glidersdiffer widely in terms of engine location and type ofpropeller.

Some are equipped with a fixed, nose-mounted engineand a full feathering propeller. On other types of self-launch gliders, the engine and propeller are located aftof the cockpit. When the engine and propeller are notin use, they are retracted into the fuselage, reducingdrag and increasing soaring performance. These typesof self-launch engines are usually coupled to a foldingpropeller, so the entire powerplant can be retractedand the bay doors closed and sealed. [Figure 2-7]

Some gliders are equipped with sustainer engines toassist in remaining aloft long enough to return to an airport. However, sustainer engines do not provide sufficient power to launch the glider from the groundwithout external assistance. A more detailed explanationof engine operations can be found in Chapter 7—Launch and Recovery Procedures and Flight Maneuvers.

LANDING GEARGliders feature a nose skid or wheel, a swiveling tailwheel, and wheels or protective metal brackets at thewingtips. Gliders designed for high speed and low dragoften feature a fully retractable main landing gear and asmall break away tail wheel or tail skid. Break awaytail skids are found on high performance gliders, andare designed to break off when placed under side loads.[Figure 2-8]

WHEEL BRAKESThe wheel brake, mounted on the main landing gearwheel, helps the glider slow down or stop after touch-down. The type of wheel brake often depends on thedesign of the glider. Many early gliders relied on fric-tion between the nose skid and the ground to come to astop. Current models of gliders are fitted with drumbrakes, disc brakes, and friction brakes. The mostcommon type of wheel brake found in modern glidersis the disc brake, which is very similar to the disc brakeon the front wheels of most cars. Most glider discbrakes are hydraulically operated to provide maximumbraking capability. Wheel brake controls vary fromone glider type to another.

Over the years, the shape of the empennage has seen dif-ferent forms. Early gliders were most often built with thehorizontal stabilizer mounted at the bottom of the verti-cal stabilizer. This type of tail arrangement is called theconventional tail. Other gliders were designed with aT-tail, and still others were designed with V-tail. T-tailgliders have the horizontal stabilizer mounted on the top of the vertical stabilizer, forming a T. V-tails have two tail surfaces mounted to form a V.V-tails combine elevator and rudder movements.

TOWHOOK DEVICESAn approved towhook is a vital part of glider equip-ment. The towhook is designed for quick release whenthe pilot applies pressure to the release handle. As asafety feature, if back pressure from either getting outof position during the tow or over running the towrope,the release will automatically open. Part of the gliderpilot’s preflight is to ensure the towhook releases prop-erly with applied forward and back pressure.

The glider may have a towhook located on or under thenose and/or under the center of gravity (CG), near themain landing gear. The forward towhook is used foraerotow. The CG hook is used for ground launch. If theglider has only a CG hook, it may be approved for aero-tow in accordance with the Glider Flight Manual/Pilot’s Operating Handbook. [Figure 2-6]

POWERPLANTSelf-launch gliders are equipped with engines powerfulenough to enable them to launch without external assis-tance. The engines also may be used to sustain flight if

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Figure 2-7. Self-launch gliders are different in performance, as well as appearance.

Figure 2-6. Towhook locations.

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Figure 2-8. Some gliders have fixed main wheels, others have retractable main wheels. Nose skids, or nosewheels, tail wheels and wing tip wheels are found on many gliders.

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To understand what makes a glider fly, you need to have an understanding of aerodynamics. This chapter discusses the fundamentals of the aerodynamics offlight.

AIRFOILAirfoil is the term used for surfaces on a glider thatproduce lift. Although many different airfoil designsexist, all airfoils produce lift in a similar manner.

Some airfoils are designed with an equal amount ofcurvature on the top and bottom surface. These arecalled symmetrical airfoils. Airfoils that have a different curvature on the bottom of the wing whencompared to the top surface are asymmetrical.

The term camber refers to the curvature of a wingwhen looking at a cross section. A wing possessesupper camber on its top surface and lower camber onits bottom surface. The term leading edge is used todescribe the forward edge of the airfoil. The rear edgeof the airfoil is called the trailing edge. The chord lineis an imaginary straight line drawn from the leadingedge to the trailing edge.

Relative wind is created by the motion of an airfoilthrough the air. Relative wind may be affected bymovement of the glider through the air, as well as windsheer. When a glider is flying through undisturbed air,the relative wind is represented by its forward velocityand is parallel to and opposite of the direction of flight.

ANGLE OF ATTACKThe angle of attack is the angle formed between the relative wind and the chord line of the wing. You havedirect control over angle of attack. By changing thepitch attitude of the glider in flight through the use ofthe elevator/stabilator, you are changing the angle ofattack of the wings. [Figure 3-1]

ANGLE OF INCIDENCEThe wings are usually mounted to the fuselage withthe chord line inclined upward at a slight angle. Thisangle, called the angle of incidence, is built into the

glider by the manufacturer and cannot be adjusted bythe pilot’s movements of the controls. It is representedby the angle between the chord line of the wing andthe longitudinal axis of the glider.

CENTER OF PRESSUREThe point along the wing chord line where lift is considered to be concentrated is called the center ofpressure . For this reason, the center of pressure issometimes referred to as the center of lift. On a typicalasymmetrical airfoil, this point along the chord linechanges position with different flight attitudes. Itmoves forward as the angle of attack increases and aftas the angle of attack decreases.

FORCES OF FLIGHTThree forces act on an unpowered glider while inflight—lift, drag, and weight. Thrust is another force offlight that enables self-launch gliders to launch on theirown and stay aloft when soaring conditions subside.The theories that explain how these forces work include

Figure 3-1. Aerodynamic terms of an airfoil.

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Magnus Effect, Bernoulli’s Principle, and Newton’slaws of motion. [Figure 3-2]

LIFTLift opposes the downward force of weight and is pro-duced by the dynamic effects of the surroundingairstream acting on the wing. Lift acts perpendicular tothe flight path through the wing’s center of lift. There isa mathematical relationship between lift, angle ofattack, airspeed, altitude, and the size of the wing. In thelift equation, these factors correspond to the terms coef-ficient of lift, velocity, air density, and wing surfacearea. The relationship is expressed in Figure 3-3.

This shows that for lift to increase, one or more of thefactors on the other side of the equation must increase.Lift is proportional to the square of the velocity, or air-speed, therefore, doubling airspeed quadruples theamount of lift if everything else remains the same.Likewise, if other factors remain the same while thecoefficient of lift increases, lift also will increase. Thecoefficient of lift goes up as the angle of attack isincreased. As air density increases, lift increases.However, you will usually be more concerned withhow lift is diminished by reductions in air density on ahot day, or as you climb higher.

MAGNUS EFFECTThe explanation of lift can best be explained by look-ing at a cylinder rotating in an airstream. The localvelocity near the cylinder is composed of the airstreamvelocity and the cylinder’s rotational velocity, whichdecreases with distance from the cylinder. On a cylin-der, which is rotating in such a way that the top surfacearea is rotating in the same direction as the airflow, thelocal velocity at the surface is high on top and low onthe bottom.

As shown in Figure 3-4, at point “A,” a stagnationpoint exists where the airstream line meets on the sur-face and then splits; some air goes over and someunder. Another stagnation point exists at “B,” wherethe two air streams rejoin and resume at identicalvelocities. We now have upwash ahead of the rotatingcylinder and downwash at the rear.

Figure 3-2. The forces that act on a glider in flight.

Figure 3-3. The lift equation is mathematicallyexpressed by the above formula.

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The difference in surface velocity accounts for a dif-ference in pressure, with the pressure being lower onthe top than the bottom. This low pressure area pro-duces an upward force known as the “Magnus Effect.”This mechanically induced circulation illustrates therelationship between circulation and lift.

BERNOULLI’S PRINCIPLEAn airfoil with a positive angle of attack develops aircirculation as its sharp trailing edge forces the rearstagnation point to be aft of the trailing edge, while thefront stagnation point is below the leading edge.[Figure 3-5]

Air flowing over the top surface accelerates. The air-foil is now subjected to Bernoulli’s Principle, or the“venturi effect.” As air velocity increases through theconstricted portion of a venturi tube, the pressuredecreases. Compare the upper surface of an airfoilwith the constriction in a venturi tube that is narrowerin the middle than at the ends. [Figure 3-6]

The upper half of the venturi tube can be replaced bylayers of undisturbed air. Thus, as air flows over theupper surface of an airfoil, the camber of the airfoilcauses an increase in the speed of the airflow. Theincreased speed of airflow results in a decrease in pres-sure on the upper surface of the airfoil. At the sametime, air flows along the lower surface of the airfoil,building up pressure. The combination of decreasedpressure on the upper surface and increased pressureon the lower surface results in an upward force.[Figure 3-7]

As angle of attack is increased, the production of lift isincreased. More upwash is created ahead of the airfoilas the leading edge stagnation point moves under theleading edge, and more downwash is created aft of thetrailing edge. Total lift now being produced is perpen-dicular to relative wind. In summary, the production oflift is based upon the airfoil creating circulation in theairstream (Magnus Effect) and creating differentialpressure on the airfoil (Bernoulli’s Principle).

NEWTON’S THIRD LAW OF MOTIONAccording to Newton’s Third Law of Motion, “forevery action there is an equal and opposite reaction.”Thus, the air that is deflected downward also producesan upward (lifting) reaction. The wing’s construction isdesigned to take advantage of certain physical laws thatgenerate two actions from the airmass. One is a posi-tive pressure lifting action from the airmass below the

Figure 3-4. Magnus Effect.

Figure 3-5. Stagnation points on an airfoil.

Figure 3-6. The upper surface of an airfoil is similarto the constriction in a venturi tube.

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wing, and the other is a negative pressure lifting actionfrom the lowered pressure above the wing.

As the airstream strikes the relatively flat lower surfaceof the wing when inclined at a small angle to its direc-tion of motion, the air is forced to rebound downward,causing an upward reaction in positive lift. At the sametime, airstream striking the upper curve section of theleading edge of the wing is deflected upward, over thetop of the wing. The speed up of air on the top of thewing produces a sharp drop in pressure. Associatedwith the lowered pressure is downwash, a downward-backward flow. In other words, a wing shaped to causean action on the air, and forcing it downward, will pro-vide an equal reaction from the air, forcing the wingupward. If a wing is constructed in such form that itwill cause a lift force greater than the weight of theglider, the glider will fly.

If all the required lift was obtained from the deflection ofair by the lower surface of the wing, a glider would needonly a flat wing like a kite. This, of course, is not thecase at all. The balance of the lift needed to support theglider comes from the flow of air above the wing.Herein lies the key to flight. The fact that the most lift isthe result of the airflow downwash from above the wing,forcing the wing upward, must be thoroughly understoodin order to continue further in the study of flight.

It is neither accurate nor does it serve a useful purpose,however, to assign specific values to the percentage oflift generated by the upper surface of the airfoil versusthat generated by the lower surface. These are not con-stant values, and will vary, not only with flight condi-tions, but also with different wing designs.

DRAGThe force that resists the movement of the gliderthrough the air is called drag. Two different types ofdrag combine to form total drag—parasite and induced.

PARASITE DRAGParasite drag is caused by any aircraft surface, whichdeflects or interferes with the smooth airflow aroundthe glider. Parasite drag is divided into three types—form drag, interference drag, and skin friction drag.[Figure 3-8]

FORM DRAGForm drag results from the turbulent wake caused bythe separation of airflow from the surface of a struc-ture. The amount of drag is related to both the size andshape of the structure protruding into the relative wind.[Figure 3-9]

INTERFERENCE DRAGInterference drag occurs when varied currents of airover a glider meet and interact. Placing two objectsadjacent to one another may produce turbulence 50 per-cent to 200 percent greater than the parts tested sepa-rately. An example of interference drag is the mixing ofair over structures, such as the wing, tail surfaces, andwing struts.

SKIN FRICTION DRAGSkin friction drag is caused by the roughness of theglider’s surfaces. Even though the surfaces may appearsmooth, they may be quite rough when viewed under amicroscope. This roughness allows a thin layer of airto cling to the surface and create small eddies, whichcontribute to drag.

INDUCED DRAGThe airflow circulation around the wing generatesinduced drag as it creates lift. The high-pressure air beneath the wing joins the low-pressure air above the wing at the trailing edge of the wingtips. This causes a spiral or vortex that trails behind eachwingtip whenever lift is being produced. These

Figure 3-8. Parasite drag increases fourfold when air-speed is doubled.

wingtip vortices have the effect of deflecting theairstream downward in the vicinity of the wing, creat-ing an increase in downwash. Therefore, the wing oper-ates in an average relative wind, which is deflecteddownward and rearward near the wing. Because the liftproduced by the wing is perpendicular to the relativewind, the lift is inclined aft by the same amount. Thecomponent of lift acting in a rearward direction isinduced drag. [Figure 3-10]

As the air pressure differential increases with anincrease in the angle of attack, stronger vortices formand induced drag is increased. The wings of a gliderare at a high angle of attack at low speed and at a lowangle of attack at high speed.

TOTAL DRAGTotal drag on a glider is the sum of parasite andinduced drag. The total drag curve represents thesecombined forces and is plotted against airspeed.[Figure 3-11]

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Figure 3-11. The low point on the total drag curveshows the airspeed at which drag is minimized.

High pressure air joins low pressure air at the trailing edge of the wing and wingtips.

Wingtip vorticesdevelop.

The downwash increases behindthe wing.

The average relative wind is inclined downward andrearward and lift is inclined aft. The rearward componentof lift is induced drag.

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L/Dmax is the point, where lift-to-drag ratio is greatest.At this speed, the total lift capacity of the glider, whencompared to the total drag of the glider, is most favor-able. In calm air, this is the airspeed you can use toobtain maximum glide distance.

DRAG EQUATIONTo help explain the force of drag, the mathematicalequation D=CDqS is used. In this equation drag (D) isthe product of drag coefficient (CD), dynamic pressure(q), and surface area (S). The drag coefficient is theratio of drag pressure to dynamic pressure. The dragcoefficient is represented graphically by Figure 3-12.This graph shows that at higher angles of attack, thedrag coefficient is greater than at low angles of attack.At high angles of attack, drag increases significantlywith small increases in angle of attack. During a stall,the wing experiences a sizeable increase in drag.[Figure 3-12]

WING PLANFORMThe shape, or planform, of the wings also has aneffect on the amount of lift and drag produced. Thefour most common wing planforms used on glidersare elliptical, rectangular, tapered, and swept-forwardwing. [Figure 3-13]

Elliptical wings produce the least amount of induceddrag for a given wing area. This design of wing is dif-ficult to manufacture. The elliptical wing is more effi-cient in terms of L/D, but stall characteristics are not asgood as the rectangular wing.

The rectangular wing is similar in efficiency to theelliptical wing but is much easier to build. Rectangularwings have very gentle stall characteristics with awarning buffet prior to stall and are easier to manufac-ture than elliptical wings. One drawback to this wingdesign is that rectangular wings create more induceddrag than an elliptical wing of comparable size.

Figure 3-12. This graph shows drag characteristicsin terms of angle of attack. As the angle of attackbecomes greater, the amount of drag increases.

Figure 3-13. Planform refers to the shape of the glider’s wing when viewed from above or below. There areadvantages and disadvantages to each planform design.

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The tapered wing is the planform found most fre-quently on gliders. Assuming equal wing area, thetapered wing produces less drag than the rectangularwing because there is less area at the tip of the taperedwing. If speed is the prime consideration, a taperedwing is more desirable than a rectangular wing, but atapered wing with no twist has undesirable stall char-acteristics.

Swept-forward wings are used to allow for the liftingarea of the wing to move forward while keeping themounting point aft of the cockpit. This wing configu-ration is used on some tandem two-seat gliders toallow for a small change in center of gravity with therear seat occupied or while flying solo.

Washout is built into wings by putting a slight twistbetween the wing root and wing tip. When washout isdesigned into the wing, the wing displays very goodstall characteristics. As you move outward along thespan of the wing, the trailing edge moves up in refer-ence to the leading edge. This twist causes the wingroot to have a greater angle of attack than the tip, and as

a result stall first. This provides ample warning of theimpending stall, and at the same time allows continuedaileron control.

Dihedral is the angle at which the wings are slantedupward from the root to the tip. The stabilizing effect ofdihedral occurs when the airplane sideslips slightly asone wing is forced down in turbulent air. This sideslipresults in a difference in the angle of attack between thehigher and lower wing with the greatest angle of attackon the lower wing. The increased angle of attack pro-duces increased lift on the lower wing with a tendencyto return the airplane to wings level flight.

ASPECT RATIOThe aspect ratio is another factor that affects the lift anddrag created by a wing. Aspect ratio is determined bydividing the wingspan (from wingtip to wingtip), bythe average wing chord. Glider wings have a highaspect ratio as shown in Figure 3-14. High-aspect ratiowings produce a comparably high amount of lift at lowangles of attack with less induced drag.

Figure 3-14. Aspect ratio is the relationship between the length and width of the wing and is one of the pri-mary factors in determining lift/drag characteristics.

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WEIGHTWeight is the third force that acts on a glider in flight.Weight opposes lift and acts vertically through the center of gravity of the glider. Gravitational pull provides the force necessary to move a glider throughthe air since a portion of the weight vector of a glider isdirected forward.

THRUSTThrust is the forward force that propels a self-launchglider through the air. Self-launch gliders have engine-driven propellers that provide this thrust. Unpoweredgliders have an outside force, such as a tow plane,winch, or automobile to launch the glider.

THREE AXES OF ROTATIONThe glider is maneuvered around three axes of rotation.These axes of rotation are the vertical axis, the lateralaxis, and the longitudinal axis. They rotate around onecentral point in the glider called the center of gravity(CG). This point is the center of the glider’s total weightand varies with the loading of the glider.

When you move the rudder left or right, you cause theglider to yaw the nose to the left or right. Yaw is move-ment that takes place around the vertical axis, whichcan be represented by an imaginary straight line drawnvertically through the CG. When you move the aileronsleft or right to bank, you are moving the glider around

the longitudinal axis. This axis would appear if a linewere drawn through the center of the fuselage fromnose to tail. When you pull the stick back or push itforward, raising or lowering the nose, you are control-ling the pitch of the glider or its movement around thelateral axis. The lateral axis could be seen if a line weredrawn from one side of the fuselage to the otherthrough the center of gravity. [Figure 3-15]

STABILITYA glider is in equilibrium when all of its forces are inbalance. Stability is defined as the glider’s ability tomaintain a uniform flight condition and return to thatcondition after being disturbed. Often during flight,gliders encounter equilibrium-changing pitch distur-bances. These can occur in the form of vertical gusts, asudden shift in CG, or deflection of the controls by thepilot. For example, a stable glider would display a ten-dency to return to equilibrium after encountering aforce that causes the nose to pitch up.

Static and dynamic are two types of stability a gliderdisplays in flight. Static stability is the initial ten-dency to return to a state of equilibrium when dis-turbed from that state. Three types of static stabilityare positive, negative, and neutral. When a gliderdemonstrates positive static stability it tends to returnto equilibrium. A glider demonstrating negative staticstability displays a tendency to increase its displace-ment. Gliders that demonstrate neutral static stability

Figure 3-15. The elevator controls pitch movement about the lateral axis, the ailerons control roll movementabout the longitudinal axis, and the rudder controls yaw movement about the vertical axis.

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have neither the tendency to return to equilibrium northe tendency to continue displacement. [Figure 3-16]

Dynamic stability describes a glider’s motion and timerequired for a response to static stability. In otherwords, dynamic stability describes the manner in whicha glider oscillates when responding to static stability. Aglider that displays positive dynamic and static stabilitywill reduce its oscillations with time. A glider demon-strating negative dynamic stability is the opposite situa-tion where its oscillations increase in amplitude withtime following a displacement. A glider displaying neu-tral dynamic stability experiences oscillations, which

remain at the same amplitude without increasing ordecreasing over time. Figure 3-17 illustrates the varioustypes of dynamic stability.

Both static and dynamic stability are particularlyimportant for pitch control about the lateral axis.Measurement of stability about this axis is known aslongitudinal stability. Gliders are designed to beslightly nose-heavy in order to improve their longitu-dinal stability. This causes the glider to tend to nosedown during normal flight. The horizontal stabilizeron the tail is mounted at a slightly negative angle ofattack to offset this tendency. When a dynamically

Figure 3-16. The three types of static stability are positive, negative, and neutral.

Figure 3-17. The three types of dynamic stability also are referred to as neutral, positive, and negative.

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stable glider oscillates, the amplitude of the oscillationsshould reduce through each cycle and eventually settledown to a speed at which the downward force on thetail exactly offsets the tendency to dive. [Figure 3-18]

Adjusting the trim assists you in maintaining a desiredpitch attitude. A glider with positive static and dynamiclongitudinal stability tends to return to the trimmedpitch attitude when the force that displaced it is removed. If a glider displays negative stability, oscillations will increase over time. If uncorrected,negative stability can induce loads exceeding thedesign limitations of the glider.

Another factor that is critical to the longitudinal stabilityof a glider is its loading in relation to the center of grav-ity. The center of gravity of the glider is the point wherethe total force of gravity is considered to act. When theglider is improperly loaded so it exceeds the aft CG limitit loses longitudinal stability. As airspeed decreases, thenose of a glider rises. To recover, control inputs must beapplied to force the nose down to return to a level flightattitude. It is possible that the glider could be loaded sofar aft of the approved limits that control inputs are notsufficient to stop the nose from pitching up. If this werethe case, the glider could enter a spin from which recov-ery would be impossible. Loading a glider with the CGtoo far forward also is hazardous. In extreme cases, theglider may not have enough pitch control to hold thenose up during an approach to a landing. For these rea-sons, it is important to ensure that your glider is withinweight and balance limits prior to each flight. Properloading of a glider and the importance of CG will be dis-cussed further in Chapter 5–Performance Limitations.

FLUTTERAnother factor that can affect the ability to control theglider is flutter. Flutter occurs when rapid vibrationsare induced through the control surfaces while theglider is traveling at high speeds. Looseness in the control surfaces can result in flutter while flying nearmaximum speed. Another factor that can reduce theairspeed at which flutter can occur is a disturbance tothe balance of the control surfaces. If vibrations arefelt in the control surfaces, reduce the airspeed.

LATERAL STABILITYAnother type of stability that describes the glider’stendency to return to wings-level flight following adisplacement is lateral stability. When a glider is rolledinto a bank, it has a tendency to sideslip in the direc-tion of the bank. In order to obtain lateral stability,dihedral is designed into the wings. Dihedral increasesthe stabilizing effects of the wings by increasing thelift differential between the high and low wing duringa sideslip. A roll to the left would tend to slip the gliderto the left, but since the glider’s wings are designedwith dihedral, an opposite moment helps to level thewings and stop the slip. [Figure 3-19]

DIRECTIONAL STABILITYDirectional stability is the glider’s tendency to remainstationary about the vertical or yaw axis. When therelative wind is parallel to the longitudinal axis, theglider is in equilibrium. If some force yaws the gliderand produces a slip, a glider with directional stabilitydevelops a positive yawing moment and returns toequilibrium. In order to accomplish this stability, the

Figure 3-19. Dihedral is designed into the wings toincrease the glider’s lateral stability.

Figure 3-18. The horizontal stabilizer is mounted at a slightly negative angle of attack to offset the glider’snatural tendency to enter a dive.

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vertical tail and the side surfaces of the rear fuselagemust counterbalance the side surface area ahead of thecenter of gravity. The vertical stabilizer is the primarycontributor to directional stability and causes a gliderin flight to act much like a weather vane. The nose ofthe glider corresponds to a weather vane’s arrowhead,while the vertical stabilizers on the glider act like thetail of the weathervane. When the glider enters asideslip, the greater surface area behind the CG helpsthe glider realign with the relative wind. [Figure 3-20]

TURNING FLIGHTBefore a glider turns, it must first overcome inertia, orits tendency to continue in a straight line. You createthe necessary turning force by using the ailerons tobank the glider so that the direction of total lift isinclined. This is accomplished by dividing the force oflift into two components; one component acts verti-cally to oppose weight, while the other acts horizon-tally to oppose centrifical force. The latter is thehorizontal component of lift.

To maintain your attitude with the horizon during aturn, you need to increase backpressure on the controlstick. The horizontal component of lift creates a forcedirected inward toward the center of rotation, which isknown as centripetal force. This center-seeking forcecauses the glider to turn. Since centripetal force worksagainst the tendency of the aircraft to continue in astraight line, inertia tends to oppose centripetal forcetoward the outside of the turn. This opposing force isknown as centrifugal force . In reality, centrifugal

force is not a true aerodynamic force; it is an apparentforce that results from the effect of inertia during theturn.

If you attempt to improve turn performance by increas-ing angle of bank while maintaining airspeed, youmust pay close attention to glider limitations due to theeffects of increasing the load factor. Load factor isdefined as the ratio of the load supported by theglider’s wings to the actual weight of the aircraft andits contents. A glider in stabilized, wings level flighthas a load factor of one. Load factor increases rapidlyas the angle of bank increases. [Figure 3-21]

In a turn at constant speed, increasing the angle ofattack must occur in order to increase lift. As the bankangle increases, angle of attack must also increase toprovide the required lift. The result of increasing theangle of attack will be a stall when the critical angle ofattack is exceeded in a turn. [Figure 3-22]

Figure 3-20. During a sideslip, the glider is helped tostay in alignment with the relative wind due to theadded surface area behind the CG.

Figure 3-21. The loads placed on a glider increase asthe angle of bank increases.

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Induced drag also increases as a result of increased liftrequired to maintain airspeed in the turn. This increasedinduced drag results in a greater rate of sink during aturn compared to level flight.

RATE OF TURNRate of turn refers to the amount of time it takes for aglider to turn a specified number of degrees. If flown atthe same airspeed and angle of bank, every glider willturn at the same rate. If airspeed increases and the angleof bank remains the same, the rate of turn will decrease.Conversely, a constant airspeed coupled with an angleof bank increase will result in a faster rate of turn.

RADIUS OF TURNThe amount of horizontal distance an aircraft uses tocomplete a turn is referred to as the radius of turn.The radius of turn at any given bank angle variesdirectly with the square of the airspeed. Therefore, ifthe airspeed of the glider were doubled, the radius ofthe turn would be four times greater. Although theradius of turn is also dependent of a glider’s airspeedand angle of bank, the relationship is the opposite ofrate of turn. As the glider’s airspeed is increased withthe angle of bank held constant, the radius of turnincreases. On the other hand if the angle of bankincreases and the airspeed remains the same, the radiusof turn is decreased. [Figure 3-23]

TURN COORDINATIONIt is important that rudder and aileron inputs are coor-dinated during a turn so maximum glider performance

can be maintained. If too little rudder is applied orif rudder is applied too late, the result will be a slip.Too much rudder or rudder applied before aileronresults in a skid. Both skids and slips swing the fuse-lage of the glider into the relative wind, creating addi-tional parasite drag, which reduces lift and airspeed.Although this increased drag caused by a slip can beuseful during approach to landing to steepen theapproach path and counteract a crosswind, itdecreases glider performance during other phases of flight.

When you roll into a turn, the aileron on the inside ofthe turn is raised and the aileron on the outside of theturn is lowered. The lowered aileron on the outsideincreases the angle of attack and produces more lift forthat wing. Since induced drag is a by-product of lift, theoutside wing also produces more drag than the insidewing. This causes a yawing tendency toward the outsideof the turn called adverse yaw. Coordinated use ofrudder and aileron corrects for adverse yaw and ailerondrag.

SLIPSA slip is a descent with one wing lowered and theglider’s longitudinal axis at an angle to the flight path.It may be used for either two purposes, or both of themcombined. A slip may be used to steepen the approachpath without increasing the airspeed, as would be thecase if a dive were used. It can also be used to makethe glider move sideways through the air to counteractthe drift, which results from a crosswind.

Figure 3-23. The radius of a turn is directly related to airspeed and bank angle.

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Formerly, slips were used as a normal means of con-trolling landing descents to short or obstructed fields,but they are now primarily used in the performance ofcrosswind and short-field landings. With the installa-tion of wing flaps and effective spoilers on moderngliders, the use of slips to steepen or control the angleof descent is no longer a common procedure. However,the pilot still needs skill in performance of forwardslips to correct for possible errors in judgment of thelanding approach.

The use of slips has definite limitations. Some pilots maytry to lose altitude by violent slipping rather than bysmoothly maneuvering and exercising good judgmentand using only a slight or moderate slip. In short-fieldlandings, this erratic practice invariably will lead to trou-ble since enough excess speed may result to preventtouching down anywhere near the proper point, and veryoften will result in overshooting the entire field.

If a slip is used during the last portion of a finalapproach, the longitudinal axis of the glider must bealigned with the runway just prior to touchdown so thatthe glider will touch down headed in the direction inwhich it is moving over the runway. This requirestimely action to discontinue the slip and align theglider’s longitudinal axis with its direction of travelover the ground at the instant of touchdown. Failure toaccomplish this imposes severe sideloads on the land-ing gear and imparts violent groundlooping tendencies.

Discontinuing the slip is accomplished by leveling thewings and simultaneously releasing the rudderpressure while readjusting the pitch attitude to thenormal glide attitude. If the pressure on the rudder isreleased abruptly the nose will swing too quickly intoline and the glider will tend to acquire excess speed.

Because of the location of the pitot tube and static vents,airspeed indicators in some gliders may have consider-able error when the glider is in a slip. The pilot must beaware of this possibility and recognize a properly per-formed slip by the attitude of the Glider, the sound ofthe airflow, and the feel of the flight controls.

FORWARD SLIPThe primary purpose of a forward slip is to dissipatealtitude without increasing the glider’s speed, particu-larly in gliders not equipped with flaps or if the spoil-ers are inoperative. There are many circumstancesrequiring the use of forward slips, such as in a landingapproach over obstacles and in making short-fieldlandings, when it is always wise to allow an extra mar-gin of altitude for safety in the original estimate of theapproach. In the latter case, if the inaccuracy of theapproach is confirmed by excess altitude when nearingthe boundary of the selected field, slipping can dissi-pate the excess altitude.

The “forward slip” is a slip in which the glider’s direc-tion of motion continues the same as before the slipwas begun. [Figure 3-24] If there is any crosswind, theslip will be much more effective if made toward thewind.

Assuming the glider is originally in straight flight, thewing on the side toward which the slip is to be madeshould be lowered by use of the ailerons.Simultaneously, the airplane’s nose must be yawed inthe opposite direction by applying opposite rudder sothat the glider’s longitudinal axis is at an angle to itsoriginal flight path. The degree to which the nose isyawed in the opposite direction from the bank shouldbe such that the original ground track is maintained.The nose should also be raised as necessary to preventthe airspeed from increasing.

Forward slips with wing flaps extended should not bedone in gliders wherein the manufacturer’s operatinginstructions prohibit such operation.

SIDE SLIPA side slip, as distinguished from a forward slip[Figure 3-24], is one during which the glider’s longi-tudinal axis remains parallel to the original flightpath but in which the flight path changes directionaccording to the steepness of the bank. To perform a

Figure 3-24. Two types of slips.

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sideslip, the upwind wing is lowered and simultane-ously the opposite rudder is applied to maintain thelanding area alignment. The sideslip is important incounteracting wind drift during crosswind landingsand is discussed in a later chapter.

STALLSIt is important to remember that a stall can occur at anyairspeed and at any flight attitude. A stall will occur whenthe critical angle of attack is exceeded. [Figure 3-25]The stall speed of a glider can be affected by many fac-tors including weight, load factor due to maneuvering,and environmental conditions. As the weight of the gliderincreases, a higher angle of attack is required to maintainthe same airspeed since some of the lift is sacrificed tosupport the increase in weight. This is why a heavilyloaded glider will stall at a higher airspeed than it willwhen lightly loaded. The manner in which this weight isdistributed also affects stall speed. For example, a for-ward CG creates a situation that requires the tail to pro-duce a greater downforce to balance the aircraft. Theresult of this configuration requires the wings to producemore lift than if the CG were located further aft.Therefore, a more forward CG also increases stall speed.

Environmental factors also can affect stall speed.Snow, ice, or frost accumulation on the wing’s surfacecan increase the weight of the wing in addition tochanging the shape and disrupting the airflow, all ofwhich will increase stall speed. Turbulence is anotherenvironmental factor that can affect a glider’s stallspeed. The unpredictable nature of turbulence cancause a glider to stall suddenly and abruptly at a higherairspeed than it would in stable conditions. The reasonturbulence has such a strong impact on the stall speedof a glider is that the vertical gusts change the directionof the relative wind and abruptly increase the angle ofattack. During landing in gusty conditions, it is impor-tant that you increase your airspeed in order to main-tain a wide margin above stall.

SPINSA spin can be defined as an aggravated stall that resultsin the glider descending in a helical, or corkscrew,path. A spin is a complex, uncoordinated flight maneu-ver in which the wings are unequally stalled. Upon

entering a spin, the wing that is more completelystalled will drop before the other, and the nose of theaircraft will yaw in the direction of the low wing.

The cause of a spin is exceeding the critical angle ofattack while performing an uncoordinated maneuver.The lack of coordination is normally caused by eithertoo much or not enough rudder control for the amountof aileron being used. If the stall recovery is notpromptly initiated, the glider is likely to enter a fullstall that may develop into a spin. Spins that occur asthe result of uncoordinated flight usually rotate in thedirection of the rudder being applied, regardless of theraised wing. When you enter a slipping turn, holdingopposite aileron and rudder, the resultant spin usuallyoccurs in the opposite direction of the aileron alreadyapplied. In a skidding turn where both aileron and rud-der are applied in the same direction, rotation will alsobe in the direction of rudder application.

Spins are normally placed in three categories as shownin Figure 3-26. The most common is the upright, orerect, spin, which is characterized by a slightly nosedown rolling and yawing motion in the same direction.An inverted spin involves the aircraft spinning upsidedown with the yaw and roll occurring in oppositedirections. A third type of spin, the flat spin, is themost hazardous of all spins. In a flat spin, the glideryaws around the vertical axis at a pitch attitude nearlylevel with the horizon. A flat spin often has a very highrate of rotation; the recovery is difficult, and some-times impossible. If your glider is properly loadedwithin its CG limits, entry into a flat spin should notoccur.

Since spins normally occur when a glider is flown inan uncoordinated manner at lower airspeeds, coordi-nated use of the flight controls is important. It is criti-cal that you learn to recognize and recover from thefirst sign of a stall or spin. Entering a spin near theground, especially during the landing pattern, is mostoften fatal. [Figure 3-27]

GROUND EFFECTGround effect is a reduction in induced drag for thesame amount of lift produced. Within one wingspan

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above the ground, the decrease in induced drag enablesthe glider to fly at a slower airspeed. In ground effect, alower angle of attack is required to produce the sameamount of lift. Ground effect enables the glider to flynear the ground at a slower airspeed. It is ground effect

that causes the glider to float as you approach thetouchdown point.

During takeoff and landing, the ground alters thethree-dimensional airflow pattern around the glider.The result is a decrease in upwash, downwash, and areduction in wingtip vortices. Upwash and downwashrefer to the effect an airfoil has on the free airstream.Upwash is the deflection of the oncoming airstreamupward and over the wing. Downwash is the down-ward deflection of the airstream as it passes over thewing and past the trailing edge.

During flight, the downwash of the airstream causesthe relative wind to be inclined downward in the vicin-ity of the wing. This is called the average relativewind. The angle between the free airstream relativewind and the average relative wind is the inducedangle of attack. In effect, the greater the downwarddeflection of the airstream, the higher the inducedangle of attack and the higher the induced drag.Ground effect restricts the downward deflection of theairstream, decreasing both induced angle of attack andinduced drag.

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Flight instruments in the glider cockpit provide information regarding the glider’s direction, altitude,airspeed, and performance. These instruments are cate-gorized according to their method of operation. Thecategories include pitot-static, magnetic, gyro-scopic,electrical, or self-contained. Examples of self-con-tained instruments and indicators that are useful to thepilot include the yaw string, inclinometer, and outsideair temperature gauge (OAT).

Gyroscopic instruments, including the attitude indica-tor, turn coordinator, and heading indicator, are dis-cussed in this chapter to give you an understanding ofhow they function. Self-launch gliders often have oneor more gyroscopic instruments on the panel. Gliderswithout power rarely have gyroscopic instrumentsinstalled.

PITOT-STATIC INSTRUMENTSThere are two major parts of the pitot-static system:(1) impact pressure lines; and (2) static pressure lines,which provide the source of ambient air pressure forthe operation of the altimeter, variometer, and the air-speed indicator.

IMPACT AND STATIC PRESSURELINESThe impact air pressure (air striking the glider becauseof its forward motion) is taken from a pitot tube, whichis mounted either on the nose or the vertical stabilizer,and aligned with the relative wind. These locations

minimize disturbance or turbulence caused by themotion of the glider through the air.

The static pressure (pressure of the still air) is takenfrom the static line, which is attached to a vent or ventsmounted flush with the side of the fuselage or tubemounted on the vertical stabilizer. Gliders using aflush-type static source with two vents, have one venton each side of the fuselage. This compensates for anypossible variation in static pressure due to erraticchanges in glider attitude.

The openings of both the pitot tube and the staticvent(s) should be checked during the preflight inspec-tion to enure they are free from obstructions. Cloggedor partially clogged openings should be cleaned by acertificated mechanic. Blowing into these openings isnot recommended because this could damage any ofthe three instruments.

AIRSPEED INDICATORThe airspeed indicator displays the speed of the gliderthrough the air. Some airspeed indicator dials providecolor-coded arcs that depict permissible airspeedranges for different phases of flight. The upper andlower limits of the arcs correspond to airspeed limita-tions specific to the glider in which the instrument ismounted. [Figure 4-1]

The airspeed indicator is the only instrument thatdepends on both pitot pressure and static pressure.When pitot pressure and static pressure are the same,zero airspeed is indicated. As pitot pressure becomesprogressively greater than static pressure, indicated air-

Figure 4-1. The airspeed indicator uses both the pitot and static system.

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speed increases. The airspeed indicator contains asmall diaphragm that drives the needle on the face ofthe instrument.

TYPES OF AIRSPEEDThere are three kinds of airspeed that the pilot shouldunderstand: indicated airspeed, calibrated airspeed, andtrue airspeed. [Figure 4-2]

INDICATED AIRSPEEDIndicated airspeed (IAS) is the direct instrument read-ing obtained from the airspeed indicator, uncorrectedfor variations in atmospheric density, installation error,or instrument error.

CALIBRATED AIRSPEEDCalibrated airspeed (CAS) is indicated airspeed corrected for installation and instrument error.Although manufacturers attempt to keep airspeederrors to a minimum, it is impossible to eliminate allerrors throughout the airspeed operating range. At cer-tain airspeeds and with certain flap/spoiler settings, theinstallation and instrument error may be significant.The error is generally greatest at low airspeeds. In thecruising and higher airspeed ranges, indicated airspeedand calibrated airspeed are approximately the same.

It is important to refer to the airspeed calibration chartto correct for possible airspeed errors because airspeedlimitations, such as those found on the color-codedface of the airspeed indicator, on placards in the cock-pit, or in the Glider Flight Manual or Pilot’s OperatingHandbook (GFM/POH), are usually calibrated air-speeds. Some manufacturers use indicated rather thancalibrated airspeed to denote the airspeed limitationsmentioned. The airspeed indicator should be calibratedperiodically.

Dirt, dust, ice, or snow collecting at the mouth of the tube may obstruct air passage and prevent correctindications, and also vibrations may destroy the sensitiv-ity of the diaphragm.

TRUE AIRSPEEDThe airspeed indicator is calibrated to indicate true air-speed only under standard atmospheric conditions atsea level (29.92 inches of mercury and 15° C or 59°F).Because air density decreases with an increase in alti-tude, the glider has to be flown faster at higher altitudesto cause the same pressure difference between pitotimpact pressure and static pressure. Therefore, for agiven true airspeed, indicated airspeed decreases asaltitude increases or for a given indicated airspeed, trueairspeed increases with an increase in altitude.

Figure 4-2. The three types of airspeed you should know include calibrated airspeed, indicated airspeed, and

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A pilot can find true airspeed by two methods. The firstmethod, which is more accurate, involves using a computer. In this method, the calibrated airspeed is corrected for temperature and pressure variation by usingthe airspeed correction scale on the computer.

A second method, which is a "rule of thumb," can beused to compute the approximate true airspeed. This isdone by adding to the indicated airspeed 2 percent ofthe indicated airspeed for each 1,000 feet of altitude.

AIRSPEED INDICATOR MARKINGSAircraft weighing 12,500 pounds or less, manufacturedafter 1945 and certificated by the FAA, are required tohave airspeed indicators that conform to a standardcolor-coded marking system. This system enables thepilot to determine at a glance certain airspeed limita-tions, which are important to the safe operation of theaircraft. For example, if during the execution of a

maneuver, the pilot notes that the airspeed needle is inthe yellow arc and is rapidly approaching the red line,immediate corrective action to reduce the airspeedshould be taken. It is essential that the pilot use smoothcontrol pressure at high airspeeds to avoid severestresses upon the glider structure. [Figure 4-3]

The following is a description of the standard color-codemarkings on airspeed indicators.

• FLAP OPERATING RANGE (the white arc).

• STALLING SPEED WITH THE WING FLAPSAND LANDING GEAR IN THE LANDINGPOSITION (the lower limit of the white arc).

• MAXIMUM FLAPS EXTENDED SPEED (theupper limit of the white arc). This is the highestairspeed at which the pilot should extend fullflaps. If flaps are operated at higher airspeeds,severe strain or structural failure could result.

• NORMAL OPERATING RANGE (the green arc).

• STALLING SPEED WITH THE WING FLAPSAND LANDING GEAR RETRACTED (thelower limit of the green arc).

• MAXIMUM STRUCTURAL CRUISINGSPEED (the upper limit of the green arc). This isthe maximum speed for normal operation.

• CAUTION RANGE (the yellow arc). The pilotshould avoid this area unless in smooth air.

• NEVER-EXCEED SPEED (the red line). This isthe maximum speed at which the glider can beoperated in smooth air. This speed should neverbe exceeded intentionally.

OTHER AIRSPEED LIMITATIONS There are other important airspeed limitations notmarked on the face of the airspeed indicator. Thesespeeds are generally found on placards in view of thepilot and in the GFM/POH.

MANEUVERING SPEED is the maximum speed atwhich the limit load can be imposed (either by gustsor full deflection of the control surfaces) without caus-ing structural damage. If during flight, rough air orsevere turbulence is encountered, the airspeed shouldbe reduced to maneuvering speed or less to minimizethe stress on the glider structure. Maneuvering speed isnot marked on the airspeed indicator.

Other important airspeeds include LANDING GEAROPERATING SPEED, the maximum speed for extendingor retracting the landing gear if using glider equippedwith retractable landing gear; the MINIMUM SINKSPEED, important when thermaling; and the BESTGLIDE SPEED, the airspeed that results in the leastamount of altitude loss over a given distance not consid-ering the effects of wind. MAXIMUM AEROTOW orGROUND LAUNCH SPEED is the maximum airspeedthat the glider may safely be towed without causing struc-tural damage.

The following are abbreviations for performancespeeds.

VA—design maneuvering speed.VC—design cruising speed.VF—design flap speed.

Figure 4-3. Airspeed indicator with color markings.

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VFE—maximum flap extended speed.VLE—maximum landing gear extended speed.VLO—maximum landing gear operating speed.VNE—never-exceed speed.VS—the stalling speed or the minimum steady flight

speed at which the glider is controllable.VS0—the stalling speed or the minimum steady flight

speed in the landing configuration.VS1—the stalling speed or the minimum steady flight

speed obtained in a specified configuration.

ALTIMETERThe altimeter measures the height of the glider above agiven level. Since it is the only instrument that givesaltitude information, the altimeter is one of the mostimportant instruments in the glider. To use the altimetereffectively, the pilot must thoroughly understand itsprinciple of operation and the effect of atmosphericpressure and temperature on the altimeter. [Figure 4-4]

PRINCIPLE OF OPERATIONThe pressure altimeter is simply an aneroid barometerthat measures the pressure of the atmosphere at thelevel where the altimeter is located, and presents analtitude indication in feet. The altimeter uses staticpressure as its source of operation. Air is denser at thesurface of the Earth than aloft, therefore as altitudeincreases, atmospheric pressure decreases. This differ-ence in pressure at various levels causes the altimeterto indicate changes in altitude.

The presentation of altitude varies considerablybetween different types of altimeters. Some have onepointer while others have more. Only the multi-pointertype will be discussed in this handbook.

The dial of a typical altimeter is graduated with numeralsarranged clockwise from 0 to 9 inclusive as shown inFigure 4-4. Movement of the aneroid element is transmittedthrough a gear train to the three hands, which sweep thecalibrated dial to indicate altitude. The shortest hand indi-

cates altitude in tens of thousands of feet; the intermedi-ate hand in thousands of feet; and the longest hand inhundreds of feet, subdivided into 20-foot increments.

The altitude indicated on the altimeter is correct only ifthe sea level barometric pressure is standard (29.92 in.Hg.), the sea level free air temperature is standard (+15°C or 59° F), and the pressure and temperature decrease ata standard rate with an increase in altitude. Since atmos-pheric pressure continually changes, a means is providedto adjust the altimeter to compensate for nonstandard conditions. This is accomplished through a system bywhich the altimeter setting (local station barometric pres-sure reduced to sea level) is set to a barometric scalelocated on the face of the altimeter. Only after the altime-ter is set properly will it indicate the correct altitude.

EFFECT OF NONSTANDARD PRESSURE ANDTEMPERATUREIf no means were provided for adjusting altimeters tononstandard pressure, flight could be hazardous. Forexample, if a flight is made from a high-pressure areato a low-pressure area without adjusting the altimeter,the actual altitude of the glider will be LOWER thanthe indicated altitude. When flying from a low-pres-sure area to a high-pressure area, the actual altitude ofthe glider will be HIGHER than the indicated altitude.Fortunately, this error can be corrected by setting thealtimeter properly.

Variations in air temperature also affect the altimeter.On a warm day, the expanded air is lighter in weightper unit volume than on a cold day, and consequentlythe pressure levels are raised. For example, the pres-sure level where the altimeter indicates 10,000 feetwill be HIGHER on a warm day than under standard con-ditions. On a cold day, the reverse is true, and the 10,000foot level would be LOWER. The adjustment made bythe pilot to compensate for nonstandard pressures doesnot compensate for nonstandard temperatures. Therefore,if terrain or obstacle clearance is a factor in the selection

Figure 4-4. The altimeter indicator.

ting of a station located along the route of flight andwithin 100 nautical miles (NM) of the aircraft. If there isno such station, the current reported altimeter setting ofan appropriate available station shall be used. In an air-craft having no radio, the altimeter shall be set to the ele-vation of the departure airport or an appropriate altimetersetting available before departure.

Many pilots confidently expect that the current altimetersetting will compensate for irregularities in atmosphericpressure at all altitudes. This is not always true becausethe altimeter setting broadcast by ground stations is thestation pressure corrected to mean sea level. The altime-ter setting does not account for the irregularities at higherlevels, particularly the effect of nonstandard temperature.

It should be pointed out, however, that if each pilot in agiven area were to use the same altimeter setting, eachaltimeter will be equally affected by temperature andpressure variation errors, making it possible to maintainthe desired separation between aircraft.

When flying over high mountainous terrain, certainatmospheric conditions can cause the altimeter to indicatean altitude of 1,000 feet, or more, HIGHER than theactual altitude. For this reason, a generous margin of alti-tude should be allowed—not only for possible altimeter

of a cruising altitude, particularly at higher altitudes,remember to anticipate that COLDER-THAN-STAN-DARD TEMPERATURE will place the glider LOWERthan the altimeter indicates. Therefore, a higher altitudeshould be used to provide adequate terrain clearance. Amemory aid in applying the above is "from a high to alow or hot to cold, look out below." [Figure 4-5]

SETTING THE ALTIMETERTo adjust the altimeter for variation in atmosphericpressure, the pressure scale in the altimeter setting win-dow, calibrated in inches of mercury (in. Hg.), isadjusted to correspond with the given altimeter setting.Altimeter settings can be defined as station pressurereduced to sea level, expressed in inches of mercury.

The station reporting the altimeter setting takes anhourly measurement of the station’s atmospheric pres-sure and corrects this value to sea level pressure. Thesealtimeter settings reflect height above sea level only inthe vicinity of the reporting station. Therefore, it is nec-essary to adjust the altimeter setting as the flight pro-gresses from one station to the next.

Title 14 of the Code of Federal Regulations (14 CFR) part91 provides the following concerning altimeter settings.The cruising altitude of an aircraft below 18,000 feetmean sea level (MSL) shall be maintained by reference toan altimeter that is set to the current reported altimeter set-

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Figure 4-5. Nonstandard pressure and temperature.

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error, but also for possible downdrafts that are particularlyprevalent if high winds are encountered.

To illustrate the use of the altimeter setting system, fol-low a cross-country flight from TSA Gliderport,Midlothian, Texas, to Winston Airport, Snyder, Texas,via Stephens County Airport, Breckenridge, Texas.Before takeoff from TSA Gliderport, the pilot receivesa current local altimeter setting of 29.85 from the FortWorth AFSS. This value is set in the altimeter settingwindow of the altimeter. The altimeter indicationshould then be compared with the known airport eleva-tion of 660 feet. Since most altimeters are not perfectlycalibrated, an error may exist. If an altimeter indicationvaries from the field elevation more than 75 feet, theaccuracy of the instrument is questionable and it shouldbe referred to an instrument repair station.

When over Stephens County Airport, assume the pilotreceives a current area altimeter setting of 29.94 andapplies this setting to the altimeter. Before entering thetraffic pattern at Winston Airport, a new altimeter set-ting of 29.69 is received from the Automated WeatherObserving System (AWOS), and applied to the altime-ter. If the pilot desires to enter the traffic pattern atapproximately 1,000 feet above terrain, and the fieldelevation of Winston Airport is 2,430 feet, an indicatedaltitude of 3,400 feet should be used (2,430 feet + 1000feet = 3,420 feet, rounded to 3,400 feet).

The importance of properly setting and reading the altimetercannot be overemphasized. Let us assume that the pilotneglected to adjust the altimeter at Winston Airport to thecurrent setting, and uses the Stephens CO area setting of29.94. If this occurred, the glider, when entering theWinston Airport traffic pattern, would be approximately250 feet below the proper traffic pattern altitude of 3,200feet, and the altimeter would indicate approximately 250

feet more than the field elevation (2,430 feet) upon land-ing.

Actual altimeter setting 29.94Correct altimeter setting 29.69Difference .25

(1 inch of pressure is equal to approximately 1,000 feetof altitude—.25 x 1,000 feet = 250 feet)

The previous calculation may be confusing, particu-larly in determining whether to add or subtract theamount of altimeter error. The following additionalexplanation is offered and can be helpful in finding thesolution to this type of problem.

There are two means by which the altimeter pointers canbe moved. One utilizes changes in air pressure while theother utilizes the mechanical makeup of the altimeter set-ting system.

When the glider altitude is changed, the changing pressure within the altimeter case expands or contractsthe aneroid barometer that through linkage rotates thepointers. A decrease in pressure causes the altimeter toindicate an increase in altitude, and an increase in pres-sure causes the altimeter to indicate a decrease in altitude.It is obvious then that if the glider is flown from a pres-sure level of 28.75 in. Hg. to a pressure level of 29.75 in.Hg., the altimeter would show a decrease of approxi-mately 1,000 feet in altitude. [Figure 4-6]

The other method of moving the pointers does not relyon changing air pressure, but the mechanical construc-tion of the altimeter. When the knob on the altimeter isrotated, the altimeter setting pressure scale moves

Figure 4-6. Flying from an area of high pressure to an area of lower pressure, without resetting your altimeter,results in your glider’s true altitude being lower than indicated.

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simultaneously with the altimeter pointers. This maybe confusing because the numerical values of pressureindicated in the window increase while the altimeterindicates an increase in altitude; or decrease while thealtimeter indicates a decrease in altitude. This is contrary to the reaction on the pointers when air pressure changes, and is based solely on the mechanicalmakeup of the altimeter. To further explain this point,assume that the correct altimeter setting is 29.50 or a.50 difference. This would cause a 500-foot error inaltitude. In this case if the altimeter setting is adjustedfrom 30.00 to 29.50, the numerical value decreases andthe altimeter indicates a decrease of 500 feet in alti-tude. Before this correction was made, the glider wasflying at an altitude of 500 feet lower than was shownon the altimeter.

TYPES OF ALTITUDEKnowing the glider’s altitude is vitally important to thepilot for several reasons. The pilot must be sure that theglider is flying high enough to clear the highest terrainor obstruction along the intended route; this is espe-

cially important when visibility is restricted. To keepabove mountain peaks, the pilot must be aware of theglider’s altitude and elevation of the surrounding terrainat all times. Knowledge of the altitude is necessary tocalculate true airspeeds.

Altitude is vertical distance above some point or levelused as a reference. There may be as many kinds of alti-tude as there are reference levels from which altitude ismeasured and each may be used for specific reasons.

The following are the four types of altitude that affectglider pilots. [Figure 4-7]

Indicated Altitude—That altitude read directly from the altimeter (uncorrected) after it is set to the currentaltimeter setting.

True Altitude—The true vertical distance of the gliderabove sea level—the actual altitude. (Often expressed in thismanner: 10,900 feet MSL.) Airport, terrain, and obstacleelevations found on aeronautical charts are true altitudes.

Absolute Altitude—The vertical distance above the terrain.

Pressure Altitude—The altitude indicated when thealtimeter setting window (barometric scale) is adjustedto 29.92. This is the standard datum plane, a theoreticalplane where air pressure (corrected to 15° C or 59° F)is equal to 29.92 in. Hg. Pressure altitude is used forcomputer solutions to determine density altitude, truealtitude, true airspeed, etc.

Density Altitude—This altitude is pressure altitudecorrected for nonstandard temperature variations.When conditions are standard, pressure altitude and den-sity altitude are the same. Consequently, if the tempera-ture is above standard, the density altitude will be higherthan pressure altitude. If the temperature is below stan-dard, the density altitude will be lower than pressure alti-tude. This is an important altitude because it is directlyrelated to the glider’s takeoff and climb performance.

VARIOMETERThe variometer gives the glider pilot information onperformance of the glider while flying through theatmosphere. The variometer operates on the same prin-ciple as the altimeter, however, it indicates rate ofclimb or descent instead of vertical distance. The vari-ometer depends upon the pressure lapse rate in theatmosphere to derive information about rate of climbor rate of descent. Most non-electrical variometers usea separate insulated tank, such as a Thermos or capac-ity flask, as a reference chamber. The tubing isplumbed from the reference chamber through the vari-ometer to an outside static port. By using differenthairsprings, the sensitivity of the variometer can becontrolled. The variometer has a very rapid responsedue to the small mass and lightweight construction ofthe moving parts.

Figure 4 -7. Types of altitude.

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Pressure differences between the air inside the variometer/reference chamber system and the air outside of the system tend to equalize as air flows fromhigh pressure areas to low pressure areas. When pressureinside the reference chamber is greater than the pressureoutside, air flows out of the reference chamber throughthe mechanical variometer to the outside environment,displacing a vane inside the variometer. The vane, inturn, drives the needle to display a climb indication.When air pressure outside the reference chamber isgreater than pressure inside, air flows through the vari-ometer and into the reference chamber until pressure isequalized. The variometer needle indicates a descent.[Figure 4-8]

Electric powered variometers offer several advantagesover the non-electric variety. These advantages includemore rapid response rates and separate audible signalsfor climb and descent.

Some electric variometers operate by the cooling effect ofairflow on an element called a thermistor, a heat-sensitiveelectrical resistor. The electrical resistance of the thermistorchanges when temperature changes. As air flows into or outof the reference chamber, it flows across two thermistors in a bridge circuit. An electrical meter measures the imbal-ance across the bridge circuit and calculates the rate ofclimb or descent. It then displays the information on thevariometer.

Newer electric variometers operate on the transducer prin-ciple. A tiny vacuum cavity on a circuit board is sealedwith a flexible membrane. Variable resistors are embed-ded in the membrane. When pressure outside the cavity

changes, minute alterations in the shape of the membraneoccur. As a result, electrical resistance in the embeddedresistors changes. These changes in electrical resistanceare interpreted by a circuit board and indicated on thevariometer dial as climb or descent.

Many electrical variometers provide audible tones orbeeps that indicate the rate of climb or rate of descent ofthe glider. Audio variometers enhance safety of flightbecause they make it unnecessary for the glider pilot tolook at the variometer to discern the rate of climb or rateof descent. Instead, the pilot can hear the rate of climb or

rate of descent. This allows the pilot to minimize timespent looking at the flight instruments and maximize timespent looking outside for other air traffic. [Figure 4-9]

Some variometers are equipped with a rotatable rim speedscale called a MacCready ring. This scale indicates the opti-mum airspeed to fly when traveling between thermals formaximum cross-country performance. During the glidebetween thermals, the index arrow is set at the rate of climbexpected in the next thermal. On the speed ring, the var-iometer needle points to the optimum speed to flybetween thermals. If expected rate of climb is slow,optimum inter-thermal cruise airspeed will be relativelyslow. When expected lift is strong, however, optimuminter-thermal cruise airspeed will be much faster.[Figure 4-10]

Variometers are sensitive to changes in pressure altitudecaused by airspeed. In still air, when the glider dives, thevariometer indicates a descent. When the glider pulls outof the dive and begins a rapid climb, the variometer indi-cates an ascent. This indication is sometimes called a "stickthermal." A glider lacking a compensated variometer mustbe flown at a constant airspeed to receive an accurate variometer indication.

TOTAL ENERGY SYSTEMA variometer with a total energy system senseschanges in airspeed and tends to cancel out the result-ing climb and dive indications (stick thermals). This isdesirable because the glider pilot wants to know howrapidly the airmass is rising or descending despitechanges in airspeed.

Figure 4-9. When an electric variometer is mountedin the glider a non-electric variometer is usuallyinstalled as a backup.

Figure 4-10. The MacCready ring.

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A popular type of total energy system consists of asmall venturi mounted in the air stream and connectedto the static outlet of the variometer. When airspeedincreases, more suction from the venturi moderates thepressure at the static outlet of the variometer. Similarly,when airspeed decreases, reduced suction from theventuri moderates the pressure at the static outlet of thevariometer. If the venturi is properly designed andinstalled, the net effect is to reduce climb and dive indi-cations caused by airspeed changes.

Another type of total energy system is designed with adiaphragm-type compensator placed in line from thepitot tube to the line coming from the capacity flask.Deflection of the diaphragm is proportional to theeffect the airspeed change has on pitot pressure. Ineffect, the diaphragm modulates pressure changes inthe capacity flask. When properly adjusted, thediaphragm compensator does an adequate job of maskingstick thermals. [Figure 4-11]

NETTOA variometer that indicates the vertical movement ofthe airmass, regardless of the sailplane’s climb ordescent rate, is called a NETTO variometer system.Some NETTO variometer systems employ a calibratedcapillary tube that functions as a tiny valve. Pitot pres-sure pushes minute quantities of air through the valveand into the reference chamber tubing. The effect is toremove the glider’s sink rate at various airspeeds fromthe variometer indication (polar sink rate). [Figure 4-12]

Electronic, computerized NETTO variometers employa different method to remove the glider performancepolar sink rate from the variometer indication. In thistype of system, sensors for both pitot pressure andstatic pressure provide airspeed information to thecomputer. The sink rate of the glider at every airspeedis stored in the computer memory. At any given air-speed, the sink rate of the glider is mathematicallyremoved, and the variometer displays the rate of ascentor descent of the airmass itself.

Figure 4-11. A total energy variometer system.

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ELECTRONIC FLIGHT COMPUTERSElectronic flight computers are found in the cockpits ofgliders that are flown in competition and cross-countrysoaring. Since non-powered gliders lack a generator oralternator, electrical components, such as the flightcomputer and VHF transceiver, draw power from theglider battery or batteries. The battery is usually a 12 or14 volt sealed battery. Solar cells are sometimesarrayed behind the pilot or on top of the instrumentpanel cover to supply additional power to the electricalsystem during flight in sunny conditions.

The primary components of most flight computer systems are an electric variometer, a coupled Global Positioning Satellite (GPS) receiver, and amicroprocessor. The variometer measures rate of climband descent. The GPS provides position information. Themicroprocessor interprets altitude, speed, and positioninformation. The microprocessor output aids the pilotin cross-country decision-making. [Figure 4-13]

The GPS-coupled flight computer can provide you withthe following information.

• Where you are.• Where you have been.• Where you are going.• How fast you are going there.• How high you need to be to glide there.• How fast you are climbing or descending.• The optimum airspeed to fly to the next area of

anticipated lift.• The optimum airspeed to fly to a location on the

ground, such as the finish line in a race, or the airport of intended landing at the end of a cross-country flight.

The primary benefits of the flight computer can easilybe divided into two areas: navigation assistance andperformance (speed) enhancement.

Fundamental to the use of the flight computer is theconcept of waypoint. A waypoint is simply a point inspace. The three coordinates of the point are latitude,longitude, and altitude. Glider races and cross-countryglider flights frequently involve flight around a seriesof waypoints called turnpoints. The course may be anout-and-return course, a triangle, a quadrilateral orother type of polygon, or a series of waypoints laid outmore or less in a straight line. The glider pilot mustnavigate from point to point, using available liftsources to climb periodically so that that flight can continue to the intended goal. The GPS-enabled flightcomputer aids in navigation and in summarizing howthe flight is going. When strong lift is encountered, andif the pilot believes it is likely that the strong lift sourcemay be worth returning to after rounding a turnpoint,the flight computer can "mark" the location of the ther-mal. Then the glider pilot can round a nearby turnpointand use the flight computer to guide the return to themarked thermal in the hopes of making a rapid climband heading out on course toward the next turnpoint.

During the climb portion of the flight, the flight computer's variometer constantly updates the achievedrate of climb. During cruise, the GPS-coupled flightcomputer aids in navigating accurately to the next turn-point. The flight computer also suggests the optimumcruise airspeed for the glider to fly, based on theexpected rate of climb in the next thermal.

During final glide to a goal, the flight computer can display glider altitude, altitude required to reach thegoal, distance to the goal, the strength of the headwindor tailwind component, optimum airspeed to fly, glider

Figure 4-13. Flight computer system display.

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groundspeed, and the amount of time it will take toreach the goal.

Most flight computers incorporate an electronic audiovi-sual variometer. The rate of climb or descent can beviewed on the computer's visual display. The variometeralso provides audible rate of climb information througha small loudspeaker. The loudspeaker allows the pilotto hear how fast the glider is climbing or descending.Because this information is received through hearing,the pilot's vision can be constantly directed outside theglider to enhance safety of flight and cross-country per-formance.

Flight computers also provide information to help thepilot select and fly the optimum airspeed for the weatherconditions being encountered. When lift is strong andclimbs are fast, higher airspeeds around the course arepossible. The flight computer detects the rapid climbsand suggests very fast cruise airspeeds to enhance performance. When lift is weak and climbs are slow,optimum airspeed will be significantly slower thanwhen conditions are strong. The flight computer, sens-ing the relatively slow rate of climb on a difficult day,compensates for the weaker conditions and suggestsoptimum airspeeds that are slower than they would be ifconditions were strong. The flight computer relieves thepilot of the chore of making numerous speed-to-fly cal-culations during cross-country flight. This freedomallows the pilot to look for other air traffic, look for sources of lift, watch the weather ahead,and plot a strategy for the remaining portion of the flight.

The presence of water ballast alters the performancecharacteristics of the glider. In racing, the ability tomake faster glides without excess altitude penalty isvery valuable. The additional weight of water in theglider's ballast tanks allows flatter glides at high air-speeds. The water-ballast glider possesses the strongestadvantage when lift conditions are strong and rapidclimbs are achievable. The flight computer compen-sates for the amount of water ballast carried, adjustingspeed-to-fly computations according to the weight andperformance of the glider. Some flight computersrequire the pilot to enter data regarding the ballast con-dition of the glider. Other flight computers automati-cally compensate for the effect of water ballast byconstantly measuring the performance of the glider anddeducting the operating weight of the glider from thesemeasurements. If the wings of the glider become con-taminated with bugs, glider performance will decline.The glide computer can be adjusted to account for theresulting performance degradation.

MAGNETIC COMPASSThe magnetic compass, which is the only direction-seek-ing instrument in the glider, is simple in construction. It

contains two steel magnetized needles fastened to afloat around which a compass card is mounted. Theneedles are parallel, with their north-seeking endspointed in the same direction. The compass card hasletters for cardinal headings, and each 30° interval isrepresented by a number, the last zero of which is omitted. For example, 30° would appear as a 3 and300° would appear as 30. Between these numbers, thecard is graduated for each 5°. [Figure 4-14]

The float assembly is housed in a bowl filled with acid-free white kerosene. The purposes of the liquidare to dampen out excessive oscillations of the com-pass card, and relieve by buoyancy part of the weightof the float from the bearings. Jewel bearings are usedto mount the float assembly on top of a pedestal. A line(called the lubber line) is mounted behind the glass ofthe instrument that can be used for a reference linewhen aligning the headings on the compass card.

Figure 4-14. A magnetic compass.

Figure 4-15. Earth magnetic force flow.

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The magnetic compass works on the principle of magnetism. The glider pilot must have a basic under-standing of the principles of operation of the magneticcompass. A simple bar magnet has two centers of mag-netism, which are called poles. Lines of magnetic forceflow out from each pole in all directions, eventuallybending around and returning to the other pole. The areathrough which these lines of force flow is called thefield of the magnet. For the purpose of this discussion,the poles are designated "north" and "south." If two barmagnets are placed near each other, the north pole ofone will attract the south pole of the other. There is evi-dence that there is a magnetic field surrounding theEarth, and this theory is applied in the design of themagnetic compass. It acts very much as though therewere a huge bar magnet running along the axis of theEarth, which ends several hundred miles below the sur-face. [Figure 4-15]

The lines of force have a vertical component (or pull),which is zero at the Equator, but builds to 100 percent ofthe total force at the poles. If magnetic needles, such asthe glider magnetic compass bars, are held along theselines of force, the vertical component causes one end ofthe needle to dip or deflect downward. The amount of dipincreases as the needles are moved closer and closer to thepoles. It is this deflection or dip that causes some of thelarger compass errors.

MAGNETIC VARIATION Although the magnetic field of the Earth lies roughlynorth and south, the Earth’s magnetic poles do not coincide with its geographic poles, which are used in theconstruction of aeronautical charts. Consequently, atmost places on the Earth’s surface, the direction-sensi-tive steel needles, which seek the Earth’s magnetic field,will not point to True North but to Magnetic North.Furthermore, local magnetic fields from mineraldeposits and other conditions may distort the Earth’smagnetic field and cause an additional error in the posi-tion of the compass’ north-seeking magnetized needles with refer-ence to True North. The angular difference between TrueNorth and the direction indicated by the magnetic com-pass—excluding deviation error—is variation. Variationis different for different points on the Earth’s surface andis shown on the aeronautical charts as broken lines con-necting points of equal variation. These lines are isogoniclines. The line where the magnetic variation is zero is anagonic line. [Figure 4-16]

MAGNETIC DEVIATION A compass is very rarely influenced solely by theEarth’s magnetic lines of force. Magnetic disturbancesfrom magnetic fields produced by metals and electricalaccessories in a glider disturb the compass needles andproduce an additional error known as deviation.

Figure 4-16. Earth’s magnetic field.

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If a glider changes heading, the compass’ direction-sensitive magnetized needles will continue to point inabout the same direction while the glider turns withrelation to it. As the glider turns, metallic and electricalequipment in the glider change their position relativeto the steel needles; hence, their influence on the com-pass needle changes and deviation changes. The devia-tion depends, in part, on the heading of the glider.Although compensating magnets on the compass areadjusted to reduce this deviation on most headings, itis impossible to eliminate this error entirely on allheadings. A deviation card is installed in the cockpit inview of the pilot, enabling the pilot to maintain thedesired magnetic headings. [Figure 4-17]

COMPASS ERRORSSince the compass card is suspended in fluid, the mag-netic compass is sensitive to in-flight turbulence. Inlight turbulence, you may be able to use the compassby averaging the readings. For example, if the com-pass swings between 40º and 70º, you can estimate theapproximate magnetic heading of 55º. In severe tur-

bulence, however, the magnetic compass may be sodisturbed that is unusable for navigation.

Since the magnetic compass is the only direction-seekinginstrument in most gliders, the pilot must be able to turnthe glider to a magnetic compass heading and maintainthis heading. It will help to remember the following char-acteristics of the magnetic compass, which are caused bymagnetic dip. These characteristics are only applicable inthe Northern Hemisphere. In the Southern Hemispherethe opposite is true.

ACCELERATION ERRORWhen on an east or west heading, no error is apparentwhile entering a turn to north or south. However, anincrease in airspeed or acceleration will cause the com-pass to indicate a turn toward north; a decrease in air-speed or acceleration will cause the compass to indicatea turn toward south. On a north or south heading, noerror will be apparent because of acceleration or decel-eration. [Figure 4-18]

Figure 4-17. Compass correction card.

Figure 4-18. Acceleration error on a compass in the Northern Hemisphere.

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TURNING ERRORThe turning error is directly related to magnetic dip; thegreater the dip, the greater the turning error. It is mostpronounced when you are turning to or from headings ofnorth or south. When you begin a turn from a heading ofnorth, the compass starts to turn in the opposite directionand it lags behind the actual heading. As the turn continues,the amount of lag decreases, then disappears, as theglider reaches a heading of east or west.

When initiating a turn from a heading of east or west toa heading of north, there is no error as you begin theturn. As the heading approaches north, the compassincreasingly lags behind the glider’s actual heading.

When you turn from a heading of south, the compass ini-tially indicates a turn in the proper direction but at afaster rate, and leads the glider’s actual heading. Thiserror also cancels out as the glider reaches a heading ofeast or west. Turning from east or west to a heading ofsouth causes the compass to move correctly at the startof a turn, but then it increasingly leads the actual headingas the glider nears a southerly direction. [Figure 4-19]

The amount of lead or lag is approximately equal to thelatitude of the glider. For example, if you are turningfrom a heading of south to a heading of west while fly-ing at 35º north latitude, the compass will rapidly turnto a heading of 215º (180º+35º). At the midpoint of theturn, the lead will decrease to approximately half(17.5º), and upon reaching a heading of west, it will bezero. The lead and lag errors discussed here are onlyvalid in the Northern Hemisphere. Lead and lag errorsin the Southern Hemisphere act in opposite directions.

YAW STRINGThe most effective, yet least expensive, slip/skid indicator is made from a piece of yarn mounted in thefree airstream in a place easily visible to the pilot asshown in Figure 4-20. The yaw string helps you coor-

Figure 4-20. The yaw string and Inclinometer.

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dinate rudder and aileron inputs. When the controls areproperly coordinated, the yarn points straight back,aligned with the longitudinal axis of the glider. Duringa slipping turn, the tail of the yaw string will be offsettoward the outside of the turn. To center the yaw stringin a slipping turn, add pressure to the rudder pedal thatis opposite the tail of the yaw string. During a skiddingturn, the tail of the yaw string will be offset toward theinside of the turn. To center the yaw string in a skid-ding turn, add pressure to the rudder pedal that is oppo-site the tail of the yaw string.

INCLINOMETERAnother type of slip/skid indicator is the inclinometer.Mounted in the bottom of a turn-and-bank indicator ormounted separately in the instrument panel, the incli-nometer consists of a metal ball in an oil-filled, curvedglass tube. When the glider is flying in coordinated fash-ion, the ball remains centered at the bottom of the glasstube. The inclinometer differs from the yaw string dur-ing uncoordinated flight. The ball moves to the inside ofthe turn to indicate a slip and to the outside of the turn toindicate a skid. If you remember the phrase "step on the

ball" in reference to the inclinometer, it will help youcoordinate the turn using rudder inputs.

GYROSCOPIC INSTRUMENTSGyroscopic instruments are found in virtually all mod-ern airplanes but are infrequently found in gliders.This section is designed to provide you with a basicunderstanding of how gyroscopic instruments func-tion. The three gyroscopic instruments found most fre-

quently in a glider are the heading indicator, the atti-tude indicator, and the turn coordinator.

RIGIDITY IN SPACERigidity in space and precession are the two fundamen-tal concepts that affect the operation of gyroscopicinstruments. Rigidity in space refers to the principlethat a gyroscope remains in a fixed position in the planein which it is spinning. By mounting this wheel, or

Figure 4-21. Regardless of the position of its base, agyro tends to remain rigid in space, with its axis ofrotation pointed tin a constant direction.

Figure 4-22. Precession of a gyroscope results froman applied deflective force.

Figure 4-23. Electric powered gyro system.

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gyroscope, on a set of gimbal rings, the gyro is able torotate freely in any direction. Thus, if the gimbal ringsare tilted, twisted, or otherwise moved, the gyroremains in the plane in which it was originally spin-ning. [Figure 4-21]

PRECESSIONPrecession is the tilting or turning of a gyro inresponse to a deflective force. The reaction to thisforce does not occur at the point where it was applied;rather, it occurs at a point that is 90° later in the directionof rotation. This principle allows the gyro to determine arate of turn by sensing the amount of pressure created bya change in direction. The rate at which the gyro pre-cesses is inversely proportional to the speed of the rotorand proportional to the deflective force. [Figure 4-22]

Gyroscopic instruments require a power source to keepthe gyro rotating at a constant rate. The most commonpower source for gliders is an electric battery. [Figure4-23]

The turn coordinator and turn-and-slip indicator bothprovide an indication of turn direction, rate, and quality.The main difference between the turn coordinator andthe turn-and-slip indicator is the manner in which turninformation is displayed. The turn coordinator uses aminiature aircraft, while the turn-and-slip indicator uti-lizes a pointer called a turn needle.

We will discuss the turn coordinator. During a turn, theminiature aircraft in the turn coordinator banks in thesame direction the glider is banked. The turn coordina-tor enables you to establish a standard-rate-turn. Youdo this by aligning the wing of the miniature aircraftwith the turn index. At this rate, the aircraft will turn 3ºper second, completing a 360º turn in two minutes. Theturn coordinator is designed to indicate the rate of turn,not the angle of bank. The turn coordinator is alsoequipped with an inclinometer to help you coordinateyour turn. [Figure 4-24]

ATTITUDE INDICATORThe attitude indicator, with its miniature aircraft andhorizon bar, displays a picture of the attitude of theglider. The relationship of the miniature aircraft to thehorizon bar is the same as the relationship of the realaircraft to the actual horizon. The instrument gives aninstantaneous indication of even the smallestchangesin attitude. [Figure 4-25]

The gyro in the attitude indicator is mounted on a horizontal plane and depends upon rigidity in spacefor its operation. The horizon bar represents the truehorizon. This bar is fixed to the gyro and remains in ahorizontal plane as the glider is pitched or bankedabout its lateral or longitudinal axis, indicating the atti-tude of the glider relative to the true horizon.

An adjustment knob is provided to allow the pilot tomove the miniature aircraft up or down to align theminiature aircraft with the horizon bar to suit the pilot’sline of vision. Normally, the miniature aircraft isadjusted so the wings overlap the horizon bar when theglider is in straight-and-level cruising flight. The atti-tude indicator is reliable and the most realistic flight

Figure 4-25. Attitude Indicator.

Figure 4-26. Setting the heading indicator.

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instrument on the instrument panel. Its indications arevery close approximations of the actual attitude of theglider.

HEADING INDICATORThe operation of the heading indicator depends uponthe principle of rigidity in space. The rotor turns in avertical plane, and fixed to the rotor is a compass card.Since the rotor remains rigid in space, the points on thecard hold the same position in space relative to the ver-tical plane. As the instrument case and the gliderrevolve around the vertical axis, the card provides clearand accurate heading information.

Because of precession, caused chiefly by friction, theheading indicator will creep or drift from a heading towhich it is set. Among other factors, the amount of driftdepends largely upon the condition of the instrument.If the bearings are worn, dirty, or improperly lubri-cated, the drift may be excessive.

Bear in mind that the heading indicator is not directionseeking, as is the magnetic compass. It is important tocheck the indications frequently and reset the headingindicator to align it with the magnetic compass whenrequired. Adjusting the heading indicator to the mag-netic compass heading should be done only when theglider is in wings-level unaccelerated flight; otherwise

erroneous magnetic compass readings may beobtained. [Figure 4-26]

G-METERAnother instrument that can be mounted in the instrumentpanel of a glider is a G-meter. The G-meter measures anddisplays the load imposed on the glider during flight.During straight, unaccelerated flight in calm air, a gliderexperiences a load factor of 1G (1.0 times the force ofgravity). During aerobatics or during flight in turbulentair, the glider and pilot experience G-loads greater than1G. These additional loads result from accelerationsimposed on the glider. Some of these accelerations resultfrom external sources, such as flying into updrafts ordowndrafts. Other accelerations arise from pilot input onthe controls, such as pulling back or pushing forward onthe control stick. G-loads are classified as positive or neg-ative. Positive G is felt when increasing pitch rapidly fora climb. Negative G is felt when pushing over into a diveor during sustained inverted flight. Each glider type isdesigned to withstand a specified maximum positive G-load and a specified maximum negative G-load. TheGFM/POH is the definitive source for this information.Exceeding the allowable limit loads may result in defor-

mation of the glider structure. In extreme cases,exceeding permissible limit loads may cause structuralfailure of the glider. The G-meter allows the pilot to mon-itor G-loads from moment to moment. This is useful inaerobatic flight and during flight in rough air. Most G-meters also record and display the maximum positive G-load and the maximum negative G-load encounteredduring flight. The recorded maximum positive and nega-tive G-loads can be reset by adjusting the control knob ofthe G-meter. [Figure 4-27]

Figure 4-27. The G-meter. Figure 4-28. A typical outside air temperature (OAT)gauge.

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OUTSIDE AIR TEMPERATUREGAUGEThe outside air temperature gauge (OAT) is a simple andeffective device mounted so that the sensing element isexposed to the outside air. The sensing element consistsof a bimetallic-type thermometer in which two dissimilarmetals are welded together into a single strip and twistedinto a helix. One end is anchored into a protective tube,and the other end is affixed to the pointer, which readsagainst the calibration on a circular face. OAT gauges arecalibrated in degrees Celsius, degrees Fahrenheit, or both.An accurate air temperature will provide the glider pilotwith useful information about temperature lapse rate withaltitude change.

When flying a glider loaded with water ballast, knowledgeof the height of the freezing level is important to safety offlight. Extended operation of a glider loaded with waterballast in below-freezing temperatures may result in frozendrain valves, ruptured ballast tanks, and structural damageto the glider. [Figure 4-28]

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5-1

Glider performance during launch phase and duringfree flight phase depends on many factors. The designof the glider itself is one factor. Weather, wind, andother atmospheric phenomena also affect glider per-formance.

FACTORS AFFECTINGPERFORMANCEGlider performance during launch depends on thepower output of the launch mechanism and on theaerodynamic efficiency of the glider itself. The threemajor factors that affect performance are density alti-tude, weight, and wind.

DENSITY ALTITUDEAir density directly affects the launch performance ofthe glider. As the density of the air increases, theengines power output of the launching vehicle (tow-plane, ground tow, or self-launch glider) and the aero-dynamic lift of the glider’s wings increase. When airdensity is less dense, the launch performancedecreases. Density altitude is the altitude above meansea level (MSL) at which a given atmospheric densityoccurs in the standard atmosphere. It can also beinterpreted as pressure altitude corrected for nonstan-dard temperature differences.

PRESSURE ALTITUDEPressure altitude is displayed as the height above astandard datum plane, which, in this case, is a theoret-ical plane where air pressure is equal to 29.92 inchesof mercury (in. Hg). Pressure altitude is the indicatedheight value on the altimeter when the altimeter settingis adjusted to 29.92 in. Hg. Pressure altitude, asopposed to true altitude, is an important value for cal-culating performance as it more accurately representsthe air content at a particular level.

The difference between true altitude and pressure alti-tude must be clearly understood. True altitude meansthe vertical height of the glider above MSL. True alti-tude is displayed on the altimeter when the altimeter isadjusted to the local atmospheric pressure setting.

For example, if the local altimeter setting is 30.12 in.Hg., and the altimeter is adjusted to this value, the

altimeter indicates exact height above sea level.However, this does not reflect conditions found at thisheight under standard conditions. Since the altimetersetting is more than 29.92 in. Hg., the air in this exam-ple has a higher pressure, and is more compressedindicative of the air found at a lower altitude.Therefore, the pressure altitude is lower than the actualheight above MSL.

To calculate pressure altitude without the use of analtimeter, remember that the pressure decreasesapproximately 1 inch of mercury for every 1,000-footincrease in altitude. For example, if the current localaltimeter setting at a 4,000-foot elevation were 30.42,the pressure altitude would be 3,500 feet. (30.42 -29.92 = .50 in. Hg. x 1,000 feet = 500 feet. Subtracting500 feet from 4,000 equals 3,500 feet).

The four factors that affect density altitude the most areatmospheric pressure, altitude, temperature, and themoisture content of the air.

ATMOSPHERIC PRESSUREDue to changing weather conditions, atmospheric pres-sure at a given location changes from day to day. Whenbarometric pressure drops, air density decreases. Thereduced density of the air results in an increase in den-sity altitude and decreased glider performance. Thisreduces takeoff and climb performance and increasesthe length of runway needed for landing.

When barometric pressure rises, air density increases.The greater density of the air results in lower densityaltitude. Thus, takeoff and climb performance improves,and the length of runway needed for landing decreases.

ALTITUDEAs altitude increases, air density decreases. At altitude,the atmospheric pressure that acts on a given volumeof air is less, allowing the air molecules to space them-selves further apart. The result is that a given volumeof air at high altitude contains fewer air molecules thanthe same volume of air at lower altitude. As altitudeincreases, density altitude increases, and glider takeoffand climb performance is reduced.

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TEMPERATURETemperature changes have a large affect on density alti-tude. When air is heated, it expands and the moleculesmove farther apart, creating less dense air. Takeoff andclimb performance is reduced, while the length of run-way required for landing is increased.

The effects are different when the air is cool. When air-cools, the molecules move closer together, creatingdenser air. Takeoff and climb performance improves,and the length of runway required for landingdecreases.

The effect of temperature on density altitude can bevery great. High temperatures cause even low eleva-tions to have high-density altitudes, resulting inreduced takeoff and climb performance. Very cold tem-peratures, on the other hand, can result in density alti-tudes that are far below those at sea level. In this dense,cold air, takeoff and climb performance is enhancedconsiderably.

MOISTURE The water vapor content of the air affects air density.Water vapor molecules, consisting of two hydrogenatoms and one oxygen atom, have a relatively lowmolecular weight. Water vapor molecules in the atmos-phere displace gas molecules with higher molecularweights. Therefore, as the water vapor content of theair increases, the air becomes less dense. The result isincreased density altitude and decreased takeoff andclimb performance.

Relative humidity refers to the amount of water vaporcontained in the atmosphere. It is expressed as a per-centage of the maximum amount of water vapor the aircan hold. Perfectly dry air (air that contains no watervapor) has a relative humidity of 0 percent, while satu-rated air (air that cannot hold any more water vapor)has a relative humidity of 100 percent.

The amount of water vapor that an airmass can sustainis affected by temperature. Cold air can hold a rela-tively small amount of water as vapor; warm air canhold much more. Increasing the temperature of an air-mass by 20°F doubles the amount of water the airmasscan hold as water vapor. Increasing the temperature ofan airmass by 40°F quadruples the amount of water theairmass can hold. Increasing the temperature of an air-mass by 60°F causes an eightfold increase and so on.

By itself, humidity usually is not considered an impor-tant factor in calculating density altitude and glider per-formance. Nevertheless, high humidity does cause aslight decrease in glider takeoff and climb perform-ance. At relatively low temperatures, the effect ofhumidity is very slight because the total amount ofwater vapor the airmass can hold is relatively small. At

relatively high temperatures, on the other hand, theeffect of humidity is more significant because the totalamount of water vapor the airmass can hold is manytimes larger. There are no rules-of-thumb or charts usedto compute the effects of humidity on density altitude.Expect a minor decrease in takeoff performance whenhumidity is high.

HIGH AND LOW DENSITY ALTITUDECONDITIONSEvery pilot must understand the terms “high densityaltitude” and “low density altitude.” In general, highdensity altitude refers to thin air, while low density alti-tude refers to dense air. Those conditions that result ina high density altitude (thin air) are high elevations,low atmospheric pressure, high temperatures, highhumidity, or some combination thereof. Lower eleva-tions, high atmospheric pressure, low temperatures andlow humidity are more indicative of low density alti-tude (dense air). However, high density altitudes maybe present at lower elevations on hot days, so it isimportant to calculate the density altitude and deter-mine performance before a flight.

One way to determine density altitude is to use chartsdesigned for that purpose. [Figure 5-1] For example,assume you are planning to depart an airport where thefield elevation is 1,165 feet MSL, the altimeter settingis 30.10, and the temperature is 70°F. What is the den-sity altitude? First, correct for nonstandard pressure(30.10) by referring to the right side of the chart andsubtracting 165 feet from the field elevation. The resultis a pressure altitude of 1,000 feet. Then, enter the chartat the bottom, just above the temperature of 70°F(21°C). Proceed up the chart vertically until you inter-cept the diagonal 1,000-foot pressure altitude line, thenmove horizontally to the left and read the density alti-

Figure 5-1. Density Altitude Chart.

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nose of the glider pointed somewhat upwind of thetarget on the ground. For instance, if the crosswind isfrom the right, during final glide the nose of theglider is pointed a bit to the right of the target on theground. The glider’s heading will be upwind (to theright, in this case) of the target, but if the angle ofcrab is correct, the glider’s track will be straighttoward the target on the ground. [Figure 5-3]

tude of approximately 2,000 feet. This means your self-launching glider or towplane will perform as if it wereat 2,000 feet MSL on a standard day.

Most performance charts do not require you to com-pute density altitude. Instead, the computation is builtinto the performance chart itself. All you have to do isenter the chart with the correct pressure altitude andthe temperature. Some charts, however, may requireyou to compute density altitude before entering them.Density altitude may be computed using a density alti-tude chart or by using a flight computer.

WINDSWind affects glider performance in many ways.Headwind during launch results in shorter ground roll,while tailwind causes longer ground roll before take-off. Crosswinds during launch require proper cross-wind procedures. [Figure 5-2]

During cruising flight, headwinds reduce the ground-speed of the glider. A glider flying at 60 knots true air-speed into a headwind of 25 knots has a groundspeedof only 35 knots. Tailwinds, on the other hand, increasethe groundspeed of the glider. A glider flying at 60knots true airspeed with a tailwind of 25 knots has agroundspeed of 85 knots.

Crosswinds during cruising flight cause glider heading(where the glider nose is pointed) and glider track (thepath of the glider over the ground) to diverge. Whengliding toward an object on the ground in the presenceof crosswind, such as on final glide at the end of across-country flight, the glider pilot should keep the

Figure 5-2. Wind effect on takeoff distance andclimb-out angle.

Figure 5-3. Crosswind effect on final glide.

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Headwind during landing results in a shortened groundroll and tailwind results in a longer ground roll.Crosswind landings require the pilot to compensate fordrift with either a sideslip or a crab. [Figure 5-4]

Some self-launch gliders are designed for extendedperiods of powered cruising flight. For these self-launch gliders, maximum range (distance) for poweredflight and maximum duration (elapsed time aloft) forpowered flight is primarily limited by the self-launchglider’s fuel capacity. Wind has no effect on flight dura-tion but does have a significant effect on range. Duringpowered cruising flight, a headwind reduces range, anda tailwind increases range. The Glider FlightManual/Pilot’s Operating Handbook (GFM/POH) pro-vides recommended airspeeds and power settings tomaximize range when flying in no-win, headwind, ortailwind conditions.

WEIGHTIn gliding, increased weight decreases takeoff andclimb performance, but increases high speed cruiseperformance. During launch, a heavy glider takeslonger to accelerate to flying speed. The heavy gliderhas more inertia making it more difficult to acceleratethe mass of a glider to flying speed. After takeoff, theheavier glider takes longer to climb out because the

heavier glider has more mass to lift to altitude thandoes the lighter glider (whether ground launch, aero-tow launch, or self-launch). [Figure 5-5]

The heavy glider has a higher stall speed and a higherminimum controllable airspeed than an otherwiseidentical, but lighter, glider. The stall speed of a gliderincreases with the square root of the increase inweight. If weight of the glider is doubled (multipliedby 2.0), then the stall speed increases by more than 40percent (1.41 is the approximate square root of 2; 1.41times the old stall speed results in the new stall speedat the heavier weight).

When circling in thermals to climb, the heavy glider isat a disadvantage relative to the light glider. Theincreased weight of the heavy glider means stall air-speed and minimum sink airspeed is faster than theywould be if the glider were operating at a light weight.At any given bank angle, the heavy glider’s faster air-speeds mean the pilot must fly larger diameter therma-ling circles than the pilot of the light glider. Since thebest lift in thermals is often found in a narrow cylindernear the core of the thermal, larger diameter circlesgenerally mean the heavy glider is unable to exploitthe strong lift of the thermal core, as well as the slower,lightweight glider. This results in the heavy glider’sinability to climb as fast in a thermal as the light glider.[Figure 5-6]

The heavy glider can fly faster than the light gliderwhile maintaining the same glide ratio as the lightglider. The advantage of the heavier weight becomesapparent during cruising flight. The heavy glider can

Figure 5-4. Wind effect on final approach and landingdistance.

Figure 5-5. Effect of weight on takeoff distance andclimbout rate and angle.

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fly faster than the light glider and still retains the samelift/drag (L/D) ratio.

If the operating weight of a given glider is increased,the stall airspeed, the minimum controllable airspeed,the minimum sink airspeed, and the best L/D airspeedwill be increased by a factor equal to the square root ofthe increase in weight. [Figure 5-7]

The addition of ballast to increase weight allows theglider to fly at faster airspeeds while maintaining itsL/D ratio. The table in Figure 5-7 shows that adding400 pounds of water ballast increases the best L/D air-speed from 60 knots to 73 knots. The heavy glider willhave more difficulty climbing in thermals than the lightglider, but if lift is strong enough for the heavy glider toclimb reasonably well, the heavy glider’s advantageduring the cruising portion of flight will outweigh theheavy glider’s disadvantage during climbs.

Water is often used as ballast to increase the weight ofthe glider. However, the increased weight will requirea higher airspeed during the approach and a longer

landing roll. Once the cross-country phase is com-pleted, the water ballast serves no further purpose. Thepilot should jettison the water ballast prior to enteringthe traffic pattern. Reducing the weight of the gliderprior to landing allows the pilot to make a normalapproach and landing. The lighter landing weight alsoreduces the loads that the landing gear of the glidermust support.

RATE OF CLIMB Rate of climb for the ground-launched glider primarilydepends on the strength of the ground-launch equip-ment. When ground launching, rates-of-climb gener-ally are quite rapid, and can exceed 2,000 feet perminute if the winch or tow vehicle is very powerful.

When aerotowing, rate-of-climb is determined by thepower of the towplane. It is important when selecting atowplane, to ensure that it is capable of towing theglider considering the existing conditions and gliderweight.

Self-launching glider rate-of-climb is determined bydesign, powerplant output and glider weight. The rate-of-climb of self-launch gliders may vary from as lowas 200 feet per minute to as much as 800 feet perminute or more in others. The pilot should consult theGFM/POH to determine rate-of-climb under the exist-ing conditions.

FLIGHT MANUALS AND PLACARDS

AREAS OF THE MANUALThe GFM/POH provides the pilot with the necessaryperformance information to operate the glider safely. AGFM/POH may include the following information.

• Description of glider primary components.

• Glider Assembly.

• Weight and balance data.

• Description of glider systems.

• Glider performance.

• Operating limitations.

Figure 5-6. Effect and added weight on thermalingturn radius.

Figure 5-7. Effect of added weight on performance airspeeds.

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PLACARDSCockpit placards provide the pilot with readily avail-able information that is essential for the safe operationof the glider. All required placards are located in theGFM/POH.

The amount of information that placards must conveyto the pilot increases as the complexity of the gliderincreases. High performance gliders may be equippedwith wing flaps, retractable landing gear, a water bal-last system, drogue chute for use in the landingapproach, and other features than are intended toenhance performance. These gliders may require addi-tional placards. [Figure 5-8]

PERFORMANCE INFORMATIONThe GFM/POH is the source provided by the manufac-turer for glider performance information. In theGFM/POH, glider performance is presented as termsof specific airspeed such as stall speed, minimum sink-ing airspeed, best L/D airspeed, maneuvering speed,rough air speed, and VNE.

Some performance airspeeds apply only to particulartypes of gliders. Gliders with wing flaps, for instance,have a maximum permitted flaps extended airspeed(VFE).

Manuals for self-launch gliders include performanceinformation about powered operations. These includerate-of-climb, engine and propeller limitations, fuelconsumption, endurance, and cruise.

GLIDER POLARSIn addition, the manufacturer provides informationabout the rate of sink in terms of airspeed, which issummarized in a graph called a polar curve, or simply apolar. [Figures 5-9].

The vertical axis of the polar shows the sink rate inknots (increasing sink downwards), while the horizon-tal axis shows airspeed in knots. Every type of gliderhas a characteristic polar derived either from theoreti-cal calculations by the designer or by actual in-flightmeasurement of the sink rate at different speeds. Thepolar of each individual glider will vary (even fromother gliders of the same type) by a few percentdepending on relative smoothness of the wing surface,the amount of sealing around control surfaces, andeven the number of bugs on the wing’s leading edge.The polar forms the basis for speed-to-fly and finalglide tools that will be discussed in Chapter 11–Cross-Country Soaring.

Minimum sink rate is determined from the polar byextending a horizontal line from the top of the polar tothe vertical axis. The minimum sink speed is foundby drawing a vertical line from the top of the polar tothe horizontal axis. [Figure 5-10]. In this example, aminimum sink of 1.9 knots occurs at 40 knots. Notethat the sink rate increases between minimum sinkspeed and the stall speed (the left-hand end point ofthe polar). The best glide speed (best L/D) is found bydrawing a tangent to the polar from the origin. Thebest L/D speed is 50 knots. The glide ratio at best L/Dspeed is determined by dividing the best L/D speed bythe sink rate at that speed, or 50/1.9, which is approxi-mately 26. Thus, this glider has a best glide ratio incalm air (no lift or sink and no headwind or tailwind)of 26:1 at 50 knots.

The best speed-to-fly in a headwind is easily deter-mined from the polar. To do this, shift the origin to theright along the horizontal axis by the speed of theheadwind and draw a new tangent line to the polar.From the new tangent point, draw a vertical line toread the best speed-to-fly. An example for a 20 knotheadwind is shown in Figure 5-11. The speed-to-flyin a 20 knot headwind is found to be 60 knots. By

Figure 5-8. Typical placards for non-motorized and self-launch glider.

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Figure 5-10. Graphic depiction of minimum sink airspeed and maximum L/D speed.

Figure 5-9. Dual and solo performance curves for a two-seat glider.

Figure 5-11. Best speed-to-fly in a 20-knot headwind.

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repeating the procedure for different headwinds, it isapparent that flying a faster airspeed as the headwindincreases will result in the greatest distance over theground. If this is done for the polar curves from manygliders, a general rule of thumb is found, namely, addhalf the headwind component to the best L/D for themaximum distance. For tailwinds, shift the origin tothe left of the ‘0’ mark on the horizontal axis. Thespeed-to-fly in a tailwind is found to lie between mini-mum sink and best L/D but never slower than mini-mum sink speed.

Sinking air usually exists between thermals, and it ismost efficient to fly faster than best L/D in order tospend less time in sinking air. How much faster to flycan be determined by the glider polar, as illustrated inFigure 5-12 for an air mass that is sinking at 3 knots.The polar graph in this figure has its vertical axisextended upwards. Shift the origin vertically by 3knots and draw a new tangent to the polar, then draw aline vertically to read the best speed-to-fly. For thisglider, the best speed-to-fly is found to be 60 knots.Note that the variometer will show the total sink of 5knots as illustrated in the figure.

If the glider is equipped with water ballast, wing flaps,or wingtip extensions, the performance characteristicsof the glider will be depicted in multiple configura-tions. [Figures 5-13, 5-14, and 5-15]. Comparing thepolar with and without ballast [Figure 5-13] it is evi-dent that the minimum sink is higher and occurs at afaster speed. With ballast, therefore, it would be moredifficult to work small, weak thermals. The best glideratio is the same, but it occurs at a higher speed. Inaddition, the sink rate at higher speeds is lower withballast. From the polar, then, ballast should be usedunder stronger thermal conditions for better speedbetween thermals. Note that the stall speed is higherwith ballast as well.

Flaps with a negative setting as opposed to a ‘0’ degreesetting during cruise also reduce the sink rate at higherspeeds, as shown in the polar [Figure 5-14].Therefore, when cruising at or above 70 knots, a –8flap setting would be advantageous for this glider. Thepolar with flaps set at –8 does not extend to speedsslower than 70 knots since the negative flap settingloses its advantage there.

Wing-tip extensions will also alter the polar, as shownin [Figure 5-15]. The illustration shows that the addi-tional 3 meters of wing span is advantageous at allspeeds. In some gliders, the low-speed performance isbetter with the tip extensions, while high-speed per-formance is slightly diminished by comparison.

WEIGHT AND BALANCEINFORMATIONThe GFM/POH provides information about the weightand balance of the glider. This information is correctwhen the glider is new as delivered from the factory.Subsequent maintenance and modifications can alterweight and balance considerably. Changes to theglider that affect weight and balance should be notedin the airframe logbook and on appropriate cockpitplacards. Maximum Fuselage Weight: 460 pounds

Weight is the force with which gravity attracts a bodytoward the center of the earth. It is a product of themass of a body and the acceleration acting on the body.Weight is a major factor in glider construction andoperation; it demands respect from all pilots. The pilotof a glider should always be aware of the comse-quences of overloading.

LIMITATIONSWhether the glider is very simple or very complex,designers and manufacturers provide operating limita-

Figure 5-12. Best speed-to-fly in sink.

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Figure 5-14. Performance polar with flaps at 0° and minus 8°.

Figure 5-13. Effect of water ballast on performance polar.

Figure 5-15. Performance polar with 15 meter and 18 meter wingspan configurations.

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tions which must be complied with to ensure the safetyof flight.Weight is a major factor in glider constructionand operation; it demands respect from all pilots. Thepilot of a glider should always be aware of the conse-quences of overloading.The V-G diagram provides thepilot with information on the design limitations of theglider such as limiting airspeeds and load factors. Pilotsfamiliarize themselves with all the operating limita-tions of each glider they fly. [Figure 5-16]

TERMS AND DEFINITIONSThe pilot should be familiar with terms used inworking the problems related to weight and balance.The following list of terms and their definitions iswell standardized, and knowledge of these terms willaid the pilot to better understand weight and balancecalculations of any glider.

• Arm (moment arm)—is the horizontal distance ininches from the reference datum line to the centerof gravity of an item. The algebraic sign is plus(+) if measured aft of the datum, and minus (–) ifmeasured forward of the datum.

• Ballast—is a removable weight installed to meetminimum balance conditions to comply with cen-ter of gravity limitations. Ballast may also be inthe form of water used to enhance the perform-ance of the glider.

• Center of gravity (CG)—is the point aboutwhich a glider would balance if it were possibleto suspend it at that point. It is the mass centerof the glider, or the theoretical point at whichthe entire weight of the glider is assumed to beconcentrated. It may be expressed in inchesfrom the reference datum, or in percent of meanaerodynamic chord (MAC).

• Center-of-gravity limits—are the specified for-ward and aft points within which the CG must belocated during flight. These limits are indicatedon pertinent glider specifications.

• Center-of-gravity range—is the distance betweenthe forward and aft CG limits indicated on perti-nent glider specifications.

• Datum (reference datum)—is an imaginary verti-cal plane or line from which all measurements ofarm are taken. The manufacturer establishes thedatum. Once the datum has been selected, allmoment arms and the location of CG range aremeasured from this point.

• Empty weight—is the weight as established bythe manufacturer, and which may be modified byaddition or deletion of equipment.

• Fuel load—is the expendable part of the load ofthe self-launch glider. It includes only usable

Figure 5-16. VG Diagram.

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fuel, not fuel required to fill the lines or thatwhich remains trapped in the tank sumps.

• Maximum gross weight—is a weight limitationestablished by the manufacturer that must not beexceeded. Some gliders may have two maximumgross weights, one with ballast and one without.

• Mean aerodynamic chord (MAC)—is the aver-age distance from the leading edge to the trailingedge of the wing. Some GFM/POHs present theacceptable CG range as a percent of the MeanAerodynamic Chord (MAC).

• Moment—is the product of the weight of an itemmultiplied by its arm. Moments are expressed inpound-inches (lb.-in). Total moment is the weightof the airplane multiplied by the distancebetween the datum and the CG.

• Moment index (or index)—is a moment dividedby a constant, such as 100, 1,000, or 10,000. Thepurpose of using a moment index is to simplifyweight and balance computations of gliderswhere heavy items and long arms result in large,unmanageable numbers.

• Standard weights—have been established fornumerous items involved in weight and balancecomputations. These weights should not be usedif actual weights are available. Some of the stan-dard weights are:

Gasoline.............................................6 lb./US galOil...................................................7.5 lb./US galWater.............................................8.35 lb./US gal

• Station—is a location in the airplane that is iden-tified by a number designating its distance ininches from the datum. The datum is, therefore,identified as station zero. An item located at sta-tion +50 would have an arm of 50 inches.

• Useful load—is the weight of the pilot, passen-gers, baggage, ballast, usable fuel, and drainableoil. It is the empty weight subtracted from themaximum allowable gross weight.

CENTER OF GRAVITYLongitudinal balance affects the stability of the longi-tudinal axis of the glider. To achieve satisfactory pitchattitude handling in a glider, the CG of the properlyloaded glider is forward of the Center of Pressure (CP).When a glider is produced the manufacturer providesglider center-of-gravity limitations, which must becomplied with. These limitations are generally foundin the GFM/POH and may also be found in the gliderairframe logbook. Addition or removal of equipment,

such as radios, batteries, flight instruments, or airframerepairs, can have an effect on the center of gravity posi-tion. Aviation maintenance technicians must recordany changes in the weight and balance data in theGFM/POH or glider airframe logbook. Weight and bal-ance placards in the cockpit must also be updated.

PROBLEMS ASSOCIATED WITH CGFORWARD OF FORWARD LIMITIf the center of gravity is within limits, pitch attitudecontrol stays within acceptable limits. However, if theglider is loaded so the CG is forward of the forwardlimit, handling will be compromised. Nose heavinesswill make it difficult to raise the nose on takeoff andconsiderable back pressure on the control stick will berequired to control the pitch attitude. Stalls will occur athigher than normal airspeeds and will be followed by arapid nose-down pitch tendency. Restoring a normalflight attitude during stall recoveries will take longer.The landing flare will be more difficult than normal, orperhaps even impossible, due to nose heaviness.Inability to flare could result in a hard nose-first landing.

The following are the most common reasons for CGforward of forward limit.

• Pilot weight exceeds the maximum permittedpilot weight.

• Seat or nose ballast weights are installed but arenot required due to the weight of the pilot.

PROBLEMS ASSOCIATED WITH CGAFT OF AFT LIMITIf the glider is loaded so the CG location is behind theaft limit, handling is compromised. The glider is saidto be tail-heavy. Tail heaviness can make pitch controlof the glider difficult or even impossible.

When the glider is tail-heavy recovering from a stallmay be difficult or impossible. When the stall occurs,the tail-heavy loading tends to make the glider nosecontinue to pitch upward, increasing angle of attackand complicating stall recovery. In extreme cases,recovery from stall or spin may be difficult or evenimpossible.

The following are the most common reasons for flightwith CG located behind permissible limits.

• Pilot weight is less than the specified minimumpilot seat weight and trim ballast weights neces-sary for the lightweight pilot are not installed inthe glider prior to flight.

• Tailwheel dolly is still attached, far aft on thetailboom of the glider.

• Foreign matter or debris (water, ice, mud, sand,and nests) has accumulated in the aft fuselage of

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the glider and was not discovered and removedprior to flight.

• A heavy, non-approved tailwheel or tail skid wasinstalled on the aft tailboom of the glider.

• Improper repair of the aft fuselage of the gliderresulted in an increase in aft weight of the fuse-lage that was not recorded in the glider airframelogbook, or not reflected in cockpit placards, orboth.

SAMPLE WEIGHT AND BALANCEPROBLEMS Some glider manufacturers provide weight and balanceinformation in a graphic presentation. A well-designedgraph provides a convenient way to determine whetherthe glider is within weight and balance limitations.

In Figure 5-17, the chart indicates that the minimumweight for the front seat pilot is 125 pounds, and thatthe maximum is 250 pounds. It also indicates that themaximum rear seat pilot weight is 225 pounds. If eachpilot weighs 150 pounds, the intersection of pilotweights falls within the envelope and the glider load iswithin the envelope and is safe for flight. If each pilotweights 225 pounds, the rear seat maximum load is

exceeded, and the glider load is outside the envelopeand not safe for flight.

DETERMINING CG WITHOUTLOADING CHARTSThe CG position can also be determined by calcula-tion using the following formulas:

Weight multiplied by Arm equals Moment

Weight x Arm = Moment

Total Moment divided by Total weight equals CGposition in inches aft of the reference datum.

Total Moment • Total Weight = CG

The computational method involves the application ofbasic math functions. The following is an example ofthe computational method.

Given:

Maximum Gross Weight....................1,100 lb.Empty Weight.......................................600 lb.Center-of-Gravity Range..........14.8 – 18.6 in.Front Seat Occupant.............................180 lb.Rear Seat Occupant..............................200 lb.

Figure 5-17. Graphic presentation of weight and balance envelope.

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To determine the loaded weight and CG, follow thesesteps.

Step 1—List the empty weight of the glider and theweight of the occupants.

Step 2—Enter the moment for each item listed.Remember “weight x arm = moment.” To simplify cal-culations, the moments may be divided by 100.

Step 3—Total the weight and moments.

Step 4—To determine the CG, divide the moments bythe weight.

NOTE: The weight and balance records for a particu-lar glider will provide the empty weight and moment aswell as the information on the arm distance. [Figure 5-18]

In Figure 5-18, the weight of each pilot has beenentered into the correct block in the table. For the frontseat pilot, multiplying 180 pounds by +30 inches yieldsa moment of +5400 inch/pounds. For the rear seat pilot,multiplying 200 pounds by -5 inches yields a momentof -1000 inch/pounds.

The next step is to find the sum of all weights, andrecord it: 980 pounds. Then, find the sum of allmoments, and record it: +16,400 inch/pounds.

Now we can find the Arm (the CG position) of theloaded glider. Divide the total moment by the totalweight to discover the CG of the loaded aircraftglider.So, +16,400 divided by 980 = +16.73 inches fromdatum. [Figure 5-20]

We now know the total weight (980 pounds) and theCG location (+16.73 inches from datum) of the loadedglider. The final step is to determine whether these twovalues are within acceptable limits. The GFM/POHlists the maximum gross weight as 1,100 pounds. Theoperating weight of 980 pounds is less than 1,100pounds maximum gross weight. The GFM/POH lists

the approved CG range as between +14.80 inches and+18.60 inches from datum. The operating CG is+16.73 inches from datum and is within these limits.We have determined that the weight and balance arewithin operating limits.

BALLAST WEIGHTBallast weight is non-structural weight that is addedto a glider. In gliding, ballast weight is used for twopurposes. Trim ballast is used to adjust the locationof the center of gravity of the glider so handlingcharacteristics remain within acceptable limits.Performance ballast is loaded into the glider toimprove high-speed cruise performance.

Removable trim ballast weights are usually made ofmetal and are bolted into a ballast receptacle incor-porated in the glider structure. The manufacturergenerally provides an attachment point well forwardin the glider cabin for trim ballast weights. Theseweights are designed to compensate for a front seatpilot who weighs less than the minimum permissiblefront seat pilot weight. The ballast weight mountedwell forward in the glider cabin helps place the CGwithin permissible limits.

Some trim ballast weights are in the form of seat cush-ions, with sand or lead shot sewn into the unit to pro-vide additional weight. This type of ballast, which isinstalled under the pilot’s seat cushion, is inferior tobolted-in ballast because of the propensity to shiftposition. Seat cushion ballast should never be usedduring acrobatic or inverted flight.

EFFECTS OF WATER BALLASTSometimes trim ballast is water placed in a tail tankin the vertical fin of the fuselage. The purpose of thefin trim ballast tank is to adjust CG location afterwater is added to, or drained from, the main wingballast tanks. Unless the main wing ballast tanks areprecisely centered on the center of gravity of theloaded aircraftglider, CG location shifts when water isadded to the main ballast tanks. CG location shifts

Figure 5-18. Weight and balance: front and rear seat pilot weights and moments.

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again when water is dumped from the main ballasttanks. Adjusting the amount of water in the fin tankcompensates for CG shifts resulting from changes inthe amount of water ballast carried in the main wingballast tanks. Water weighs 8.35 pounds per gallon.Because the tail tank is located far aft, it does not takemuch water to have a considerable effect on CG loca-tion. For this reason, tail tanks do not need to contain alarge volume of water. Tail tank maximum watercapacity is generally less than two gallons of water.

Although some older gliders employed bags of sand orbolt-in lead weights as performance ballast, water isused most commonly to enhance high-speed perform-ance in modern sailplanes. Increasing the operatingweight of the glider increases the optimum speed-to-flyduring wings-level cruising flight. The higher ground-speed that result provide a very desirable advantage incross-country soaring and in sailplane racing.

Water ballast tanks are located in the main wing panels.Clean water is added through fill ports in the top ofeach wing. In most gliders, the water tanks or bags canbe partially or completely filled, depending on thepilot’s choice of operating weight. After water is added,the filler caps are replaced to prevent water from slosh-ing out of the filler holes.

Drain valves are fitted to the bottom of each tank. Thevalves are controlled from inside the cockpit. The tankscan be fully or partially drained while the glider is onthe ground to reduce the weight of the glider prior tolaunch, if the pilot so desires. The ballast tanks also canbe partially or completely drained in flight—a processcalled dumping ballast. The long streaks of white spraybehind a speeding airborne glider are dramatic evi-dence that the glider pilot is dumping water ballast,most likely to lighten the glider prior to landing. Thefiller caps are vented to allow air to enter the tanks toreplace the volume of water draining from the tanks. It

is important to ensure that the vents are working prop-erly to prevent wing damage when water ballast isdrained or jettisoned. [Figures 5-19 and 5-20]

It is important to check the drain valves for correctoperation prior to flight. Water ballast should drainfrom each wing tank at the same rate. Unequal drainingleads to a wing-heavy condition that makes in-flighthandling, as well as landings, more difficult. If thewing-heavy condition is extreme, it is possible the pilotwill lose control of the glider.

Ballast drains should also be checked to ensure thatwater ballast drains properly into the airstream,rather than leaking into the fuselage and pooling inthe bottom of the fuselage. Water that is trapped inthe fuselage may flow through or over bulkheads,causing dislocation of the CG of the glider. This canlead to loss of control of the glider.

The flight manual provides guidance as to the length oftime it takes for the ballast tanks to drain completely.For modern gliders, it takes about 3 to 5 minutes todrain a full tank. When landing is imminent, dump bal-last early enough to give the ballast drains sufficienttime to empty the tanks.

Use of water ballast when ambient temperatures arelow can result in water freezing the drain valve. If thedrain valve freezes, dumping ballast is difficult orimpossible. If water in the wings is allowed to freeze,serious wing damage is likely to occur. Damage occursbecause the volume of water expands during the freez-ing process. The resulting increased volume candeform ribs and other wing structures, or cause gluebonds to de-laminate. When weather or flight condi-tions are very cold, do not use water ballast unless anti-freeze has been added to the water. Prior to using ananti-freeze solution, consult the glider flight manual toensure that anti-freeze compounds are approved for usein the glider.

A glider carrying large amounts of water ballast hasnoticeably different handling characteristics than thesame glider without water ballast. Water ballast:

• Reduces the rate of acceleration of the glider atthe beginning of the launch due to the increasedglider weight.

• Increases the length of ground roll prior to gliderliftoff.

• Increases stall speed.

• Reduces aileron control during the takeoff roll,increasing the chance of uncontrolled wing dropand resultant ground loop.

• Reduces rate of climb during climb-out.

• Reduces aileron response during free flight. Theaddition of large amounts of water increases lat-

Figure 5-19. Water ballast tank vented filler cap.

5-15

eral stability substantially. This makes quickbanking maneuvers difficult or impossible to per-form.

Water ballast is routinely dumped before landing toreduce the weight of the glider. Dumping ballast:

• Decreases stall speed.

• Decreases the optimum airspeed for the landingapproach.

• Shortens landing roll.

• Reduces the load that glider structures must sup-port during landing and rollout.

The performance advantage of water ballast duringstrong soaring conditions is considerable. However,there is a down side. The pilot should be aware thatwater ballast degrades takeoff performance, climb rate,and low speed handling. Before committing to launch-ing with water ballast aboard, the pilot should reviewoperating limitations to ensure the safety of flight willnot be comprised.

Figure 5-20. Water ballast drain valve handles.

5-16

5-17

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Operating a glider requires meticulous assembly andpreflight. Proper assembly techniques, followed by aclose inspection of the glider using checklists con-tained in the Glider Flight Manual/Pilot’s OperatingHandbook (GFM/POH), are essential for flightsafety. In order to ensure correct and safe proceduresfor assembly of a glider, students and pilots unfamil-iar with glider assembly should seek instruction froma knowledgable glider flight instructor or certificatedprivate or higher glider pilot. Safely launching aglider requires careful inspection, appropriate use ofchecklists, and quality teamwork. Launch proceduresshould be carried out systematically and consistentlyeach time you fly.

ASSEMBLY TECHNIQUESWhile preparing to assemble a glider, consider the fol-lowing elements: location, number of crewmembers,tools and parts necessary, and checklists that detail theappropriate assembly procedures. The GFM/POHshould contain checklists for assembling and preflight-ing your glider. If not, develop your own and follow itevery time you fly. Haphazard assembly and preflightprocedures can lead to unsafe flying conditions.

Before assembling a glider, find a location that shieldsthe project from the elements and offers enough roomfor completion. Wind is an important factor to considerduring an outdoor assembly. Each wing is an airfoilregardless of whether or not it is connected to the fuse-lage; even a gentle breeze is enough to produce lift onthe wings, making them cumbersome or impossible tohandle. If assembling the glider in a spot shielded fromthe wind, great care must still be taken when handlingthe wings.

When performing the assembly inside a hangar,ensure there is enough room to maneuver the glider’scomponents throughout the process. Also, considerthe length of time you anticipate to complete the entireprocedure, and choose an area that allows completeundisturbed assembly. Moving the glider duringassembly may cause parts or tools to be misplaced.

Wing stands, pliers, screwdrivers, and lubricantsshould be on hand when assembling the glider. [Figure6-1] To stay organized, use a written assembly check-

list, and keep an inventory of parts and tools. Once theassembly is complete account for all parts and tools.Objects inadvertently misplaced in the glider couldbecome jammed in the flight controls, making controldifficult if not impossible.

Depending on the type of glider, two or more peoplemay be required for assembly. It is important for every-one involved to maintain focus throughout the assem-bly process in order to avoid missed steps. Outsidedisturbances should also be avoided. Once the assem-bly is finished, a thorough inspection of all attachpoints ensures that bolts and pins were installed andsecured properly.

TRAILERING Trailers are used to transport, store, and retrieve glid-ers. [Figure 6-2] The components of the glider shouldfit snuggly without being forced, be guarded againstchafing, and be well secured within the trailer. Oncethe loading is completed, take a short drive, stop, andcheck for rubbing or chafing of components.

Figure 6-1. Wing stand used during glider assembly.

Figure 6-2. Open and closed trailers.

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Prior to taking the trailer on the road, complete a thor-ough inspection. Inspect the tires for proper inflationand adequate tread; check all lights to make sure theyare operating; ensure the hitch is free moving and welllubricated; make sure the vehicle attachment is ratedfor the weight of the trailer; check the vehicle andtrailer brake operation.

When using a trailer, there are other precautions tonote. First, avoid towing with too much or too littletongue weight as this causes the trailer to fishtail at cer-tain speeds, and it may become uncontrollable. Second,take care when unloading the glider to avoid damage.

TIEDOWN AND SECURINGAnytime the glider is left unattended it should be tieddown. When selecting a tiedown location, choose aspot that faces into the wind if possible. Permanenttiedowns are often equipped with straps, ropes, orchains for the wings and tail, and a release hook for thenose. Check the condition of these tiedowns before use.

If strong winds are expected, tie the spoilers open withseat belts, or place a padded stand under the tail toreduce the angle of attack of the wings. This reducesthe pull of the glider against the tiedowns. When secur-ing the glider outside for an extended period of time,install gust locks on the control surfaces to preventthem from banging against their stops in the wind.Cover the pitot tube and the total energy probe to keepspiders, wasps, and other insects or debris from caus-ing an obstruction. [Figure 6-3]

Always use a cover to protect the glider canopy. It canbe damaged by blowing dust and sand or scratched byapparel, such as watches or belt buckles. A cover pro-tects the canopy from damage while shielding theinterior of the cockpit from ultra-violet (UV) rays.[Figure 6-4]

GROUND HANDLINGMoving a glider on the ground requires special han-dling procedures, especially during high winds.Normally, gliders are pushed or pulled by hand ortowed with a vehicle. When moving a glider, ensurethat all appropriate personnel have been briefed onprocedures and signals.

When using a vehicle to tow a glider, use a towropethat is more than half the wingspan of the glider. If onewingtip stops moving for any reason, this length pre-vents the glider from pivoting and striking the towvehicle with the opposite wingtip. One half thewingspan plus 10 feet provides safe operation.

When starting, slowly take up slack in the line with thevehicle to prevent sudden jerking of the glider. Thetowing speed should be no faster than a brisk walk.When towing a glider, always use at least one wing-walker. The wingwalker and the driver of the tow vehi-cle function as a team, alert for obstacles, wind, andany other factor that may affect the safety of the glider.The driver should always stay alert for any signalsfrom the wingwalkers. [Figure 6-5]

If it is necessary to move the glider during high winds,use two or more crewmembers placed at the wingtipsand tail. Also, have a pilot in the cockpit, with thespoilers deployed, holding the controls appropriatelyto reduce lift on the glider. Strong winds and gusts cancause damage to the glider during ground handling, soexercise care during these conditions.

LAUNCH EQUIPMENT INSPEC-TIONPrior to making a flight, it is important to inspect thecondition of the towrope. The towrope should be freefrom excess wear; all strands should be intact, and therope should be free from knots. [Figure 6-6]

Figure 6-3. Protecting the pitot tube and total energy

Figure 6-4. Protecting the canopy.

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the towrope. The safety link is constructed of towropewith a towring on one end and the other end splicedinto a loop. The weak link at the glider attach end of thetowrope must be 80 to 200 percent of the maximumcertificated operating weight of the glider. The safetylink at the tow plane attach end must be of greaterstrength than the safety link at the glider attach end ofthe towrope, but not more than 25 percent greater norgreater than 200 percent of the maximum certificatedweight of the glider. Towropes and weak links areassembled using a towring that is appropriate for theoperation. [Figure 6-7]

The towhooks on both the glider and the towplane needto be inspected. The two most common types oftowhook are an over-the-top design, such as a

Title 14 of the Code of Federal Regulations (14 CFR)part 91, section 91.309 requires that the strength of thetowrope be within a range of 80 to 200 percent of themaximum certificated weight of the glider. A knot inthe towrope reduces its strength by up to 50 percent,and causes a high spot in the rope that is more suscep-tible to wear. Pay particular attention to the ring areathat the glider attaches to because this is also a highwear area.

If the towrope exceeds the required strength it is neces-sary to use a weak link, or safety link, at both ends of

Figure 6-5. Positioning the glider for the tow vehicle.

Figure 6-6. Inspecting the towrope. Figure 6-7. The weak link.

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Schweizer hook, or a grasping style, such as a Tosthook. Any towhook must be freely operating, and freefrom damage. [Figure 6-8]

GLIDER PREFLIGHT INSPECTIONA thorough inspection of the glider should be accom-plished before launch. A preflight checklist for a glidershould be in the GFM/POH. If not, develop a checklistusing the guidelines contained in Appendix A—Preflight Checklist.

COCKPIT MANAGEMENTPrior to launch, passengers should be briefed on the useof safety belts, shoulder harnesses, and emergency pro-cedures. If ballast is used, it must be properly secured.Organize the cockpit so items needed in flight areaccessible. All other items must be securely stowed.The necessary charts and cross-country aids should bestowed within easy reach of the pilot.

PERSONAL EQUIPMENT If a parachute is to be used, 14 CFR part 91 requiresthat a certified rigger repack it within the preceding 120days. The packing date information is usually found ona card contained in a small pocket on the body of theparachute.

14 CFR part 91 also requires that the pilot in command(PIC) use supplemental oxygen for flights more than30 minutes in duration above 12,500 feet, and at alltimes during a flight above 14,000 feet. If supplemen-tal oxygen is used, the system should be checked forflow and availability.

The glider pilot should carry water on every flight toprevent dehydration. The effects of dehydration on apilot’s performance are subtle, but can be dangerousand are especially a factor in warmer climates.

PRELAUNCH CHECKLISTAdjustments to the pilot or passenger seats, as well asthe pedals, should be made prior to buckling in. At thispoint, especially if the glider has just been assembled,it is appropriate to do a positive control check with thehelp of one crewmember. While the pilot moves thecontrol stick, the crewmember alternately holds eachaileron and the elevator to provide resistance. This alsoapplies to the spoilers and flaps. This ensures that thecontrol connections are correct and secure. If the stickmoves freely while the control surfaces are beingrestricted, the connections are not secure, and theglider is not airworthy. [Figure 6-9]

If the GFM/POH does not provide a specific prelaunchchecklist, then a good generic checklist is ABCC-CDD, which stands for:

A—Altimeter set to correct elevation.

B—Seat belts and shoulder harnesses fastened and tightened.

C—Controls checked for full and free move-ment.

C—Cable or towrope properly connected to thecorrect hook.

C—Canopy closed, locked, and checked.

D—Dive brakes closed and locked.

D—Direction of wind checked and emergency plan reviewed.

Figure 6-8. Schweizer-type towhook.

Figure 6-9. Positive control check of spoilers.

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• Begin by assessing the overall condition ofthe fiberglass or fabric.

• Be alert for signs of damage or excessivewear.

• Check that the canopy is clean and free fromdamage.

• Verify the interior wing and control connec-tions are safe and secure.

• If a battery is used, ensure that it is charged,and safely fastened in the proper spot.

• Check that seat harnesses are free from exces-sive wear.

• To prevent it from inadvertently interferingwith the controls, buckle and tighten any har-ness that will not be used.

• Test the tow hook to make sure it is operatingcorrectly.

• Inspect top, bottom, and leading edge ofwings, making sure they are free from excessdirt, bugs, and damage.

• Inspect spoilers/dive brakes for mechanicaldamage. They should be clear of obstructions.

• Inspect the wingtip and wingtip skid or wheelfor general condition.

• Inspect ailerons for freedom of movement,the condition of hinges and connections, andthe condition of the gap seal.

• Check the condition of flaps for freedom fromdamage and appropriate range of motion.

• Inspect the general condition of the empen-nage.

• Check static ports, pitot tube, total energyprobe to ensure they are free from obstruc-tion.

• Check top, bottom, and leading edge oftailplane for freedom of bugs, dirt, and dam-age.

• Check the landing gear for signs of damage orexcessive wear. The brake pads should bechecked if they are visible, otherwise thebrakes can be checked by pulling the gliderforward and applying the brakes. It should benoted that the landing gear is frequently aproblem area for gliders used in training.

• Check elevator and trim tab for condition ofconnections, freedom of movement, and con-dition of gap seal.

• Check rudder freedom of movement and con-dition of connections.

APPENDIX A—Preflight Checklist

Add to this list any items that are appropriate for your particular glider.

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This chapter discusses glider launch and takeoff proce-dures, traffic patterns, landing and recovery proce-dures, and flight maneuvers.

AEROTOW LAUNCH SIGNALSLaunching a non-powered glider requires the useof visual signals for communication and coordina-tion between the glider pilot, towpilot, and launchcrewmembers. If the aircraft and launchcrewmembers are equipped with compatible

radios, communication is enhanced over hand sig-nals. Aerotow launch signals consist of pre-launchsignals and in-flight signals.

PRE-LAUNCH SIGNALS FOR AEROTOW LAUNCHESAerotow pre-launch signals facilitate communicationbetween pilots and launch crewmembers preparing forthe launch. These signals are shown in Figure 7-1.

Check Controls Open Towhook Close Towhook Raise Wingtipto Level Position(Thumb moves thru circle.)

(Arm moves slowly backand forth thru arc.)

Take Up Slack Hold Begin Takeoff!(Arms straight out and held steady.) (Arm makes rapid circles.)

(Wave arms.) (Draw arm across throat.)Stop Operation Immediately! Release Towrope or Stop Engine NowStop!

Figure 7-1. Aerotow pre-launch signals.

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IN-FLIGHT AEROTOW VISUAL SIGNALS Visual signals allow the towpilot and the glider pilot tocommunicate with each other. The signals are dividedinto two types: those from the towpilot to the gliderpilot, and those from the glider pilot to the towpilot.These signals are shown in Figure 7-2.

TAKEOFF PROCEDURESAND TECHNIQUES Takeoff procedures for gliders require close coordina-tion between launch crewmembers and pilots. Both the

glider and towpilot must be familiar with the appropri-ate tow procedures.

AEROTOW TAKEOFFS Normal takeoffs are made into the wind. Prior to take-off, the towpilot and glider pilot must reach an agree-ment on the plan for the aerotow. The glider pilotshould ensure that the launch crewmember is aware ofsafety procedures concerning the tow. Some of theseitems would be proper runway and pattern clearingprocedures and glider configuration checks (spoilersclosed, tailwheel dolly removed, canopy secured).When the required checklists have been completed

Figure 7-2. In-flight aerotow visual signals.

Glider Cannot Release!

(Glider moves to left side of towplane and rocks wings.)

Something Is Wrong With Glider — Close Airbrakes! (Towplane fans rudder.)

Towplane PleaseTurn Left

(Glider pulls towplane tail to right.)

Towplane PleaseTurn Right

(Glider pulls towplane tail to left.)

Decrease Tow Airspeed!

(Glider yaws repeatedly.)

Increase Tow Airspeed!(Glider rocks wings repeatedly.)

Glider: Release Immediately!(Towplane rocks wings.)

Towplane Cannot Release!

(After receiving signal that glider cannotrelease, towplane yaws repeatedly.)

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the towplane should remain in ground effect until theglider is off the ground. Climb-out must not begin untilthe previously agreed upon climb airspeed has beenachieved.

CROSSWIND AEROTOW TAKEOFFSCrosswind takeoff procedures are a modification of thenormal takeoff procedure. The following are the maindifferences in crosswind takeoffs.

• The glider tends to yaw, or weathervane, into the wind any time the main wheel is touching the ground. The stronger the crosswind, the greater the tendency of the glider to turn into the wind.

• After liftoff, the glider tends to drift toward thedownwind side of the runway. The stronger thecrosswind, the greater the glider’s tendency to drift downwind.

Prior to takeoff, the glider pilot should coordinate withthe launch crewmember to hold the upwind wingslightly low during the initial takeoff roll. If a cross-wind is indicated, full aileron should be held into thewind as the takeoff roll is started. This control positionshould be maintained while the glider is accelerating

and both the glider and towplane are ready for takeoff,the glider pilot signals the launch crewmember to hookthe towrope to the glider.

NORMAL TAKEOFFS The hook-up should be done deliberately and correctly,and the release mechanism should be checked forproper operation. The launch crewmember applies ten-sion to the towrope and signals the glider pilot to acti-vate the release. The launch crewmember shouldverify that the release works properly and signals theglider pilot. When the towline is hooked up to theglider again, the launch crewmember repositions to thewing that is down. When the glider pilot signals “readyfor takeoff” the launch crewmember clears both thetakeoff and landing area, then signals the towpilot to“take up slack” in the towrope. Once the slack is out ofthe towrope, the launch crewmember verifies that theglider pilot is ready for takeoff, then raises the wingsto a level position. With the wings raised, the launchcrewmember does a final traffic pattern check and sig-nals the towpilot to takeoff. At the same time, theglider pilot signals the towpilot by wagging the rudderback and forth, concurring with the launch crewmem-ber’s takeoff signal. The procedures may differ some-what from site to site, so follow local convention.

As the launch begins and the glider accelerates, thelaunch crewmember runs alongside the glider, hold-ing the wing level. If there is a crosswind, the launchcrewmember should hold the wing down into thewind, but not in a way as to steer the glider from thewingtip.

When the glider achieves lift-off airspeed, the gliderpilot eases the glider off the ground and climbs to analtitude within three to five feet of the runway surface,while the towplane continues to accelerate to lift-offspeed. The glider pilot should maintain this altitude byapplying forward stick pressure, as necessary, whilethe glider is accelerating. Once the towplane lifts off, itaccelerates in ground effect to the desired climb air-speed, then the climb begins for both the glider and thetowplane.

During the takeoff roll, use the rudder pedals to steer theglider. Control the bank angle of the wings with aileron.Full deflection of the flight controls may be necessary atlow airspeeds, but the flight controls become moreeffective as airspeed increases. [Figure 7-3]

In most takeoffs, the glider achieves flying airspeedbefore the towplane. However, if the glider is a heavilyballasted glider, the towplane may be able to achieveliftoff airspeed before the glider. In such a situation,

Ground Track

Crab into the wind to track the runway centerline until clear of obstacles and terrain features.

Figure 7-3.Tracking the runway centerline.

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and until the ailerons start becoming sufficiently effec-tive for maneuvering the glider about its longitudinal(roll) axis. With the aileron held into the wind, the take-off path must be held straight with the rudder. Thisrequires application of downwind rudder pressure,since the glider tends to weathervane into the windwhile on the ground. [Figure 7-4]

As the forward speed of the glider increases and thecrosswind becomes more of a relative headwind, themany mechanical application of full aileron into thewind should be reduced. It is when increasing pressureis being felt on the aileron control that the ailerons arebecoming more effective. Because the crosswind com-ponent effect does not completely dissipate, someaileron pressure must be maintained throughout thetakeoff roll to prevent the crosswind from raising theupwind wing. If the upwind wing rises, exposing moresurface to the crosswind, a “skipping” action mayresult, as indicated by a series of small bounces occur-ring when the glider attempts to fly and then settlesback onto the runway. This side skipping imposes sideloads on the landing gear. Keeping the upwind wingtipslightly lower than the downwind wingtip prevents thecrosswind from getting underneath the upwind wing

and lifting it. If the downwind wingtip touches theground, the resulting friction may cause the glider toyaw in the direction of the dragging wingtip. This couldlead to loss of directional control.

While on the runway throughout the takeoff, the gliderpilot uses the rudder to maintain directional control andalignment behind the towplane. Yawing back and forthbehind the towplane should be avoided, as this effectsthe ability of the towplane pilot to maintain control. Ifglider controllability becomes a problem, the gliderpilot must release and stop the glider on the remainingrunway. Remember, as the glider slows, the crosswindmay cause it to weathervane into the wind.

Prior to the towplane becoming airborne and after theglider lifts off, the glider pilot should turn into the windand establish a wind correction angle to remain behindthe towplane. This is accomplished by using coordi-nated control inputs to turn the glider. Once the tow-plane becomes airborne and establishes a windcorrection angle, the glider pilot repositions to alignbehind the towplane.

COMMON ERRORS• Improper glider configuration for takeoff.• Improper initial positioning of flight controls.• Improper use of visual launch signals.• Failure to maintain alignment behind towplane

before towplane becomes airborne.• Improper alignment with the towplane after

becoming airborne.• Climbing too high after liftoff and causing a

towplane upset.

TAKEOFF EMERGENCY PROCEDURES The most common emergency situations on takeoffdevelop when a towrope breaks, there is an inadvertenttowrope release, or towplane loses power. There are fiveplanning situations regarding in-motion towropebreaks, uncommanded release, or power loss of the tow-plane. While the best course of action depends on manyvariables, such as runway length, airport environment,and wind, all tow failures have one thing in common:the need to maintain control of the glider. Two possibil-ities are stalling the glider, or dragging a wingtip on theground during a low altitude turn and cartwheeling theglider. [Figure 7-5]

Situation 1. If the towrope breaks or is inadvertentlyreleased prior to the towplane’s liftoff, the standardprocedure is for the towplane to continue the takeoffand clear the runway, or abort the takeoff and remainon the left side of the runway. If the towplane losespower during the takeoff, the towpilot should maneu-ver the towplane to the left side of the runway. If theglider is still on the runway, the glider pilot should pull

Upwind Wing Slightly Lower Than Downwind Wing

Full Downwind Rudder Deflection to Start Crosswind Takeoff Roll

Figure 7-4. Crosswind correction or takeoff.

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the release, decelerate using the wheel brake, and beprepared to maneuver to the right side of the runway. Ifthe rope breaks, is inadvertently released, or the tow-plane loses power after the glider is airborne, the gliderpilot should pull the towrope release, land straightahead, and be prepared to maneuver to the right side ofthe runway. Pulling the towrope release in either caseensures that the rope is clear of the glider. Since localprocedures vary, both the glider and towpilot must befamiliar with the specific gliderport/airport procedures.

Situation 2. This situation occurs when both the tow-plane and glider are airborne and at a low altitude. If aninadvertent release, towrope break, or a signal torelease from the towplane occurs at a point in which

the glider has insufficient runway directly ahead andhas insufficient altitude to make a safe turn, the bestcourse of action is to land the glider straight ahead.After touchdown, use wheel brake, as necessary, toslow and stop as conditions permit. At low altitude,attempting to turn prior to landing is very risky becauseof the likelihood of dragging a wingtip on the groundand cartwheeling the glider. Slowing the glider as muchas possible prior to touching down and rolling ontounknown terrain generally is the safest course of action.Low speed means low impact forces, which reduce thelikelihood of injury and reduce the risk of significantdamage to the glider.

Situation 3. If an inadvertent release, towrope break, ora signal to release from the towplane occurs after the

Very low altitude, prematurerelease/rope break with runwaystill available. Land on runway,use wheel break to stop. Ifnecessary alter course to theright to avoid towplane.

Very low altitude, premature release/rope break with insuficient runway available.

Above 200 ft. if suitable, turn into wind, make 180° turn, land downwind.

At higher altitudes, multiple options are usually available.

Figure 7-5. Situations for towline break, uncommanded release, or power loss of the towplane.

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towplane and glider are airborne, and the glider pos-sesses sufficient altitude to make a 180° turn, then adownwind landing on the departure runway may beattempted.

The 180° turn and downwind landing option should beused only if the glider is within gliding distance of theairport or landing area. In ideal conditions, a minimumaltitude of 200 feet above ground level is required to com-plete this maneuver safely. Such things as a hot day, weaktowplane, strong wind, or other traffic may require agreater altitude to make a return to the airport a viableoption.

The responsibility of the glider pilot is to avoid thetowplane or other aircraft. If the tow was terminatedbecause the towplane was in distress, the towpilot isalso dealing with an emergency situation and maymaneuver the aircraft abruptly.

After releasing from the towplane at low altitude, if theglider pilot chooses to make a 180° turn and a down-wind landing, the first responsibility is to maintain fly-ing speed. The pilot must immediately lower the noseto achieve the proper pitch attitude necessary to main-tain the appropriate approach airspeed.

Make the initial turn into the wind. Use a medium bankangle to align the glider with the landing area. Usingtoo shallow a bank angle may not allow enough timefor the glider to align with the landing area. Too steepa bank angle may result in an accelerated stall. If theturn is made into the wind, only minor course correc-tions should be necessary to align the glider with theintended landing area. Throughout the maneuver thepilot must maintain the appropriate approach speedand proper coordination.

Downwind landings result in higher groundspeed dueto the effect of tailwind. The glider pilot must maintainthe appropriate approach airspeed. During the straight-in portion of the approach, spoilers/dive breaks shouldbe used as necessary to control the descent path.Landing downwind requires a shallower than normalapproach. Groundspeed will be higher during a down-wind landing and especially noticeable during theflare. After touchdown, spoilers/dive breaks, andwheel brakes should be used as necessary to slow andstop the glider as quickly as possible. During the laterpart of the roll-out, the glider will feel unresponsive tothe controls despite the fact that it is rolling along therunway at a higher than normal groundspeed. It isimportant to stop the glider before any loss of direc-tional control.

Situation 4. When the emergency occurs at or above800 feet above the ground, the glider pilot may havemore time to assess the situation. Depending on glid-erport/airport environment, the pilot may choose toland on a cross runway, land into the wind on thedeparture runway, or land on a taxiway. In some situa-tions an off gliderport/airport landing may be saferthan attempting to land on the gliderport/airport.

Situation 5. If an emergency occurs above the trafficpattern altitude, the glider pilot should maneuver awayfrom the towplane, release the towrope if still attached,and turn toward the gliderport/airport. The glider pilotshould evaluate the situation to determine if there issufficient altitude to search for lift or if it is necessaryto return to the gliderport/airport for a landing.

AEROTOW CLIMB-OUTAND RELEASE PROCEDURESOnce airborne and climbing, the glider can fly one oftwo tow positions. High tow is aerotow flight with theglider positioned above the wake of the towplane. Lowtow is aerotow flight with the glider positioned belowthe wake of the towplane. [Figure 7-6] Climbing turnsare made with shallow bank angles and the glider inthe high tow position.

High tow is the preferred position for climbing outbecause the glider is above the turbulence of the tow-plane wake. High tow affords the glider pilot an ampleview of the towplane and provides a measure of pro-tection against fouling if the towrope breaks or isreleased by the towplane because the towrope fallsbelow the glider in this position.

Low tow offers the glider pilot a better view of thetowplane, but puts the glider at risk from towrope foul-ing if the towrope breaks or is released by the tow-plane. Low tow is used for cross-country and levelflight aerotows.

During level flight aerotows, positioning the gliderabove the wake of the towplane has several disadvan-tages. One is that the towplane wake is nearly levelrather than trailing down and back as it does duringclimbing aerotow operations. Because the towplanewake is nearly level, the glider must take a higher posi-tion relative to the towplane to ensure the glider staysabove the wake. This higher position makes it difficultto see the towplane over the nose of the glider. Easingthe stick forward to get a better view of the towplaneaccelerates the glider toward the towplane, causing thetowrope slack. Positioning the glider beneath the wakeof the towplane in level flight offers an excellent viewof the towplane, but the danger of fouling from a

7-7

towrope failure or inadvertent release is greater whenflying in the low tow position. Gliders using a centerof gravity (CG) tow hook during low tow position onlevel flight aerotows may encounter the towrope slid-ing up and to the side of the glider nose, causingpossible damage.

Straight ahead climbs are made with the glider in thehigh tow position. The towpilot should maintain asteady pitch attitude and a constant power setting tomaintain the desired climb airspeed. The glider pilotuses visual references on the towplane to maintain lat-eral and vertical position.

Climbing turns are made with shallow bank angles inthe high tow position. During turns, the glider pilotobserves and matches the bank angle of the towplane’swings. In order to stay in the same flight path of thetowplane, the glider pilot must aim the nose of theglider at the outside wingtip of the towplane. Thisallows the glider’s flight path to coincide with the tow-plane’s flight path. [Figure 7-7]

If the glider’s bank is steeper than the towplane’s bank,the glider’s turn radius is smaller than the towplane’sturn radius. [Figure 7-8 on page 7-8] If this occurs, thereduced tension on the towrope causes it to bow andslack, allowing the glider’s airspeed to slow. As a

High Tow Position

Low Tow Position

Wake

Wake

Figure 7-6. Aerotow climb-out.

During a turn, the glider flies the same path through the air that the towplane flew.

Figure 7-7. Aerotow climbing turns.

7-8

result, the glider begins to sink, relative to the tow-plane. The correct course of action is to reduce theglider’s bank angle so the glider flies the same radiusof turn as the towplane. If timely corrective action is

not taken, and if the glider slows and sinks below thetowplane, the towplane may rapidly pull the towropetaut and possibly cause it to fail and/or cause structuraldamage to both aircraft.

If the glider’s bank is shallower than the towplane, theglider’s turn radius is larger than the towplane’s turnradius. [Figure 7-9] If this occurs, the increased ten-sion on the towrope causes the glider to accelerate andclimb. The correct course of action to take when theglider is turning outside the towplane radius of turn isto increase the glider’s bank angle, so the glider easesback into position behind the towplane and flies thesame radius of turn as the towplane. If timely correc-tive action is not taken, and if the glider acceleratesand climbs above the towplane, the towplane may loserudder and elevator control. In this situation, the gliderpilot should release the towrope and turn to avoid thetowplane.

COMMON ERRORS• Faulty procedures maintaining vertical and

lateral positions during high and/or low tow.

• Inadvertent entry into towplane wake.

• Failure to maintain glider alignment during turns on aerotow.

AEROTOW RELEASEStandard aerotow release procedures provide safetybenefits for both the glider pilot and the towpilot.When the aerotow has reached a predetermined alti-tude, the glider pilot should clear the area for otheraircraft in all directions, especially to the right. Whenready to release, the glider pilot should pull therelease handle, and visually confirm that towrope hasreleased from the glider as shown in Figure 7-10, item1. Next, bank to the right, accomplishing 90° of head-ing change, then level the wings and fly straight,away from the release point. [Item 2] This 90° changeof heading achieves maximum separation betweentowplane and glider in minimum time. After confirm-ing that the glider has released and has turned awayfrom the towplane, the towpilot should turn left awayfrom the release point. [Item 3] Once clear of theglider and other aircraft, the towpilot then begins adescent.

COMMON ERRORS• Lack of proper tension on towrope.• Failure to clear the area prior to release.• Failure to make turn in proper direction after

release.• Release in close proximity of other aircraft.

AEROTOW ABNORMAL PROCEDURESMechanical equipment failure, environmental factors,and pilot errors can cause abnormal aerotow occur-rences during climb-out.

Glider turns toward outside oftowplane turn. towline tensionincreases causing glider toaccelerate and climb.

Figure 7-9. Glider bank too shallow, causing turn outsidetowplane turn.

Glider turns toward inside of towplane turn. Gliderslows, slack towline develops.

Figure 7-8. Aerotow induced slack towline by turning insidetowplane.

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Mechanical equipment failures can be caused bytowrope and towhook failures, towplane mechanicalfailures, and/or glider mechanical failures. Towropefailure (one that breaks unexpectedly) can result fromusing an under-strength or worn towrope. Towropefailures can be avoided by using appropriately ratedtowrope material, weak links when necessary, propertowrings, and proper towrope maintenance.

Towhook system failures include uncommandedtowrope releases or the inability to release. These fail-ures can occur in either the towplane or the glidertowhook system. Proper preflight and maintenance ofthese systems should help to avoid these types of fail-ures. Towplane mechanical failures can involve thepowerplant and/or flight control. When the towpilotencounters a mechanical failure, he or she should sig-

nal the glider pilot to release immediately. This is oneof many situations that make it vitally important thatboth the towpilot and glider pilot have a thoroughknowledge of aerotow visual signals.

Glider mechanical failure can include towhook systemmalfunctions, flight control problems, and/or improperassembly or rigging. If a mechanical failure occurs, theglider pilot must assess the situation to determine thebest course of action. In some situations, it may be ben-eficial to remain on the aerotow, while other situationsmay require immediate release.

If the glider release mechanism fails, the towpilotshould be notified either by radio or tow signal and theglider should maintain the high tow position. The tow-pilot should tow the glider over the gliderport/airport

Glider release

Glider turns right, 90°heading change

Glider continues away, towpilotconfirms glider release, turns left

Figure 7-10. Aerotow release.

7-10

and release the glider from the towplane. The towropeshould fall back and below the glider. The design of thetowhook mechanism is such that the rope pulls freefrom the glider by it’s own weight. Since some glidersdo not “back release,” the glider pilot should pull therelease to ensure the towrope is in fact released.

Failure of both the towplane and glider release mecha-nisms is extremely rare. If it occurs, however, radio ortow signals between the glider and towpilot should ver-ify this situation. The glider pilot should move down tothe low tow position once the descent has started to thegliderport/airport. The glider pilot needs to use spoil-ers/dive breaks to maintain the low tow position and toavoid over taking the towplane. The towpilot shouldplan the approach to avoid obstacles. The approachshould be shallow enough so that the glider touchesdown first. The glider pilot should use the spoilers/divebreaks to stay on the runway, and use the wheel brakeas necessary to avoid overtaking the towplane.Excessive use of the glider wheel break may result inthe towplane landing hard.

Environmental factors include encountering clouds,mountain rotors, or restricted visibility. Any of thesefactors also may require the glider pilot to release fromthe aerotow. During the aerotow, each pilot is responsi-ble for avoiding situations that would place the otherpilot at risk. For the towplane pilot, examples of piloterror include deliberately starting the takeoff before theglider pilot has signaled the glider is ready for launch,using steep banks during the aerotow without priorconsent of the glider pilot, or frivolous use of aerotowsignals, such as “release immediately!” For the gliderpilot, examples of pilot error include rising high abovethe towplane during takeoff and climb, or leaving air-brakes open during takeoff and climb.

One of the most dangerous occurrences during theaerotow is allowing the glider to rise high above andlosing sight of the towplane. The tension on thetowrope by the glider pulls the towplane tail up, lower-ing its nose. If the glider continues to rise pulling thetowplane tail higher, the towpilot may not be able toraise the nose. Ultimately, the towpilot may run out ofup elevator authority. Additionally, the towpilot maynot be able to release the towrope from the towplane.This situation can be critical if it occurs at altitudesbelow 500 feet AGL. Upon losing sight of the tow-plane, the glider pilot must release immediately.

SLACK LINESlack line is a reduction of tension in the towrope. Ifthe slack is severe enough it might entangle the glider,or cause damage to the glider or towplane. The follow-ing situations may result in a slack line.

• Abrupt power reduction by the towplane.

• Aerotow descents.• Turning the glider inside the towplane turn

radius. [Figure 7-8] • Turbulence.• Abrupt recovery from a high tow position.

[Figure 7-11]

Slack line recovery procedures should be initiated assoon as the glider pilot becomes aware of the situation.The pilot’s initial action should be to yaw away fromthe bow in the line. In the event the yawing motion failsto reduce the slack sufficiently, careful use of spoil-ers/dive brakes can be used to decelerate the glider andtake up the slack. When the towline tightens, stabilizethe tow, then gradually resume the desired aerotowposition. When the slack in the line is excessive, orbeyond the pilot’s capability to safely recover, the pilotshould immediately release from the aerotow.

COMMON ERRORS• Failure to take corrective action at the first

indication of a slack line.• Use of improper procedure to correct slack

line, causing excessive stress on tow rope, towplane, and glider.

BOXING THE WAKEBoxing the wake is a performance maneuver designedto demonstrate a pilot’s ability to accurately maneuverthe glider around the towplane’s wake during aerotow.[Figure 7-12]

Boxing the wake requires flying a rectangular patternaround the towplane’s wake. Before starting themaneuver, the glider should descend through the waketo the center low tow position as a signal to the towpi-lot that the maneuver is about to begin. The pilot usescoordinated control inputs to move the glider out to oneside of the wake and holds that lower corner of the rec-tangle momentarily with rudder pressure. Applyingback pressure to the control stick starts a verticalascent, then rudder pressure is used to maintain equal

Glider, having risen too high above towplane, dives down on towplane, inducing slack towline.

Figure 7-11. Diving on towplane.

7-11

distance from the wake. The pilot holds the wings levelwith the ailerons to parallel the towplane’s wings.When the glider has attained high corner position, thepilot momentarily maintains this position.

As the maneuver continues, the pilot reduces the rud-der pressure and uses coordinated flight controls tobank the glider to fly along the top side of the box. Theglider should proceed to the opposite corner usingaileron and rudder pressure, as appropriate. The pilotmaintains this position momentarily with rudder pres-sure, then begins a vertical descent by applying for-ward pressure to the control stick. Rudder pressure isused to maintain glider position at an equal distancefrom the wake. The pilot holds the wings level with the

ailerons to parallel the towplane’s wings. When theglider has attained low corner position, the pilotmomentarily maintains this position. The pilot releasesthe rudder pressure and, using coordinated flight con-trols, banks the glider to fly along the bottom side ofthe box until reaching the original center low tow posi-tion. From center low tow position, the pilot maneu-vers the glider through the wake to the center high towposition, completing the maneuver.

COMMON ERRORS• Performing an excessively large rectangle

around the wake.• Improper control coordination and procedure• Abrupt or rapid changes of position.

Upper Left Corner

Lower Left Corner

Upper Right Corner

Lower Right CornerNormal LowTow Position

Normal HighTow Position

Tow Ring

Automatic backrelease. Checkbefore everylaunch.

If pulling the towline release handle fails to release the towline, cycle release handle and try again several times.If handle still fails to release, fly over winch/auto and allow the back release to function.

Figure 7-13.Testing the towhook.

Figure 7-12. Boxing the wake.

7-12

GROUND LAUNCH TAKEOFF When ground launching, it is essential to use a towhook that has an automatic back-release feature. Thisprotects the glider if the pilot is unable to release thetowline during the launch. The failure of the tow releasecould cause the glider to be pulled to the ground as itflies over the launching vehicle or winch. Since theback-release feature of the tow hook is so important, itshould be tested prior to every flight. [Figure 7-13]

GROUND LAUNCH SIGNALS

PRE-LAUNCH SIGNALS FOR GROUNDLAUNCHES (WINCH/AUTOMOBILE)Pre-launch visual signals for a ground launch opera-tion allow the glider pilot, the glider wing runner, thesafety officer, and the launch crew to communicateover considerable distances. When ground launchingwith an automobile, the glider and launch automobilemay be 1,000 or more feet apart. When launching with

a winch, at the beginning of the launch the glider maybe 4,000 feet or more from the winch. Because of thegreat distances involved, members of the groundlaunch crew use colored flags or large paddles toenhance visibility as shown in Figure 7-14.

When complex information must be relayed over greatdistances, visual pre-launch signals can be augmentedwith direct voice communications between crewmem-ber stations. Hard-wired ground telephones, two-wayradios, or wireless telephones can be used to commu-nicate between stations, adding protection against pre-mature launch and facilitating an aborted launch if anunsafe condition arises.

IN-FLIGHT SIGNALS FOR GROUND LAUNCHES Since ground launches are of short duration, in-flightsignals for ground launches are limited to signals tothe winch operator or ground vehicle driver to increaseor decrease speed. [Figure 7-15]

Figure 7-14. Winch and aerotow pre-launch signals.

Check Controls Open Towhook Close Towhook Raise Wingtipto Level Position(Thumb moves thru circle.)

(Arm moves slowly backand forth thru arc.)

Take Up Slack Hold Begin Takeoff!(Arms straight out and held steady.) (Arm makes rapid circles.)

(Wave arms.) (Draw arm across throat.)Stop Operation Immediately! Release Towrope or Cut Towline Now

TOW SPEEDS Proper ground launch tow speed is critical for a safelaunch. Figure 7-16 compares various takeoff profilesthat result when tow speeds vary above or below thecorrect speed.

Each glider certified for ground launch operations has aplacarded maximum ground launch tow speed. Thisspeed is normally the same for automobile or winchlaunches. The glider pilot should fly the launch stayingat or below this speed to prevent structural damage tothe glider during the ground tow.

Glider pilot yaws glider repeatedly to signalground operator to reduce tow speed.

Glider pilot rocks wings to signalground operator to increase tow speed.

Figure 7-15. In-flight signals for ground launch.

Tow Speed Correct: Glider climbs to altitude safely.

Tow Speed Too Fast: Glider cannot raise nose to climb because doing so would exceed maximum permitted ground launch airspeed.

Tow Speed Too Slow: Glider cannot climb because it is not possible to achieve safe margin above stall speed.

Figure 7-16. Ground launch tow speed.

7-13

7-14

AUTOMOBILE LAUNCHDuring automobile ground launches, the glider pilotand driver should have a thorough understanding ofwhat ground speeds are to be used prior to any launch.Before the first launch, the pilot and vehicle drivershould determine the appropriate vehicle ground towspeeds considering the surface wind velocity, theglider speed increase during launch, and the wind gra-dient encountered during the climb. They shouldinclude a safety factor so as not to exceed this maxi-mum vehicle ground tow speed.

The tow speed can be determined by using the follow-ing calculations.

1. Subtract the surface winds from the maximumplacarded ground launch tow speed for the particular glider.

2. Subtract an additional five miles per hour for the airspeed increase during the climb.

3. Subtract the estimated wind gradient increaseencountered during the climb.

4. Subtract a 5 MPH safety factor.

Maximum ground launch speed 75 MPH

1. Surface winds 10 MPH 65 MPH

2. Airspeed increase during climb5 MPH 60 MPH

3. Estimated climb wind gradient5 MPH 55 MPH

4. Safety factor of 5 MPH 50 MPH

Automobile tow speed 50 MPH

During winch launches, the winch operator appliesfull power smoothly and rapidly until the gliderreaches an angle of 30° above the horizon. At thispoint, the operator should start to reduce the power

until the glider is about 60° above the horizon whereonly about 20 percent of the power is needed. As theglider reaches the 70° point above the horizon, thepower is reduced to idle. The winch operator monitorsthe glider continuously during the climb for any sig-nals to increase or decrease speed from the gliderpilot. [Figure 7-17]

NORMAL INTO-THE-WIND GROUND LAUNCH Normal takeoffs are made into the wind. Prior tolaunch, the glider pilot, ground crew, and launch equip-ment operator must be familiar with the launch signalsand procedures. When the required checklists for theglider and ground launch equipment have been com-pleted and the glider pilot, ground crew, and launchequipment operator are ready for takeoff, the gliderpilot should signal the ground crewmember to hook thetowline to the glider. The hook-up must be done delib-erately and correctly. The release mechanism should bechecked for proper operation. To accomplish this, theground crewmember should apply tension to thetowrope and signal the glider pilot to activate therelease. The ground crewmember should verify that therelease has worked properly and signal the glider pilot.When the towline is hooked up to the glider again, theground crewmember takes a position at the wingtip ofthe down wing. When the glider pilot signals “readyfor takeoff,” the ground crewmember clears both thetakeoff and landing area. When the ground crewmem-ber has assured the traffic pattern is clear, the groundcrewmember then signals the launch equipment opera-tor to “take up slack” in the towline. Once the slack isout of the towline, the ground crewmember again veri-fies that the glider pilot is ready for takeoff. Thenground crewmember raises the wings to a level posi-tion, does a final traffic pattern check, and signals tothe launch equipment operator to begin the takeoff.

NOTE: The glider pilot should be prepared for atakeoff anytime the towline is attached to the glider.

The length, elasticity, and mass of the towline used forground launching has several effects on the gliderbeing launched. First, it is difficult or impossible to pre-vent the glider from moving forward as the long tow-line is tautened. Elasticity in the towline causes theglider to creep forward as the towline is tightened. Forthis reason, the towline is left with a small amount ofslack prior to beginning the launch. It is important forthe pilot to be prepared for the launch prior to givingthe launch signal. If the launch is begun before the pilotgives the launch signal, the glider pilot should pull thetowline release handle promptly. In the first severalseconds of the launch, the glider pilot should hold thestick forward to avoid kiting.

During the launch, the glider pilot tracks down the run-way centerline and monitors the airspeed. (Figure 7-18,item 1) When the glider accelerates and attains liftoff

60°70°

30°

ReleasePoint

20% Takeoff Power

BeginReducing Winch

Power

Figure 7-17. Winch procedures.

7-15

speed the glider pilot eases the glider off the ground. Thetime interval from standing start to liftoff may be asshort as three to five seconds. After the initial liftoff, thepilot should smoothly raise the nose to the proper pitchattitude, watching for an increase in airpseed. If the noseis raised too soon, or too steeply, the pitch attitude willbe excessive while the glider is still at low altitude. If thetowline breaks or the launching mechanism loses power,recovery from such a high pitch attitude may be difficultor impossible. Conversely, if the nose is raised tooslowly, the glider may gain excessive airspeed, and mayexceed the maximum ground launch tow speed. Theshallow climb may result in the glider not attainingplanned release altitude. If this situation occurs, the pilotshould pull the release, and land straight ahead, avoidingobstacles and equipment.

As the launch progresses, the pilot should ease the noseup gradually (item 2), while monitoring the airspeed toensure that it is adequate for launch but does notexceed the maximum permitted ground launch tow air-speed. When optimum pitch attitude for climb isattained (item 3), the glider should be approximately200 feet above ground level. The pilot must monitorthe airspeed during this phase of the climb-out toensure the airspeed is adequate to provide a safe mar-gin above stall speed but below the maximum groundlaunch airspeed. If the towline breaks or if the launch-ing mechanism loses power at or above this altitude,the pilot will have sufficient altitude to release the tow-line and lower the nose from the climb attitude to theapproach attitude that provides an appropriate airspeedfor landing straight ahead.

As the glider nears its maximum altitude (item 4), itbegins to level off above the launch winch or tow vehi-cle, and the rate of climb decreases. In this final phaseof the ground launch, the towline is pulling steeplydown on the glider. The pilot should gently lower the

nose of the glider to reduce tension on the towline, andthen pull the towline release two or three times toensure the towline has released. The pilot will feel therelease of the towline as it departs the glider. The pilotshould enter a turn to visually confirm the fall of thetowline. If only a portion of the towline is seen fallingto the ground, it is possible that the towline is brokenand a portion of the towline is still attached to the glider.

If pulling the tow release handle fails to release thetowline, the back-release mechanism of the towhookautomatically releases the towline as the glider over-takes and passes the launch vehicle or winch.

CROSSWIND TAKEOFF AND CLIMB—GROUND LAUNCH The following are the main differences betweencrosswind takeoffs and climb procedures and normaltakeoff and climb procedures.

• During the takeoff roll, the weathervaning ten-dency, although present, is much less due to the rapid acceleration to liftoff airspeed.

• After liftoff, the glider tends to drift toward the downwind side of the runway. The stronger the crosswind, the greater the glider’stendency to drift downwind.

After liftoff, the glider pilot should establish a windcorrection angle toward the upwind side of the runwayto prevent drifting downwind. This prevents down-wind drift and allows the glider to work upwind of therunway during the climb-out. When the towline isreleased at the top of the climb, it will tend to drift backtoward the centerline of the launch runway, as shownin Figure 7-19 on the next page. This helps keep the tow-line from fouling nearby wires, poles, fences, aircraft,

Start Rotation

200 ft. AGL

Deck AngleFully Established

Launch is NearingMaximum Prudent HeightRelease Imminent

Figure 7-18. Ground launch takeoff profile.

7-16

and other obstacles on the side of the launching run-way. Should the glider drift to the downwind side ofthe runway, the towline may damage items, such asother aircraft, runway lights, nearby fences, structures,and obstacles.

GROUND TOW LAUNCH—CLIMB-OUT AND RELEASE PROCEDURESThe pitch attitude/airspeed relationship during groundlaunch is unique. During the launch, pulling back on thestick tends to increase airspeed, and pushing forwardtends to reduce airspeed. This is opposite of the normalpitch/airspeed relationship. The wings of the gliderdivert the towing force of the launch vehicle in anupward direction, enabling rapid climb. The greater thediversion from horizontal pulling power to vertical lift-ing power, the faster the airspeed. This is true, provided

the tow vehicle is powerful enough to meet the energydemands the glider is making on the launch system.

COMMON ERRORS• Improper glider configuration for takeoff.• Improper initial positioning of flight controls.• Improper use of visual launch signals.• Improper crosswind procedure.• Improper climb profile.• Faulty corrective action for adjustment of air

speed and porpoising.• Exceeding maximum launch airspeed.• Improper towline release procedure.

ABNORMAL PROCEDURES, GROUND LAUNCHThe launch equipment operator manages groundlaunch towline speed. Because the launch equipmentoperator is remote from the glider, it is not uncommonfor initial tow speed to be too fast or too slow. If thetowline speed is too fast, the glider will not be able toclimb very high because of excessive airspeed. If thetowline speed is too slow, the glider may be incapableof liftoff, possibly stall after becoming airborne oronce airborne be incapable of further climb. The pilotshould use appropriate signals to direct the launchoperator to increase or decrease speed. The pilot mustanticipate and be prepared to deal with these situa-tions. In the event these abnormal situations develop,the pilot’s only alternative may be to release the tow-line and land straight ahead.

Wind gradient (a sudden increase in wind speed withheight) can have a noticeable effect on groundlaunches. If the wind gradient is significant or sudden,or both, and the pilot maintains the same pitch attitudethe indicated airspeed will increase, possibly exceed-ing the maximum ground launch tow speed. The pilotmust adjust the airspeed to deal with the effect of thegradient. When encountering a wind gradient the pilotshould push forward on the stick to reduce the indi-cated airspeed. [Figure 7-20] The only way for theglider to resume climb without exceeding the maxi-mum ground launch airspeed is for the pilot to signalthe launch operator to reduce tow speed. After thereduction of the towing speed, the pilot can resumenormal climb. If the tow speed is not reduced, theglider may be incapable of climbing to safe altitude.

Ground launch may be interrupted by a ground launchmechanism malfunction. A gradual deceleration in rateof climb and/or airspeed may be an indication of sucha malfunction. If you suspect a launch mechanismmalfunction, release and land straight ahead.

EMERGENCY PROCEDURES—GROUND LAUNCH The most common type of problem is a broken tow-line. [Figure 7-21] When there is a towline failure, the

ground tow climb-out. Towlineground tow climb-out. Tog Crab into crosswind duringtterline after release.nwill drift toward runway cen

Figure 7-19. Ground launch crosswind drift correction.

7-17

glider pilot must pull the release handle and immedi-ately lower the nose of the glider to achieve and main-tain a safe airspeed. The distinguishing features of theground launch are nose-high pitch attitude and a rela-tively low altitude for a significant portion of thelaunch and climb. If a towline break occurs and theglider pilot fails to respond promptly, the nose-high atti-

tude of the glider may result in a stall. Altitude may beinsufficient for recovery unless the pilot recognizes andresponds to the towline break by lowering the nose.

If the glider tow release mechanism fails, the pilotshould fly at an airspeed no slower than best lift/drag(L/D) airspeed over and away from the ground launch

Wind 20 Knots

Wind 10 KnotsWind Gradient

60 Kts.

70 Kts.

Effect of wind gradient on airspeed during ground launch. Pilot must monitor airspeed indicator carefully. Goal is to fly fast enough to maintain safe margin above stall speed, but slower than maximum permitted ground launch airspeed.

Figure 7-20. Ground launch wind gradient.

Figure 7-21. Ground launch towline break.

Very early break! Land straight ahead. Tow vehicles, if used, should clear runway to make way for the glider.

Airborne break! Lower nose, land straight ahead promptly.

If towline is parachute equipped, avoid parachute when lowering nose after towline break or normal release.

BANG

BANG

7-18

equipment, allowing the back release to activate or theweak link to fail. The ground launch equipment is alsoequipped with an emergency release mechanism in theevent the glider tow release fails. If a winch is used, itwill be equipped with a guillotine to cut the towline.An automobile used for ground launch is normallyequipped with some form of backup release mecha-nism.

SELF-LAUNCH TAKEOFF PROCEDURES PREPARATION AND ENGINE STARTThe self-launching glider has many more systems thana non-motorized glider, so the preflight inspection ismore complex. A positive control check is just as criti-cal as it is in any other glider. Ailerons, elevator, rud-der, elevator trim tab, flaps, and spoiler/dive breaksmust all be checked. In addition, numerous other sys-tems must be inspected and readied for flight. Theseinclude the fuel system, the electrical system, theengine, the propeller, the cooling system, and anymechanisms and controls associated with extending orretracting the engine or propulsion system. Instruments,gauges, and all engine and propulsion system controlsmust be inspected for proper operation.

After preflighting the self-launching glider and clear-ing the area, start the engine in accordance with themanufacturer’s instructions. Typical items on a self-launching glider engine-start checklist include fuelmixture control, fuel tank selection, fuel pump switch,engine priming, propeller pitch setting, cowl flap set-ting (if cowl flaps are fitted), throttle setting, magnetoor ignition switch setting, and electric starter activa-tion. After starting the oil pressure, oil temp, alterna-tor/generator charging, and suction instruments shouldbe checked. If the engine and propulsion systems areoperating within normal limits, taxi operations canbegin.

COMMON ERRORS

• Failure to use or improper use of checklist.• Improper or unsafe starting procedures.• Excessively high RPM after starting.• Failure to ensure proper clearance of propeller.

TAXIING THE SELF-LAUNCHING GLIDERSelf-launching gliders are designed with a variety oflanding gear configurations. These include tricycle-landing gear and tailwheel-landing gear. Other types ofself-launch gliders rest primarily on the main landinggear wheel in the center of the fuselage and depend onoutrigger wheels or skids to prevent the wingtips fromcontacting the ground. These types of gliders often fea-ture a retractable powerplant for drag reduction. Afterthe launch, the powerplant is retracted into the fuse-lage and stowed.

Due to the long wingspan and low wingtip groundclearance, many airport taxiways, and some run-ways, may not be wide enough to accommodate aself-launch glider. Additionally, limited crosswindcapability may lead to directional control difficultiesduring taxi operations.

Taxiing on soft ground requires additional power. Self-launch gliders with outrigger wingtip wheels may losedirectional control if a wingtip wheel bogs down.Well-briefed wing walkers should hold the wings levelduring low-speed taxi operations on soft ground.

COMMON ERRORS

• Improper use of brakes.• Failure to comply with airport markings,

signals, and clearances.• Taxiing too fast for conditions.• Improper control positioning for wind.

conditions.• Failure to consider wingspan and space

required to maneuver during taxiing.

BEFORE TAKEOFF CHECK—SELF-LAUNCHING GLIDER The manufacturer provides a takeoff checklist. Asshown in Figure 7-22, the complexity of many self-launching gliders makes a written takeoff checklist anessential safety item. Before takeoff items on a self-launch glider may include fuel quantity check, fuelpressure check, oil temperature check, oil pressurecheck, engine run-up, throttle/RPM check, propellerpitch setting, cowl flap setting, and vacuum check. Inaddition, other items also must be completed. Theseinclude making sure seat belts and shoulder harnessesare latched or secured, doors and windows are closedand locked, canopies are closed and locked, airbrakesare closed and locked, altimeter is set, VHF radiotransceiver is set, and the directional gyros is set.

COMMON ERRORS

• Improper positioning of the self-launch gliderfor run-up.

• Failure to use or improper use of checklist.• Improper check of flight controls.• Failure to review takeoff emergency

procedures.

NORMAL TAKEOFF—SELF-LAUNCHING GLIDERWhen the before takeoff checklist is complete, thepilot should check for traffic and prepare for takeoff.If operating from an airport with an operating controltower, request and receive an ATC clearance prior to

7-19

taxi. The pilot should make a final check for conflict-ing traffic, then taxi out on to the active runway andalign the glider with the centerline.

The pilot should smoothly apply full throttle and beginthe takeoff roll, tracking down the centerline of therunway, easing the self-launch glider off the runway atthe recommended lift-off airspeed, and allowing theglider to accelerate in ground effect until reaching theappropriate climb airspeed. If the runway has an obsta-cle ahead, this will be best angle of climb airspeed (Vx)until the obstacle is cleared. If no obstacle is present,the preferred airspeed will be either best rate of climbairspeed (Vy), or the airspeed for best engine coolingduring climb. The pilot should monitor the engine andinstrument systems during climb out. If the self-launchglider has a time limitation on full throttle operation,the throttle should be adjusted as necessary during theclimb.

CROSSWIND TAKEOFF—SELF-LAUNCHING GLIDERThe long wingspan and low wingtip clearance of thetypical self-launch glider makes it vulnerable to wingtip strikes on runway border markers, light stanchions,and other obstacles along the edge of the runway. Thetakeoff roll should be started with upwind aileron anddownwind rudder. In a right crosswind, for example,the control stick should be held to the right and the rud-der held to the left. The aileron input keeps the cross-wind from lifting the upwind wing, and the downwindrudder minimizes the weathervaning tendency of theself-launch glider in a crosswind. As airspeed increases,control effectiveness will improve, and the pilot cangradually decrease some of the control. The self-launchglider should be lifted off at the appropriate lift-off air-speed, and accelerate to climb airspeed. During theclimb, a wind correction angle should be established sothat the self-launch glider will track the extended cen-terline of the takeoff runway. [Figure 7-23]

Complexity of the self-launching glider requires a complex instrument panel and a lengthy pre-takeoff checklist.

Figure 7-22. Self-launch glider instrument panels.

Crab into wind to holdrunway centerline.

Liftoff

Figure 7-23. Self-launch glider—crosswind takeoff.

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COMMON ERRORS

• Improper initial positioning of flight controls.• Improper power application.• Inappropriate removal of hand from throttle.• Poor directional control.• Improper use of flight controls.• Improper pitch attitude during takeoff.• Failure to establish and maintain proper climb

attitude and airspeed.• Improper crosswind control technique.

SELF-LAUNCH—CLIMB-OUTAND SHUTDOWN PROCEDURESSelf-launch gliders have powerplant limitations, aswell as aircraft performance and handling limitations.Powerplant limits include temperature limits, maxi-mum RPM limit, maximum manifold pressure limit,useable fuel limit, and similar items. The Glider FlightManual (GFM) or Pilot’s Operating Handbook (POH)provides useful information about recommendedpower settings and target airspeed for best angle ofclimb, best rate-of-climb, best cooling performanceclimb, and level flight cruise operation while underpower. If full-throttle operation is time limited toreduce engine wear, the GFM/POH describes the rec-ommended operating procedures. Aircraft perform-ance limits include weight and balance limits,minimum and maximum front seat weight restrictions,maximum permitted airspeed with engine extended,maximum airspeed to extend or retract the engine, flapoperating airspeed range, airbrake operating airspeedrange, maneuvering speed, rough air speed limitations,and never exceed speed.

The engine heats up considerably during takeoff andclimb, so cooling system mismanagement or failurecan lead to dangerously high temperatures in a shorttime. An overheated engine cannot supply full power,meaning climb performance will be reduced. Extendedoverheating can cause an in-flight fire. To minimizethe chances of engine damage or fire, monitor enginetemperatures carefully during high power operations,and observe the engine operating limits described inthe GFM/POH.

Many self-launch gliders have a time limitation on fullthrottle operation to prevent overheating and prematureengine wear. If the self-launch glider is equipped withcowl flaps for cooling, make certain the cowl flaps areset properly for high-power operations. In some self-launch gliders, operating at full power with cowl flapsclosed can result in an overheated, ruined engine in aslittle as 2 minutes. If abnormally high engine systemtemperatures are encountered, follow the proceduresdescribed in the GFM/POH. Typically, these requirereduced power along with higher airspeed to enhance

engine cooling. Cowl flap instructions may be providedas well. If these measures are ineffective in reducinghigh temperatures, the safest course of action may be toshut down the engine and make a precautionary land-ing. A safe landing, whether on or off the airport, isalways preferable to an in-flight fire.

Handling limitations for a given self-launch glidermay be quite subtle and may include minimum con-trollable airspeed with power on, minimum control-lable airspeed with power off, and other limitationsdescribed in the GFM/POH. Self-launch gliders comein many configurations. Those with a top-mountedretractable engine and/or propeller have a thrust linethat is quite distant from the longitudinal axis of theglider. The result is that significant changes of powersettings tend to cause substantial pitch attitudechanges. For instance, full power setting in these self-launch gliders introduces a nose-down pitchingmoment because the thrust line is high above the lon-gitudinal axis of the glider. To counteract this pitchingmoment, the pilot should hold the control stick back.If power is quickly reduced from full power to idlepower while the control stick is held steady, these glid-ers tend to pitch up considerably. The nose-up pitchingmoment may be vigorous enough to induce a stall!

During climb-out, the pilot should hold a pitch attitudethat results in climbing out at the desired airspeed,adjusting elevator trim as necessary. Climbs in self-launch gliders are best managed with smooth controlinputs and, when power changes are necessary, smoothand gradual throttle adjustments.

When climbing under power, most self-launch glidersexhibit a left- or right-turning tendency (depending onwhether the propeller is turning clockwise or counter-clockwise) due to P-factor. P-factor is caused by theuneven distribution of thrust caused by the differencein the angle of attack of the ascending propeller bladeand the descending propeller blade. Use the rudder tocounteract P-factor during climbs with power.

Turns are accomplished with a shallow bank anglebecause steep banks result in a much-reduced rate ofclimb. As with all turns in a glider, properly coordinat-ing aileron and rudder results in more efficient flightand a faster climb rate. The pilot should clear for otherair traffic before making any turn.

Detailed engine shutdown procedures are described inthe GFM/POH. A guide to shutdown procedures isdescribed below, but the GFM/POH is the authorita-tive source for any self-launch glider.

Engines reach high operating temperatures duringextended high-power operations. To reduce or elimi-

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nate shock cooling, and to reduce the possibility of in-flight fire, the manufacturer provides engine cool-down procedures to reduce engine systemtemperatures prior to shutdown. Reducing throttle set-ting allows the engine to begin a gradual cool down.The GFM/POH may also instruct the pilot to adjustpropeller pitch at this time. Lowering the nose toincrease airspeed provides faster flow of cooling air tothe engine cooling system. Several minutes of reducedthrottle and increased cooling airflow are enough toallow the engine to be shut down. If the engine isretractable, additional time after engine shutdown maybe necessary to reduce engine temperature to accept-able limits prior to retracting and stowing the engine inthe fuselage. Consult the GFM/POH for details.[Figure 7-24]

Retractable-engine self-launch gliders are aerodynam-ically efficient when the engine is stowed, but producehigh-drag when the engine is extended and not provid-ing thrust. Stowing the engine is critical to efficientsoaring flight. Prior to stowing, the propeller must bealigned with the longitudinal axis of the glider, so thepropeller blades do not interfere with the engine baydoors. Since the engine/propeller installation in thesegliders is aft of the pilot’s head, these gliders usuallyhave a mirror, enabling the pilot to perform a visualpropeller alignment check prior to stowing theengine/propeller pod. Detailed instructions for stowingthe engine and propeller are found in the GFM/POH

for the particular glider. If a malfunction occurs duringengine shutdown and stowage, the pilot cannot counton being able to get the engine restarted. The pilotshould have a landing area within power-off glidingdistance in anticipation of this eventuality.

Some self-launch gliders use a nose-mounted engine/pro-peller installation that resembles the typical installationfound on single-engine airplanes. In these self-launchgliders, the shutdown procedure usually consists ofoperating the engine for a short time at reduced powerto cool the engine down to acceptable shutdown tem-perature. After shutdown, the cowl flaps, if installed,should be closed to reduce drag and increase glidingefficiency. The manufacturer may recommend a timeinterval between engine shutdown and cowl flap clo-sure, to prevent excess temperatures from developingin the confined, tightly cowled engine compartment.These temperatures may not be harmful to the engineitself, but may degrade the structures around theengine, such as composite engine mounts or installedelectrical components. Excess engine heat may resultin fuel vapor lock.

If the propeller blade pitch can be controlled by thepilot while in flight, the propeller is usually set tocoarse pitch, or if possible, feathered, to reduce pro-peller drag during non-powered flight. Some self-launch gliders require the pilot to set the propeller tocoarse pitch prior to engine shutdown. Other self-launch gliders require the pilot to shut down the enginefirst, then adjust propeller blade pitch to coarse pitch orto feathered position. As always, follow the shutdownprocedures described in the GFM/POH.

COMMON ERRORS

• Failure to follow manufacturer’s recom-mended procedure for engine shutdown, feath-ering, and stowing procedure (if applicable).

• Failure to maintain positive aircraft control while performing engine shutdown procedures.

LANDINGSIf the self-launch glider is to land under power, the pilotshould perform the engine restart procedures at a safealtitude to allow time to reconfigure. The pilot shouldfollow the manufacturer’s recommended pre-startingchecklist. Once the engine is started, the pilot shouldallow time for it to warm up. After the engine is startedthe pilot should ensure that all systems necessary forlanding are operational, such as the electrical systemand landing gear.

The pilot should fly the traffic pattern so as to landinto the wind and plan the approach path to avoid allobstacles. The landing area should be of sufficientlength to allow for touchdown and roll-out within theFigure 7-24.Types of self-launch gliders.

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performance limitations of the particular self-launchglider. The pilot should also take into considerationany crosswind conditions and the landing surface.After touchdown, the pilot should maintain directioncontrol, and slow the self-launch glider so as to clearthe landing area. The after landing checklist should becompleted when appropriate.

COMMON ERRORS

• Poor judgment of approach path.• Improper use of flaps, spoilers, and/or dive

brakes.• Improper approach and landing speed.• Improper crosswind correction.• Improper technique during roundout and

touchdown.• Poor directional control after landing.• Improper use of brakes.• Failure to use the appropriate checklist.

EMERGENCY PROCEDURES

SELF-LAUNCHING GLIDER The pilot of a self-launching glider should formulateemergency plans for any type of failure that mightoccur. Thorough knowledge of aircraft performancedata, normal takeoff/landing procedures, and emer-gency procedures, as outlined in the GFM/POH, isessential to the successful management of any emer-gency situation. Mismanagement of the aircraft sys-tems through lack of knowledge may cause seriousdifficulty. For instance, if the spoilers/dive brakes areallowed to open during takeoff and climbout, the self-launch glider may be incapable of generating sufficientpower to continue climbing. Other emergency situa-tions may include in-flight fire, structural failure,encounters with severe turbulence/wind shear, canopyfailure, and inadvertent encounter with instrumentmeteorological conditions.

Possible options for handling emergencies are influ-enced by the altitude above the terrain, wind, weatherconditions, density altitude, glider performance, take-off runway length, landing areas near the gliderport,and other air traffic. Emergency options may includelanding straight ahead on the remaining runway, land-ing off-field, or returning to the gliderport to land onan available runway. The appropriate emergency pro-cedures may be found in the GFM/POH for the spe-cific self-launch glider.

PERFORMANCE MANEUVERS

STRAIGHT GLIDESTo perform a straight glide the glider pilot must hold aconstant heading and airspeed. The heading referenceshould be some prominent point in front of the glider

on the Earth’s surface. The pilot will also note that dur-ing a straight glide each wingtip should be an equaldistance above the earth surface. With the wings level,the pitch attitude is established with reference to apoint on or below the horizon to establish a specifiedairspeed. Any change in pitch attitude will result in achange in airspeed. There will be a pitch attitude refer-ence for best glide speed, another for the minimumsink speed, and another for slow flight. The pitch atti-tude is adjusted with the elevator to hold the specificairspeed. The glider elevator trim control allows thepilot to trim the glider to hold a constant pitch attitude,therefore a constant airspeed. Straight glides should becoordinated as indicated by a centered yaw string orslip-skid ball.

The glider pilot should also stay alert to airflow noisechanges. At a constant airspeed in coordinated flight,wind noise should be constant. Any changes in air-speed or coordination cause a change in the windnoise. Gusts that cause the airspeed to change momen-tarily can be ignored. Holding a constant pitch attituderesults in maintaining the desired airspeed.

The glider pilot should learn to fly throughout a widerange of airspeeds; from minimum controllable airspeedto maximum allowable airspeed. This enables the pilotto learn the feel of the controls of the glider throughoutits speed range. If the glider is equipped withspoilers/dive brakes and/or flaps, the glider pilot shouldbecome familiar with the changes that occur in pitchattitude and airspeed when these controls are used.

COMMON ERRORS

1. Rough or erratic pitch attitude and airspeed control.

2. Rough, uncoordinated, or inappropriate con-trol applications.

3. Failure to use the trim or improper use of trim.4. Improper use of controls when using spoilers,

dive breaks and/or flaps.

TURNS The performance of turns involves coordination of allthree flight controls: ailerons, rudder, and elevator. Forpurposes of this discussion, turns are divided into thefollowing three classes as shown in Figure 7-25.

• Shallow turns are those in which the bank (less than approximately 20°) is so shallow that the inherent lateral stability of the glider is acting to level the wings unless some aileron is applied to maintain the bank.

• Medium turns are those resulting from a degree of bank (approximately 20° to 45°) at which the lateral stability is overcome by the

7-23

overbanking tendency, resulting in no control inputs (other than elevator) being required to maintain the angle.

• Steep turns are those resulting from a degree of bank (45° or more) at which the “overbanking tendency” of a glider overcomes stability, and the bank increases unless aileron is applied to prevent it.

Before starting any turn, the pilot must clear the air-space in the direction of the turn. A glider is turned bybanking (lowering the wing in the direction of thedesired turn, thus raising the other). When the glider isflying straight, the total lift is acting perpendicular tothe wings and to the earth. As the glider is banked intoa turn, total lift becomes the resultant of two compo-

nents. One, the vertical lift component, continues to actperpendicular to the earth and opposes gravity. Second,the horizontal lift component (centripetal) acts parallelto the earth’s surface and opposes inertia (apparent cen-trifugal force). These two lift components act at rightangles to each other, causing the resultant total liftingforce to act perpendicular to the banked wing of theglider. It is the horizontal lift component that actuallyturns the glider, not the rudder.

When applying aileron to bank the glider, the aileronon the rising wing is lowered produces a greater dragthan the raised aileron on the lowering wing. Thisincreased drag causes the glider to yaw toward the ris-ing wing, or opposite to the direction of turn. To coun-teract this adverse yawing moment, rudder pressuremust be applied in the desired direction of turn simul-taneously with aileron pressure. This action is requiredto produce a coordinated turn.

After the bank has been established in a mediumbanked turn, all pressure applied to the aileron may berelaxed. The glider will remain at the selected bankwith no further tendency to yaw since there is no longera deflection of the ailerons. As a result, pressure mayalso be relaxed on the rudder pedals, and the rudderallowed to streamline itself with the direction of theslipstream. Rudder pressure maintained after establish-ing the turn will cause the glider to skid to the outsideof the turn. If a definite effort is made to center the rud-der rather than let it streamline itself to the turn, it isprobable that some opposite rudder pressure will beexerted inadvertently. This will force the glider to yawopposite its turning path, causing the glider to slip tothe inside of the turn. The yaw string or ball in the slipindicator will be displaced off-center whenever theglider is skidding or slipping sideways. In proper coor-dinated flight, there is no skidding or slipping.

In all gliding, constant airspeed turns, it is necessary toincrease the angle of attack of the wing as the bankprogresses by adding nose-up elevator pressure. This isrequired because the total lift must be equal to the ver-tical component of lift plus the horizontal lift compo-nent. To stop the turn, coordinated use of the aileronand rudder pressure are added to bring the wings backto level flight, and elevator pressure is relaxed.

There is a direct relationship between, airspeed, bankangle, and rate and radius of turn. The rate of turn atany given true airspeed depends on the horizontal liftcomponent. The horizontal lift component varies inproportion to the amount of bank. Therefore, the rate ofturn at a given true airspeed increases as the angle ofbank is increased. On the other hand, when a turn ismade at a higher true airspeed at a given bank angle, theinertia is greater and the horizontal lift componentrequired for the turn is greater, causing the turning rate

20°

45°

60°

Figure 7-25. Shallow, medium, and steep turns.

7-24

to become slower. Therefore, at a given angle of bank, ahigher true airspeed will make the radius of turn largerbecause the glider will be turning at a slower rate.

As the angle of bank is increased from a shallow bankto a medium bank, the airspeed of the wing on the out-side of the turn increases in relation to the inside wing.The additional lift so developed balances the lateralstability of the glider. No aileron pressure is requiredto maintain the bank. At any given airspeed, aileronpressure is not required to maintain the bank.

If the bank is increased from a medium bank to a steepbank, the radius of turn decreases even further. Thegreater lift of the outside wing then causes the bank tosteepen and opposite aileron is necessary to keep thebank constant.

As the radius of the turn becomes smaller, a significantdifference develops between the speed of the insidewing and the speed of the outside wing. The wing onthe outside of the turn travels a longer circuit than theinside wing, yet both complete their respective circuitsin the same length of time. Therefore, the outside wingtravels faster than the inside wing, and as a result, itdevelops more lift. This creates an overbanking ten-dency that must be controlled by the use of the ailerons.Because the outboard wing is developing more lift, italso has more induced drag. This causes a slip duringsteep turns that must be corrected by rudder usage.

To establish the desired angle of bank, the pilot shoulduse visual reference points on the glider, the Earth'ssurface, and the natural horizon. The pilot's posturewhile seated in the glider is very important, particu-larly during turns. It will affect the interpretation ofoutside visual references. The beginning pilot may leanaway from or into the turn rather than ride with theglider. This should be corrected immediately if thepilot is to properly learn to use visual references.

Applications of large aileron and rudder producesrapid roll rates and allow little time for correctionsbefore the desired bank is reached. Slower (small con-trol displacement) roll rates provide more time to makenecessary pitch and bank corrections. As soon as theglider rolls from the wings-level attitude, the nose willstart to move along the horizon, increasing its rate oftravel proportionately as the bank is increased.

COMMON ERRORS

• Failure to clear turn.• Nose starts to move before the bank starts—

rudder is being applied too soon.• Bank starts before the nose starts turning, or

the nose moves in the opposite direction—the rudder is being applied too late.

• Nose moves up or down when entering a bank—excessive or insufficient elevator is being applied.

As the desired angle of bank is established, aileron andrudder pressures should be relaxed. This stops the bankfrom increasing because the aileron and rudder controlsurfaces will be neutral in their streamlined position.The up-elevator pressure should not be relaxed, butshould be held constant to maintain the desired air-speed. Throughout the turn, the pilot should crosscheckthe airspeed indicator to verify the proper pitch is beingmaintained. The crosscheck should also include outsidevisual references. If gaining or losing airspeed, the pitchattitude should be adjusted in relation to the horizon.

During all turns, the ailerons, rudder, and elevator areused to correct minor variations in pitch and bank justas they are in straight glides.

The roll-out from a turn is similar to the roll-in exceptthe flight controls are applied in the opposite direction.Aileron and rudder are applied in the direction of theroll-out or toward the high wing. As the angle of bankdecreases, the elevator pressure should be relaxed, asnecessary, to maintain airspeed.

Since the glider will continue turning as long as there isany bank, the roll-out must be started before reachingthe desired heading. The amount of lead required toroll-out on the desired heading depends on the degreeof bank used in the turn. Normally, the lead is one halfthe degrees of bank. For example, if the bank is 30°,lead the roll-out by 15°. As the wings become level, thecontrol pressures should be smoothly relaxed so thecontrols are neutralized as the glider returns to straightflight. As the roll-out is being completed, attentionshould be given to outside visual references, as well asthe airspeed and heading indicators to determine thatthe wings are being leveled and the turn stopped.

COMMON ERRORS

• Rough or uncoordinated use of controls during the roll-in and roll-out.

• Failure to establish and maintain the desired angle of bank.

• Overshooting/undershooting the desired heading.

In a slipping turn, the glider is not turning at the rateappropriate to the bank being used, since the glider isyawed toward the outside of the turning flight path.The glider is banked too much for the rate of turn, sothe horizontal lift component is greater than the cen-trifugal force. Equilibrium between the horizontal liftcomponent and centrifugal force is reestablished eitherby decreasing the bank (ailerons), increasing yaw(rudder), or a combination of the two. [Figure 7-26]

7-25

A skidding turn results from an excess of centrifugalforce over the horizontal lift component, pulling theglider toward the outside of the turn. The rate of turn istoo great for the angle of bank. Correction of a skid-ding turn thus involves a decrease in yaw (rudder), anincrease in bank (aileron), or a combination of the twochanges. [Figure 7-27]

The yaw string identifies slips and skids. In flight, therule to remember is simple: step away from the tail ofthe yaw string. If the tail of the yaw string is to the leftof center, press the right rudder pedal to coordinate theglider and center the yaw string. If the tail of the yawstring is right of center, pressure the left rudder pedalto coordinate the glider and center the yaw string.[Figure 7-28]

The ball in the slip/skid indicator also indicates slipsand skids. When using this instrument for coordina-tion, you should apply rudder pressure on the side thatthe ball is offset (step on the ball).

Correction for uncoordinated condition should beaccomplished by using appropriate rudder and aileroncontrol pressures simultaneously to coordinate the glider.

STEEP TURNSSoaring flight requires competence in steep turns. Inthermalling flight, small-radius turns are often neces-sary to keep the glider in or near the core of the thermalupdraft, where lift is usually strongest and rapid climbsare possible. At any given airspeed, increasing the angleof bank will decrease the radius of the turn and increasethe rate of turn. The radius of a turn at any given bankangle varies directly with the square of the airspeed atwhich the turn is made, therefore the slower the air-speed the smaller the turn radius. To keep the radius ofturn small, it is necessary to bank steeply, while main-taining an appropriate airspeed, such as minimum sinkor best glide speed. The pilot must be aware that as thebank angle increases, the stall speed increases.

Before starting the steep turn, the pilot should ensurethat the area is clear of other traffic since the rate ofturn will be quite rapid. After establishing the appro-priate airspeed, the glider should be smoothly rolledinto a coordinated steep turn with at least 45° ofbank. The pilot should use outside visual referenceto establish and maintain the desired bank angle. Ifthe pilot does not add back pressure to maintain thedesired airspeed after the bank is established, theglider will have a tendency to enter a spiral. To coun-teract the overbanking tendency caused by the steepturn, the pilot should apply top aileron pressure.Because the top aileron pressure pulls the nose awayfrom the direction of the turn, the pilot also has toapply bottom rudder pressure. A coordinated (no slipor skid) steep turn requires back pressure on the ele-vator for airspeed control, top aileron pressure forbank control, and bottom rudder pressure to streamline the fuselage with the flight path.

COMMON ERRORS

• Failure to clear turn.• Uncoordinated use of controls.• Loss of orientation.• Failure to maintain airspeed within tolerance.• Unintentional stall or spin.• Excessive deviation from desired heading

during roll-out.

SPIRAL DIVEAllowing the nose of the glider to get excessively lowduring a steep turn may result in a significant increase

Skidding Turn: Excess rudder appliedduring banked turn.

Yaw StringIndication

Slipping Turn: Insufficient rudder appliedduring banked turn.

Yaw StringIndication

Coordinated Turn

Yaw StringIndication

Figure 7-27. Skidding turn.

Figure 7-26. Slipping turn.

Figure 7-28. Coordinated turn.

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in airspeed and loss in altitude. This is known as aspiral dive. If the pilot attempts to recover from thissituation by only applying back elevator pressure, thelimiting load factor may be exceeded, causing struc-tural failure. To properly recover from a spiral dive,the pilot should first reduce the angle of bank withcoordinated use of the rudder and aileron, thensmoothly increase pitch to the proper attitude.

COMMON ERRORS

• Failure to recognize when a spiral dive is developing.

• Rough, abrupt, and/or uncoordinated control application during recovery.

• Improper sequence of control applications.

MANEUVERING AT MINIMUM CONTROLAIRSPEED, STALLS, AND SPINSAll pilots must be proficient in maneuvering at minimumcontrollable airspeed and stall recognition and recovery.In addition, all flight instructor applicants must be profi-cient in spins entries, spins, and spin recovery.

MANEUVERING AT MINIMUM CONTROLLABLEAIRSPEED Maneuvering during slow flight demonstrates theflight characteristics and degree of controllability of aglider at minimum speeds. By definition, the term“flight at minimum controllable airspeed” means aspeed at which any further increase in angle of attackor load factor causes an immediate stall. Pilots mustdevelop an awareness of the particular glider flightcharacteristics in order to recognize and avoid stalls,which may inadvertently occur during the slow air-speeds used in takeoffs, climbs, thermalling, andapproaches to landing.

The objective of maneuvering at minimum control-lable airspeed is to develop the pilot’s sense of feel andability to use the controls correctly, and to improveproficiency in performing maneuvers that require slowairspeeds. Maneuvering at minimum controllable air-speed should be performed using outside visual refer-ence. It is important that pilots form the habit offrequently referencing the pitch attitude of the gliderfor airspeed control while flying at slow speeds.

The maneuver is started from either best glide or mini-mum sink speed. The pitch attitude is smoothly andgradually increased. While the glider is losing air-speed, the position of the nose in relation to the hori-zon should be noted and should be adjusted asnecessary until the minimum controllable airspeed isestablished. During these changing flight conditions, itis important to re-trim the glider, as necessary, to com-pensate for changes in control pressures. Excessive ortoo aggressive back pressure on the elevator control

may result in an abrupt increase in pitch attitude and arapid decrease in airspeed, which leads to a higherangle of attack and a possible stall. When the desiredpitch attitude and airspeed have been established, it isimportant to continually crosscheck the pitch attitudeon the horizon and the airspeed indicator to ensureaccurate control is being maintained.

When minimum controllable airspeed is established instraight flight, turns should be practiced to determinethe glider’s controllability characteristics at thisselected airspeed. During the turns the pitch attitudemay need to be decreased in order to maintain the air-speed. If a steep turn is encountered, and the pitch atti-tude is not decreased, the increase in load factor mayresult in a stall. A stall may also occur as a result ofabrupt or rough control movements resulting inmomentary increases in load factor. Abruptly raisingthe flaps during minimum controllable airspeed willresult in sudden loss of lift, possibly causing a stall.

Minimum controllable airspeed should also be prac-ticed with extended spoilers/dive breaks. This willprovide additional understanding of the changes inpitch attitude caused by the increase in drag from thespoilers/dive breaks.

Actual minimum controllable airspeed depends uponvarious conditions, such as the gross weight and CGlocation of the glider and the maneuvering loadimposed by turns and pull-ups. Flight at minimumcontrollable airspeed requires positive use of rudderand ailerons. The diminished effectiveness of the flightcontrols during flight at minimum controllable air-speed will help pilots develop the ability to estimatethe margin of safety above the stalling speed.

COMMON ERRORS• Failure to establish or to maintain minimum

controllable airspeed.

• Improper use of trim.

• Rough or uncoordinated use of controls.

• Failure to recognize indications of a stall.

STALL RECOGNITION AND RECOVERYA stall can occur at any airspeed and in any attitude. Inthe case of the self-launch glider under power, a stallcan also occur with any power setting. A stall occurswhen the smooth airflow over the glider’s wing is dis-rupted and the lift decreases rapidly. This occurs whenthe wing exceeds its critical angle of attack.

The practice of stall recovery and the development ofawareness of stalls are of primary importance in pilottraining. The objectives in performing intentionalstalls are to familiarize the pilot with the conditions

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that produce stalls, to assist in recognizing anapproaching stall, and to develop the habit of takingprompt preventive or corrective action.

Intentional stalls should be performed so the maneuveris completed by 1,500 feet above the ground for recov-ery and return to normal, wings-level flight. Though itdepends on the degree to which a stall has progressed,most stalls require some loss of altitude during recov-ery. The longer it takes to recognize the approachingstall, the more complete the stall is likely to become,and the greater the loss of altitude to be expected.

Pilots must recognize the flight conditions that are con-ducive to stalls and know how to apply the necessarycorrective action since most gliders do not have anelectrical or mechanical stall warning device. Pilotsshould learn to recognize an approaching stall by sight,sound, and feel. The following cues may be useful inrecognizing the approaching stall.

Vision is useful in detecting a stall condition by notingthe attitude of the glider. This sense can only be reliedon when the stall is the result of an unusual attitude ofthe glider. Since the glider can also be stalled from anormal attitude, vision in this instance would be of lit-tle help in detecting the approaching stall.

Hearing is also helpful in sensing a stall condition. Inthe case of a glider, a change in sound due to loss ofairspeed is particularly noticeable. The lessening of thenoise made by the air flowing along the glider struc-ture as airspeed decreases is also quite noticeable, andwhen the stall is almost complete, aerodynamic vibra-tion and incident noises often increase greatly.

Kinesthesia, or the sensing of changes in direction orspeed of motion, is probably the most important andthe best indicator to the trained and experienced pilot.If this sensitivity is properly developed, it will warn ofa decrease in speed or the beginning of a settling ormushing of the glider.

The feeling of control pressures is also very important.As speed is reduced, the resistance to pressures on thecontrols become progressively less. Pressures exertedon the controls tend to become movements of the con-trol surfaces. The lag between these movements and theresponse of the glider becomes greater, until in a com-plete stall all controls can be moved with almost noresistance, and with little immediate effect on the glider.

Signs of an impending stall include the following.

• High nose attitude.

• Low airspeed indication.

• Low airflow noise.

• Back pressure on sticks.

• Mushy controls, especially ailerons.

• Buffet.

Always make clearing turns before performing stalls.During the practice of intentional stalls, the real objec-tive is not to learn how to stall a glider, but to learnhow to recognize an approaching stall and take promptcorrective action. The recovery actions must be takenin a coordinated manner.

First, at the indication of a stall, the pitch attitude andangle of attack must be decreased positively and imme-diately. Since the basic cause of a stall is always anexcessive angle of attack, the cause must first be elimi-nated by releasing the back-elevator pressure that wasnecessary to attain that angle of attack or by moving theelevator control forward. This lowers the nose andreturns the wing to an effective angle of attack. Theamount of elevator control pressure or movement to usedepends on the design of the glider, the severity of thestall, and the proximity of the ground. In some gliders,a moderate movement of the elevator control—perhapsslightly forward of neutral—is enough, while in othersa forcible push to the full forward position may berequired. An excessive negative load on the wingscaused by excessive forward movement of the elevatormay impede, rather than hasten, the stall recovery. Theobject is to reduce the angle of attack, but only enoughto allow the wing to regain lift. [Figure 7-29]

BuffetStall

InitiateRecovery

IncreaseAirspeed

Recovery inStraight Glide

Figure 7-29. Stall recovery.

progresses toward the roots. Thus, the ailerons can beused to level the wings.

Using the ailerons requires finesse to avoid an aggra-vated stall condition. For example, if the right wingdropped during the stall and excessive aileron controlwas applied to the left to raise the wing, the aileronthat was deflected downward (right wing) would pro-duce a greater angle of attack (and drag). Possibly, amore complete stall would occur at the tip because thecritical angle of attack would be exceeded. Theincrease in drag created by the high angle of attack onthat wing might cause the airplane to yaw in that direc-tion. This adverse yaw could result in a spin unlessdirectional control was maintained by rudder, and/orthe aileron control was sufficiently reduced.

Even though excessive aileron pressure may havebeen applied, a spin will not occur if directional (yaw)control is maintained by timely application of coordi-nated rudder pressure. Therefore, it is important thatthe rudder be used properly during both the entry andthe recovery from a stall. The primary use of the rud-der in stall recoveries is to counteract any tendency ofthe glider to yaw or slip. The correct recovery tech-nique would be to decrease the pitch attitude by apply-ing forward elevator pressure to reduce the angle ofattack and while simultaneously maintaining direc-tional control with coordinated use of the aileron andrudder.

Due to engineering design variations, the stall charac-teristics for all gliders cannot be specificallydescribed; however, the similarities found in glidersare noteworthy enough to be considered. The factorsthat affect the stalling characteristics of the glider areweight and balance, bank and pitch attitude, coordina-tion, and drag. The pilot should learn the effect of thestall characteristics of the glider being flown and theproper correction. It should be reemphasized that astall can occur at any airspeed, in any attitude, or atany power setting in the case of a self-launch glider,depending on the total number of factors affecting theparticular glider.

Whenever practicing stalls while turning, a constantbank angle should be maintained until the stall occurs.After the stall occurs coordinated control inputsshould be made to return the glider to level flight.

ADVANCED STALLSAdvanced stalls include secondary, accelerated, andcrossed-control stalls. These stalls are extremely use-ful for pilots to expand their knowledge of stall/spinawareness.

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If stalls are practiced or encountered in a self-launchglider, the maximum allowable power should beapplied during the stall recovery to increase the self-launch glider’s speed and assist in reducing the wing’sangle of attack. Generally, the throttle should bepromptly, but smoothly, advanced to the maximumallowable power. Although stall recoveries should bepracticed without, as well as with the use of power, inself-launch gliders during actual stalls the applicationof power is an integral part of the stall recovery.Usually, the greater the power applied, the less the lossof altitude. Maximum allowable power applied at theinstant of a stall usually does not cause overspeedingof an engine equipped with a fixed-pitch propeller,due to the heavy air load imposed on the propeller atslow airspeeds. However, it will be necessary toreduce the power as airspeed is gained after the stallrecovery so the airspeed does not become excessive.When performing intentional stalls, the tachometerindication should never be allowed to exceed the redradial line (maximum allowable RPM) as marked onthe instrument.

Whether in a glider or self-launched glider, wingslevel, straight flight should be regained with coordi-nated use of all controls. The first few practices shouldconsist of approaches to stalls, with recovery initiatedas soon as the first buffeting or partial loss of control isnoted. In this way, the pilot can become familiar withthe indications of an approaching stall without fullystalling the glider.

Stall accidents usually result from an inadvertent stallat a low altitude in which a recovery was not accom-plished prior to contact with the surface. As a preven-tive measure, stalls should be practiced at an altitudethat allows recovery at no lower than 1,500 feet AGL.

Different types of gliders have different stall character-istics. Most gliders are designed so the wings stall pro-gressively outward from the wing roots (where thewing attaches to the fuselage) to the wingtips. This isthe result of designing the wings so the wingtips have asmaller angle of incidence than the wing roots. Such adesign feature causes the wingtips to have a smallerangle of attack than the wing roots during flight.

Exceeding the critical angle of attack causes a stall.Since the wing roots will exceed the critical anglebefore the wingtips, they will stall first. The wings aredesigned in this manner so aileron control will beavailable at high angles of attack (slow airspeed) andgive the glider more stable stalling characteristics.When the glider is in a stalled condition, the wingtipscontinue to provide some degree of lift, and theailerons still have some control effect. During recov-ery from a stall, the return of lift begins at the tips and

7-29

SECONDARY STALLThis stall is called a secondary stall because it mayoccur after a recovery from a preceding stall. It iscaused by attempting to hasten the completion of a stallrecovery before the glider has regained sufficient fly-ing speed and the critical angle of attack is againexceeded. When this stall occurs, the back-elevatorpressure should again be released just as in a normalstall recovery. When sufficient airspeed has beenregained, the glider can then be returned to wings-level,straight flight. This stall usually occurs when the pilotuses abrupt control input to return to wings-level,straight flight after a stall or spin recovery.

ACCELERATED STALLSThough the stalls already discussed normally occur at aspecific airspeed, the pilot must thoroughly understandthat all stalls result solely from attempts to fly at exces-sively high angles of attack. During flight, the angle ofattack of a glider wing is determined by a number offactors, the most important of which are the airspeed,the gross weight of the glider, and the load factorsimposed by maneuvering.

At gross weight, the glider will consistently stall at thesame indicated airspeed if no acceleration is involved.The glider will, however, stall at a higher indicated air-speed when excessive maneuvering loads are imposedby steep turns, pull-ups, or other abrupt changes in itsflight path. Stalls entered from such flight situationsare called “accelerated maneuver stalls,” a term thathas no reference to the airspeeds involved.

Stalls that result from abrupt maneuvers tend to bemore rapid or severe than the unaccelerated stalls, andbecause they occur at higher-than-normal airspeeds,they may be unexpected by pilots. Failure to takeimmediate steps toward recovery when an acceleratedstall occurs may result in a complete loss of flightcontrol, possibly causing a spin.

Accelerated maneuver stalls should not be performedin any glider in which the maneuver is prohibited in theGFM/POH. If they are permitted, they should be per-formed with a bank of approximately 45°, and in nocase at a speed greater than the glider manufacturer’srecommended airspeeds or the design maneuveringspeed specified for the glider. The design maneuveringspeed is the maximum speed at which the glider can bestalled or the application of full aerodynamic controlwill not exceed the glider’s limit load factor. At orbelow this speed, the glider is designed so that it stallsbefore the limit load factor can be exceeded.

The objective of demonstrating accelerated stalls is notto develop competency in setting up the stall, butrather to learn how they may occur and to develop the

ability to recognize such stalls immediately, and totake prompt, effective recovery action. It is importantthat recoveries are made at the first indication of astall, or immediately after the stall has fully devel-oped; a prolonged stall condition should never beallowed.

A glider will stall during a coordinated turn as it doesfrom straight flight except the pitching and rollingactions tend to be more sudden. If the glider is slippingtoward the inside of the turn at the time the stall occurs,it tends to roll rapidly toward the outside of the turn asthe nose pitches down because the outside wing stallsbefore the inside wing. If the glider is skidding towardthe outside of the turn, it will have a tendency to roll tothe inside of the turn because the inside wing stallsfirst. If the coordination of the turn at the time of thestall is accurate, the glider’s nose will pitch away fromthe pilot just as it does in a straight flight stall, sinceboth wings stall simultaneously.

Glider pilots enter an accelerated stall demonstrationby establishing the desired flight attitude, thensmoothly, firmly, and progressively increasing theangle of attack until a stall occurs. Because of the rap-idly changing flight attitude, sudden stall entry, andpossible loss of altitude, it is extremely vital that thearea be clear of other aircraft and the entry altitude beadequate for safe recovery.

Actual accelerated stalls most frequently occur duringturns in the traffic pattern close to the ground or whilemaneuvering during soaring flight. The demonstrationof accelerated stalls is accomplished by exerting exces-sive back-elevator pressure. Most frequently, it wouldoccur during improperly executed steep turns, stall andspin recoveries, and pullouts from steep dives. Theobjectives are to determine the stall characteristics ofthe glider and develop the ability to instinctivelyrecover at the onset of a stall at other-than-normal stallspeed or flight attitudes. An accelerated stall, althoughusually demonstrated in steep turns, may actually beencountered any time excessive back-elevator pressureis applied and/or the angle of attack is increased toorapidly.

From straight flight at maneuvering speed or less, theglider should be rolled into a steep banked (maximum45°) turn and back-elevator pressure gradually applied.After the bank is established, back-elevator pressureshould be smoothly and steadily increased. The result-ing apparent centrifugal force pushes the pilot’s bodydown in the seat, increases the wing loading, anddecreases the airspeed. Back-elevator pressure shouldbe firmly increased until a definite stall occurs.

When the glider stalls, recovery should be madepromptly by releasing back-elevator pressure. If the

greater lift on that wing. To keep that wing from risingand to maintain a constant angle of bank, oppositeaileron pressure is required. The added inside rudderpressure will also cause the nose to lower in relation tothe horizon. Consequently, additional back-elevatorpressure would be required to maintain a constant-pitch attitude. The resulting condition is a turn withrudder applied in one direction, aileron in the oppositedirection, and excessive back-elevator pressure—apronounced cross-control condition.

Since the glider is in a skidding turn during the cross-control condition, the wing on the outside of the turnspeeds up and produces more lift than the inside wing;thus, the glider starts to increase its bank. The downaileron on the inside of the turn helps drag that wingback, slowing it up and decreasing its lift. This furthercauses the glider to roll. The roll may be so fast that itis possible the bank will be vertical or past verticalbefore it can be stopped.

For the demonstration of the maneuver, it is importantthat it be entered at a safe altitude because of the pos-sible extreme nose down attitude and loss of altitudethat may result. Before demonstrating this stall, thepilot should clear the area for other air traffic. Whilethe gliding attitude and airspeed are being established,the glider should be re-trimmed. When the glide is sta-bilized, the glider should be rolled into a medium-banked turn to simulate a final approach turn thatwould overshoot the centerline of the runway. Duringthe turn, excessive rudder pressure should be appliedin the direction of the turn but the bank held constantby applying opposite aileron pressure. At the sametime, increased back-elevator pressure is required tokeep the nose from lowering.

All of these control pressures should be increased untilthe glider stalls. When the stall occurs, releasing thecontrol pressures, simultaneously decreasing the angleof attack initiates the recovery. In a cross-control stall,the glider often stalls with little warning. The nosemay pitch down, the inside wing may suddenly drop,and the glider may continue to roll to an inverted posi-tion. This is usually the beginning of a spin. It is obvi-ous that close to the ground is no place to allow this tohappen.

Recovery must be made before the glider enters anabnormal attitude (vertical spiral or spin); it is a sim-ple matter to return to wings-level, straight flight bycoordinated use of the controls. The pilot must be ableto recognize when this stall is imminent and must takeimmediate action to prevent a completely stalled con-dition. It is imperative that this type of stall not occurduring an actual approach to a landing, since recovery

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turn is uncoordinated, one wing may tend to drop sud-denly, causing the glider to roll in that direction. If thisoccurs, the glider should be returned to wings-level,straight flight with coordinated control pressure.

A glider pilot should recognize when an acceleratedstall is imminent and take prompt action to prevent acompletely stalled condition. It is imperative that a pro-longed stall, excessive airspeed, excessive loss of alti-tude, or spin be avoided.

CROSSED-CONTROL STALLThe objective of a crossed-control stall demonstrationmaneuver is to show the effect of improper controltechnique and to emphasize the importance of usingcoordinated control pressures whenever making turns.This type of stall occurs with the controls crossed—aileron pressure applied in one direction and rudderpressure in the opposite direction, and the critical angleof attack is exceeded. [Figure 7-30]

This is a stall that is most likely to occur during apoorly planned and executed base-to-final approachturn, and often is the result of overshooting the center-line of the runway during that turn. Normally, theproper action to correct for overshooting the runway isto increase the rate of turn by using coordinated aileronand rudder. At the relatively low altitude of a base-to-final approach turn, improperly trained pilots may beapprehensive of steeping the bank to increase the rateof turn. Rather than steeping the bank, they hold thebank constant and attempt to increase the rate of turnby adding more rudder pressure in an effort to alignwith the runway.

The addition of rudder pressure on the inside of the turncauses the speed of the outer wing to increase, creating

Left AileronDeflected Up

Right AileronDeflected Down

RudderDeflected Right

Figure 7-30. Crossed-control approach to a stall.

7-31

may be impossible prior to ground contact due to thelow altitude.

COMMON ERRORS

• Improper pitch and bank control during straight-ahead and turning stalls.

• Rough or uncoordinated control procedures.• Failure to recognize the first indications of a

stall.• Failure to achieve a stall.• Poor recognition and recovery procedures.• Excessive altitude loss or airspeed or encoun-

tering a secondary stall during recovery.

SPINS A spin may be defined as an aggravated stall that resultsin what is termed “autorotation” wherein the glider fol-lows a downward corkscrew path. As the glider rotatesaround a vertical axis, the rising wing is less stalledthan the descending wing, creating a rolling, yawing,and pitching motion. The glider is basically beingforced downward by rolling, yawing, and pitching in aspiral path. [Figure 7-31]

The autorotation results from an unequal angle ofattack on the glider’s wings. The rising wing has adecreasing angle of attack, in which the relative liftincreases and the drag decreases. In effect, this wing isless stalled. Meanwhile, the descending wing has anincreasing angle of attack, past the wing’s critical angleof attack (stall) where the relative lift decreases anddrag increases.

A spin is caused when the glider’s wing exceeds itscritical angle of attack (stall) with a side slip or yawacting on the glider at, or beyond, the actual stall.During this uncoordinated maneuver, a pilot may notbe aware that a critical angle of attack has beenexceeded until the glider yaws out of control towardthe lowering wing. If stall recovery is not initiatedimmediately, the glider may enter a spin.

If this stall occurs while the glider is in a slipping orskidding turn, this can result in a spin entry and rota-tion in the direction that the rudder is being applied,regardless of which wingtip is raised.

Many gliders have to be forced to spin and requiregood judgment and technique to get the spin started.These same gliders may be put into a spin accidentallyby mishandling the controls in turns, stalls, and flightat minimum controllable airspeeds. This fact is addi-tional evidence of the necessity for the practice of stallsuntil the ability to recognize and recover from them isdeveloped.

Often a wing drops at the beginning of a stall. Whenthis happens, the nose will attempt to move (yaw) inthe direction of the low wing. This is when use of therudder is important during a stall. The correct amountof opposite rudder must be applied to keep the nosefrom yawing toward the low wing. By maintainingdirectional control and not allowing the nose to yawtoward the low wing before stall recovery is initiated,a spin will be averted. If the nose is allowed to yawduring the stall, the glider will begin to skid in thedirection of the lowered wing and will enter a spin.

A glider must be stalled in order to enter a spin; there-fore, continued practice of stall recognition will helpthe pilot develop a more instinctive and prompt reac-tion in recognizing an approaching spin. It is essentialto learn to apply immediate corrective action any timeit is apparent the glider is approaching spin conditions.If it is impossible to avoid a spin, the pilot shouldimmediately execute spin recovery procedures.

The flight instructor should demonstrate spins and spinrecovery techniques with emphasis on any special spinprocedures or techniques required for a particularFigure 7-31. Autorotation of spinning glider.

DEVELOPED PHASEThe developed phase occurs when the glider’s angularrotation rate, airspeed, and vertical speed are stabilizedwhile in a flight path that is nearly vertical. This iswhen glider aerodynamic forces and inertial forces arein balance, and the attitude, angles, and self-sustainingmotions about the vertical axis are constant or repeti-tive. The spin is in equilibrium.

RECOVERY PHASEThe recovery phase occurs when the angle of attack ofthe wings drops below the critical angle of attack andautorotation slows. Then the nose drops below the spinpitch attitude and rotation stops. This phase may lastfor a quarter turn to several turns.

To recover, control inputs are initiated to disrupt thespin equilibrium by stopping the rotation and stall. Toaccomplish spin recovery, the manufacturer’s recom-mended procedures should be followed. In the absenceof the manufacturer’s recommended spin recoveryprocedures, the following general spin recovery pro-cedures are recommended.

Step 1—Position the ailerons to neutral. Aileronsmay have an adverse effect on spin recovery. Aileroncontrol in the direction of the spin may speed up therate of rotation and delay the recovery. Aileron controlopposite the direction of the spin may cause the downaileron to move the wing deeper into the stall andaggravate the situation. The best procedure is to ensurethat the ailerons are neutral. If the flaps are extendedprior to the spin, they should be retracted as soon aspossible after spin entry.

Step 2—Apply full opposite rudder against therotation. Make sure that full (against the stop) oppo-site rudder has been applied.

Step 3—Apply a positive and brisk, straight for-ward movement of the elevator control past neutralto break the stall. This should be done immediatelyafter full rudder application. The forceful movementof the elevator will decrease the excessive angle ofattack and break the stall. The controls should be heldfirmly in this position. When the stall is “broken,” therotation stops.

Step 4—After spin rotation stops, neutralize therudder. If the rudder is not neutralized at this time, theensuing increased airspeed acting upon a deflected rud-der will cause a yawing or skidding effect. Slow andoverly cautious control movements during spin recov-ery must be avoided. In certain cases it has been foundthat such movements result in the glider continuing to

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glider. Before beginning any spin operations, the fol-lowing items should be reviewed.

• GFM/POH limitations section, placards, or type certification data sheet, to determine if the glider is approved for spins.

• Weight and balance limitations.• Proper recommended entry and recovery

procedures.• The requirements for parachutes. It would be

appropriate to review current Title 14 of the Code of Federal Regulations (14 CFR) part 91 for the latest parachute requirements.

A thorough glider preflight should be accomplishedwith special emphasis on excess or loose items thatmay affect the weight, CG, and controllability of theglider. Slack or loose control cables (particularly rud-der and elevator) could prevent full anti-spin controldeflections and delay or preclude recovery in somegliders.

Prior to beginning spin training, the flight area, aboveand below the glider, must be clear of other air traffic.Clearing the area may be accomplished while slowingthe glider for the spin entry. All spin training should beinitiated at an altitude high enough for a completedrecovery at or above 1,500 feet AGL.

There are four phases of a spin: entry, incipient, devel-oped, and recovery.

ENTRY PHASEIn the entry phase, the pilot provides the necessary ele-ments for the spin, either accidentally or intentionally.The entry procedure for demonstrating a spin is similarto a stall. As the glider approaches a stall, smoothlyapply full rudder in the direction of the desired spinrotation while applying full back (up) elevator to thelimit of travel. Always maintain the ailerons in the neu-tral position during the spin procedure unless theGFM/POH specifies otherwise.

INCIPIENT PHASEThe incipient phase takes place between the time theglider stalls and rotation starts until the spin has fullydeveloped. This change may take up to two turns formost gliders. Incipient spins that are not allowed todevelop into a steady-state spin are the most commonlyused in the introduction to spin training and recoverytechniques. In this phase, the aerodynamic and inertialforces have not achieved a balance. As the incipientspin develops, the indicated airspeed should be near orbelow stall airspeed.

The incipient spin recovery procedure should be com-menced prior to the completion of 360° of rotation. Thepilot should apply full rudder opposite the direction ofrotation.

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spin indefinitely, even with anti-spin inputs. A briskand positive technique, on the other hand, results in amore positive spin recovery.

Step 5—Begin applying back-elevator pressure toraise the nose to level flight. Caution must be usednot to apply excessive back-elevator pressure after therotation stops. Excessive back-elevator pressure cancause a secondary stall and result in another spin. Careshould be taken not to exceed the “G” load limits andairspeed limitations during recovery.

It is important to remember that the above-spin recov-ery procedures are recommended for use only in theabsence of the manufacturer’s procedures. Before anypilot attempts to begin spin training, the pilot must befamiliar with the procedures provided by the manufac-turer for spin recovery.

The most common problems in spin recovery includepilot confusion in determining the direction of spinrotation and whether the maneuver is a spin versus spi-ral. If the airspeed is increasing, the glider is no longerin a spin but in a spiral. In a spin, the glider is stalledand the airspeed is at or below stalling speed.

COMMON ERRORS

• Failure to clear area before spins.

• Failure to establish proper configuration priorto spin entry.

• Failure to recognize conditions leading to a spin.

• Failure to achieve and maintain stall during spin entry.

• Improper use of controls during spin entry, rotation, and/or recovery.

• Disorientation during spin.

• Failure to distinguish a spiral dive and a spin.

• Excessive speed or secondary stall during spinrecovery.

• Failure to recovery with minimum loss of altitude.

MINIMUM SINK AIRSPEED Minimum sink airspeed is defined as the airspeed atwhich the glider loses the least amount of altitude in agiven period of time. Minimum sink airspeed varieswith the weight of the glider. Glider manufacturerspublish the altitude loss in feet per minute or metersper second (e.g. 122 ft/min or 0.62 m/sec) at a speci-fied weight. Flying at minimum sink airspeed resultsin maximum duration in the absence of convection inthe atmosphere.

The minimum sink airspeed given in the GFM/POH isbased on the following conditions.

• The glider is wings-level and flying a straightflight path; load factor is 1.0 G.

• The glider flight controls are perfectlycoordinated.

• Wing flaps are set to zero degrees and airbrakes are closed and locked.

• The wing is free of bugs or othercontaminants.

• The glider is at a manufacturer-specified weight.

While flying in a thermalling turn, the proper airspeedis the minimum sink airspeed appropriate to the loadfactor, or G-load, that the glider is undergoing. Theglider’s stall speed increases with load factor. The min-imum sink speed needs to be increased with anincrease in load factor. For example, if a glider stallspeed is 34 knots and the wings-level minimum sinkairspeed is 40 knots, consider the following for ther-malling.

• In a 30° banked turn, load factor is 1.2 Gs. Theapproximate square root of 1.2 is 1.1. Thirty-four knots times 1.1 yields a 37 knots stall speed. The minimum sink speed is still above the stall speed but by only approximately 3 knots. The margin of safety is decreasing and the pilot should consider increasing the mini-mum sink speed by a factor proportionate to the stall speed increase, in this case 44 knots.

• In a 45° banked turn, load factor is 1.4 Gs. Theapproximate square root of 1.4 is 1.2. Thirty-four knots times 1.2 yields a 41 knots stall speed. The minimum sink speed is now below the stall speed. If the pilot increases the minimum sink speed proportionately to the stall airspeed, the new speed would be 48 knots, a 7 knot safety factor.

• In a 60° banked turn, load factor is 2.0 Gs. Theapproximate square root of 2.0 is 1.4. Thirty-four knots times 1.4 yields a 48 knots stall speed. The minimum sink speed is now below the stall speed. The pilot should increase the minimum sink speed proportionately to 56 knots, yielding an 8 knot safety factor.

Minimum sink airspeed is always slower than best L/Dairspeed at any given operating weight. If the oper-ating weight of the glider is noticeably less thanmaximum gross weight, then the actual minimumsink airspeed at that operating weight will be slowerthan that published.

flying conditions in order to be successful in conduct-ing cross-country flights or during competition.

COMMON ERRORS

• Improper determination of speed-to-fly.• Failure to maintain proper pitch attitude

and airspeed control.

TRAFFIC PATTERNS The pilot must be familiar with the approach and land-ing traffic pattern at the local gliderport/airportbecause the approach actually starts some distanceaway. Most gliderports/airports use an initial point (IP)from which to begin the approach for each landingarea. The IP may be located over the center of the glid-erport/airport or at a remote location near the trafficpattern. As shown in Figure 7-32, the sequence of anormal approach is from over the IP to the downwindleg, base leg, final approach, flare, touchdown, roll-out, and stop. Once the landing roll is completed, it isimportant to clear the active runway as soon as possi-ble to allow other pilots to land safely.

Once over the IP, the pilot flies along the downwindleg of the planned landing pattern. The pilot shouldplan to be over the IP at an altitude of 800 to 1,000 feetAGL or as recommended by the local field operatingprocedures. During this time it is important to look forother aircraft and to listen on the communicationsradio, if one is installed, for other aircraft in the vicin-ity of the gliderport/airport. Glider pilots should beaware of other activities located at the gliderport/air-port, and it is important that they are familiar with goodoperating practices established in the FAAAeronautical Information Manual and AdvisoryCirculars. Glider operations usually establish the pat-terns for their operation with other activities in mind.Pilots new to a gliderport/airport should obtain a thor-ough checkout before conducting any flights.

Pilots should complete the landing checklist prior tothe downwind leg. A good landing checklist is knownas FUSTALL.

• Flaps—Set (if applicable).• Undercarriage—Down and locked (if

applicable).• Speed—Approach speed established.• Trim—Set.• Air brakes (spoilers/dive brakes)—Checked

for correct operation.• Landing area—Look for wind, other aircraft,

and personnel.• Land the glider.

This checklist can be modified as necessary for anyglider.

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COMMON ERRORS

• Improper determination of minimum sink speed.

• Failure to maintain proper pitch attitude and airspeed control.

BEST GLIDE AIRSPEED Best glide (Lift/Drag) airspeed is defined as the air-speed that results in the least amount of altitude lossover a given distance. This allows the glider to glidethe greatest distance in still air. This performance isexpressed as glide ratio. The manufacturer publishesthe best glide airspeed for specified weights and theresulting glide ratio. For example, a glide ratio of 36:1means that the glider will loose 1 foot of altitude forevery 36 feet of forward movement in still air at thisairspeed. The glide ratio will decrease at airspeedsabove or below best glide airspeed. The best glidespeed can be found from the glider polars in Chapter5—Performance Limitations.

COMMON ERRORS

• Improper determination of best glide airspeedfor given condition.

• Failure to maintain proper pitch attitude and airspeed control.

SPEED-TO-FLY Speed-to-fly refers to the optimum airspeed for pro-ceeding from one source of lift to another. Speed-to-flydepends on the following.

1. The rate-of-climb the pilot expects to achieve in the next thermal or updraft.

2. The rate of ascent or descent of the air mass through which the glider is flying.

3. The glider’s inherent sink rate at all airspeeds between minimum sink airspeed and never exceed airspeed.

4. Headwind or tailwind.

The object of speed-to-fly is to minimize the timeand/or altitude required to fly from the current positionto the next thermal. Speed-to-fly information is pre-sented to the pilot in one or more of the followingways.

• By placing a speed-to-fly ring (MacCready ring) around the variometer dial.

• By using a table or chart.• By using an electronic flight computer that

displays the current optimum speed-to-fly.

The pilot determines the speed-to-fly during initialplanning and than constantly updates this informationin flight. The pilot must be aware of changes in the

7-35

After accomplishing the checklist, concentrate on judg-ing your approach angle and staying clear of other air-craft while monitoring your airspeed. Medium turnsshould be used in the traffic pattern. The approachshould be made using spoilers/dive brakes as necessaryto dissipate excess altitude. Use the elevator to controlthe approach speed.

Strong crosswinds, tailwinds, or high sink rates that areencountered in the traffic pattern will require the pilotto modify the individual pattern leg. A strong tailwindor headwind will require a shortening or lengthening ofthe leg respectively. A sudden encounter with a highsink rate may require the pilot to turn toward the land-ing area sooner than normal. The pilot should not con-duct a 360° turn once established on the downwind leg.Throughout the traffic pattern the pilot should be con-stantly aware of the approach speed.

When at an appropriate distance from the IP, the pilotshould maneuver the glider to enter the downwind leg.

The distance from downwind leg to the landing areashould be approximately 1/4 to 1/2 mile. This will varyat different locations. On the downwind, leg the glidershould be descending to arrive abeam the touchdownpoint at an altitude between 500 and 600 feet AGL. Ondownwind leg, the groundspeed will be higher due tothe tailwind. The pilot should use the spoilers/divebrakes as necessary to arrive at this altitude. The pilotshould also monitor the gliders position with referenceto the touchdown area. If the wind is pushing the glideraway from or toward the touchdown area, the pilotshould stop the drift by establishing a wind correctionangle into the wind. Failure to do so will affect thepoint where the base leg should be started.

The base leg should be started when the touchdownpoint is approximately 45° over the pilot’s shoulderlooking back at the touchdown area. Once establishedon the base leg, the pilot should scan the extended finalapproach path in order to detect any aircraft that might

Downwind LegBase Leg

Final Approach45°

Entry Leg

Initial Point(IP)(IP)

Downwind Leg

Base Leg

Final Approach

Entry L

eg

Initial Point(IP)

Touchdown Point

Figure 7-32.Traffic pattern.

greater the crab angle. Prior to flare, the pilot must beprepared to align the glider with the landing area. Thepilot should use the rudder to align the glider prior totouchdown and deflect the ailerons into the wind tocontrol the side drift caused by the crosswind.

In the slip method, the pilot uses rudder and ailerons toslip the glider into the wind to prevent drifting down-wind of the touchdown area. The disadvantage of theslip method is that the sink rate of the glider increases,forcing the pilot to adjust the spoilers/dive brakes, asnecessary, to compensate for this additional sink rate.

Whether the pilot selects the slip or crab method forcrosswind landing is personal preference. The impor-tant action is to stabilize the approach early enough onfinal so as to maintain a constant approach angle andairspeed to arrive at the selected touchdown point.

COMMON ERRORS

• Improper glide path control.• Improper use of flaps, spoilers/dive brakes.• Improper airspeed control.• Improper correction of crosswind.• Improper procedure for touchdown/landing.• Poor directional control during/after landing.• Improper use of wheel brakes.

SLIPS A slip is a descent with one wing lowered. It may beused for either of two purposes, or both of them com-bined. A slip may be used to steepen the approach pathwithout increasing the airspeed, as would be the caseif the spoilers/dive brakes were inoperative or to clearan obstacle. It can also be used to make the glidermove sideways through the air to counteract the driftwhich results from a crosswind.

Formerly, slips were used as a normal means of con-trolling landing descents to short or obstructed fields,but they are now primarily used in the performance ofcrosswind landings and short/off-field landings.

With the installation of effective spoilers/dive brakeson modern gliders, the use of slips to steepen or con-trol the angle of descent is no longer a common proce-dure. However, the pilot still needs skill inperformance of forward slips to correct for possibleerrors in judgment of the landing approach.

The primary purpose of forward slips is to dissipatealtitude without increasing the glider’s airspeed, par-ticularly in gliders not equipped with flaps or those

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be on long final approach to the landing area in use.The turn to base leg should be timely in order to keepthe point of intended touchdown area within easy glid-ing range. The pilot should adjust the turn to correct forwind drift encountered on the base leg. On base leg, thepilot should adjust the spoilers/dive brakes, as neces-sary, to position the glider at the desired glide angle.

The turn onto the final approach is made so as to lineup with the centerline of the touchdown area. The pilotshould adjust the spoilers/dive brakes as necessary tofly the desired approach angle to the aim point. Theselected aim point should be prior to the touchdownpoint to accommodate the landing flair. The pilot flairsthe glider at or about three to five feet AGL and theglider floats some distance until it touches down.

When within three to five feet of the ground, begin theflare with slight back elevator. As the airspeeddecreases, the pilot holds the glider in a level or tail lowattitude so as to touchdown at the slowest possiblespeed while the glider still is under aerodynamic con-trol. After touchdown the pilot should concentrate onrolling out straight down the centerline of the touch-down area.

Tracking down the centerline of the touchdown area isan important consideration in gliders. The long, lowwingtips of the glider are susceptible to damage fromrunway border markers, runway light stanchions, ortaxiway markers. Turning off the runway should bedone only if and when the pilot has the glider undercontrol.

Landing in high, gusty winds or turbulent conditionsmay require higher approach airspeeds to improve con-trollability and provide a safer margin above stall air-speed. A rule of thumb is to add 1/2 the gust factor to thenormal approach airspeed. This increased approach air-speed affords better penetration into the headwind onfinal approach. The adjusted final approach airspeedshould not be greater than the maneuvering speed (VA)or maximum turbulence penetration speed (VB),whichever is lower.

CROSSWIND LANDINGS Crosswind landings require a crabbing or slippingmethod to correct for the effects of the wind on the finalapproach. Additionally, the pilot must land the gliderwithout placing any unnecessary side load on the land-ing gear.

The crab method requires the pilot to point the nose ofthe glider into the wind and fly a straight track alongthe desired ground path. The stronger the wind, the

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with inoperative spoilers/dive brakes. There are manycircumstances requiring the use of forward slips, suchas in a landing approach over obstacles and in mak-ing off-field landings. It is always wise to allow anextra margin of altitude for safety in the original esti-mate of the approach. In the latter case, if the inaccu-racy of the approach is confirmed by excess altitudewhen nearing the boundary of the selected field, slip-ping may dissipate the excess altitude.

The use of slips has definite limitations. Some pilotsmay try to lose altitude by violent slipping ratherthan by smoothly maneuvering and exercising goodjudgment and using only a slight or moderate slip. Inoff-field landings, this erratic practice invariably willlead to trouble since enough excess speed may resultin preventing touching down anywhere near thetouchdown point, and very often will result in over-shooting the entire field.

The forward slip is a slip in which the glider’s direc-tion of motion continues the same as before the slipwas begun. [Figure 7-33] If there is any crosswind, theslip will be much more effective if made into the wind.Assuming the glider is originally in straight flight, thewing on the side that the slip is to be made should belowered by using the ailerons. Simultaneously, theglider’s nose must be yawed in the opposite directionby applying opposite rudder so the glider’s longitudi-nal axis is at an angle to its original flight path. Thedegree to which the nose is yawed in the oppositedirection from the bank should be such that the origi-nal ground track is maintained. The nose should alsobe raised as necessary to prevent the airspeed fromincreasing.

If a slip is used during the last portion of a finalapproach, the longitudinal axis of the glider must bealigned with the runway just prior to touchdown so theglider touches down headed in the direction in which itis moving. This requires timely action to discontinuethe slip and align the glider’s longitudinal axis with itsdirection of travel over the ground well before theinstant of touchdown. Failure to accomplish thisimposes severe sideloads on the landing gear andimparts violent ground looping tendencies.

Discontinuing the slip is accomplished by leveling thewings and simultaneously releasing the rudder pres-sure while readjusting the pitch attitude to the normalglide attitude. If the pressure on the rudder is releasedabruptly, the nose will swing too quickly into line andthe glider will tend to acquire excess airspeed.

Because of the location of the pitot tube and staticvents, airspeed indicators in some gliders may haveconsiderable error when the glider is in a slip. The pilotmust be aware of this possibility and recognize a prop-erly performed slip by the attitude of the glider, thesound of the airflow, and the feel of the flight controls.

A sideslip, [Figure 7-34] as distinguished from a for-ward slip, is one during which the glider’s longitudi-nal axis remains parallel to the original flight path, butin which the flight path changes direction according tothe steepness of the bank. The sideslip is important incounteracting wind drift during crosswind landingsand is discussed in crosswind landing section of thischapter.

Figure 7-33. Forward slip. Figure 7-34. Side slip.

AFTER-LANDING AND SECURING After landing, move or taxi the glider clear of all run-ways. If the glider is to be parked for a short intervalbetween flights, choose a spot that does not inconven-ience other gliderport/airport users. Protect the gliderfrom wind by securing a wingtip with a weight or bytying it down. Consult the manufacturer’s handbookfor the recommended methods for securing the glider.Remember that even light winds can cause gliders tomove about, turn sideways, or cause the higher wingin a parked glider to slam down onto the ground.Because gliders are particularly vulnerable to windeffects, the glider should be secured any time it is unat-tended.

When the glider is done flying for the day, move it tothe tiedown area. Secure the glider in accordance withthe recommendation in the GFM/POH. The tiedownanchors should be strong and secure. Apply externalcontrol locks to the glider flight control surfaces.Control locks should be large, well marked, andbrightly painted. If a cover is used to protect the pitottube, the cover should be large and brightly colored. Ifa canopy cover is used, secure it so that the canopycover does not scuff the canopy in windy conditions.

If the glider is stored in a hangar, be careful whilemoving the glider to avoid damaging it or other air-craft in the hangar. Chock the main wheel and tail-wheel of the glider when it is in position in the hangar.If stored in a wings-level position, put a wing standunder each wingtip. If stored with one wing high,place a weight on the lowered wing to hold it down.

If the glider is to be disassembled and stored in atrailer, tow the glider to the trailer area and align thefuselage with the long axis of the trailer. Collect alltools, dollies, and jigs required to disassemble andstow the glider. Secure the trailer so that loading theglider aboard does not move or upset the trailer ortrailer doors. Follow the disassembly checklist in theGFM/POH. Stow the glider components securely inthe trailer. When the glider has been stowed andsecured, collect all tools and stow them properly.Close trailer doors and hatches. Secure the traileragainst wind and weather by tying it down properly.

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COMMON ERRORS

• Improper glide path control.• Improper use of slips.• Improper airspeed control.• Improper correction for crosswind.• Improper procedure for touchdown/landing.• Poor directional control during/after landing.• Improper use of brakes.

DOWNWIND LANDINGS Downwind landings present special hazards and shouldbe avoided when an into-the-wind landing is available.However, factors such as gliderport/airport layout,presence of insurmountable obstacles, such as high ter-rain at one end of the runway, runway slope or grade,or a launch failure at low altitude can require you tomake a downwind landing. The pilot must use the nor-mal approach airspeed during a downwind landing.Any airspeed in excess only causes the approach areaand runway needed for approach and landing toincrease.

The tailwind increases the touchdown groundspeed andlengthens the landing roll. The increased distance forlanding can be determined by dividing the actual touch-down speed by the normal touchdown speed, andsquaring the result. For example, if the tailwind is 10knots and the normal touchdown speed is 40 knots, theactual touchdown speed is 50 knots. This touchdownspeed is 25 percent more than the normal speed, a fac-tor of 1.25. A factor of 1.25 squared equals 1.56. Thismeans the landing distance will increase 56 percentover the normal landing distance.

On downwind approaches, a shallower approach angleshould be used, depending on obstacles in the approachpath. Use the spoilers/dive brakes and perhaps a for-ward slip as necessary to achieve the desired glide path.

After touchdown, use the wheel brake to reducegroundspeed as soon as is practical. This is necessaryto maintain aerodynamic control of the glider.

COMMON ERRORS

• Improper glide path control.• Improper use of slips.• Improper airspeed control.• Improper correction of crosswind.• Improper procedure for touchdown/landing.• Poor directional control during/after landing.• Improper use of wheel brakes.

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Training for abnormal and emergency procedures is anessential element in becoming a glider pilot.Knowledge of procedures for coping with control prob-lems and instrument or equipment malfunction is espe-cially important in soaring activities. Knowing how touse emergency equipment and survival gear is a practi-cal necessity.

PORPOISINGPorpoising is a general term that refers to pitch oscilla-tions that can occur in gliders. In most cases, pilotsinduce these oscillations through over-controlling theglider as they attempt to stop the oscillations fromoccurring in the first place.

PILOT—INDUCED OSCILLATIONS The instability of a glider’s attitude that arises whenthe pilot fails to recognize the lag time inherent incontrolling the glider is known as a pilot-inducedoscillation (PIO). Typically, PIOs occur when theglider fails to respond instantly to control input andthe pilot quickly increases the pressure on the con-trols. By the time the pilot judges that the glider isresponding satisfactorily, the extra control pressureshave resulted in such a vigorous response that theglider overshoots the desired flight attitude.Alarmed, the pilot moves the controls rapidly in theopposite direction, overcompensating for the mis-take. The undesired glider motion slows, stops for aninstant, and then reverses. The alarmed pilot main-tains significant control pressures to try to increasethe rate of response. The glider, now in rapid motionin the desired direction in response to heavy-handedcontrol inputs, again shoots past the desired attitudeas the now thoroughly alarmed pilot jerks the flightcontrols in the opposite direction. Unless the pilotunderstands that these oscillations are the directresult of over-controlling the glider, it is unlikely thatthe oscillations will cease. More likely, they willincrease in intensity until there is a complete loss ofcontrol.

Although pilot-induced oscillations can occur at anytime, these situations arise most commonly duringprimary training. They tend to disappear as pilotexperience grows because pilots gain familiarity withthe lag time inherent in the flight controls. These

types of oscillations may also occur when a pilot ismaking flights in unfamiliar types of gliders. For thisreason, particular care must be taken when the pilot ispreparing to fly a single seat glider in which the pilothas no prior experience. When checking out in a newtype of single seat glider, the lag time of the flight con-trols must be learned without the obvious benefit ofhaving an experienced glider flight instructor aboardduring flight to offer advice or, if necessary, to inter-vene. While most PIO discussions are devoted to pitchoscillations, consideration will be given to roll and yawinduced oscillations.

The first step toward interrupting the PIO cycle is torecognize the lag time inherent in the glider’sresponse. Any change in glider flight attitude takes anappreciable amount of time to accomplish as the flightcontrols take affect, and the mass of the gliderresponds to the pilot’s control inputs. The second stepis to modify control inputs to avoid over-controllingthe glider. The correct technique is to pressure the con-trols until the glider begins to respond in the desireddirection, then ease off the pressure. As the glidernears the desired attitude, center the appropriate flightcontrol so that overshooting does not occur.

PILOT-INDUCED PITCH OSCILLATIONS DURING LAUNCHPilot-induced oscillations are most likely to occur dur-ing launch because the glider’s lag time changes rap-idly as the glider accelerates. During the first momentsof the takeoff roll, aerodynamic control is poor, thecontrol feel of the glider is very sluggish, and lag timeis great. As the glider gains speed, aerodynamicresponse improves; control feel becomes crisper, andlag time decreases. When the glider has acquired safeflying speed, lag time is short, the controls feel “nor-mal,” and pilot-induced oscillations become much lesslikely.

FACTORS INFLUENCING PIOSThe pitch effect of the towhook/towline combinationcharacteristic of the glider being flown, which maycause uncommanded pitch excursions, contributes toPIOs during aerotow launch. In addition, the propwashand wing vortices of the towplane, through which theglider must pass if there is little or no crosswind, affectthe flight attitude and control response of the glider. To

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minimize the influence of the towplane’s wake, usea towline of adequate length—200 feet is the mini-mum length for normal operations. A longer towlineprovides more isolation from towplane wake duringaerotow launch. Short towlines, on the other hand,keep the glider closer to the towplane and its turbu-lent wake, complicating the problem of controllingthe glider.

There are several techniques that reduce the likelihoodand severity of PIOs during aerotow launch. Do not tryto lift off until confident that flying speed and goodaerodynamic control have been achieved. Also, justafter the moment of liftoff, allow the glider to rise sev-eral feet above the runway before stabilizing the alti-tude of the glider. Two to three feet is high enough thatminor excursions in pitch attitude, if correctedpromptly, do not result in the glider smacking back tothe ground, but not high enough for you to lose sight ofthe towplane below the nose of the glider. Althoughvisually attractive to onlookers, the practice of tryingto stabilize the glider just a few inches above theground provides little margin for error if a PIO occurs.

IMPROPER ELEVATOR TRIM SETTINGThe elevator trim control position also contributes toPIOs in pitch attitude. The takeoff checklist includes acheck to confirm that the flight controls including ele-vator trim are properly set for takeoff. If the trim isproperly set for takeoff, elevator pressure felt throughthe control stick is normal and the likelihood of PIO isreduced. If the elevator trim is set incorrectly, however,elevator pressure felt through the control stick may con-tribute to PIOs. If the trim is set excessively nose-down,the pilot needs to hold back pressure on the control stickto achieve and maintain the desired pitch attitude dur-ing launch and climb-out. If the trim is set excessivelynose-up, the pilot needs to hold forward pressure. Themore pressure that is needed, the more likely it is thatthe pilot will over-control the glider.

Although all gliders exhibit these tendencies if the trimis improperly set, the effect is most pronounced onthose gliders with an aerodynamic elevator trim tab oran anti-servo tab on the elevator. The effect usually is

less pronounced on those glider fitted with a simplespring system elevator trim. Regardless of the type ofelevator trim installed in the glider, error prevention issuperior to error correction. Use a comprehensive pre-takeoff checklist and set the elevator trim in the appro-priate position prior to launch to help prevent PIOsattributable to elevator trim miss-use. [Figure 8-1]

IMPROPER WING FLAPS SETTINGThe likelihood of PIOs increases if the wing flapsare not correctly set in the desired takeoff position.For the majority of flap-equipped gliders, mostGlider Flight Manuals/Pilot Operating Handbook(GFM/POH) recommend that flaps be set at zerodegrees for takeoff (check the GFM/POH for themanufacturer recommendations). If the flaps areincorrectly set to a positive flap setting, whichincreases wing camber and wing lift, the glidertends to rise off the runway prematurely, perhapseven before the elevator control is sufficient to con-trol the pitch attitude. Attempting to prevent theglider from ballooning high above the runway, thepilot may exert considerable forward pressure on thecontrol stick. As the glider continues to accelerate,this forward pressure on the control stick exerts arapidly increasing nose-down force on the gliderdue to the increasing airflow over the elevator.When the glider eventually pitches down, the pilotmay exert considerable back pressure on the stick toarrest the descent. PIOs are likely to result. Ifallowed to continue, a hard landing may result, withpotential for glider damage and personal injury.

If the wing flaps are incorrectly set to a negative flapsetting, decreasing wing camber and wing lift, thentakeoff may be delayed so long that the towplane willlift off and begin to climb out while the glider is stillrolling down the runway, unable to get airborne.Powerful back pressure on the stick may eventuallyassist the glider in leaving the runway, but the relativelyhigh airspeed at liftoff translates into a very effectiveelevator, and ballooning may occur as a result of theelevator position. The pilot, startled once again by themagnitude of this pitch excursion, tries to correct by

Figure 8-1. Premature takeoffs and PIOs.

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applying considerable forward pressure on the controlstick. A series of PIOs may result. If the PIOs continue,a hard landing may occur.

PILOT-INDUCED ROLL OSCILLATIONSDURING LAUNCHPilot-induced roll oscillations occur primarily duringlaunch, particularly via aerotow. As the towpilotapplies full throttle, the glider moves forward, bal-anced laterally on its main wheel. If a wingtip beginsto drop toward the ground before the glider achievessignificant speed, aileron control is marginal and con-siderable stick displacement must be applied to elicit aresponse from the glider. As the glider accelerates, thecontrol response improves and the latency of responsefrom the glider shortens. As acceleration continues, thepilot must recognize the quickening response of theglider to avoid over-controlling the glider. [Figure 8-2]

Although roll oscillations can develop during groundlaunch operations, they occur less often than duringaerotow operations because excellent aerodynamiccontrol of the glider is quickly achieved thanks to therapid acceleration. Since control improves as acceler-ation increases, operations that use a powerful winchor launch vehicle are less likely to be hampered byoscillations.

Wing mass also affects roll oscillations. If the wings donot stay level, the pilot applies considerable aileronpressure to return the wings to level attitude. Because ofthe large mass and considerable aerodynamic dampingthat long-winged gliders exhibit, there is a considerablelag time from the moment pressure is applied until themoment the wings are level again. Inexperienced pilotsmaintain considerable pressure on the ailerons until thewings are level, then release the pressure. The wingscontinue their rolling moment due to their mass, length,and momentum about the longitudinal axis of the glider.The pilot senses this momentum too late, and appliesconsiderable pressure in the opposite direction inanother attempt to level the wings.

After a time, the wings respond and roll back to level,whereupon the pilot centers the ailerons once again. Asbefore, the momentum of the wings about the longitu-dinal axis is considerable, and the wings continue theirmotion in roll. This series of PIOs may continue untilone wingtip contacts the ground, possibly with consid-erable force, causing wing damage or a groundloop andan aborted launch. To reduce the likelihood of this typeof roll oscillation, anticipate the momentum of theglider wings about the longitudinal axis and reduceaileron control pressure as the wings approach the levelposition.

PILOT-INDUCED YAW OSCILLATIONSDURING LAUNCHPilot-induced yaw oscillations are usually caused byovercontrolling the rudder. As with roll oscillations, theproblem is the failure of the pilot to recognize that theglider is accelerating and has considerable momentum.If the glider is veering away from the towplane, rudderapplication in the appropriate direction helps correctthe situation. If the rudder pressure is held too long, thelarge yaw momentum of the glider wings and fuselageresults in overshooting the desired yaw position andveering off in the opposite direction. The alarmed pilotnow applies considerable rudder pressure in the direc-tion opposite from the original rudder pressure. As theglider continues to accelerate, the power of the rudderincreases and the lag time decreases. In extreme cases,the glider may veer off the runway and collide withrunway border markers, airport lights, parked glider, orFigure 8-2. Pilot-induced roll oscillations during take-

off roll.

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other obstacles. The cure for this type of yaw oscilla-tion is to anticipate the momentum of the glider wingsand fuselage about the vertical axis and reduce rudderpedal pressure when the nose of the glider begins toyaw in the desired direction in response to rudderinputs. [Figure 8-3]

When a wingtip contacts the ground during takeoffroll, an uncommanded yaw results. The drag of thewingtip on the ground induces a yaw in the directionof the grounded wingtip. The yaw usually is mild ifthe wingtip is on smooth pavement but much more

vigorous if the wingtip is dragging through tall grass.If appropriate aileron pressure fails to raise thewingtip off the ground quickly, the only solution is torelease the towline and abort the takeoff attemptbefore losing all control of the glider.

The greater the mass of the wings and the longer thewingspan, the more momentum the glider will exhibitwhenever roll or yaw oscillations arise. Some veryhigh performance gliders feature remarkably long andheavy wings, meaning once in motion, they tend toremain in motion for a considerable time. This is truenot only of forward momentum, but yaw and rollmomentum as well. The mass of the wings, coupledwith the very long moment arm of large-span wings,results in substantial lag times in response to aileronand rudder inputs during the early portion of the take-off roll and during the latter portion of the landing roll-out. Even highly proficient glider pilots find takeoffsand landings in these gliders to be challenging. Manyof these gliders are designed for racing or cross-coun-try flights and have provisions for adding water ballastto the wings. Adding ballast increases mass, whichresults in an increase in lag time.

If there is an opportunity to fly such a glider, study theGFM/POH thoroughly prior to flight. It is also a goodidea to seek out instruction from an experiencedpilot/flight instructor in what to expect during takeoffroll and landing rollout in gliders with long/heavywings.

GUST-INDUCED OSCILLATIONS Gusty headwinds can induce pitch oscillations becausethe effectiveness of the elevator varies due to changesin the speed of the airflow over the elevator.Crosswinds also can induce yaw and roll oscillations.A crosswind from the right, for instance, tends toweathervane the glider into the wind, causing anuncommanded yaw to the right. Right crosswind alsotends to lift the upwind wing of the glider. When cross-winds are gusty, these effects vary rapidly as the speedof the crosswind varies.

Local terrain can have a considerable effect on thewind. Wind blowing over and around obstacles can begusty and chaotic. Nearby obstacles, such as hangars,groves or lines of trees, hills, and ridges can have apronounced effect on low altitude winds, particularlyon the downwind side of the obstruction. In general,the effect of an upwind obstacle is to induce additionalturbulence and gustiness in the wind. These conditionsare usually found from the surface to an altitude ofthree hundred feet or more. If flight in these conditionscannot be avoided, then the general rule during takeoffis to achieve a faster than normal speed prior to liftoff.The additional speed increases the responsiveness ofthe controls and simplifies the problem of correctingFigure 8-3. Pilot-induced yaw oscillations during

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for turbulence and gusts. This provides a measure ofprotection against PIOs. The additional speed also pro-vides a safer margin above stall airspeed. This is verydesirable on gusty days because variations in the head-wind component will have a considerable effect onindicated airspeed.

VERTICAL GUSTS DURING HIGH-SPEED CRUISEAlthough PIOs occur most commonly during launch,they can occur during cruising flight, even when cruis-ing at high speed. Turbulence usually plays a role inthis type of PIO, as does the elasticity and flexibility ofthe glider structure. An example is an encounter withan abrupt updraft during wings-level high-speedcruise. The upward-blowing gust increases the angleof attack of the main wings, which bend upward veryquickly, storing elastic energy in the wing spars. For amoment, the G-loading in the cabin is significantlygreater than one G. Like a compressed coil spring seek-ing release, the wing spars reflex downward, loftingthe fuselage higher. When the fuselage reaches the topof this motion, the wing spars are now storing elasticenergy in the downward direction, and the fuselage issprung downward in response to the release of elasticenergy in the wing spars. The pilot now experiencesreduced G, accompanied perhaps by a head bangagainst the top of the canopy. During these excursions,the weight of the pilot’s hand and arm on the controlstick may cause the control stick to move a significantdistance forward or aft. With positive G the increasedapparent weight of the pilot’s arm tends to move thecontrol stick aft, further increasing the angle of attackof the main wing and increasing the positive G factoras a result, in a type of vicious circle. During negativeG the reduced apparent weight of the pilot’s arm tendsto result in forward stick motion, reducing the angle ofattack and reducing the G factor still further; onceagain, in a sort of vicious circle. In short, the effect ofrapid alternations in load factor is to increase the inten-sity of load factor variations. One protection againstthis is to slow down when cruising through turbulentair. Another protection is to brace both arms and useboth hands on the control stick when cruising throughturbulent air at high speed. It is worth noting that someglider designs incorporate a parallelogram control sticklinkage to reduce the tendency toward PIOs duringhigh-speed cruise.

PILOT-INDUCED PITCH OSCILLATIONS DURING LANDINGInstances of PIO may occur during the landingapproach in turbulent air for the same reasons previ-ously stated. Landing the glider involves interactingwith ground effect during the flare and keeping pre-cise control of the glider even as airspeed decays andcontrol authority declines. A pilot can cause a PIO byover-controlling the elevator during the flare, caus-

ing the glider to balloon well above the landing sur-face even as airspeed is decreasing. If the pilot reactsby pushing the stick well forward, the glider will soonbe diving for the ground with a fairly rapid rate ofdescent. If the pilot pulls the control stick back to arrestthis descent while still in possession of considerableairspeed, the glider balloons again and the PIO cyclecontinues. If airspeed is low when the pilot pulls backon the stick to avoid a hard landing, there is not likelyto be sufficient lift available to arrest the descent. Ahard or a nose-first landing may result.

To reduce ballooning during the flare, stabilize theglider at an altitude of 3 or 4 feet, and then begin theflare anew. Do not try to force the nose of the gliderdown on to the runway. If airspeed during the balloon-ing is slow and the ballooning takes the glider higherthan a normal flare altitude, it may be necessary toreduce the extension of the spoilers/dive breaks in orderto moderate the descent rate of the glider. Care must betaken to avoid abrupt changes. Partial retraction of thespoilers/dive breaks allows the wing to provide a bitmore lift despite decaying airspeed.

Another source of PIOs during the approach to landingis a too abrupt adjustment of the spoilers/dive breakssetting. The spoilers/dive breaks on most modern glid-ers provide a very large amount of drag when fullydeployed, and they reduce the lift of the wing consider-ably. Over-controlling the spoilers/dive breaks duringthe approach to land can easily lead to oscillations inpitch attitude and airspeed. The easiest way to guardagainst these oscillations is to make smooth adjustmentsin the spoilers/dive breaks setting whenever spoil-ers/dive breaks adjustment is necessary. This becomesparticularly important during the landing flare just priorto touchdown. If the spoilers/dive breaks are extendedfurther with anything less than a very smooth and surehand, the resultant increase in sink rate may cause theglider to contact the runway suddenly. This can lead to arebound into the air, setting the stage for a series ofPIOs. As before, the cure is to stabilize the glider thenresume the flare. If the spoilers/dive breaks are retractedabruptly during the flare, the glider will likely ballooninto the air. Pilot reaction may result in over-controllingand PIOs may result. During the flare, it is best to leavethe spoilers/dive breaks extension alone unless theglider balloons excessively. If you must adjust the spoil-ers/dive breaks, do so with smooth, gentle motion.

GLIDER INDUCED OSCILLATIONS

PITCH INFLUENCE OF THE GLIDER TOWHOOK POSITIONThe location of the glider’s aerotow towhook influ-ences pitch attitude control of the glider during aerotowoperations. During these operations, the towline isunder considerable tension. If the towline is connected

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to a glider towhook located more or less directly on thelongitudinal axis of the glider, the towline tension haslittle effect on the pitch attitude of the glider. This isthe case when the towhook is located in the most for-ward part of the gliders nose, such as in the air ventintake hole. This is the ideal location for the aerotowhook for most gliders.

The towhook on many gliders is located below or aftof this ideal location. In particular, many Europeangliders have the towhook located on the belly of theglider, just forward of the main landing gear, far belowthe longitudinal axis of the glider. The glider’s centerof mass is well above the location of the towhook inthis position. In fact, virtually all of the glider’s massis above the towhook. The mass of the glider has iner-tia and resists acceleration when the towline tensionincreases. In these bellyhook-equipped gliders, anincrease in tension on the towline causes an uncom-manded pitch-up of the glider nose as shown inFigure 8-4. Decrease in towline tension results in anuncommanded pitch-down.

Rapid changes in towline tension, most likely to occurduring aerotow in turbulent air, cause these effects inalternation. Naturally, on days when good lift is avail-able, the aerotow will be conducted in turbulent air.The potential for inducing pitch oscillations is obvi-ous, as rapid alternations in towline tension inducerapid changes in the pitch attitude of the glider. Tomaintain a steady pitch attitude during aerotow in abellyhook-equipped glider, the pilot must be alert tovariations in towline tension and adjust pressure on thecontrol stick to counteract the pitch effect of variationsin towline tension.

SELF-LAUNCH GLIDER OSCILLATIONSDURING POWERED FLIGHTGliders equipped with an extended pod engine andpropeller located high above the glider’s longitudinalaxis exhibit a complex relationship between powersetting and pitch attitude. When power changes aremade, the location of the thrust line of the propeller in

this location has a noticeable effect on pitch attitude.The changing speed of the propwash over the elevatorcauses considerable variation in elevator effectiveness,modifying pitch attitude still further. Prior to flight,study the GFM/POH carefully to discover what theseundesired effects are and how to counteract them.When throttle settings must be changed, it is goodpractice to move the throttle control smoothly andgradually. This gives the pilot time to recognize andcounteract the effect the power setting change has onpitch attitude. In most self-launched gliders, the effectis greatest when flying at or near minimum control-lable airspeed (MCA). Self-launch glider pilots avoidslow flight when flying at low altitude under power.[Figure 8-5]

Self-launch gliders may also be susceptible to PIOsduring takeoff roll, particularly those with a pylonengine mounted high above the longitudinal axis. Thehigh thrust line and the propeller wash influence onthe air flow over the self-launch glider’s elevator maytend to cause considerable change in the pitch attitudeof the glider when power changes are made.

NOSEWHEEL GLIDER OSCILLATIONSDURING LAUNCHES AND LANDINGSMany tandem two-seat fiberglass gliders, and somesingle-seat fiberglass gliders as well, feature a three-wheel landing gear configuration. The main wheel isequipped with a traditional large pneumatic tire; thetailwheel and the nosewheel are equipped with smallerpneumatic tires. During taxi operations, if the pneu-matic nosewheel remains in contact with the ground,any bump will compress the nosewheel tire. When thepneumatic nosewheel tire rebounds, an uncommandedpitch-up occurs. If the pitch-up is sufficient, as is likelyto be the case after hitting a bump at fast taxi speeds,the tailwheel will contact the runway, compress, andrebound. This can result in porpoising, as the nose-wheel and tailwheel alternate in hitting the runway,compressing, and rebounding. In extreme cases, thefuselage of the glider may be heavily damaged.

Figure 8-4. Effect of increased towline on pitch altitude of bellyhook-equipped glider during aerotow.

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During takeoff roll, the best way to avoid porpoisingin a nosewheel-equipped glider is to use the elevatorto lift the nosewheel off the runway as soon as practi-cable, then set the pitch attitude so the glider’s mainwheel is the only wheel in contact with the ground. Toavoid porpoising during landing, hold the glider offduring the flare until the mainwheel and tailwheeltouch simultaneously. During rollout, use the elevatorto keep the nosewheel off the ground for as long aspossible.

TAILWHEEL/TAILSKID EQUIPPED GLIDEROSCILLATIONS DURING LAUNCHES ANDLANDINGSSome two-seat gliders, self-launch gliders, and single-seat gliders have a tailwheel. When loaded and readyfor flight, these gliders have the mainwheel and the tail-wheel or tailskid in contact with the ground. In thesegliders, the center of gravity is aft of the main wheel(s).Because of this, any upward thrust on the main landinggear tends to pitch the nose of the glider upward unlessthe tail wheel or tailskid is in contact with the groundand prevents the change in pitch attitude.

Upward thrust on the main landing gear can occur innumerous circumstances. One cause is a bump in therunway surface during takeoff or landing roll. If theresultant pitch-up is vigorous enough, it is likely thatthe glider will leave the ground momentarily. If air-speed is slow, the elevator control is marginal. As thepilot reacts to the unexpected bounce or launch,overcontrolling the elevator will result in a PIO.[Figure 8-6]

Improper landing technique in a tailwheel glider alsocan lead to upward thrust on the main landing gear andsubsequent PIOs. Landing a tailwheel glider in a nose-down attitude, or even in a level pitch attitude, can leadto trouble. If the main wheel contacts the groundbefore the tailwheel or tailskid, the compression ofthe pneumatic tire and its inevitable rebound will pro-vide significant upward thrust. The glider nose maypitch up, the angle of attack will increase, and theglider will become airborne. As before, overcontrolof the elevator leads to PIOs.

To prevent this type of PIO, do not allow the glider tosettle onto the landing surface with a nose-down atti-tude or with excess airspeed. During the landing flare,hold the glider off a few inches above the ground withgentle backpressure on the control stick as necessary.The speed will decay and the pitch attitude will gradu-ally change to a slightly nose-up pitch attitude. Theideal touchdown is simultaneous gentle contact ofmain wheel and tailwheel or tailskid. Delaying thetouchdown just a small amount results in the tailwheelor tailskid contacting the landing surface an instantbefore the mainwheel. This type of landing is veryacceptable and desirable for almost all tailwheel glid-ers because it makes a rebound into the air veryunlikely. Consult the GFM/POH for the glider beingflown for further information about recommended pro-cedure for touchdown.

OFF-FIELD LANDING PROCE-DURES

Figure 8-5. Pitch attitude power setting relationshipsfor self-launch glider with engine pod.

Figure 8-6. Pneumatic tire rebound during hard landing.

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The possibility of an off-field landing is present on vir-tually every cross-country soaring flight, even whenflying in a self-launch glider. If the engine or powersystem fails and there is no airport within glidingrange, then an off-field landing may be inevitable. Itshould be noted that many glider pilots who were notflying cross-country have faced the necessity of per-forming an off-field landing. Root causes of off-fieldlandings while engaged in soaring in the vicinity of thelaunching airport include rapid weather deterioration,a significant change in wind direction, unanticipatedamounts of sinking air, disorientation, or lack of situa-tional awareness. In these situations, it usually is saferto make a precautionary off-field landing than it is toattempt a low, straight-in approach to the airport. If theglide back to the airport comes up short for any reason,the landing is likely to be poorly executed and mayresult in damage to the glider or injury to the pilot.

On cross-country soaring flights, off-field landings arenot usually considered emergency landings. As a mat-ter of fact, they are expected and are considered whilepreparing for flight. On the other hand, if equipmentfailure leads to the necessity of performing an off-fieldlanding, then the landing can be characterized ordescribed as an emergency landing. Whatever the rea-son for the off-field landing, each glider pilot must beprepared at all times to plan and execute the landingsafely.

Unlike airport landings, no off-field landing is entirelyroutine. An extra measure of care must be undertakento achieve a safe outcome. The basic ingredients for asuccessful off-field landing are awareness of winddirection, wind strength at the surface, and approachpath obstacles. The glider pilot must be able to identifysuitable landing areas, have the discipline to select asuitable landing area while height remains to allowsufficient time to perform a safe approach and landing,and the ability to consistently make accurate landingsin the glider type being flown. These ingredients canbe summarized as follows:

• Recognize the possibility of imminent off-fieldlanding.

• Select a suitable area, then a suitable landingfield within that area.

• Plan your approach with wind, obstacles, andlocal terrain in mind.

• Execute the approach, land, and then stop theglider as soon as possible.

The most common off-field landing planning failure isdenial. The pilot, understandably eager to continue theflight and return to an airport, is often reluctant to initi-ate planning for an off-field landing because to do so,

in the pilot’s mind, will probably result in such a land-ing. Better, the pilot thinks, to concentrate on continu-ing the flight and finding a way to climb back up andfly away. The danger of this false optimism is thatthere will be little or no time to plan an off-field land-ing if the attempt to climb away does not succeed. It ismuch better and safer to thoroughly understand thetechniques for planning an off-field landing and to beprepared for the occurrence at any time.

Wind awareness, knowing wind direction and inten-sity, is key when planning an off-field landing.Heading downwind offers a greater geographicalarea to search than flying upwind. A tailwind duringdownwind cruise results in a greater range, headwindduring upwind cruise reduces the range. Wind aware-ness is also essential to planning the orientation anddirection of the landing approach. Visualize the windflowing over and around the intended landing area.Remember that the area downwind of hills, build-ings, and other obstructions will probably be turbu-lent at low altitude. Also, be aware that landing intowind shortens landing rolls.

Decision heights are altitudes at which pilots take crit-ical steps in the off-field landing process. If the terrainbelow is suitable for landing, select a general area nolower than 2,000 feet above ground level (AGL).Select the intended landing field no lower than 1,500feet AGL. At 1,000 feet AGL, commit to flying theapproach and landing off-field. If the terrain below isnot acceptable for an off-field landing, the best courseof action is to move immediately toward more suitableterrain.

For many pilots there is a strong temptation during theoff-field landing process to select a landing locationbased primarily on the ease of retrieval. The conven-ience of an easy retrieval is of little consequence if thelanding site is unsuitable and results in damage to theglider or injury to the pilot. Select the landing site withsafety foremost in mind. During an off-field landingapproach, the precise elevation of the landing site nor-mally will not be available to the pilot. This renders thealtimeter more or less useless. Fly the approach andassess the progress by recognizing and maintaining theangle that puts the glider at the intended landing spotsafely. If landing into strong headwind, the approachangle is steep. If headwind is light or non-existent, theapproach angle is shallower unless landing over anobstacle. When landing with a tailwind (due to slope orone-way entry into the selected field due to terrain orobstacles) the angle will be shallower. Remember toclear each visible obstacle with safe altitude, clearingany wires by a safe margin.

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Select a field of adequate length and, if possible, onewith no visible slope. Any slope that is visible from theair is likely to be steep. Slope can often be assessed bythe color of the land. High spots often are lighter incolor than low spots because soil moisture tends to col-lect in low spots, darkening the color of the soil there.If level landing areas are not available and the landingmust be made on a slope, it is better to land uphill thandownhill. Even a slight downhill grade during landingflare allows the glider to float prior to touchdown,which may result in collision with objects on the farend of the selected field.

Knowledge of local vegetation and crops is also veryuseful. Tall crops are generally more dangerous to landin than low crops. Know the colors of local seasonalvegetation to help identify crops and other vegetationfrom the air. Without exception, avoid discontinuitiessuch as lines or crop changes. Discontinuities usuallyexist because a fence, ditch, irrigation pipe, or someother obstacle to machinery or cultivation is present.

Other obstacles may be present in the vicinity of thechosen field. Trees and buildings are easy to spot, butpower and telephone lines and poles are harder to seefrom pattern altitude. Take a careful look around tofind them. Power lines and wires are nearly impossibleto see from pattern altitude; assume every pole is con-nected by wire to every other pole. Also assume thatevery pole is connected by wire to every building, andthat every building is connected by wire to every otherbuilding. Plan your approach to over fly the wires thatmay be present, even if you cannot see them. The moreyou see of the landing area during the approach, thefewer unpleasant surprises there are likely to be.

The recommended approach procedure is to fly the fol-lowing legs in the pattern.

• Crosswind leg on the downwind side of the field.

• Upwind leg.

• Crosswind leg on the upwind side of the field.

• Downwind leg.

• Base leg.

• Final approach.

This approach procedure provides the opportunity tosee the intended landing area from all sides. Use everyopportunity while flying this approach to inspect thelanding area and look for obstacles or other hazards.[Figure 8-7]

Landing over an obstacle or a wire requires skill andvigilance. The first goal in landing over an obstacle isto clear the obstacle! Next, you must consider how theobstacle effects the length of landing area that is actu-

ally going to be available for touchdown, rollout, andstopping the glider. If an obstacle is 50 feet high, thefirst 500 feet or so of the landing area will be overflown as you descend to flare and land. If the fieldselected has obstacles on the final approach path,remember that the field will have to be long enough toaccommodate the descent to flare altitude after clearingthe obstacle.

Hold the glider off during the flare and touch down atthe lowest safe speed manageable. After touchdown,use the wheelbrake immediately and vigorously to stopthe glider as soon as possible. Aggressive braking helpsprevent collision with small stakes, ditches, rocks, orother obstacles that cannot easily be seen, especially ifthe vegetation in the field is tall.

AFTER LANDING OFF-FIELD

OFF-FIELD LANDING WITHOUT INJURY

Figure 8-7. Off-field landing approach.

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If uninjured, tend to personal needs then secure theglider. Make contact with the retrieval crew or emer-gency crew as promptly as possible. If the wait is likelyto be long, use the daylight to remove all items neces-sary for darkness and cold. It is worth rememberingthat even a normal retrieval can take many hours if thelanding was made in difficult terrain or in an areaserved by relatively few roads. Use a cell phone to call911 if nervous about personal safety. To help identifyyour position, relay the GPS coordinates, if available,to ease the job for the retrieval crew or rescue person-nel. It is a good idea to write down the GPS coordi-nates if the GPS battery is exhausted or if the GPSreceiver shuts down for any reason. Use the glider two-way radio to broadcast your needs on the internationaldistress frequency 121.5 MHz. Many aircraft, includ-ing civil airliners, routinely monitor this frequency.Their great height gives the line-of-sight aviationtransceiver tremendous range when transmitting to, orreceiving from, these high altitude aircraft. Once con-tact has been made with outsiders to arrange forretrieval, take care of minor items such as collectingany special tools that are needed for glider de-riggingor installing gust locks on the glider’s flight controls.

OFF-FIELD LANDING WITH INJURYIf injured, tend to critical injuries first. At the firstopportunity make contact with emergency responsepersonnel, with other aircraft, or any other source ofassistance you can identify. Use the glider radio, ifoperable, to broadcast a Mayday distress call on theemergency frequency 121.5 MHz. Many in-flight air-craft routinely monitor this frequency. Also try anyother frequency likely to elicit a response. Some glid-ers have an Emergency Locator Transmitter (ELT) onboard. If the glider is equipped with an ELT and assis-tance is needed, turn it on. The ELT broadcasts contin-uous emergency signals on 121.5 MHz. Search aircraftcan home in on this signal, reducing the time spentsearching for your exact location. If the two-way radiois operable and you want to transmit a voice messageon 121.5 MHz, turn the ELT switch to OFF in order forthe voice message to be heard. If cell phone coverageis available, dial 911 to contact emergency personnel.If possible, include a clear description of your location.If the glider is in a precarious position, secure it if pos-sible but do not risk further personal injury in doing so.If it is clearly not safe to stay with the glider, move to anearby location for shelter but leave clear writteninstructions, in a prominent location in the glider,detailing where to find you.

It is best, if at all possible, to stay with the glider. Theglider bulk is likely to be much easier to locate fromthe air than is an individual person. The pilot may beable to obtain a measure of protection from the ele-ments by crawling into the fuselage, crawling under awing, or using the parachute canopy to rig a makeshift

tent around the glider structure. After attending tomedical needs and contacting rescue personnel, attendto clothing, food, and water issues. The pilot shouldmake every attempt to conserve energy.

SYSTEMS AND EQUIPMENT MALFUNCTIONS FLIGHT INSTRUMENT MALFUNCTIONSInstrument failures can result from careless maintenancepractices and from internal or external causes. Removaland replacement of the airspeed indicator but failure toconnect the instrument correctly to pitot and static linesis an example of careless maintenance. A clogged pitottube due to insect infestation or water ingress is an exam-ple of external cause of instrument failure.

AIRSPEED INDICATOR MALFUNCTIONSIf the airspeed indicator appears to be erratic or inaccu-rate, fly the glider by pitch attitude. Keep the nose ofthe glider at the proper pitch attitude for best glide orminimum sink airspeed. Additional cues to airspeedinclude control “feel” and wind noise. At very low air-speeds, control feel is very mushy and wind noise isgenerally low. At higher airspeeds, control feel iscrisper and wind noise takes on a more insistent hissingquality. The sound of the relative wind can be ampli-fied, and made more useful in airspeed control, byopening the sliding window installed in the canopy andby opening the air vent control. During the landingapproach, maintain adequate airspeed using cues otherthan the airspeed indicator. Fly the approach with anadequate margin above stall airspeed. If conditions areturbulent or the wind is gusty, additional airspeed isnecessary to penetrate the convection and to ensureadequate control authority. If in doubt, it is better to be10 knots faster than optimum airspeed than it is to be10 knots slower.

ALTIMETER MALFUNCTIONSAltimeter failure may result from internal instrumentfailure or from external causes such as water ingressin the static lines. Regardless of the cause, it is impor-tant to maintain sufficient altitude to allow a safeglide to a suitable landing area. During the approachto land without a functioning altimeter, it is necessaryto rely on perception of maintaining a safe glidingangle to the target landing area. The primary risk tosafety is entering the approach from an altitude that islower than normal. It is better to enter the approachfrom a normal height, or even from a higher-than-nor-mal height. During the approach, judge the angle tothe target area frequently. If the angle is too steep,apply full spoilers/dive breaks to steepen the descentpath. If necessary, apply a forward slip or turning slipto lose additional altitude. If the approach angle isbeginning to appear shallow, close the spoilers/divebreaks and, if necessary, modify the approach path to

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shorten the distance necessary to glide to make it tothe target landing area.

Static line contamination affects both the altimeter andthe airspeed indicator. If it is suspected either instrumentis malfunctioning because of static line contamination,remember that the indications of the other instrument(s)connected to the static line may also be incorrect. Use theexternal cues described above to provide multiple cross-checks on the indications of all affected instruments. If indoubt about the accuracy of any instrument, it is best tobelieve the external cues and disregard the instrumentindications. After landing and prior to the next flight,have an aviation maintenance professional evaluate theinstrument system.

It is essential that a glider pilot be familiar with the proce-dures for making a safe approach without a functioningairspeed indicator or altimeter. An excellent opportunityto review these procedures is when accompanied by aglider flight instructor during the flight review.

VARIOMETER MALFUNCTIONSVariometer failure can make it difficult for the pilot tolocate and exploit sources of lift. If an airport is nearby,a precautionary landing should be made so the source ofthe problem can be uncovered and repaired. If no airportis nearby, search for cues to sources of lift. Some cuesmay be external, such as a rising smoke column, acumulus cloud, a dust devil, or a soaring bird. Othersources are internal, such as the altimeter. Use thealtimeter to gauge rate of climb or descent in the absenceof a functioning variometer. Tapping the altimeter withthe forefinger often overcomes internal friction in thealtimeter, allowing the hand to move upward or down-ward. The direction of the movement gives an idea ofthe rate of climb or descent over the last few seconds.When lift is encountered, stay with it and climb.

COMPASS MALFUNCTIONSCompass failure is rare but it does occur. If the com-pass performs poorly or not at all, cross-check yourposition with aeronautical charts and with electronicmethods of navigation, such as GPS, if available. Theposition of the sun, combined with knowledge of thetime of day, can help in orientation also. Section linesand major roads often provide helpful cues to orienta-tion as well.

GLIDER CANOPY MALFUNCTIONSCanopy-related emergencies are often the result ofpilot error. The most likely cause is failure to lock thecanopy in the closed position prior to takeoff.Regardless of the cause, if the canopy opens unexpect-edly during any phase of flight, the first duty is to flythe glider. It is important to maintain adequate airspeedwhile selecting a suitable landing area.

GLIDER CANOPY OPENS UNEXPECTEDLY

If the canopy opens while on aerotow, it is vital to main-tain a normal flying attitude to avoid jeopardizing thesafety of the glider occupants and the safety of the tow-plane pilot. Only when the glider pilot is certain thatglider control can be maintained should any attentionbe devoted to trying to close the canopy. If flying a two-seat glider with a companion aboard, concentrate onflying the glider while the other person attempts toclose and lock the canopy. If the canopy cannot beclosed, the glider may still be controllable. Drag will behigher than normal, so when flying the approach it isbest to plan a steeper-than-normal descent path. Thebest prevention against unexpected opening of thecanopy is proper use of the pre-takeoff checklist.

BROKEN GLIDER CANOPY If the canopy plexiglas is damaged or breaks duringflight the best response is to land as soon as practica-ble. Drag will be increased if the canopy is shattered,so plan a steeper-than-normal descent path during theapproach.

FROSTED GLIDER CANOPY Extended flight at high altitude or in low ambient tem-peratures may result in obstructed vision as moisturecondenses as frost on the inside of the canopy. Open theair vents and the side window to ventilate the cabin andto evacuate moist air before the moisture can condenseon the canopy. Descend to lower altitudes or warmer airto reduce the frost on the canopy. Flight in direct sunlighthelps diminish the frost on the canopy.

WATER BALLAST MALFUNCTIONSWater ballast systems are relatively simple and majorfailures are not very common. Nevertheless, ballastsystem failures can threaten the safety of flight. Oneexample of ballast failure is asymmetrical tank drain-ing (one wing tank drains properly but the other wingtank does not). The result is a wing-heavy glider thatmay be very difficult to control during slow flight andduring the latter portion of the landing rollout.Another example is leakage. Some water ballast sys-tems drain into a central pipe that empties out throughthe landing gear wheel well. If the drain connectionsfrom either wing leak significantly, water from thetanks can collect in the fuselage. If the water flows farforward or far aft in the fuselage, pitch control of theglider may be severely degraded. Pitch control can beaugmented by flying at mid to high airspeeds, givingthe elevator more control authority to correct for theout-of-balance situation and affording time to deter-mine whether the water can be evacuated from thefuselage. If pitch control is dangerously degraded,then abandoning the glider may be the safest choice.The best prevention for water ballast problems areregular maintenance and inspection combined withperiodic tests of the system and its components.

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RETRACTABLE LANDING GEARMALFUNCTIONSLanding gear difficulties can arise from severalcauses. Landing gear failures arising from mechanicalmalfunction of the gear extension mechanism generallycannot be resolved during flight. Fly the approach atnormal airspeed. If the landing gear is not extended, thetotal drag of the glider is less than it is normally duringan approach with the landing gear extended. It may benecessary to use more spoiler/dive break than normalduring the approach. Try to land on the smoothest sur-face available. Allow the glider to touch down at aslightly faster airspeed than would be used if the land-ing gear were extended. This helps avoid a tailwheel-first landing, and a hard thump of the glider onto therunway. Avoiding the hard thump will help to avoidback injury. The glider will make considerable noise asthe glider slides along the runway, and wingtip clear-ance above the ground will be much reduced. Keep thewings level for as long as possible. Try to keep theglider going as straight as possible using the rudder toyaw the glider. The primary goal is to avoid collisionwith objects on the ground or along the runway border.Accept the fact that minor damage to the glider isinevitable if the gear cannot be extended and locked.Concentrate on personal safety during the approach andlanding. Any damage to the glider can be repaired afteran injury-free landing.

PRIMARY FLIGHT CONTROL SYSTEMSFailure of any primary flight control system presents aserious threat to safety. The most frequent cause ofcontrol system failures is incomplete assembly of theglider in preparation for flight. To avoid this, use awritten checklist to guide each assembly operation andinspect every connection and safety pin thoroughly. Donot allow interruptions during assembly. If interruptionis unavoidable, start the checklist again from the verybeginning. Perform a positive control check with thehelp of a knowledgeable assistant. Do not assume thatany flight surface and flight control is properlyinstalled and connected during the post-assemblyinspection. Instead, assume that every connection issuspect. Inspect and test until certain that every com-ponent is ready for flight.

ELEVATOR MALFUNCTIONSThe most serious control system malfunction is a fail-ure of the elevator flight control. Causes of elevatorflight control failure include the following.• An improper connection of the elevator control

circuit during assembly.• An elevator control lock that was not removed

before flight.• Separation of the elevator gap seal tape.• Interference of a foreign object with free and full

travel of the control stick or elevator circuit.

• A lap belt or shoulder harness in the back seatthat was used to secure the control stick and notremoved prior to flight.

• A structural failure of the glider due to over-stressing or flutter.

To avoid a failure, ensure that control locks areremoved prior to flight, that all flight control connec-tions have been completed properly and inspected, thatall safety pins have been installed and latched prop-erly. Ensure that a positive control check againstresistance applied has been performed.

If the elevator irregularity or failure is detected early inthe takeoff roll, release the towline (or reduce power toidle), maneuver the glider to avoid obstacles, and usethe brakes firmly to stop the glider as soon as possible.

If the elevator control irregularity or failure is notnoticed until after takeoff, a series of complicateddecisions must be made quickly. If the glider is closeto the ground and has a flat or slightly nose low pitchattitude, releasing the towline (or reducing power tozero) is the best choice. If this is an aerotow launch,consider the effect the glider has on the safety of thetowpilot. If there is sufficient elevator control duringclimb, then it is probably best to stay with the launchand achieve as high an altitude as possible. If wearinga parachute, high altitude gives more time to abandonthe glider and deploy the parachute.

If the decision is to stay with the glider and continuethe climb, experiment with the effect of other flightcontrols on the pitch attitude of the glider. Theseinclude the effects of various wing flap settings, spoil-ers/dive breaks, elevator trim system, and raising orlowering the landing gear. If flying a self-launchglider, experiment with the effect of power settings onpitch attitude.

If aileron control is functioning, bank the glider anduse the rudder to moderate the attitude of the nose rel-ative to the horizon. When the desired pitch attitude isapproached, adjust the bank angle to maintain thedesired pitch attitude. Forward slips may have a pre-dictable effect on pitch attitude and can be used tomoderate it. Usually, a combination of these tech-niques is necessary to regain some control of pitch atti-tude. While these techniques may be a poor substitutefor the glider elevator itself, they are better than noth-ing. If an altitude sufficient to permit bailing out andusing a parachute is achieved, chances of survival aregood because parachute failures are exceedingly rare.

Elevator gap seal tape, if in poor condition, candegrade elevator responsiveness. If the adhesive that

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bonds the gap seal leading edge to the horizontal stabi-lizer begins to fail, the leading edge of the gap seal maybe lifted up by the relative wind. This will provide, ineffect, a small spoiler that disturbs the airflow over theelevator just aft of the lifted seal. Elevator blankingoccurring across a substantial portion of the span of theelevator seriously degrades pitch attitude control. Inextreme cases, elevator authority may be compromisedso drastically that the glider elevator will be useless.The pilot may be forced to resort to alternate methodsto control pitch attitude as described above. Bailing outmay be the safest alternative. Inspection of the gap sealbonds for all flight control surfaces prior to flight is thebest prevention.

AILERON MALFUNCTIONSAileron failures can cause serious control problems.Causes of aileron failures include the following.

• An improper connection of the aileron controlcircuit during assembly.

• An aileron control lock that was not removedbefore flight.

• A separation of the aileron gap seal tape.

• An interference of a foreign object with free andfull travel of the control stick or aileron circuit.

• A seat belt or shoulder harness in the back seatthat was used to secure the control stick and notremoved prior to flight.

• A structural failure and/or aileron flutter.

These failures can sometimes be counteracted success-fully. Part of the reason for this is that there are twoailerons. If one aileron is disconnected or locked by anexternal control lock, the degree of motion still avail-able in the other aileron may exert some influence onbank angle control. Use whatever degree of aileronavailable to maintain control of the glider. The glidermay be less difficult to control at medium to high air-speeds than at low airspeeds.

If the ailerons are not functioning adequately and rollcontrol is compromised, the secondary effect of therudder can be used to make gentle adjustments in thebank angle so long as a safe margin above stall speed ismaintained. The primary effect of the rudder is to yawthe glider. The secondary effect of the rudder is subtlerand takes longer to assert itself. In wings-level flight, ifleft rudder is applied, the nose yaws to the left. If thepressure is held, the wings begin a gentle bank to theleft. If right rudder pressure is held and applied, theglider yaws to the right, then begins to bank to theright. This bank effect is a secondary effect of the rud-der. If the pilot must resort to using the rudder to bank

the glider wings, keep all banks shallow. The second-ary effect of the rudder works best when the wings arelevel or held in a very shallow bank, and is enhanced atmedium to high airspeeds. Try to keep all banks veryshallow. If the bank angle becomes excessive, it will bedifficult or impossible to recover to wings-level flightusing the rudder alone. If the bank is becoming toosteep, use any aileron influence available, as well as allavailable rudder to bring the wings back to level. If aparachute is available and the glider becomes uncon-trollable at low airspeed, the best chance to escape seri-ous injury may be to bail out of the glider from a safealtitude.

RUDDER MALFUNCTIONSRudder failure is extremely rare because removing andinstalling the vertical fin/rudder combination is not partof the normal sequence of rigging and de-rigging theglider (as it is for the horizontal stabilizer/elevator andfor the wing/aileron combinations). Poor directionalcontrol is so obvious to the pilot from the very begin-ning of the launch that, if rudder malfunction is sus-pected, the launch can be aborted early.

Rudder malfunctions most likely occur due to failure toremove the rudder control lock prior to flight or whenan unsecured object in the cockpit interferes with thefree and full travel of the rudder pedals. Preflightpreparation must include removal of all flight controllocks and safe stowage of all items on board. The pre-takeoff checklist includes checking all primary flightcontrols for correct, full travel prior to launch.

Although rudder failure is quite rare, the consequencesare serious. If a control lock causes the problem, it ispossible to control the glider airspeed and bank attitudebut directional control is compromised due to limitedrudder movement. In the air, some degree of directionalcontrol can be obtained by using the adverse yaw effectof the ailerons to yaw the glider. During rollout from anaborted launch or during landing rollout, directionalcontrol can sometimes be obtained by deliberatelygrounding the wingtip toward the direction of desiredyaw. Putting the wingtip on the ground for a fraction ofa second causes a slight yaw in that direction; holdingthe wingtip firmly on the ground usually causes a vig-orous yaw or groundloop in the direction of thegrounded wingtip.

Careless stowage of cockpit equipment can result inrudder pedal interference at any time during a flight.During soaring flight, if an object is interfering with orjamming the rudder pedals, attempt to remove it. Ifremoval is not possible, attempt to deform, crush, ordislodge the object by applying force on the rudder

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pedals. It also may be possible to dislodge the objectby varying the load factor, but be careful that dislodg-ing the object does not result in its lodging in a worseplace, where it could jam the elevator or aileron con-trols. If the object can not be retrieved and stowed, aprecautionary landing may be required.

SECONDARY FLIGHT CONTROL SYSTEMSSecondary flight control systems include the elevatortrim system, wing flaps, and spoilers/dive brakes.Problems with any of these systems can be just as seri-ous as problems with primary controls.

ELEVATOR TRIM MALFUNCTIONSCompensating for a malfunctioning elevator trim sys-tem is usually as simple as applying pressure on thecontrol stick to maintain the desired pitch attitude, thenbringing the flight to safe conclusion. Inspect andrepair the trim system prior to the next flight.

SPOILER/DIVE BRAKE MALFUNCTIONSSpoiler/dive brake system failures can arise from rig-ging errors or omissions, environmental factors, andmechanical failures. Interruptions or distractions duringglider assembly can result in failure to properly connectcontrol rods to one or both spoilers/dive brakes. Properuse of a comprehensive checklist reduces the likelihoodof assembly errors. If neither of these spoilers/divebrakes are connected, then one or both of thespoilers/dive brakes may deploy at any time and retrac-tion will be impossible. This is a very hazardous situa-tion for several reasons. One reason is that thespoilers/dive brakes are likely to deploy during thelaunch or the climb, causing a launch emergency.Another reason is that the spoilers/dive brakes mightdeploy asymmetrically: one spoiler/dive brakeretracted, the other spoiler/dive brake extended. Thisresults in a yaw tendency and a roll tendency that doesnot arise when the spoilers/dive brakes deploy symmet-rically. The final reason is that it will not be possible tocorrect the situation by retracting the spoiler/divebrake(s) because the failure to connect the controlsproperly usually means that pilot control of thespoiler/dive brake has been lost.

If asymmetrical spoiler/dive brake extension occursand the extended spoiler/dive brake cannot beretracted, several choices must be made. Roll and yawtendencies due to asymmetry must be overcome oreliminated. One way to solve this problem is to deploythe other spoiler/dive brake, relieving the asymmetry.The advantages include immediate relief from yaw androll tendencies and protection against stalling with onespoiler/dive brake extended and the other retracted,which could result in a spin. The disadvantage ofdeploying the other spoiler/dive brake is that the glideratio is reduced.

If the spoiler/dive brake asymmetry arises duringlaunch or climb, the best choice is to abort the launch,extend the other spoiler/dive brakes to relieve theasymmetry, and make a precautionary or emergencylanding.

Environmental factors include cold or icing duringlong, high altitude flights, such as might occur duringa mountain wave flight. The cold causes contractionof all glider components. If the contraction is uneven,the spoilers/dive brakes may bind and be difficult orimpossible to deploy. Icing can also interfere withoperation of the spoilers/dive brakes. High heat, onthe other hand, causes all glider components toexpand. If the expansion is uneven, the spoilers/divebrakes may bind in the closed position. This is mostlikely to occur while the glider is parked on theground in direct summer sunlight. The heating can bevery intense, particularly for a glider with wingspainted a color other than reflective white.

Mechanical failures can cause asymmetricalspoiler/dive brake extension. For example, thespoiler/dive brake extend normally during the pre-landing checklist but only one spoiler/dive brakeretracts on command. The other spoiler/dive brakeremains extended, due perhaps to a broken weld in thespoiler/dive brake actuator mechanism, a defectivecontrol connector, or other mechanical failure. If adecision is made to fly with one spoiler/dive brakeextended and the other retracted, the wing with theextended spoiler/dive brake creates less lift and moredrag than the other wing. The glider yaws and bankstoward the wing with the extended spoiler/dive brake.Aileron and rudder are required to counteract thesetendencies. To eliminate any possibility of entering astall/spin, maintain a safe margin above stall airspeed.If the decision to deploy the other spoiler/dive brake ismade to relieve the asymmetry, controlling the gliderwill be much easier but gliding range will be reduceddue to the additional drag of the second spoiler/divebrake. This may be a significant concern if the terrainis not ideal for landing the glider. Nevertheless, it isbetter to make a controlled landing, even in less thanideal terrain, than it is to stall or spin.

MISCELLANEOUS FLIGHT SYSTEMMALFUNCTIONSTOWHOOK MALFUNCTIONSTowhooks can malfunction just like any othermechanical device. Failure modes include uncom-manded towline release and failure to release oncommand. Pilots must be prepared to abort anytowed launch, whether ground or aerotow launch, atany time. Uncommanded towline release must beanticipated prior to every launch. Assess the wind

8-15

and the airport environment, and then form an emer-gency plan prior to launch. If the towhook fails torelease on command, try to release the towline againafter removing tension from the line. Pull the releasehandle multiple times under varying conditions oftowline tension. If the towrope still cannot release,alert the towpilot and fol low the emergency proce-dures described in Chapter 7—Flight Maneuvers andTraffic Patterns.

OXYGEN SYSTEM MALFUNCTIONSOxygen is essential for flight safety at high altitude. Ifa suspected or detected failure in any component of theoxygen system, descend immediately to an altitudewhere supplemental oxygen is not essential for contin-ued safe flight. Remember that the first sign of oxygendeprivation is a sensation of apparent well being.Problem-solving capability is diminished. If the pilothas been deprived of sufficient oxygen, even for a shortinterval, critical thinking capability has been compro-mised. Do not be lulled into thinking that the flight cansafely continue at high altitude. Descend immediatelyand breathe normally at these lower altitudes for a timeto restore critical oxygen to the bloodstream. Try toavoid hyperventilation, which will prolong the dimin-ished critical thinking capability. Give enough time torecover critical thinking capability before attemptingan approach and landing.

DROGUE CHUTE MALFUNCTIONSSome gliders are equipped with a drogue chute to adddrag during the approach to land. This drag supplementsthe drag the spoilers/dive breaks provide. The droguechute is packed and stowed in the aft tip of the fuselage orin a special compartment in the base of the rudder. Droguechutes are very effective when deployed properly andmake steep approaches possible. The drogue chute isdeployed and jettisoned on pilot command, such as wouldbe necessary if the drag of the glider was so great that theglider would not otherwise have the range to make it tothe spot of intended landing. There are several failuremodes for drogue chutes. If it deploys accidentally orinadvertently during takeoff roll or during climb, the rateof climb will be seriously degraded and it must be jetti-soned. During the approach to land, an improperly packedor damp drogue chute may fail to deploy on command. Ifthis happens, use the rudder to sideslip for a moment, orfan the rudder several times to yaw the tail of the gliderback and forth in rapid alternation. Make certain to havesafe flying speed before attempting the slip or fanning therudder. Either technique increases the drag on the tailconethat pulls the parachute out of the compartment.

If neither technique deploys the drogue chute, thedrogue canopy may deploy at a later time during theapproach without further control input from the pilot.This will result in a considerable increase in drag. Ifthis happens, be prepared to jettison the drogue chute

immediately if sufficient altitude to glide to theintended landing spot has not been reached.

Another possible malfunction is when the drogue chuteevacuates the chute compartment, but fails to inflatefully. If this happens, the canopy will “stream” like atwisting ribbon of nylon, providing only a fraction ofthe drag that would occur if the canopy had fullyinflated. Full inflation is unlikely after streamingoccurs, but if it does occur, drag will increase substan-tially. If in doubt regarding the degree of deploymentof the drogue chute, the safest option may be to jetti-son the drogue.

SELF-LAUNCH GLIDERSIn addition to the standard flight control systems foundon all gliders, self-launch gliders have multiple sys-tems to support flight under power. These systems mayinclude, but are not limited to the following.

• Fuel tanks, lines, and pumps.

• Engine and/or propeller extension and retractionsystems.

• Electrical system including engine starter system.

• Lubricating oil system.

• Engine cooling system.

• Engine throttle controls.

• Propeller blade pitch controls.

• Engine monitoring instruments and systems.

The complexity of these systems demands thoroughfamiliarity with the GFM/POH for the self-launchglider being flown. Any malfunction of these systemscan make it impossible to resume powered flight.

SELF-LAUNCH GLIDER ENGINE FAILUREDURING TAKEOFF OR CLIMBEngine failures are the most obvious source of equip-ment malfunction in self-launch gliders. Engine fail-ures can be subtle (a very slight power loss at fullthrottle) or catastrophic and sudden (engine crankshaftfailing during a full power takeoff). High on the list ofpossible causes of power problems are fuel contamina-tion or exhaustion.

To provide adequate power, the engine system musthave fuel and ignition, as well as adequate cooling andlubrication. Full power operation is compromised ifany of these requirements are not satisfied. Monitorthe engine temperature, oil pressure, fuel pressure, andRPM carefully to ensure engine performance is notcompromised. Warning signs of impending difficultyinclude excess engine temperatures, excess engine oiltemperatures, low oil pressure, low RPM despite high

8-16

throttle settings, low fuel pressure, and engine missingor backfiring. Abnormal engine performance may be aprecursor to complete engine failure. Even if totalengine failure does not occur, operation with an enginethat cannot produce full power translates into an inabil-ity to climb or perhaps an inability to hold altitudedespite application of full throttle. The best course ofaction, if airborne, is to make a precautionary landingand discover the source of the trouble after safely onthe ground.

Regardless of the type of engine failure, the pilot’sfirst responsibility is to maintain flying airspeed andadequate control of the glider. If power failureoccurs, lower the nose as necessary to maintain ade-quate airspeed. Pilots flying self-launch gliders witha pod-mounted external engine above the fuselageneed to lower the nose much more aggressively inthe event of total power loss than those with anengine mounted in the nose. In the former, the thrustof the engine during full power operations tends toprovide a nose-down pitching moment. If powerfails, the nose-down pitching moment disappears andis replaced by a nose-up pitching moment due to thesubstantial parasite drag of the engine pod highabove the longitudinal axis of the fuselage.Considerable forward motion on the control stickmay be required to maintain flying airspeed. If alti-tude is low, there is not enough time to stow theengine and reduce the drag that it creates. Land theglider with the engine extended. Glide ratio in thisconfiguration will be poor due to the drag of theextended engine and propeller. The authoritativesource for information regarding the correctsequence of pilot actions in the event of power fail-ure is contained in the GFM/POH. The pilot must bethoroughly familiar with its contents to operate aself-launch glider safely.

If the power failure occurs during launch or climb,time to maneuver may be limited. Concentrate on fly-ing the glider and selecting a suitable landing area.Remember that the high drag configuration of theglider may limit the distance of the glide withoutpower. Keep turns to a minimum and land the glider assafely as you can. Do not try to restart the engine whileat very low altitude because it distracts from the pri-mary task of maintaining flying airspeed and making asafe precautionary landing. Even if you could manageto restore power in the engine system, chances are thatfull power will not be available. The problem thatcaused the power interruption in the first place is notlikely to solve itself while trying to maneuver from lowaltitude and climb out under full power. If the problemrecurs, as it is likely to do, the pilot may place theglider low over unlandable terrain with limited glidingrange and little or no engine power to continue theflight. Even if the engine continues to provide limited

power, flight with partial power may quickly put theglider in a position in which the pilot is unable to clearobstacles such as wires, poles, hangars, or nearby ter-rain. If a full-power takeoff or climb is interrupted bypower loss, it is best to make a precautionary landing.The pilot can sort out the power system problems afterreturning safely to the ground.

INABILITY TO RE-START A SELF-LAUNCHGLIDER ENGINE WHILE AIRBORNEPower loss during takeoff roll or climb are seriousproblems, but they are not the only types of problemsthat may confront the self-launch glider pilot. Otherengine failures include an engine that refuses to startin response to airborne start attempts. This is a seriousproblem if the terrain below is unsuitable for a safeoff-field landing.

One of the great advantages of the self-launch glider isthe option to terminate a soaring flight by starting theengine and flying to an airport/gliderport for landing.Nearly all self-launch gliders have a proceduredesigned to start the engine while airborne. This pro-cedure would be most valuable during a soaring flightwith engine off during which the soaring conditionshave weakened. The prospect of starting the engineand flying home safely is ideal under such conditions.As a precaution an airborne engine start should beattempted at an altitude high enough so that if a mal-function occurs there will be sufficient time to takecorrective action. If the engine fails to start promptly,or fails to start at all, there may be little time to planfor a safe landing. If there is no landable area below,then failure to start the engine will result in an emer-gency off-field landing in unsuitable terrain. Gliderdamage and personal injury may result. To avoid thesedangers, self-launch glider pilots should never allowthemselves to get into a situation that can only beresolved by starting the engine and flying up and away.It is best to always keep a landable field within easygliding range. There are many reasons that a self-launch glider engine may fail to start or fail to providefull power in response to efforts to resume full-poweroperations while airborne. These include lack of fuelor ignition, low engine temperature due to cold soak,low battery output due to low temperatures or batteryexhaustion, fuel vapor lock, lack of propeller responseto blade pitch controls, and other factors. It is impor-tant for the pilot to have an emergency plan in theevent that full engine power is not available during anyphase of flight.

SELF-LAUNCH GLIDER PROPELLERMALFUNCTIONSPropeller failures include propeller damage and disin-tegration, propeller drive belt or drive gear failure, or

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failure of the variable blade pitch control system. Toperform an air-driven engine restart, for example,many self-launch gliders require that the propellerblades be placed in a particular blade pitch position. Ifthe propeller blades can not be properly adjusted, thenthe propeller will not deliver enough torque to turn theengine over. The result is a failure to obtain an air-driven engine start.

SELF-LAUNCH GLIDER ELECTRICAL SYSTEM MALFUNCTIONSAn electrical system failure in a self-launch glider maymake it impossible to control the propeller pitch if thepropeller is electrically controlled. It may also result inthe inability to deploy a pod engine successfully for anair re-start attempt. Self-launch gliders that require afunctioning electric starter for an air re-start will beunable to resume flight under power. If an airport iswithin gliding range, an on-airport precautionary land-ing can be made. If there is no airport within glidingrange and the flight can be safely continued withoutelectrical power, the pilot may be able to soar to thevicinity of an airport and land safely. If no airport iswithin gliding range and flight cannot be sustainedwithout power, an emergency off-airport landing hasto be made.

Some self-launch gliders are occasionally used fornight flight, cruising under power and operating the

necessary aeronautical lighting. If an electrical systemfailure occurs during night operations, pilots of nearbyaircraft are not able to see the self-launch glider due tothe extinguished position lights. Inside the cockpit, it isdifficult or impossible to see the flight instruments orelectrical circuit breakers. Carry a flashlight for such anemergency. Check the circuit breakers and reset anybreaker that has overloaded unless the smell of smoke ispresent or any other indication of an overheating circuit.[Figure 8-8] Head directly for the nearest airport andprepare for a precautionary landing there. The aviationtransceiver installed in the instrument panel may notfunction if electrical failure is total, so it is a good ideato have a portable battery-operated aviation two-wayradio aboard for use in such an emergency.

IN-FLIGHT FIREIn-flight fires are the most serious emergencies a pilotcan encounter. If a fire has ignited, or if there is a smellof smoke or any similar smell, do everything possibleto reduce the possibilities that the fire spreads and landas soon as possible. The self-launch glider GFM/POHis the authoritative source for emergency response tosuspected in-flight fire. The necessary procedures are.

• reduce throttle to idle;

• shut off fuel valves;

• shut off engine ignition;

• land immediately and stop as quickly as possible; and

• evacuate the self-launch glider immediately.

After landing, get far away from the glider. Keeponlookers away from the glider as well. The principaldanger after evacuating the glider is that the fuel willignite and explode, with the potential to injure personnelat considerable distance from the glider.

EMERGENCY EQUIPMENT AND SURVIVAL GEAR Emergency equipment and survival gear is essentialfor safety of flight for all soaring flights.

Figure 8-8. Self-launch glider circuit breakers.

8-18

SURVIVAL GEAR ITEM CHECKLISTSChecklists help to assemble the necessary equipment inan orderly manner. The essentials for survival includereliable and usable supplies of water, food, and air oroxygen. Maintenance of an acceptable body temperature,which is difficult to manage in extreme cold or extremeheat, is also important. Blankets and appropriate seasonalclothing help to ensure safe body temperatures.

FOOD AND WATER An adequate supply of water and food (high-energyfoods such as energy bars, granolas, and dried fruitsare usually best) are of utmost importance duringcross-country flight. Water from ballast tanks can beused in an emergency if free of contaminants such asantifreeze. Water and food should be available andreachable during the entire flight. Pilot relief for urina-tion should also be easy to access and use.

CLOTHINGPilots also need seasonal clothing that is appropriate tothe local environment, including hat or cap, shirts,sweaters, pants, socks, walking shoes, space blanket,gloves or mittens. Layered clothing provides flexibil-ity to meet the demands of the environment. Desertareas may be very hot in the day and very cold at night.Prolonged exposure to either condition can be debili-tating. Layered clothing traps air between layers,increasing heat retention. The parachute canopy can beused as an effective layered garment when wrappedaround the body to conserve body heat or to providerelief from excessive sunlight. Eye protection such assunglasses are more than welcome if conditions duringthe day are bright, as they often are on good soaringdays.

COMMUNICATIONCommunication can be electronic, visual, or audible.Radios, telephones, and cell phones are electronicmethods. Signal mirrors, flashlight or light beacons atnight, signal fire flames at night, signal smoke duringdaylight hours, signal flares, and prominent parachutecanopy displays are visual methods. Shouting andother noisemaking activities are audible methods butusually have very limited range.

Coin, cash, or credit cards are often necessary tooperate pay phones. Charged batteries are required tooperate cell phones, two-way radios, and emergencylocator transmitters. Batteries are also necessary tooperate flashlights or position lights on the glider forsignal purposes. A list of useful telephone numbersaids rapid communication. The aviation transceivercan be tuned to broadcast and receive on the emer-

gency frequency 121.5 MHz or any other useable fre-quency that will elicit a response. The ELT can beused to provide a continuous signal on 121.5 MHz.The parachute canopy and case can be employed tolay out a prominent marker to aid recognition fromthe air by other aircraft. Matches and a combustiblematerial can provide flame for recognition by nightand provide smoke that may be seen during daylighthours.

NAVIGATION EQUIPMENTAviation charts help to navigate during flight and helppinpoint the location when an off-airport landing ismade. Sectional charts have the most useful scale forcross-country soaring flights. Local road maps (withlabeled roads) should be carried in the glider during allcross-country flights. Local road maps make it mucheasier to give directions to the ground crew, allowingthem to arrive as promptly as possible. GPS coordi-nates also help the ground crew if they are equippedwith a GPS receiver and appropriate charts and maps.Detailed GPS maps are commercially available andmake GPS navigation by land easier for the groundcrew.

MEDICAL EQUIPMENTCompact, commercially made medical or first aid kitsare widely available. These kits routinely includebandages, medical tape, painkillers and other medi-cines, disinfectants, a tourniquet, matches, a knife orscissors, bug and snake repellent, and other usefulitems. Ensure that the kit contains medical items suit-able to the environment in which you are operating.Stow the kit so it is secure from in-flight turbulencebut is accessible after an emergency landing, even ifinjured.

STOWAGEStowing equipment properly means securing all equip-ment to protect occupants and ensure integrity of allflight controls and glider system controls. Items car-ried aboard must be secure even in the event thatsevere in-flight turbulence is encountered. Items mustalso remain secured in the event of a hard or off-fieldlanding. No item carried in the glider should have anychance of coming loose in flight to interfere with theflight controls. Stowed objects should be adequatelysecured to prevent movement during a hard landing.

OXYGEN SYSTEMThe oxygen system is a life support system duringflights at high altitude. Ensure that all components ofthe system are in working condition and that the bottlehas a sufficient charge of aviators’ breathing oxygen.The oxygen bailout bottle should be in good conditionand in an easy-to-reach position should the need toabandon the glider at very high altitude arise. Thebailout bottle is most commonly stowed aboard the

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glider when embarking on high-altitude flights inmountain wave conditions.

PARACHUTEThe parachute should be clean, dry, and be stored in acool place when not in use. The parachute must havebeen inspected and repacked within the allowable timeframe. For synthetic canopy parachutes this interval is120 days.

9-1

Glider pilots face a multitude of decisions, startingwith the decision to take to the air. Pilots must deter-mine if weather conditions are safe, and whether theconditions will support soaring flight. Gliders, beingpowered by gravity, are always sinking through the air.Therefore, glider pilots must seek air that rises fasterthan the sink rate of the glider to enable prolongedflight. Glider pilots refer to rising air as lift, not to beconfused with the lift created by the wing.

THE ATMOSPHEREThe atmosphere is a mixture of gases surrounding theEarth. Without it, there would be no weather (wind,clouds, precipitation) or protection from the sun’srays. Though this protective envelope is essential tolife, it is extraordinarily thin. When compared to theradius of the Earth, 3,438 nautical miles, the verticallimit of the atmosphere represents a very small dis-tance. Although there is no specific upper limit to theatmosphere—it simply thins to a point where it fadesaway into space—the layers up to approximately164,000 feet (about 27 nautical miles) contain 99.9percent of atmospheric mass. At that altitude, theatmospheric density is approximately one-thousandththe density of that at sea level. [Figure 9-1]

COMPOSITIONThe Earth’s atmosphere is composed of a mixture ofgases, with small amounts of water, ice, and other par-ticles. Two gases, nitrogen (N2) and oxygen (O2), com-prise approximately 99 percent of the gaseous contentof the atmosphere; the other one percent is composedof various trace gases. Nitrogen and oxygen are bothconsidered permanent gases, meaning their propor-tions remain the same to approximately 260,000 feet.Water vapor (H2O), on the other hand, is considered avariable gas. Therefore, the amount of water in theatmosphere depends on the location and the source ofthe air. For example, the water vapor content over trop-ical areas and oceans accounts for as much as four per-cent of the gases displacing nitrogen and oxygen.Conversely, the atmosphere over deserts and at high

altitudes exhibits less than one percent of the watervapor content. [Figure 9-2]

Although water vapor exists in the atmosphere in smallamounts as compared to nitrogen and oxygen, it has asignificant impact on the production of weather. This isbecause it exists in two other physical states: liquid(water) and solid (ice). These two states of water con-tribute to the formation of clouds, precipitation, fog,and icing, all of which are important to aviationweather. In addition, by absorbing the radiant energyfrom the Earth’s surface, water vapor reduces surfacecooling, causing surface temperatures to be warmer.

Alt

itu

de

(Fee

t)

18,000

Sea Level

53,000

164,000

99.9% ofMass BelowThis Level

90% ofMass BelowThis Level

50% ofMass BelowThis Level

Figure 9-1. Atmospheric mass by altitude.

9-2

PROPERTIESThe state of the atmosphere is defined by fundamentalvariables, namely temperature, density, and pressure.These variables change over time and, combined withvertical and horizontal differences, lead to dailyweather conditions.

TEMPERATUREThe temperature of a gas is the measure of the averagekinetic energy of the molecules of that gas. Fast mov-ing molecules are indicative of high kinetic energy andwarmer temperatures. Conversely, slow moving mole-cules reflect lower kinetic energy and lower tempera-tures. Air temperature is commonly thought of in termsof whether it feels hot or cold. For quantitative meas-urements, the Celsius scale is used in aviation, althoughthe Fahrenheit scale is still used in some applications.

DENSITYThe density of any given gas is the total mass of mole-cules in a specified volume, expressed in units of massper volume. Low air density means a fewer number of

air molecules in a specified volume while high air den-sity means a greater number of air molecules in thesame volume. Air density affects aircraft performance,as noted in Chapter 5–Glider Performance.

PRESSUREMolecules in a given volume of air not only posses acertain kinetic energy and density, but they also exertforce. The force per unit area defines pressure. At theEarth’s surface, the pressure exerted by the atmosphereis due to its weight. Therefore, pressure is measured interms of weight per area. For example, atmosphericpressure is measured in pounds per square inch(lb./in.2). From the outer atmosphere to sea level, a typ-ical value of atmospheric pressure is 14.7 lb./in.2 Thisforce measured at sea level is commonly reported as29.92 inches of mercury (in. Hg.) (from the level ofmercury at standard sea-level pressure in a mercurialbarometer). In aviation weather reports, the commonreporting unit is millibars. When 29.92 in. Hg. is con-verted, it becomes 1013.2 millibars. The force createdby the moving molecules act equally in all directionswhen measured at a given point.

260,000 ft.

78% Nitrogen

1% Other Gases

21% Oxygen

Atmosphere

Figure 9-2.The composition of the atmosphere.

9-3

in this layer. The lower part of the troposphere inter-acts with the land and sea surface, providing thermals,mountain waves, and sea-breeze fronts. Although tem-peratures decrease as altitude increases in the tropo-sphere, local areas of temperature increase (inversions)are common.

The top of the troposphere is called the tropopause.The pressure at this level is only about ten percent ofMSL (0.1 atmospheres) and density is decreased toabout 25 percent of its sea-level value. Temperaturereaches its minimum value at the tropopause, approxi-mately -55° Celsius (−67°F). For pilots this is animportant part of the atmosphere because it is associ-ated with a variety of weather phenomena such asthunderstorm tops, clear air turbulence, and jetstreams. The vertical limit altitude of the tropopausevaries with season and with latitude. The tropopause islower in the winter and at the poles; it is higher in thesummer and at the equator.

The tropopause separates the troposphere from thestratosphere. In the stratosphere, the temperature tendsto first change very slowly with increasing height.However, as altitude increases the temperatureincreases to approximately 0° Celsius (32°F) reachingits maximum value at about 160,000 feet MSL. Unlikethe troposphere where the air moves freely both verti-cally and horizontally, the air within the stratospheremoves mostly horizontally.

Gliders have reached into the lower stratosphere usingmountain waves. At these altitudes, pressurizationbecomes an issue, as well as the more obvious breathing

Dry air behaves almost like an “ideal” gas, meaning itobeys the gas law given by P/DT = R, where P is pres-sure, D is density, T is temperature, and R is a constant.This law states that the ratio of pressure to the productof density and temperature must always be the same.For instance, at a given pressure if the temperature ismuch higher than standard, then the density must bemuch lower. Air pressure and temperature are usu-ally measured, and using the gas law, density of theair can be calculated and used to determine aircraftperformance under those conditions.

STANDARD ATMOSPHEREUsing a representative vertical distribution of thesevariables, the standard atmosphere has been definedand is used for pressure altimeter calibrations. Sincechanges in the static pressure can affect pitot-staticinstrument operation, it is necessary to understandbasic principles of the atmosphere. To provide acommon reference for temperature and pressure, adefinition for the standard atmosphere, also calledInternational Standard Atmosphere (ISA), has beenestablished. In addition to affecting certain flightinstruments, these standard conditions are the basisfor most aircraft performance data. At sea level, thestandard atmosphere consists of a barometric pressureof 29.92 in. Hg., (1013.2 millibars) and a temperatureof 15°C (59°F). This means that under the standardconditions, a column of air at sea level weighs14.7 lb./in.2.

Since temperature normally decreases with altitude, astandard lapse rate can be used to calculate tempera-ture at various altitudes. Below 36,000 feet, the stan-dard temperature lapse rate is 2°C (3.5°F) per 1,000feet of altitude change. Pressure does not decrease lin-early with altitude, but for the first 10,000 feet, 1in.Hg. for each 1,000 feet approximates the rate ofpressure change. It is important to note that the stan-dard lapse rates should only be used for flight plan-ning purposes with the understanding that largevariations from standard conditions can exist in theatmosphere. [Figure 9-3]

LAYERS OF THE ATMOSPHEREThe Earth’s atmosphere is divided into four strata orlayers: troposphere, stratosphere, mesosphere, andthermosphere. These layers are defined by the temper-ature change with increasing altitude. The lowest layer,called the troposphere, exhibits an average decrease intemperature from the Earth’s surface to about 36,000feet above mean sea level (MSL). The troposphere isdeeper in the tropics and shallower in Polar Regions. Italso varies seasonally, being higher in the summer andlower in the winter months.

Almost all of the Earth’s weather occurs in the tropo-sphere as most of the water vapor and clouds are found

Temperature (°C)

-55 -35 -15 0 +15Sea Level

10,000

20,000

30,000

40,000

50,000

Alt

itu

de

(Fee

t)

STANDARD ATMOSPHERE

Figure 9-3. Standard Atmosphere.

9-4

oxygen requirements. Layers above the stratosphere,the mesosphere and thermosphere, have some interest-ing features that are normally not of importance toglider pilots. However, interested pilots might refer toany general text on weather or meteorology.

SCALE OF WEATHER EVENTSWhen preparing forecasts, meteorologists consideratmospheric circulation on many scales. To aid theforecasting of short- and long-term weather, variousweather events have been organized into three broadcategories called the scales of circulations. The sizeand life span of the phenomena in each scale is roughlyproportional, so that larger size scales coincide withlonger lifetimes. The term microscale refers to featureswith spatial dimensions of 1/10th to 1 nautical mile andlasting for seconds to minutes. An example is an indi-vidual thermal. Mesoscale refers to horizontaldimensions of 1 to 1,000 nautical miles and lastingfor many minutes to weeks. Examples include moun-tain waves, sea-breeze fronts, thunderstorms, andfronts. Research scientists break down the mesoscaleinto further subdivisions to better classify variousphenomena. Macroscale refers to horizontal dimen-sions greater than 1,000 nautical miles and lasting forweeks to months. These include the long waves in thegeneral global circulation and the jetstreams imbed-ded within those waves. [Figure 9-4]

Smaller-scale features are imbedded in larger scalefeatures. For instance, a microscale thermal may bejust one of many in a mesoscale convergence line,like a sea-breeze front. The sea-breeze front mayoccur only under certain synoptic conditions, whichis controlled by the macroscale circulations. Thescales interact, with feedback from smaller to larger

scales and vice versa, in ways that are not yet fullyunderstood by atmospheric scientists. Generally,the behavior and evolution of macroscale features ismore predictable, with forecast skill decreasing asscale diminishes. For instance, forecasts up to a fewdays for major events, such as a trough with an asso-ciated cold front have become increasingly accu-rate. However, nobody would attempt to forecastthe exact time and location of an individual thermalan hour ahead of time. Since most of the features ofinterest to soaring pilots lies in the smallermesoscale and microscale range, prediction of soar-ing weather is a challenge.

Soaring forecasts should begin with the macroscale,that is, identifying large-scale patterns that producegood soaring conditions. This varies from site to site,and depends, for instance, on whether the goal isthermal, ridge, or wave soaring. Then, mesoscalefeatures should be considered. This may includeitems, such as the cloudiness and temperature struc-ture of the airmass behind a cold front, as well asthe amount of rain produced by the front.Understanding lift types, and environments inwhich they form, is the first step to understandinghow to forecast soaring weather.

THERMAL SOARING WEATHER A thermal is a rising mass of buoyant air. Thermals arethe most common updraft used to sustain soaring flight.In the next sections, several topics related to thermalsoaring weather are explored, including thermal struc-ture, atmospheric stability, the use of atmosphericsoundings, and air masses conducive to thermal soar-ing.

General Circulation, Monsoon Circulation

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Figure 9-4. Scale of circulation—horizontal dimensions and life spans of associated weather events.

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Convection refers to an energy transfer involving massmotions. Thermals are convective currents and are onemeans by which the atmosphere transfers heat energyvertically. Advection is the term meteorologists use todescribe horizontal transfer, for instance, cold-airadvection after the passage of a cold front. As a note ofcaution, meteorologists sometimes are careless withthe use of the word “convection” and use it to mean“deep convection,” that is, thunderstorms.

Unfortunately, there is often a fine meteorological linebetween a warm, sunny day with plenty of thermals,and a warm, sunny day that is stable and produces nothermals. To the earthbound general public, it matterslittle–either is a nice day. Glider pilots, however, needa better understanding of these conditions and mustoften rely on their own forecasting skills.

THERMAL SHAPE AND STRUCTURETwo primary conceptual models exist for the structureof thermals, the bubble model and the column or plumemodel. Which model best represents thermals encoun-tered by glider pilots is a topic of ongoing debateamong atmospheric scientists. In reality, thermals fit-ting both conceptual models likely exist. A blend of themodels, such as individual strong bubbles rising withinone plume, may be what occurs in many situations. Itmust be kept in mind, these models attempt to simplifya complex and often turbulent phenomenon, so thatmany exceptions and variations are to be expectedwhile actually flying in thermals. Many books, articles,and Internet resources are available for further readingon this subject.

The bubble model describes an individual thermalresembling a vortex ring, with rising air in the middleand descending air on the sides. The air in the middleof the vortex ring rises faster than the entire thermalbubble. The model fits occasional reports from gliderpilots. At times, one glider may find no lift, when only200 feet below another glider that climbs away. Atother times, one glider may be at the top of the bubbleclimbing only slowly, while a lower glider climbs rap-idly in the stronger part of the bubble below. [Figure 9-5]

More often, a glider flying below another glider circlingin a thermal is able to contact the same thermal andclimb, even if the gliders are displaced vertically by a1,000 feet or more. This suggests the column or plumemodel of thermals is more common. [Figure 9-6]

Which of the two models best describes thermalsdepends on the source or reservoir of warm air near thesurface. If the heated area is rather small, one singlebubble may rise and take with it all the warmed surfaceair. On the other hand, if a large area is heated and onespot acts as the initial trigger, surrounding warm air

flows into the relative void left by the initial thermal.The in-rushing warm air follows the same path, creat-ing a thermal column or plume. Since all the warmedair near the surface is not likely to have the exact sametemperature, it is easy to envision a column with a fewor several imbedded bubbles. Individual bubbleswithin a thermal plume may merge, while at othertimes, two adjacent and distinct bubbles seem to existside by side. No two thermals are exactly alike sincethe thermal sources are not the same.

Figure 9-5.The bubble or vortex ring model of a thermal.

Figure 9-6.The column or plume model of a thermal.

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Whether the thermal is considered a bubble or column,the air in the middle of the thermal rises faster than theair near the sides of the thermal. A horizontal slicethrough an idealized thermal provides a bulls-eye pat-tern. Real thermals usually are not perfectly concentric;techniques for best using thermals are discussed in thenext chapter. [Figure 9-7]

The diameter of a typical thermal cross section is onthe order of 500–1,000 feet, though the size varies con-siderably. Typically, due to mixing with the surround-ing air, thermals expand as they rise. Thus, the thermalcolumn may actually resemble a cone, with the narrow-est part near the ground. Thermal plumes also tilt in asteady wind and can become quite distorted in the pres-ence of vertical shear. If vertical shear is strong enough,thermals can become very turbulent or become com-pletely broken apart. A schematic of a thermal life-cycle in wind shear is shown in Figure 9-8.

ATMOSPHERIC STABILITYStability in the atmosphere tends to hinder verticalmotion, while instability tends to promote verticalmotion. A certain amount of instability is desirable forglider pilots, since without it, thermals would notdevelop. If the air is moist enough, and the atmosphericinstability deep enough, thunderstorms and associatedhazards can form. Thus, an understanding of atmos-pheric stability and its determination from availableweather data is important for soaring flight and safety.As a note, the following discussion is concerned withvertical stability of the atmosphere. Other horizontalatmospheric instabilities, for instance, in the evolutionof large-scale cyclones, are not covered here.

Generally, a stable dynamic system is one in which adisplaced element will return to its original position.An unstable dynamic system is one in which a dis-placed element will accelerate further from its originalposition. In a neutrally stable system, the displaced ele-ment neither returns to nor accelerates from its originalposition. In the atmosphere, it is easiest to use a parcelof air as the displaced element. The behavior of a stableor unstable system is analogous to aircraft stability dis-cussed in Chapter 3–Aerodynamics of Flight.

For simplicity, assume first that the air is completelydry. Effects of moisture in atmospheric stability areconsidered later. A parcel of dry air that is forced to riseexpands due to decreasing pressure and cools in theprocess. By contrast, a parcel of dry air that is forcedto descend is compressed due to increasing pressureand warms. If there is no transfer of heat between thesurrounding, ambient air, and the displaced parcel, theprocess is called adiabatic. Assuming adiabaticmotion, a rising parcel cools at a lapse rate of 3°C(5.4°F) per 1,000 feet, known as the dry adiabaticlapse rate (DALR). As discussed below, on a ther-modynamic chart, parcels cooling at the DALR aresaid to follow a dry adiabat. A parcel warms at theDALR as it descends. In reality, heat transfer oftenoccurs. For instance, as a thermal rises, the circulationin the thermal itself (recall the bubble model) mixes insurrounding air. Nonetheless, the DALR is a goodapproximation.

The DALR represents the lapse rate of the atmospherewhen it is neutrally stable. If the ambient lapse rate insome layer of air is less than the DALR (for instance,1°C per 1,000 feet), then that layer is stable. If the lapserate is greater than the DALR, it is unstable. An unsta-ble lapse rate usually only occurs within a few hundredfeet of the heated ground. When an unstable layerdevelops aloft, the air quickly mixes and reduces thelapse rate back to DALR. It is important to note thatthe DALR is not the same as the standard atmosphericlapse rate of 2°C per 1,000 feet. The standard atmos-phere is a stable one.

Another way to understand stability is to imagine twoscenarios, each with a different temperature at 3,000feet above ground level (AGL), but the same tempera-ture at the surface, nominally 20°C. In both scenarios,a parcel of air that started at 20°C at the surface hascooled to 11°C by the time it has risen to 3,000 feet atthe DALR. In the first scenario, the parcel is stillwarmer than the surrounding air, so it is unstable andthe parcel keeps rising—a good thermal day. In thesecond scenario, the parcel is cooler than the sur-rounding air, so it is stable and will sink. The parcel inthe second scenario would need to be forced to 3,000feet AGL by a mechanism other than convection,

Figure 9-7. Cross-section through a thermal. Darker greenis stronger lift, red is sink.

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being lifted up a mountainside or a front for instance.[Figure 9-9]

Figure 9-9 also illustrates factors leading to instability.A stable atmosphere can turn unstable in one of twoways. First, if the surface parcel warmed by more than2°C (greater than 22°C), the layer to 3,000 feet wouldthen become unstable in the second scenario. Thus, ifthe temperature of the air aloft remains the same,warming the lower layers causes instability and betterthermal soaring. Second, if the air at 3,000 feet iscooler, as in the first scenario, the layer becomesunstable. Thus, if the temperature on the groundremains the same, cooling aloft causes instability andbetter thermal soaring. If the temperature aloft and atthe surface warm or cool by the same amount, then thestability of the layer remains unchanged. Finally, if theair aloft remains the same, but the surface air-cools(for instance due to a very shallow front) then the layerbecomes even more stable.

An inversion is a layer in which the temperature warmsas altitude increases. Inversions can occur at any altitudeand vary in strength. In strong inversions, the temperaturecan rise as much as 10°C over just a few hundred feet ofaltitude gain. The most notable effect of an inversion is tocap any unstable layer below. Along with trapping haze orpollution below, they also effectively provide a cap to anythermal activity.

So far, only completely dry air parcels have been con-sidered. However, moisture in the form of water vaporis always present in the atmosphere. As a moist parcelof air rises, it cools at the DALR until it reaches its dewpoint, at which time the air in the parcel begins to con-dense. During the process of condensation, heat(referred to as latent heat) is released to the surround-ing air. Once saturated, the parcel continues to cool, butsince heat is now added, it cools at a rate slower thanthe DALR. The rate at which saturated air-cools withheight is known as the saturated adiabatic lapse rate(SALR). Unlike the DALR, the SALR varies substan-tially with altitude. At lower altitudes, it is on the order

Figure 9-8. Life cycle of a typical thermal with cumulus cloud.

Figure 9-9. Stable and unstable parcels of air.

9° °C 3,000 11° °Cft. ft.

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of 1.2°C per 1,000 feet, whereas in mid levels itincreases to 2.2°C per 1,000 feet. Very high up, aboveabout 30,000 feet, little water vapor exists to condense,and the SALR approaches the DALR.

UNDERSTANDING SOUNDINGSThe so-called Skew-T/Log-P (or simply Skew-T forshort) is an example of the thermodynamic dia-gram most commonly used in the United States. TheSkew-T part of the name comes from the fact thattemperature lines on the chart are slanted, while theLog-P is a reminder that pressure does not decreaselinearly in the atmosphere. A temperature and dew-point sounding presented on a Skew-T shows arecord of the current atmospheric stability, moisturecontent, and winds versus altitude. Given surface fore-cast temperatures, the potential for thermal soaring,including the likelihood of cumulus and/or over-development can then be forecast. Using Skew-T dia-grams to their fullest potential requires practice.[Figure 9-10]

There are five sets of lines on a standard Skew-T.Other types of thermodynamic charts, for instance

the Tephigram often used in Great Britain, have thesame lines, but with a somewhat different presenta-tion. The colors and actual number of lines vary, butthe main diagram components should always bepresent. The following discussion refers to theSkew-T in Figure 9-10.

Horizontal blue lines indicate pressure levels and arelabeled every 100 millibars (mb) along the left side ofthe diagram. On this diagram, the approximate height(in feet) of each pressure level in the standard atmos-phere is shown on the right. The actual height of eachpressure level varies from day to day. Slanted(skewed) blue lines indicate temperature and arelabeled every 10°C along the right side of theisotherm. Thin red lines slanted at an angle almostperpendicular to the temperature lines indicate dryadiabats. (An air parcel following a dry adiabat ischanging temperature with height at the DALR.) Thingreen lines curving in the same direction as, but at adifferent angle to, the dry adiabats represent saturatedadiabats. (An air parcel that is saturated follows a sat-urated adiabat is changing temperature with height atthe SALR.) The thin orange lines slanting in the same

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Figure 9-10. Skew-T from an actual sounding.

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direction, but at an angle to the temperature lines rep-resent the ratio of water vapor to dry air, called themixing ratio. Lines of constant mixing ratio arelabeled in grams of water vapor per kilogram of dryair, abbreviated g/kg.

Over the continental United States, several dozensounding balloons are launched twice daily, at 00 and12 Universal Coordinated Time (UTC). These sound-ing balloons record temperature, humidity, and windsat several mandatory levels, as well as “significant”levels, where notable changes with height occur. InFigure 9-10, the actual temperature sounding (shownin bold red), the actual dew-point temperature (shownin bold green), and the winds aloft (shown in windbarbs on the right side) for this day are shown.

The basic analysis for forecasting the potential fordry thermals based on a sounding is achieved byanswering the question, “At what levels is a parcel ofair rising from the surface warmer than the ambientair?” Assume on this day, the surface temperature isforecast to reach 23°C. This point is marked on theSkew-T; the parcel of air at 23°C is warmer than thesurrounding air and starts to rise at the DALR. Whenthe parcel has risen along a dry adiabat (parallel to theslanted red line) to 900 mb (3,200 feet), it has cooledto 17.2°C, which is warmer than the surrounding airat 15°C. Continuing upward along the dry adiabat,at about 780 mb (7,100 feet) the air parcel and sur-rounding air are at the same temperature, and the airno longer rises due to its buoyancy. The ThermalIndex (TI) at each level is defined as the tempera-ture of the air parcel having risen at the DALR sub-tracted from the ambient temperature. Experience hasshown that a TI should be -2 for thermals to form andbe sufficiently strong for soaring flight. Larger nega-tive numbers favor stronger conditions, while valuesof 0 to –2 may produce few or no thermals. On this day,with a surface temperature of 23°C, the TI is found tobe 15–17.2 or -2.2 at 900 mb, sufficient for at leastweak thermals to this level. At 780 mb, the TI is 0, andas mentioned, the expectation is that this would be theapproximate top of thermals.

Thermal strength is difficult to quantify based on theTI alone since many factors contribute to thermalstrength. For instance, in the above example, the TI at800 mb (6,400 feet) was –1. The thermal may or maynot weaken at this level depending on the thermal sizeand the amount of vertical wind shear. These factorstend to mix in ambient air and can decrease the thermalstrength.

It is important to remember that the TI calculated asabove is based on a forecast temperature at the sur-face. If the forecast temperature is incorrect, the

analysis above produces poor results. As a furtherexample, assume that on this day the temperature onlyreached 20°C. From a point on the surface at 20°C andfollowing a dry adiabat upwards, the TI reaches 0 only1,000 feet AGL, making the prospects for workablethermals poor. On the other hand, if temperaturesreached 25°C on this day, thermals would reach about730 mb (8,800 feet), be stronger, and have more nega-tive TI values.

The previous analysis of the morning sounding calcu-lated the TI and maximum thermal height based upona maximum afternoon temperature. In reality, thesounding evolves during the day. It is not untypicalfor a morning sounding to have an inversion as shownin Figure 9-10. A weaker inversion on another day isshown in Figure 9-11. This sounding was taken at 12UTC, which is 05 local time (LT) at that location. Thesurface temperature was 13°C at the time of thesounding. A shallow inversion is seen near the surfacewith a nearly isothermal (no temperature change)layer above. Two hours after the sounding was taken(07 LT), the surface temperature had risen to only14°C. By 09 LT, the temperature had risen to 17°C.The line labeled “09” shows how the sounding shouldlook at this time. It was drawn by taking the surfacetemperature at that time, and following the DALRuntil TI is 0, which is the same as intercepting theambient temperature. Lines at other times are drawnin a similar fashion. At 10 LT, the TI becomes 0 atabout 2,200 feet AGL, so the first thermals may bestarting. By 12 LT, at 25°C, thermals should extend to4,000 feet AGL. Because of the isothermal layer, ther-mal heights increased steadily until about 16 LT, whentemperatures reached 31°C, at which time theyreached about 8,000 feet AGL. Understanding thisevolution of the convective layer can help predictwhen thermals will first form, as well as if and whenthey might reach a height satisfactory for an extendedor cross-country flight. [Figure 9-11, on next page]

The analysis presented thus far has neglected the pos-sibility of cumulus clouds, for which the orangeslanted mixing ratio lines on the Skew-T need to beconsidered. The assumption that a rising parcel con-serves its mixing ratio is also needed. For instance, ifan air parcel has a mixing ratio of 8 g/kg at the surface,it will maintain that value as it rises in a thermal.Typically, this is true, though factors, such as mixingwith much drier air aloft can cause errors.

Refer to the sounding in Figure 9-12. The temperatureon this day reached 26°C during the afternoon. In orderto determine if cumulus clouds would be present, drawa line from 26°C at the surface parallel to a red dry adi-abat as before. Draw a second line from the surface

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dew point temperature parallel to the orange mixingratio lines. The two lines intersect at a point before theparcel has a zero TI. This is the base of the cumulus,called the convective condensation level (CCL). Inthis case, cloudbase occurs at about 750 mb (8,100feet). Since the parcel is saturated above this level, itno longer cools at the DALR, but at the SALR. Next,from the CCL, draw a line parallel to a saturated adia-bat until it intersects the original sounding temperaturecurve. This shows the maximum cumulus height, atabout 670 mb (11,000 feet). [Figure 9-12]

The above analysis leads to a rule of thumb for esti-mating the CCL. The temperature and dew pointconverge at about 4.4°F per 1,000 feet of altitudegain. This is the same as saying for every degree ofsurface temperature and dew point spread inFahrenheit, multiply by 225 feet to obtain the base ofthe convective cloud (if any). Since aviation surfacereports are reported in degrees Centigrade, convertthe data by multiplying every degree of surface tem-perature and dew point spread in degrees Centigradeby 400 feet. For example, if the reported temperature

is 28ºC and the reported dew point is 15°C, wewould estimate cloud base as (28 – 15) x 400 = 5200feet AGL.

Notice that in Figure 9-12, the dew point curve showsa rapid decrease with height from the surface value. Asthermals form and mixing begins, it is likely that thedrier air just above the surface will be mixed in withthe moister surface air. A more accurate estimate of theCCL is found by using an average dew point value inthe first 50 mb rather than the actual surface value.This refinement can change the analyzed CCL by asmuch as 1,000 feet.

The second example, Figure 9-11, would only producedry thermals, even at this day’s maximum temperatureof 32°C. Following a line parallel to a mixing ratio linefrom the surface dew point, the height of any cumuluswould be almost 12,000 feet AGL, while at 32°C, ther-mals should only reach 9,000 feet AGL. The elevatedinversion at 9,000 to 10,000 feet AGL effectively capsthermal activity there.

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Figure 9-12. Skew-T from an actual sounding.

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It is also important to recognize the limitations of asounding analysis. The sounding is a single snapshotof the atmosphere, taken at one time in one location.(This is not absolutely true since the sounding balloonrises at about 1,000 feet per minute (fpm), so it takesabout 30 minutes to reach 30,000 feet, during whichtime it has also drifted with the winds aloft from thelaunch point). The analysis is limited by how well thesounding is representative of the greater area. This mayor may not be a factor depending on the larger-scaleweather situation, and in any case, tends to be lessvalid in regions of mountainous terrain. In addition,the upper air patterns can change during the day dueto passing fronts or smaller-scale, upper-air features.For example, local circulation patterns near mountainscan alter the air aloft over nearby valleys during theday. A temperature change aloft of only a few degreesalso can make a large difference. Despite these limita-tions, the sounding analysis is still an excellent toolfor soaring pilots.

In recent years, with the advent of the Internet, sound-ings from numerical weather model forecasts havebecome available in graphical form, like the Skew-T.Thus, forecast soundings are available for a variety oflocations (far more numerous than the observationalsounding network) and at many intervals over the fore-cast cycle. The advantage of using model forecastsoundings is a dramatic increase in both space and timeresolution. For instance, maps of the predicted thermaltops can be made over a large (e.g., multi-state) areafrom model data spaced every 10 miles or closer. Greatdetail in the forecast distribution of thermals is avail-able. In addition, model output can be produced farmore frequently than every 12 hours. For instance,hourly model soundings can be produced for a loca-tion. This is a tremendous potential aide to planningboth local and cross-country flights. The disadvantageis that these forecasts are not real data. They are amodel forecast of what the real atmosphere should do.Model forecasts of critical items, such as temperaturesat the surface and aloft, are often inaccurate. Thus, themodel-forecast soundings are only as good as themodel forecast. Fortunately, models show continualimprovement, so this new tool should become moreuseful in the future.

AIR MASSES CONDUCIVE TO THERMAL SOARINGGenerally, the best air masses for thermals are thosewith cool air aloft, with conditions dry enough to allowthe sun’s heating at the surface, but not too dry socumulus form. Along the West Coast of the continentalUnited States, these conditions are usually found afterpassage of a pacific cold front. Similar conditions arefound in the eastern and mid-west United States,except the source air for the cold front is from polarcontinental regions, such as the interior of Canada. In

both cases, high pressure building into the region isfavorable, since it is usually associated with an inver-sion aloft, which keeps cumulus from growing intorain showers or thundershowers. However, as the highpressure builds after the second or third day, the inver-sion has often lowered to the point that thermal soaringis poor or no longer possible. This can lead to warmand sunny, but very stable conditions, as the soaringpilot awaits the next cold front to destabilize the atmos-phere. Fronts that arrive too close together can alsocause poor post-frontal soaring, as high clouds fromthe next front keep the surface from warming enough.Very shallow cold fronts from the northeast (with coldair only one or two thousand feet deep) often have astabilizing effect along the Plains directly east of theRocky Mountains. This is due to cool low-level airundercutting warmer air aloft advecting from the west.

In the desert southwest, the Great Basin, and inter-mountain west, good summertime thermal soaringconditions are often produced by intense heating frombelow, even in the absence of cooling aloft. This dryair mass with continental origins produces cumulusbases 10,000 feet AGL or higher. At times, this air willspread into eastern New Mexico and western Texas aswell. Later in the summer, however, some of theseregions come under the influence of the NorthAmerican Monsoon, which can lead to widespread anddaily late-morning or early afternoon thundershowers.

CLOUD STREETSCumulus clouds are often randomly distributed acrossthe sky, especially over relatively flat terrain. Underthe right conditions, however, cumulus can becomealigned in long bands, called cloud streets. These aremore or less regularly spaced bands of cumulus clouds.Individual streets can extend 50 miles or more whilean entire field of cumulus streets can extend hundredsof miles. The spacing between streets is typically threetimes the height of the clouds. Cloud streets are alignedparallel to the wind direction, thus they are ideal for adownwind cross-country flight. Glider pilots can oftenfly many miles with little or no circling, sometimesachieving glide ratios far exceeding the still-air value.

Cloud streets usually occur over land with cold-air out-breaks, for instance, following a cold front. Brisk sur-face winds and a wind direction remaining nearlyconstant up to cloud base are favorable cloud streetconditions. Wind speed should increase by 10 to 20knots between the surface and cloud base, with a max-imum somewhere in the middle of or near the top ofthe convective layer. Thermals should be capped by anotable inversion or stable layer.

A vertical slice through an idealized cloud street illus-trates a distinct circulation, with updrafts under the

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clouds and downdrafts in between. Due to the circula-tion, sink between streets may be stronger than typicallyfound away from cumulus. [Figure 9-13]

Thermal streets, with a circulation like Figure 9-13,may exist without cumulus clouds. Without clouds asmarkers, use of such streets is more difficult. A gliderpilot flying upwind or downwind in consistent sink

should alter course crosswind to avoid inadvertentlyflying along a line of sink between thermal streets.

THERMAL WAVESFigure 9-14 shows a wave-like form for the inversioncapping the cumulus clouds. If the winds above theinversion are perpendicular to the cloud streets andincreasing at 10 kts per 5,000 feet or more, wavescalled cloud-street waves can form in the stable airabove. Though usually relatively weak, thermal wavescan produce lift of a 100 to 500 fpm and allow smoothflight along streets above the cloud base. [Figure 9-14]

So-called cumulus waves also exist. These are similarto cloud-street waves, except the cumulus clouds arenot organized in streets. Cumulus waves require a cap-ping inversion or stable layer and increasing windabove cumulus clouds. However, directional shear isnot necessary. Cumulus waves may also be short-lived, and difficult to work for any length of time. Anexception is when the cumulus is anchored to somefeature, such as a ridge line or short mountain range.

Figure 9-13. Circulation across a cloud street.

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Figure 9-14. Cloud street wave.

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In these cases, the possible influence of the ridge ormountain in creating the wave lift becomes uncertain.Further discussion of atmospheric waves appears laterin this chapter. As a final note, thermal waves can alsoform without clouds present.

THUNDERSTORMSAn unstable atmosphere can provide great conditionsfor thermal soaring. If the atmosphere is too moistand unstable, however, cumulonimbus (Cb) or thun-derclouds can form. Thunderstorms are local stormsproduced by Cb and are accompanied by lightning,thunder, rain, graupel or hail, strong winds, turbu-lence, and even tornadoes. Not all precipitating, largecumulo-form clouds are accompanied by lightning andthunder, although their presence is usually an indica-tion that conditions are ripe for full-blown thunder-storms. Forecasters sometimes use the term “deepconvection” to refer to convection that rises to highlevels, which usually means thunderstorms. Thetremendous amount of energy associated with Cbstems from the release of latent heat as condensationoccurs with the growing cloud.

Thunderstorms can occur any time of year, thoughthey are more common during the spring and summerseasons. They can occur anywhere in the continentalUnited States but are not common along the immedi-ate West Coast, where on average only about one per

year occurs. During the summer months, the desertsouthwest, extending northeastward into the RockyMountains and adjacent Great Plains, experiences anaverage of 30 to 40 thunderstorms annually.Additionally, in the southeastern United States, espe-cially Florida, between 30 and 50 thunderstormsoccur in an average year. Thunderstorms in the coolseasons usually occur in conjunction with some forc-ing mechanism, such as a fast moving cold front or astrong upper-level trough. [Figure 9-15]

The lifecycle of an air-mass or ordinary thunderstormconsists of three main stages: cumulus, mature, anddissipating. We will use the term “ordinary” todescribe this type of thunderstorm consisting of a sin-gle Cb, since other types of thunderstorms (describedbelow) can occur in a uniform large-scale air mass.The entire lifecycle takes on the order of an hour,though remnant cloud from the dissipated Cb can lastsubstantially longer.

The cumulus stage is characterized by a cumulusgrowing to a towering cumulus (Tcu), or cumuluscongestus. During this stage, most of the air within thecloud is going up. The size of the updraft increases,while the cloud base broadens to a few miles in diam-eter. Since the cloud has increased in size, the strongupdraft in the middle of the cloud is not susceptible toentrainment of dryer air from the outside. Often, other

Figure 9-15.Thunderstorm frequency in the summertime.

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smaller cumulus in the vicinity of the Tcu are sup-pressed by general downward motion around the cloud.Towards the end of the cumulus stage, downdrafts andprecipitation begin to form within the cloud. On somedays, small cumulus can be around for hours, beforeTcu form, while on other days, the air is so unstablethat almost as soon as any cumulus form, they becomeTcu. [Figure 9-16]

As the evolution of the thunderstorm continues, itreaches its mature stage. By this time, downdrafts reachthe ground and spread out in what are known as down-bursts or microbursts. These often lead to strong andsometimes damaging surface winds. Lightning andthunder form along with precipitation (rain, graupel, orhail) below cloud base, which has now increased toseveral miles in diameter. It may become difficult todiscern cloud from precipitation after this stage. Thecloud top reaches to the tropopause, or nearly so, andsometimes strong cells even extend into the strato-sphere. The cloud top forms a cirrus anvil indicatingthe mature stage. The direction in which the anvilstreams provides an estimate of the direction of thun-derstorm movement. Often organized circulations formwithin the Cb and the longevity of the thunderstormpartly depends on the nature of those circulations. Thegreatest storm intensity and hazards (discussed below)are attained during the mature stage.

The precipitation and downdrafts in an ordinary thun-derstorm are eventually responsible for its demise, asthe supply of heat and moisture is cut off, leading to thedissipating stage. As the Cb dissipates, the mid-levelcloud becomes more stratiform (spread out). Remnantcloud can linger for some time after the storm begins todissipate, especially the upper-level cirrus anvil, whichconsists mostly of ice. In hazy conditions, or with Cbimbedded in widespread cloudiness, judging the stageof the Cb lifecycle can be difficult.

Thunderstorms frequently last longer than an hour. Asan ordinary thunderstorm reaches its mature stage,cool and sometimes quite strong surface outflows arecreated by Cb downdrafts reaching the ground andspreading out. The outflows can act as a focus for lift-ing warm, moist air that may still be ahead of theadvancing storm. New cells form in the direction ofstorm movement, for instance, a Cb moving eastwardwill generate new storms on the east side. The new cellundergoes a mature and dissipating stage as it pro-gresses towards the back of what has become a clusterof Cb. This is an example of a multi-cell thunder-storm, which, depending on the vertical shear of thewind, will continue to regenerate new cells as long asunstable air exists ahead of the moving storm. Multi-cell thunderstorms can last for several hours and travel100 miles or more. As usual when dealing withweather phenomena, there is no clear distinctionbetween an ordinary and multi-cell thunderstorm. Forinstance, a thunderstorm may last one to two hoursafter having undergone regeneration two or threetimes. Pilots need to closely watch apparently dissi-pating thunderstorms for new dark, firm bases thatindicate a new cell forming. In addition, outflow fromone Cb may flow several miles before encountering anarea where the air is primed for lifting given an extraboost. The relatively cool air in the outflow can pro-vide that boost, leading to new a Cb, which is nearby,but not connected to the original Cb. [Figure 9-17]

Another type of thunderstorm is the supercell. Thesehuge and long-lasting storms are usually associatedwith severe weather: strong surface winds exceeding50 knots, hail at least 3/4 inch in diameter, and/or tor-nadoes. Supercells can occur anywhere in the UnitedStates, but are most common in the southern GreatPlains. They differ from ordinary thunderstorms intwo ways. First supercells are much larger in size.Second, they form in an unstable environment with

A B C

Figure 9-16. Lifecycle of an ordinary thunderstorm (A) cumulus stage, (B) mature stage, (C) dissipating stage.

9-15

large vertical direction and speed shear, which causesthe updraft to be tilted or even twisted so that is locatedaway from the main downdraft. This leads to an organ-ized circulation within the storm, hence the longevityof a supercell. These dangerous storms should beavoided. [Figure 9-18]

Thunderstorms sometimes exist in clusters, known tometeorologists as Mesoscale Convective Systems(MCS). Most commonly, MCSs form east of theRocky Mountains in the spring and summer months.Squall lines are MCSs that are organized in a line orarc, sometimes hundreds of miles long. A cold front or

upper-level trough advancing on unstable air can bethe forcing mechanism for squall-line development.Strong lift can be found ahead of advancing squall lineand some extended cross-country flights have beenmade using them. Unfortunately, they come with allthe dangers of severe thunderstorms, so their use is notrecommended. Another type of MCS has a similarname, the Mesoscale Convective Complex (MCC),which form as a cluster of storms not along any dis-tinct line or arc. When viewed from satellite, MCCsreveal a circular or elliptical shape to the cirrus anvil,which can be a few hundred miles across. Severe thun-derstorms are often embedded within the MCC.Fortunately, the huge cirrus shield tends to suppressthermals away from the thunderstorm, so soaringpilots should not have the opportunity to approach anMCS. However, since they can contain severeweather, the forecast of a possible MCS or other severethunderstorm may inspire the glider pilot to avoidleaving a glider outside overnight if other options areavailable, e.g., an enclosed trailer. Securing the trailerextra well would also be advisable.

Using the Skew-T and a morning sounding, the possi-bility of thunderstorms can be predicted. Figure 9-19illustrates a late-spring morning sounding from thesoutheast United States. The temperature and dewpoint are within about a degree below a shallow sur-face inversion, indicating the likelihood of haze andthe possibility of fog. In addition, a shallow layer

40

30

20

10

0

0 5 10 15Distance (n.m.)

Gust Front

Shelf Cloud

Cumulus

Storm MotionMature

Dissipating

Alt

itu

de

(Th

ou

san

ds

of

feet

)

Figure 9-17. Multi-cell thunderstorm.

Anvil

Cumulonimbus

Flanking Line

Wall Cloud

PrecipitationRain-Free Cloud Base

Overshooting Tops

Figure 9-18. Supercell thunderstorm. Air enters on left into the bottom of the storm and exits at top towards the reader.

9-16

where temperature and dew point coincide are alsolocated at about 12,000 feet, indicating a thin, mid-levelcloud.

As the day warms to 28°C, cumulus should form atabout 2,500 feet AGL, using the same analysis asbefore. By the time surface the temperature reaches31°C, the CCL should be around 4,000 feet AGL.Recall that once condensation occurs, the parcel fol-lows the SALR. Following parallel to the nearest satu-rated adiabat from the CCL, the parcel does notintersect the ambient temperature line again untilalmost 40,000 feet. Thunderstorms are possible if thesurface temperature reaches 31°C. [Figure 9-19]

Two common indices are routinely reported using thistype of analysis, the Lifted Index (LI) and the K-Index(KI). The LI is determined by subtracting the tempera-

ture of a parcel that has been lifted (as in Figure 9-19)to 500 mb from the temperature of the ambient air.This index does not give the likelihood of occurrence;rather it gives an indication of thunderstorm severity ifthey occur. In the example above, LI would be givenby –9 – (-4) = -5. Looking at Figure 9-20, a LI of –5indicates moderately severe thunderstorms if theydevelop. [Figure 9-20]

The KI is used to determine the probability of thunder-storm occurrence and uses information about tempera-ture and moisture at three levels. It is given by theequation KI = (T850 – T500) + Td850 – (T700-Td700). Here, T stands for temperature, Td is the dewpoint, and 500, 700, or 850 indicate the level in mb.All values are obtained from a morning sounding. Inthe above example, using values from the sounding KI= (16 –[-9]) + 12 – (6 –0) = 31. This indicates about a

4 1 2 3 5 8

12 16 20

300

400

500

600

700

800

900

1000

-10

-10

-20

-20

2020

-30

-30

3030

01010

5 10 14 18 22 26 30

18300

23600

30100

38700

360

3200

6400

9900

13800

Figure 9-19. Skew-T from an actual sounding for a thunderstorm day.

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60 percent probability that thunderstorms will occur.[Figure 9-21] As discussed below, charts showing boththe LI and KI for all the sounding sites in the continen-tal United States are produced daily.

Thunderstorms have several hazards, including turbu-lence, strong up and down drafts, strong shifting sur-face winds, hail, icing, poor visibility and/or lowceilings, lightning, and even tornadoes. Once a cloudhas grown to be a Cb, hazards are possible, whether ornot there are obvious signs. Since thermal soaringweather can rapidly deteriorate into thunderstormweather, recognition of each hazard is important.Knowledge of the many hazards may inspire the pilotto land and secure the glider when early signs of thun-derstorm activity appear—the safest solution.

Moderate turbulence is common within several milesof a thunderstorm and it should be expected. Severe oreven extreme turbulence (leading to possible structuralfailure) can occur anywhere within the thunderstorm

itself. The inside of a thunderstorm is no place forglider pilots of any experience level. Outside of thestorm, severe turbulence is common. One region ofexpected turbulence is near the surface gust front ascool outflow spreads from the storm. Violent updraftscan be followed a second or two later by violentdowndrafts, with occasional side gusts adding to theexcitement–not a pleasant proposition while in thelanding pattern. At somewhat higher altitudes, butbelow the base of the Cb, moderate to severe turbu-lence can also be found along the boundary betweenthe cool outflow and warm air feeding the Cb.Unpredictable smaller-scale turbulent gusts can occuranywhere near a thunderstorm, so recognizing andavoiding the gust front does not mean safety fromsevere turbulence.

Large and strong up and downdrafts accompany thun-derstorms in the mature stage. Updrafts under the Cbbase feeding into the cloud can easily exceed 1,000fpm. Near the cloud base, the distance to the edge ofthe cloud can be deceptive; trying to avoid beinginhaled into the cloud by strong updrafts can be diffi-cult. In the later cumulus and early mature stage,updrafts feeding the cloud can cover many squaremiles. As the storm enters its mature stage, strongdowndrafts, called downbursts or microbursts, can beencountered, even without very heavy precipitationpresent. Downbursts can also cover many square mileswith descending air of 2,000 fpm or more. A pilotunlucky enough to fly under a forming downburst,which may not be visible, could encounter sink of2,000 or 3,000 fpm, possibly more in extreme cases. Ifsuch a downburst is encountered at pattern altitude, itcan cut the normal time available to the pilot for plan-ning the approach. For instance, a normal three-minutepattern from 800 feet AGL to the ground happens in amere 19 seconds in 2,500 fpm sink!

When a downburst or microburst hits the ground, thedowndraft spreads out leading to strong surface winds,that is, thunderstorm outflow referred to earlier.Typically, the winds strike quickly and give little warn-ing of their approach. While soaring, pilots shouldkeep a sharp lookout between the storm and theintended landing spot for signs of a wind shift.Blowing dust, smoke, or wind streaks on a lake indi-cating wind from the storm are clues that a gust front israpidly approaching. Thunderstorm outflow winds areusually 20 to 40 knots for a period of 5 to 10 minutesbefore diminishing. However, winds can easily exceed60 knots, and in some cases, with a slow-moving thun-derstorm, strong winds can last substantially longer.Although damaging outflow winds usually do notextend more than 5 or 10 miles from the Cb, winds of20 or 30 knots can extend 50 miles or more from largethunderstorms.

0 to -2

-3 to -5

< = -6

Weak

Moderate

Strong

Lifted Index Chance of SevereThunderstorm

Figure 9-20. Lifted Index (LI) vs. thunderstorm severity.

near 0

15

15

to 20 20

21 to 25 20 to 40

26 to 30 40 to 60

31 to 35 60 to 80

36 to 40 80 to 90

>40 near 100

K Index ThunderstormProbability (%)

<

Figure 9-21. K-Index (KI) vs. probability of thunderstormoccurrence.

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Hail is possible with any thunderstorm and can exist aspart of the main rain shaft. Hail can also occur manymiles from the main rain shaft, especially under thethunderstorm anvil. Pea-sized hail usually will notdamage a glider, but hail with a severe storm (3/4 inchdiameter or larger) can dent metal gliders or damagethe gelcoat on composite gliders, whether on theground or in the air.

Icing is generally only a problem within a cloud, espe-cially at levels where the outside temperature is around–10°C. Under these conditions, super-cooled waterdroplets (that is, water droplets existing in a liquid stateat below 0°C) can rapidly freeze onto wings and othersurfaces. At the beginning of the mature stage, earlyprecipitation below cloud base may be difficult to see.At times, precipitation can even be falling through anupdraft feeding the cloud. Snow, graupel, or ice pelletsfalling from the forming storm above can stick to theleading edge of the wing, causing degradation in per-formance. Rain on the wings can be a problem sincesome airfoils can be adversely affected by water.

Poor visibility due to precipitation and possible lowceilings as the air below the thunderstorm is cooled isyet another concern. Even light or moderate precipita-tion can reduce visibility dramatically. Often, under aprecipitating Cb, there is no distinction between pre-cipitation and actual cloud.

Lightning in a thunderstorm occurs in-cloud, cloud-to-cloud (in the case of other nearby storms, such as amulticell storm), or cloud-to-ground. Lightning strikesare completely unpredictable, and cloud-to-groundstrikes are not limited to areas below the cloud. Somestrikes emanate from the side of the Cb and travel hor-izontally for miles before turning abruptly towards theground. In-flight damage to gliders has included burntcontrol cables and blown off canopies. In some cases,strikes have caused little more than mild shock andcosmetic damage. On the other extreme, a compositetraining glider in Great Britain suffered a strike thatcaused complete destruction of one wing; fortunately,both pilots parachuted to safety. In that case, the gliderwas two or three miles from the thunderstorm. Finally,ground launching, especially with a metal cable, any-where near a thunderstorm should be avoided.

Severe thunderstorms can sometimes spawn tornadoes,which are rapidly spinning vortices, generally a fewhundred to a few thousand feet across. Winds canexceed 200 mph. Tornadoes that do not reach theground are called funnel clouds. By definition, torna-does form from severe thunderstorms. Obviously, theyshould be avoided on the ground or in the air.

WEATHER FOR SLOPE SOARING Slope or ridge soaring refers to using updrafts pro-duced by the mechanical lifting of air as it encountersthe upwind slope of a hill, ridge, or mountain. Slopesoaring requires two ingredients: elevated terrain andwind.

Slope lift is the easiest lift source to visualize. When itencounters topography, wind is deflected either hori-zontally, vertically, or in some combination of the two.Not all topography produces good slope lift.Individual or isolated hills do not produce slope liftbecause the wind tends to deflect around the hill,rather than over it. A somewhat broader hill with awindward face at least a mile or so long, might pro-duce some slope lift, but the lift will be confined to asmall area. The best ridges for slope soaring are at leasta few miles long.

Slope lift can extend to a maximum of two or threetimes the ridge height. However, the pilot may only beable to climb to ridge height. As a general rule, thehigher the ridge above the adjacent valley, the higherthe glider pilot can climb. Ridges only one or two hun-dred feet high can produce slope lift. The problem withvery low ridges is maintaining safe maneuvering alti-tude, as well as sufficient altitude to land safely in theadjacent valley. Practically speaking, 500 to 1,000 feetabove the adjacent valley is a minimum ridge height.[Figure 9-22]

In addition to a ridge being long and high enough, thewindward slope needs to be steep enough as well. Anideal slope is on the order of 1 to 4. Shallower slopesdo not create a vertical wind component strong enoughto compensate for the glider’s sink rate. Very steep,almost vertical slopes, on the other hand, may not be

Best Lift

Lift Zone

Figure 9-22. Slope soaring.

9-19

ideal either. Such slopes create slope lift, but can pro-duce turbulent eddies along the lower slope or any-where close to the ridge itself. In such cases, only theupper part of the slope may produce updrafts, althoughsteeper slopes do allow a quick escape to the adjacentvalley. [Figure 9-23]

A ridge upstream can block the wind flow, so that nolow-level flow occurs upwind of an otherwise prom-ising ridge, and hence no updraft. Additionally, iflee waves are produced by an upstream ridge ormountain, slope lift can be enhanced or destroyed,depending on the wavelength of the lee waves.Locally, the downdraft from a thermal just upwindof the ridge can cancel the slope lift for a short dis-tance. The bottom line: never assume slope lift ispresent. Always have an alternative.

Just as the flow is deflected upward on the windwardside of a ridge, it is deflected downward on the lee sideof a ridge.[Figure 9-24] This downdraft can be alarm-ingly strong—up to 2,000 fpm or more near a steepridge with strong winds (A). Even in moderate winds,the downdraft near a ridge can be strong enough tomake penetration of the upwind side of the ridgeimpossible. Flat-topped ridges also offer little refuge,since sink and turbulence can combine to make anupwind penetration impossible (B). Finally, an unevenupwind slope, with ledges or “steps,” require extracaution since small-scale eddies along with turbulenceand sink can form there (C).

Three-dimensional effects are important as well. Forinstance, a ridge with cusps or bowls may produce better

lift in upwind-facing bowls if the wind is at an anglefrom the ridge. However, sink may be encountered onthe lee side of the bowl. If crossing ridges in windyconditions, always plan for heavy sink on the lee sideand make sure an alternative is available. [Figure 9-25]

Depending on the slope, wind speed should be 10-15knots and blowing nearly perpendicular to the ridge.Wind directions up to 30° or 40° from perpendicularmay still produce slope lift. Vertical wind shear is alsoa consideration. High ridges may have little or no windalong the lower slopes, but the upper parts of the ridgemay be in winds strong enough to produce slope liftthere.

Eddy

Lift Zone

Figure 9-23. Slope lift and eddy with near-vertical slope.

A

B

C

Figure 9-24. Airflow along different ridges.

The area of best lift varies with height. Below the ridgecrest, the best slope lift is found within a few hundredfeet next to the ridge, again depending on the slope andwind strength. As mentioned, very steep ridges requireextra speed and caution, since eddies and turbulencecan form even on the upwind side. Above the ridgecrest, the best lift usually is found further upwind fromthe ridge the higher one climbs. [Figure 9-22]

When the air is very stable, and the winds are suffi-cient but not too strong, slope lift can be very smooth,enabling safe soaring close to the terrain. If the air isnot stable, thermals may flow up the slope. Dependingon thermal strength and wind speed, the thermal mayrise well above the ridge top, or it may drift into the leedowndraft and break apart. Downdrafts on the sides ofthermals can easily cancel the slope lift; hence, extraspeed and caution is required when the air is unstable,especially below the ridge crest near the terrain. Thecombination of unstable air and strong winds can makeslope soaring unpleasant or even dangerous for thebeginning glider pilot.

Moisture must be considered. If air rising in the slopelift is moist and cools sufficiently, a so-called cap cloudmay form. The cloud may form above the ridge, and ifthe air moistens more with time, the cloud will slowlylower onto the ridge and down the upwind slope, limit-ing the usable height of the slope lift. Since the updraftforms the cloud, it is very easy to climb into the capcloud—obviously a dangerous situation. Under certainconditions, a morning cap cloud may rise as the daywarms, then slowly lower again as the day cools.

WAVE SOARING WEATHERWhere there is wind and stable air, there is the likeli-hood of waves in the atmosphere. Most of the wavesthat occur throughout the atmosphere are of no use tothe glider pilot. However, often mountains or ridgesproduce waves downstream, the most powerful ofwhich have lifted gliders to 49,000 feet. Indirect meas-urements show waves extending to heights around

100,000 feet. If the winds aloft are strong and wide-spread enough, mountain lee waves can extend thelength of the mountain range. Pilots have achievedflights in mountain wave using three turn points ofover 2,000 km. Another type of wave useful to soaringpilots is generated by thermals, which were discussedin the previous section.

A common analogy to help visualize waves created bymountains or ridges uses water flowing in a stream orsmall river. A submerged rock will cause ripples(waves) in the water downstream, which slowlydampen out. This analogy is useful, but it is importantto realize that the atmosphere is far more complex,with vertical shear of the wind and vertical variationsin the stability profile. Wind blowing over a mountainwill not always produce downstream waves.

Mountain wave lift is fundamentally different fromslope lift. Slope soaring occurs on the upwind side of aridge or mountain, while mountain wave soaringoccurs on the downwind side. (Mountain wave liftsometimes tilts upwind with height. Therefore, attimes near the top of the wave, the glider pilot may bealmost directly over the mountain or ridge that hasproduced the wave). The entire mountain wave systemis also more complex than the comparatively simpleslope soaring scenario.

MECHANISM FOR WAVE FORMATIONWaves form in stable air when a parcel is verticallydisplaced and then oscillates up and down as it tries toreturn to its original level, illustrated in Figure 9-26. Inthe first frame, the dry parcel is at rest at its equilib-rium level. In the second frame, the parcel is displacedupward along a DALR, at which point it is cooler thanthe surrounding air. The parcel accelerates downwardtoward its equilibrium level, but due to momentum, itovershoots the level and keeps going down. The thirdframe shows that the parcel is now warmer than thesurrounding air, and thus starts upward again. Theprocess continues with the motion damping out. Thenumber of oscillations depends on the initial parceldisplacement and the stability of the air. In the lowerpart of the figure, wind has been added, illustrating thewave pattern that the parcel makes as it oscillates ver-tically. If there were no wind, a vertically displacedparcel would just oscillate up and down, while slowlydamping, at one spot over the ground, much like aspring. [Figure 9-26]

The lower part of Figure 9-26 also illustrates twoimportant features of any wave. The wavelength is thehorizontal distance between two adjacent wave crests.Typical mountain wavelengths vary considerably,between 2 and 20 miles. The amplitude is half the ver-tical distance between the trough and crest of thewave. Amplitude varies with altitude and is smallest

Figure 9-25. Three-dimensional effects of oblique winds andbowls.

9-20

9-21

near the surface and at upper levels. As a note, moun-tain lee waves are sometimes simply referred to asmountain waves, lee waves, and sometimes, standingwaves.

In the case of mountain waves, it is the airflow over themountain that displaces a parcel from its equilibriumlevel. This leads to a two-dimensional conceptualmodel, which is derived from the experience of manyglider pilots along with post-flight analysis of theweather conditions. Figure 9-27 illustrates a mountainwith wind and temperature profiles. Note the increase

in wind speed (blowing from left to right) with altitudeand a stable layer near mountaintop with less stable airabove and below. As the air flows over the mountain, itdescends the lee slope (below its equilibrium level ifthe air is stable) and sets up a series of oscillationsdownstream. The wave flow itself is usually incrediblysmooth. Beneath the smooth wave flow is what isknown as a low-level turbulent zone, with an imbed-ded rotor circulation under each crest. Turbulence,especially within the individual rotors is usually mod-erate to severe, and on occasion can become extreme.[Figure 9-27]

Equilibrium

DALR

T

ParcelMotion

Hei

gh

t (T

ho

usa

nd

s o

f F

eet)

Temperature

Temperature

30

25

20

15

10

5

Wind

Win

d

StableLayer

Tropopause

CCSL

ACSL Lee Wave Region

Lower Turbulent Zone

Roll Cloud

Main Downdraft Main Update Horizontal Distance

Cap Cloud

Figure 9-26. Parcel displaced vertically and oscillating around its equilibrium level.

Figure 9-27. Mountain lee wave system.

9-22

This conceptual model is often quite useful and repre-sentative of real mountain waves, but many exceptionsexist. For instance, variations to the conceptual modeloccur when the topography has many complex, three-dimensional features, such as individual higher peak,large ridges or spurs at right angles to the main range.Variations can occur when a north-south range curvingto become oriented northeast-southwest. In addition,numerous variations of the wind and stability profilesare possible.

Turbulence associated with lee waves deserves respect.Low-level turbulence can range from unpleasant toodangerous. Glider pilots refer to any turbulence underthe smooth wave flow above as “rotor”. The nature ofrotor turbulence varies from location to location as wellas with different weather regimes. At times, rotor tur-bulence is widespread and fairly uniform, that is, it isequally rough everywhere below the smooth waveflow. At other times, uniformly moderate turbulence isfound, with severe turbulence under wave crests. Onoccasion, no discernable turbulence is noted except formoderate or severe turbulence within a small-scalerotor under the wave crest. Typically, the worst turbu-lence is found on the leading edge of the primary rotor.Unfortunately, the type and intensity of rotor turbu-lence is difficult to predict. However, the general ruleof thumb is that higher amplitude lee waves tend tohave stronger rotor turbulence.

Clouds associated with the mountain wave system arealso indicated in Figure 9-27. A cap cloud flowing overthe mountain tends to dissipate as the air forced downthe mountain slope warms and dries. The first (or pri-mary) wave crest features a roll or rotor cloud with oneor more lenticulars (or lennies using glider terminol-ogy) above. Wave harmonics further downstream (sec-ondary, tertiary, etc.) may also have lennies and/or rotorclouds. If the wave reaches high enough altitudes,lennies may form at cirrus levels as well. It is importantto note that the presence of clouds depends on theamount of moisture at various levels. The entire moun-tain wave system can form in completely dry condi-tions with no clouds at all. If only lower level moistureexists, only a cap cloud and rotor clouds may be seenwith no lennies above as in Figure 9-28(A). On otherdays, only mid-level or upper-level lennies are seenwith no rotor clouds beneath them. When low and midlevels are very moist, a deep rotor cloud may form,with lennies right on top of the rotor cloud, with noclear air between the two cloud forms. In wet climates,the somewhat more moist air can advect in, such thatthe gap between the cap cloud and primary rotor closescompletely, stranding the glider on top of the clouds(B). Caution is required when soaring above clouds invery moist conditions.

Suitable terrain is required for mountain wave soaring.Even relatively low ridges of 1,000 feet or less verticalrelief can produce lee waves. Wave amplitude dependspartly on topography shape and size. The shape ofthe lee slope, rather than the upwind slope is impor-tant. Very shallow lee slopes are not conducive toproducing waves of sufficient amplitude to support aglider. A resonance exists between the topographywidth and lee wavelength that is difficult to predict.One particular mountain height, width, and lee slopeis not optimum under all weather conditions.Different wind and stability profiles favor differenttopography profiles. Hence, there is no substitute forexperience at a particular soaring site when predict-ing wave-soaring conditions. Uniform height of themountaintops along the range is also conducive tobetter-organized waves.

The weather requirements for wave soaring includesufficient wind and a proper stability profile. Windspeed should be at least 15 to 20 knots at mountaintoplevel with increasing winds above. The wind directionshould be within about 30° of perpendicular to theridge or mountain range. The requirement of a stablelayer near mountaintop level is more qualitative. Asounding showing a DALR, or nearly so, near themountaintop would not likely produce lee waves evenwith adequate winds. A well-defined inversion at ornear the mountaintop with less stable air above is best.

Weaker lee waves can form without much increase inwind speed with height, but an actual decrease in windspeed with height usually caps the wave at that level.When winds decrease dramatically with height, forinstance, from 30 to 10 knots over two or three thou-sand feet, turbulence is common at the top of the wave.On some occasions, the flow at mountain level may besufficient for wave, but then begins to decrease withaltitude just above the mountain, leading to a phenom-enon called “rotor streaming.” In this case, the air

A

B

Figure 9-28. Small Foehn Gap under most conditions.

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downstream of the mountain breaks up and becomesturbulent, similar to rotor, with no lee waves above.

Lee waves experience diurnal effects, especially inthe spring, summer, and fall. Height of the topographyalso influences diurnal effects. For smaller topography,as morning leads to afternoon, and the air becomesunstable to heights exceeding the wave-producingtopography, lee waves tend to disappear. On occasion,the lee wave still exists but more height is needed toreach the smooth wave lift. Toward evening as ther-mals again die down and the air stabilizes, lee wavesmay again form. During the cooler season, when theair remains stable all day, lee waves are often presentall day, as long as the winds aloft continue. The day-time dissipation of lee waves is not as notable for largemountains. For instance, during the 1950s Sierra WaveProject, it was found that the wave amplitude reacheda maximum in mid- to late afternoon, when convectiveheating was a maximum. Rotor turbulence alsoincreased dramatically at that time.

Topography upwind of the wave-producing range canalso create problems, as illustrated in Figure 9-29. Inthe first case (A), referred to as destructive interfer-ence, the wavelength of the wave from the first rangeis out of phase with the distance between the ranges.Lee waves do not form downwind of the second rangedespite winds and stability aloft being favorable. In thesecond case (B), referred to as constructive interfer-ence, the ranges are in phase, and the lee wave fromthe second range has a larger amplitude than it mightotherwise.

Isolated small hills or conical mountains do not form“classic” lee waves. In some cases, they do form wavesemanating at angle to the wind flow similar to waterwaves created by the wake of a ship. A single peak mayonly require a mile or two in the dimension perpendi-cular to the wind for high-amplitude lee waves to form,

though the wave lift will be confined to a relativelysmall area in these cases.

LIFT DUE TO CONVERGENCE Convergence lift is most easily imagined as easterlyand westerly winds meet. When the air advected by thetwo opposing winds meet, it must go up. Air does notneed to meet “head on” to go up, however. Whereverair piles up, it leads to convergence and rising air.[Figure 9-30]

Examples of converging air leading to rising air havealready been discussed though not specifically referredto as convergence. In Figure 9-17, convergence alongthe outflow leads to air rising into the multi-cell thun-derstorm. In Figure 9-13, the circulation associatedwith cloud streets leads to convergence under thecumulus. A synoptic-scale example of convergence isfound along cold fronts. Convergence can occur alongdistinct, narrow lines (convergence or shear lines), asin Figure 9-30 (A), or can cause lifting over an areaseveral miles across (convergence zones), as in Figure9-30 (B). At times convergence lines produce steadylift along a line many miles long, while at other timesthey simply act as a focus for better and more frequentthermals.

One type of convergence line commonly found nearcoastal areas is the so-called sea-breeze front. Inlandareas heat during the day, while the adjacent sea main-tains about the same temperature. Inland heating leadsto lower pressure, drawing in cooler sea air. As thecooler air moves inland, it behaves like a miniatureshallow cold front, and lift forms along a convergenceline. Sometimes consistent lift can be found along thesea-breeze front while at other times it acts as a triggerfor a line of thermals. If the inland air is quite unstable,

Wavelength

WavelengthA

B

Figure 9-29. Constructive and destructive interference.

Figure 9-30. Convergence examples. (A) Wind from differentdirections. (B) Wind slows and “piles up.”

A

B

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the sea-breeze front can act as a focus for a line of thun-derstorms. Additionally, since the air on the coast sideof the sea-breeze front is rather cool, passage of thefront can spell the end of thermal soaring for the day.

Sea air often has a higher dew point than drier inlandair. As shown in Figure 9-31, a “curtain” cloud some-times forms, marking the area of strongest lift. Due tothe mixing of different air along the sea-breeze front, attimes the lift can be quite turbulent. At other times,weak and fairly smooth lift is found.

Several factors influence the sea-breeze front character(e.g., turbulence, strength, and speed of inland penetra-tion, including the degree of inland heating and theland/sea temperature difference). For instance, if theland/sea temperature difference at sunrise is small andovercast cirrus clouds prevent much heating; only aweak sea-breeze front, if any, will form. Another factoris the synoptic wind flow. A weak synoptic onshoreflow may cause quicker inland penetration of the sea-breeze front, while a strong onshore flow may preventthe sea-breeze front from developing at all. On theother hand, moderate offshore flow will generally pre-vent any inland penetration of the sea-breeze front.

Other sources of convergence include thunderstormoutflow boundaries already mentioned. Since this typeof convergence occurs in an overall unstable environ-ment, it can quickly lead to new thunderstorms. Moresubtle convergence areas form the day after ordinarythunderstorms have formed. If an area has recentlybeen subject to spotty heavy rains, wet areas will warmmore slowly than adjacent dry areas. The temperaturecontrast can give rise to a local convergence line, whichacts similar to a sea-breeze front, and may be markedby a line of cumulus.

Convergence can also occur along and around moun-tains or ridges. In Figure 9-32(A), flow is deflectedaround a ridgeline and meets as a convergence line onthe lee side of the ridge. The line may be marked bycumulus or a boundary with a sharp visibility contrast.The latter occurs if the air coming around one end ofthe ridge flows past a polluted urban area such as inthe Lake Elsinore soaring area in southern California.In very complex terrain, with ridges or ranges orientedat different angles to one another, or with passesbetween high peaks, small-scale convergence zonescan be found in adjacent valleys depending on windstrength and direction. Figure 9-32(B) illustrates asmaller-scale convergence line flowing around a sin-gle hill or peak and forming a line of lift stretchingdownwind from the peak.

Convergence also can form along the top of a ridgelineor mountain range. In Figure 9-33, drier synoptic-scalewinds flow up the left side of the mountain, while amore moist valley breeze flows up the right side of theslope. The two flows meet at the mountain top andform lift along the entire range. If cloud is present, theair from the moist side condenses first often formingone cloud with a well-defined “step,” marking theconvergence zone.

As a final example, toward evening in mountainousterrain as heating daytime abates, a cool katabatic ordrainage wind flows down the slopes. The flow downthe slope converges with air in the adjacent valley toform an area of weak lift. Sometimes the convergenceis not strong enough for general lifting, but acts as atrigger for the last thermal of the day. In narrow val-leys, flow down the slope from both sides of the valleycan converge and cause weak lift. [Figure 9-34]

Figure 9-31. Sea-breeze front.

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Many local sites in either flat or mountainous terrainhave lines or zones of lift that are likely caused orenhanced by convergence. Chapter 10–SoaringTechniques covers locating and using convergence.

OBTAINING WEATHER INFORMATIONOne of the most important aspects of flight planning isobtaining reliable weather information. Fortunately,

pilots have several outlets to receive reliable weatherreports and forecasts to help them determine if a pro-posed flight can be completed safely. For VFR flights,federal regulations only require pilots to gatherweather reports and forecasts if they plan to depart theairport vicinity. Nevertheless, it is always a good ideato be familiar with the current and expected weatheranytime a flight is planned. Preflight weather informa-tion sources include Automated Flight Service Stations(AFSS) and National Weather Service (NWS) tele-phone briefers, the Direct User Access TerminalSystem (DUATS), and the Internet. In addition, a mul-titude of commercial venders provide custom services.

The following pages give a comprehensive synopsis ofavailable weather services and products. For completedetails, refer to the current version of AC 00-45,Aviation Weather Services.

AUTOMATED FLIGHT SERVICE STATIONSAutomated flight service stations (AFSS) are a primarysource of preflight weather information. A briefing canbe obtained from an AFSS, 24 hours a day by callingthe toll free number, 1-800-WX BRIEF. The NationalWeather Service may also provide pilot weatherbriefings. Telephone numbers for NWS facilities andadditional numbers for AFSSs can be found in theAirport/Facility Directory (A/FD) or the U.S.Government section of the telephone directory underDepartment of Transportation, Federal AviationAdministration, or Department of Commerce,National Weather Service.

PREFLIGHT WEATHER BRIEFINGTo obtain a briefing, certain background informationmust be supplied to the weather specialist: type offlight planned (VFR or IFR), aircraft number or pilot’sname, aircraft type, departure airport, route of flight,destination, flight altitude(s), estimated time of depar-ture (ETD), and estimated time enroute (ETE). Atmany gliderports the operator or dispatcher will obtainthe weather reports and forecasts from the AFSS orNWS at various times throughout the day and postthem on a bulletin board for easy reference.

A

B

nce LinenenConveverererge

Convergence Lineveergengeerge

Figure 9-32. Convergence induced by flow around topography.

Figure 9-33. Mountain-top convergence.

Slow Lift

Figure 9-34. Convergence induced by flow around topography.

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Weather briefers do not actually predict the weather,they simply translate and interpret weather reports andforecasts within the vicinity of the airport, route offlight, or the destination airport, if the flight is a cross-country. A pilot may request one of three types of brief-ings standard, abbreviated, or outlook.

A standard briefing is the most complete weather brief-ing and should be requested when a preliminary brief-ing has not been obtained or when the proposed flightis a cross-country. When a standard briefing isrequested the following information will be providedby the briefer.

ADVERSE CONDITIONS—This includes the type ofinformation that might influence the go, no-godecision.

VFR FLIGHT RECOMMENDATION—If the weatherspecialist indicates that VFR flight is not recom-mended, it means that, in the briefer’s judgment,it is doubtful that the flight can be conductedunder VFR conditions. Although, the final go, no-go decision, does rest with the pilot.

SYNOPSIS—This is a broad overview of the majorweather systems or airmasses that will affect theflight.

CURRENT CONDITIONS—This information is arundown of existing conditions including perti-nent hourly, pilot, and radar weather reports. It isnormally omitted when the departure time ismore than 2 hours in the future.

ENROUTE FORECAST—This information summa-rizes the forecast conditions along the route offlight for cross-country flights and is omitted forlocal flights.

DESTINATION FORECAST—For cross-countryflights, the briefer will provide the forecast forthe destination airport for 1 hour before and afterthe estimated time of arrival (ETA).

WINDS AND TEMPERATURES ALOFT—This canbe of particular interest to soaring pilots. This issummary of the winds along a route of flight. Atthe pilots request, the weather briefer can inter-polate wind direction and speed between levelsand reporting stations for various altitudes.Temperature is also provided only on request.

NOTICES TO AIRMEN—The briefer will supplynotices to airman (NOTAM) information perti-nent to the proposed flight. However, information,

which has already been published in theNOTAM publication, is only provided onrequest.

AIR TRAFFIC CONROL DELAYS—This informa-tion advises of any known Air Traffic Control(ATC) delays. Soaring pilots don’t normallyneed this information, unless they are flying aself-launch glider and the flight will terminate atan airport with a control tower.

OTHER INFORMATION—Upon request the briefercan provide other information, such as densityaltitude data, military operations areas (MOA),military training routes (MTR) within 100 nauti-cal miles of the fight plan area.

An abbreviated briefing is used to update weatherinformation from a previous briefing or when request-ing specific information. This allows the briefer tolimit the search for weather data to that informationthat has changed or can have a significant impact onthe proposed flight. The briefer will automaticallyinclude adverse weather conditions, both present orforecast.

For a flight with a departure time of 6 or more hoursaway, an outlook briefing should be requested. Thisbriefing provides forecast information appropriate tothe proposed flight in order to help make a go no-godecision. An outlook briefing is designed for planningpurposes only and a standard briefing should berequested just before the departure time to acquire cur-rent conditions and the latest forecasts.

DIRECT USER ACCESS TERMINAL SYSTEMThe FAA-funded direct user access terminal system(DUATS), allows pilots with a current medical certifi-cate to receive weather briefings and file flight plansdirectly via personal computer and modem. The infor-mation on DUATS sites is presented in textual format,which requires some skill and practice to interpret.Information for the current DUATS providers can befound in the Aeronautical Information Manual (AIM).

ON THE INTERNETWeather related information can be found on theInternet including sites directed toward aviation.These sites can be found using a variety of Internetsearch engines. It is import to verify the timeliness andsource of the weather information provided by theInternet sites to ensure the information is up-to-dateand accurate. Pilots should exercise caution whenaccessing weather information on the Internet espe-cially if the information cannot be verified. One sourceof accurate weather information is the NationalWeather Service site located at: www.nws.noaa.gov.

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INTERPRETING WEATHER CHARTS,REPORTS, AND FORECASTSKnowing how and where to gather weather informa-tion is important but the ability to interpret and under-stand the information requires additional knowledgeand practice. Weather charts and reports are merelyrecords of observed atmospheric conditions at certainlocations at specific times. Trained observers usingelectronic instruments, computers, and personal obser-vations produce the weather products necessary forpilots to determine if a flight can be conducted safely.This same information can be used by soaring pilots todetermine where they can find lift and how long the liftwill be usable for soaring flight.

GRAPHIC WEATHER CHARTSReports of observed weather are graphically depictedin a number of weather products. Among them are thesurface analysis chart, weather depiction chart, radarsummary chart, and composite moisture stability chart.

SURFACE ANALYSIS CHARTA surface analysis chart is a computer-generatedgraphic that covers the 48 contiguous states and adja-cent areas, for the valid time shown on the chart. Thechart is prepared and disseminated every 3 hours byhuman observers.

A review of this chart provides a picture of the atmos-pheric pressure patterns at the earth’s surface. [Figure9-35] In addition, the chart depicts the amount of skycover, the velocity and direction of the wind, the tem-perature, humidity, dewpoint, and other importantweather data at specific locations. The observationsfrom these locations are plotted on the chart to aid inanalyzing and interpreting the surface weather fea-tures. [Figure 9-36, on next page.]

WEATHER DEPICTION CHARTThe weather depiction chart provides an overview offavorable and adverse weather conditions for the charttime and is an excellent resource to help determinegeneral weather conditions during flight planning.Information plotted on this chart is derived from avia-tion routine weather reports (METARs). Like the sur-face chart, the weather depiction chart is prepared andtransmitted by computer every 3 hours and is valid atthe time the data is plotted.

On this chart, a simplified station model is used todepict the type of weather, amount of sky cover, theheight of the cloud base or ceiling, obstructions tovision, and visibility. Unlike the station model on a sur-face analysis chart, a bracket symbol is placed to theright of the circle to indicate an observation made by

High Pressure Center

Low Pressure Center

Cold Front

Warm Front

Stationary Front

Occluded Front

Squall Line

Trough

Ridge

SYMBOL DESCRIPTION

Figure 9-35. Surface Analysis Chart.

9-28

an automated system only. [Figure 9-37] The observedceiling and visibility for a general area is shown forIFR, MVFR, and VFR.

IFR—Ceilings less than 1,00 feet and/or visibility lessthan 3 miles are depicted in the hatched area out-lined by a smooth line.

MVFR (Marginal VFR)—Ceiling 1,000 to 3,000 feetand/or visibility 3 to 5 miles is depicted in a non-hatched area outlined by a smooth line.

VFR—No ceiling or ceiling greater than 3,000 feet andvisibility greater than 5 miles are not outlined.

RADAR SUMMARY CHARTThe computer-generated radar summary chart isproduced 35 minutes past each hour and depicts a

collection of radar weather reports (SDs). Thischart displays areas and type of precipitation,intensity, coverage, echo top, and cell movement.In addition, an area of severe weather is plotted if theyare in effect when the chart is valid. [Figure 9-38]

U.S. LOW-LEVEL SIGNIFICANT WEATHERPROGNOSTICATION CHARTThe low-level significant weather prognostic chart isdivided into two forecast periods. The two panels onthe left show the weather prognosis for a 12-hourperiod and those on the right for a 24-hour period. Thevalid times and titles for each panel are shown in thelower left corner of the respective panel.

The two upper panels depict cloud cover, altitudes ofthe freezing level, and areas where turbulence can beexpected. The two lower panels depict the forecastersbest estimate of the location of frontal and pressure sys-tems, as well as the areas and types of precipitation. It

Figure 9-36. Station Model and Explanation.

Missingor Partial

Obscuration

Breaksin

Overcast

PRECIPITATIONThe precipitation over the last 6-hour period is given to the nearest hundredths of an inch. In the example, 0.45 inch of precipitation has fallen in the last 6 hours.

STATION IDENTIFIERThe station identifier is shown to the lower left of the station model. This observation is from KABI, or Abilene Regional Airport.

PRESSURE CHANGE/TENDENCYThe pressure change in tenths of millibars over the past 3 hours is shown below the sea level pressure. The tendency of pressure change is depicted using a symbol to the right of the change. In the example, pressure has increased 2.8 mb (hPa) over the past 3 hours, and is increasing more slowly or holding steady. Other symbols may be decoded using information available in various FAA publications and at flight service stations.

SEA LEVEL PRESSURESea level pressure is shown in three digits to the nearest tenth of a millibar (hPa). For 1000 mb or greater, add a 10 to the 3 digits. For less than 1000 mb, add a 9 to the 3 digits. In this example, the sea level pressure is 1014.7 mb (hPa).

PRESENT WEATHEROver 100 symbols are available to depict the present weather. Decoding information for these symbols is available in various FAA publications and at flight service stations. In this example, continuous snowfall is occurring.

DEWPOINTDewpoint is shown in degrees Fahrenheit. In the example, the dewpoint is 32°F.

SKY COVERSky cover is depicted in the center of the station model. The eight possible symbols are shown below.

TEMPERATURETemperature is shown in degrees Fahrenheit. For example, the temperature at the sample station is 34°F.

CLOUDSLow cloud symbols are placed below the station model, while middle and high cloud symbols are placed immediately above it. A typical station model may include only one cloud type; seldom are more than two included. Decoding information for these symbols is available in various FAA publications and at flight service stations.

WINDSymbols extending out from the station circle give wind information. The symbol shows the general true direction of the surface wind and the velocity in knots. The absence of a wind symbol and a double circle around the station means calm wind. True wind direction is shown by the orientation of the wind pointer. Velocity is indicated by barbs and/or pennants attached to the wind pointer. One short barb is 5 knots, a longer barb is 10 knots, and a pennant is 50 knots. For example, the wind pointer in the sample station model shows the wind is from the northwest at 15 knots.

Clear Few Scattered Broken Overcast Obscured

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1/4

3

5

30

1

5

3

20

11/2

10

250

Total sky obscuration and the vertical visibilityinto the obscuration is 300 feet, visibility 1/4,fog, bracket indicates fog was determined byan automated system

FEW sky coverage, (no cloud height isindicated with FEW

SCT sky coverage, cloud height 3,000' AGL,visibility 5 miles, haze

BKN sky coverage, ceiling height 2,000' AGL,visibility 3 miles, continuous rain

OVC sky coverage, ceiling height 500' AGL,visibility 1 mile, intermittent

SCT sky coverage, cloud height 25,000' AGL

BKN sky coverage, ceiling height 1,000' AGL,visibility 11/2 mile, thunderstorm with rainshower

Missing cloud (or sky cover) observation orpartial obscuration

Figure 9-37. Weather Depiction Chart.

DIGIT

123456

PRECIPITATIONINTENSITY

LightModerate

HeavyVery Heavy

IntenseExtreme

RAINFALL RATEIN./HR. STRATAFORM

Less than 0.10.1 - 0.50.5 - 1.01.0 - 2.02.0 - 5.0

More than 5.0

RAINFALL RATEIN./HR. CONVECTIVE

Less than 0.20.2 - 1.11.1 - 2.22.2 - 4.54.5 - 7.1

More than 7.1

Symbol Meaning Symbol Meaning

R Rain

RW Rain shower

S Snow

SW Snow shower

T Thunderstorm

NA Not available

NE No echoes

OM Out for maintenance

SYMBOLS USED ON CHART

35

LM

WS9999

WT210

SLD

Cell Movement to thenortheast at 35 knots

Little movement

Severe thunderstorm watchnumber 999

Tornado watch number 210

8/10 or greater coveragein a line

Line of echoes

Figure 9-38. Radar Summary Chart.

9-30

is important to remember that a prognostic chart is aforecast and actual conditions may vary due to a num-ber of factors. [Figure 9-39]

An area that is expected to have continuous of intermit-tent precipitation is enclosed by a solid line. If onlyshowers are expected, the area is enclosed with a dot-dash pattern. Areas where precipitation is expected tocover one-half or more of the area is shaded. On theprognostic chart, special symbology is used to indicatevarious types of precipitation and how it will occur.[Figure 9-40]

WINDS AND TEMPERATURES ALOFT CHARTThe winds and temperatures aloft chart (FD) is a 12-hour chart that is issued at 0000Z and 1200Z daily. It isprimarily used to determine expected wind directionand velocity, and temperatures for the altitude of aplanned cross-country flight. The chart contains eightpanels that correspond to forecast levels6,000;9,000; 12,000; 18,000; 24,000; 30,000; 34,000; and39,000 feet MSL. Soaring pilots planning to attempt aproficiency award for altitude should be aware that thelevels below 18,000 feet are in true altitude, and levels18,000 feet and above are reported in pressure altitude.

The predicted winds are depicted using an arrow from thestation circle pointing in the direction of the wind. Thesecond digit of the wind direction is given near the outerend of the arrow. Pennants and barbs are used to depictwind speed in much the same manner as the surface

analysis chart. When calm winds are expected the arrowis eliminated and 99 is entered below the station circle.Forecast temperatures are shown as whole degreesCelsius near the station circle. In the example, the tem-perature is 3° Celsius and the wind is 160° at 25 knots.[Figure 9-41]

COMPOSITE MOISTURE STABILITY CHARTThe composite moisture stability chart is a four-panelchart, which depicts stability, precipitable water,freezing level, and average relative humidity. It is acomputer-generated chart derived from upper-airobservation data and is available twice daily with avalid time of 0000Z and 1200Z. This chart is usefulfor determining the characteristics of a particularweather system with regard to atmospheric stability,moisture content and possible hazards to aviation haz-ards, such as thunderstorms and icing. [Figure 9-42]

The stability panel located in the upper left corner ofthe chart outlines areas of stable and unstable air.[Figure 9-43] The numbers on this panel resemblefractions, the top number is the lifted index (LI), andthe lower number is the K index (KI). The lifted indexis the difference between the temperature of a parcelof air being lifted from the surface to the 500-millibarlevel (approximately 18,000 feet MSL) and the actualtemperature at the 500-millibar level. If the number ispositive, the air is considered stable. For example, alifted index of +8 is very stable, and the likelihood ofsevere thunderstorms is weak. Conversely, an index of

Figure 9-39. U.S. Low-Level Significant Weather Prognostic Chart.

9-31

SYMBOL MEANING SYMBOL MEANING SYMBOL MEANING

Showery precipitation (thunderstorms/rain-showers) covering half or more of the area.

Continuous precipitation(rain) covering half or more of the area.

Showery precipitation (snow showers) covering less than half of the area.

Intermittent precipitation (drizzle) covering less than half of the area.

Rain Shower

Snow Shower

Thunderstorms

Freezing Rain

Tropical Storm

Hurricane (Typhoon)

Moderate Turbulence

Severe Turbulence

Moderate Icing

Severe Icing

Rain

Snow

Drizzle

Figure 9-40. Prognostic Chart Symbology.

3

Figure 9-41. Winds and Temperatures Aloft (FD) chart.

Figure 9-42. Composite Moisture Stability Chart.

-4

22Figure 9-43. Stability Panel.

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–6 or less is considered very unstable, and severe thun-derstorms are likely to occur. A zero index is neutrallystable. [Figure 9-44]

The K index indicates whether the conditions arefavorable for airmass thunderstorms. The K index isbased on temperature, low-level moisture, and satura-tion. A K index of 15 or less would be forecast as a 0percent probability for airmass thunderstorms, and anindex of 40 or more would be forecast as 100 percentprobability.

The chart shows relative instability in two ways. First,the station circle is darkened when the lift index is zeroor less. Second, solid lines are used to delineate areaswhich have an index of +4 or less at intervals of 4 (+4,0, -4, -8). The stability panel is an important preflightplanning tool because the relative stability of an air-mass is indicative of the type of clouds that can befound in a given area. For example, if the airmass is

stable, a pilot can expect smooth air and given suffi-cient moisture, steady precipitation. On the other hand,if the airmass is unstable convective turbulence andshowery precipitation can be expected.

The lower left panel of the chart is the freezing levelpanel. [Figure 9-45] This panel plots the observedfreezing level data gathered from upper air observa-tions. When the freezing level (0° Celsius isotherm) isat the surface, it is shown as a dashed contour line. Theabbreviation “BF” is used to indicate a station that isreporting a temperature below freezing. As the freezinglevel increases in height, it is depicted on the chart as asolid line. These isotherms, lines of equal temperature,are given in 4,000-foot intervals but are labeled in hun-dreds of feet MSL. For example, an isotherm labeled40 indicates that the freezing level is at 4,000 feet MSL.Since the freezing level panel plots an overall view ofthe isotherms, it is easy to determine at which altitudestructural icing is probable. An inversion, with warmair above the freezing level is indicated by multiplecrossings of 0° Celsius isotherms.

The precipitable water panel, located in the upper rightcorner of the composite moisture stability chart, graphi-cally depicts the atmospheric water vapor available forcondensation. The coverage for this panel is from thesurface to the 500-millibars level. The top number inthe station model represents the amount of precipitablewater in hundredths of an inch. The lower number is thepercent of normal value for the month. For example,when the value is .68/205, there is 68 hundredths of aninch of precipitable water, which is 205 percent of thenormal (above average) for any day during the month.When a station symbol is darkened, the precipitablewater value at the station is 1 inch or more. Isoplethsare also plotted on the chart for every 1/4-inch. To differ-entiate the isopleths, a heavier line is used to indicate1/2-inch of precipitable water. [Figure 9-46]

0 to -2

-3 to -5

< -6

Weak

Moderate

Strong

<1515-1920-2526-3031-3536-40>40

near 0%20%

21-40%41-60%61-80%81-90%

near 100%

AIRMASS THUNDERSTORM

PROBABILITY K INDEX

SEVEREPOTENTIAL

LIFTED INDEX (LI)

THUNDERSTORM POTENTIAL

Figure 9-44.Thunderstorm Potential.

Freezing level at the surface

7957

BF

0 iostherm crosses at 5,700 feet and 7,900 feet

Temperature is belowfreezing at the surface

PLOTTEDDATA

Figure 9-45. Freezing Level Panel. Figure 9-46. Precipitable Water Panel.

9-33

This panel is used primarily by meteorologists who areconcerned with predicting localized flooding. However,when used with reference to the other panels it addscredibility to the prediction and probability of severeweather.

In the lower right corner of the composite moisture sta-bility chart is the average relative humidity panel. Thevalues for each station are plotted as a percentage andare valid from the surface to the 500-millibar level. Forquick reference isohumes are drawn and labeled forevery 10 percent, with heavier isohumes drawn for 10,50, and 90 percent. When the stations is reportinghumidity higher than 50 percent, the station symbol isdarkened. If relative humidity data is missing, an “M”is placed above the station symbol. [Figure 9-47]

For flight planning, this chart is useful for determiningaverage air saturation at altitudes from the surface to18,000 feet MSL. Average relative humidity of 50 per-cent or higher is frequently associated with areas ofclouds and possible precipitation. However, an areawith high humidity may or may not be indicative ofhigh water vapor content (precipitable water). Forexample, Kansas City may have the same relativehumidity as New Orleans, but if the precipitable watervalue were .13 inches in Kansas City and .66 inches inNew Orleans, greater precipitation would be expectedin New Orleans.

While each panel of the composite moisture stabilitychart provides important information for predictingweather over a wide area of the United States, it ismore important to reference all four panels to developthe best weather picture.

PRINTED REPORTS AND FORECASTSWeather reports and forecasts are beneficial in numerousways. For example, predictions of warm temperaturessignal the beginning of thermal soaring in the northernclimates, if it were only that simple. Printed reports andforecasts provide much more information to help pilots

decide if a flight can be conducted safely. To that end,wide varieties of weather products are available to assistpilots in that decision-making process.

PRINTED WEATHER REPORTSIn the simplest of terms, a weather report is a record ofobserved weather conditions at a particular locationand time. Weather information gathered by trainedobservers, radar systems, and pilots is disseminated ina variety of reports. The types of reports pilots arelikely to encounter include aviation routine weatherreports, radar weather reports, and pilot reports.

AVIATION ROUTINE WEATHER REPORTAn aviation routine weather report (METAR) is aweather observer’s interpretation of weather condi-tions at the time of the observation. This report is usedby the aviation community and the National WeatherService to determine the flying category of the airportwhere the observation is made. Based on the observedweather conditions, this determination dictateswhether the pilots will operate under visual flight rules(VFR), marginal visual flight rules (MVFR), or instru-ment flight rules (IFR) in the vicinity of the airport.Additionally, the METAR is used to produce an avia-tion terminal forecast (TAF).

Although, the code that makes-up a METAR is usedworldwide, some variations of the code used in theUnited States exist in other countries. In the UnitedStates, temperature and dewpoint are reported indegrees Celsius, using current units of measure for theremainder of the report.

A METAR consists of a sequence of observed weatherconditions or elements, if an element is not occurringor cannot be observed at the time of the observation,the element is omitted from the report. The elementsof the report are separated by a space except tempera-ture and dewpoint, which are separated by a slash (/).A non-routine METAR report, referred to as a SPECIreport, is issued any time the observed weather meetsthe SPECI criteria. The SPECI criteria includes initialvolcanic eruptions and the beginning or ending ofthunderstorms as well as other hazardous weatherconditions.

The METAR for Los Angles in Figure 9-48 was givenon the 14th day of the month, at 0651 UTC. When aMETAR is derived from a totally automated weatherobservation station, the modifier AUTO follows thedate/time element. The wind was reported to be 140°at 21 knots with gusts to 29 knots. The reported surfacevisibility is 1 statute mile. Runway visual range (RVR)is based on the visual distance measured by a machinelooking down the runway. In the example above, therunway visual range for runway 36 left is 4,500 feetvariable to 6,000 feet. The weather phenomena is rain

Figure 9-47. Average Relative Humidity Panel.

9-34

(RA) and mist (BR), note the minus sign preceding theRA indicates light rain is falling. The sky condition ele-ment indicates there are broken clouds at 3,000 feetabove the ground. Temperature and dewpoint arereported in a two-digit format in whole degrees Celsiusseparated by a slash. In the example, the temperature is10°C and the dewpoint is 10°C. The altimeter setting isreported in inches and hundredths of inches of mercuryusing a four-digit format prefaced by an A and isreported as 29.90 in. Hg. The Remarks element isincluded in a METAR or SPECI when it is appropriate.If the reporting station is automated, AO1 or AO2 willbe noted. Certain remarks are included to enhance orexplain weather conditions that are considered signifi-cant to flight operations. The types of information that

may be included are wind data, variable visibility,beginning and ending times of a particular weatherphenomenon, pressure information, and precise tem-perature/dewpoint readings. Refer to Appendix A atthe end of this chapter for further explanation of TAFand METAR codes and references.

PILOT REPORTSOf all of the weather reports available to pilots,PIREPs provide the most timely weather informationfor a particular route of flight. The advantage for pilotsis significant because unforecast adverse weather con-ditions, such as low in-flight visibility, icing condi-tions, wind shear, and turbulence can be avoided alonga route of flight. When significant conditions arereported or forecast, ATC facilities are required tosolicit PIREPs. When unexpected weather conditionsare encountered, pilots should not wait for ATC torequest a PIREP of conditions, but offer them to aidother pilots. [Figure 9-49]

Another type of PIREP is an AIREP (ARP) or airreport. These reports are disseminated electronicallyand are used almost exclusively by commercial air-lines. However, pilots may see AIREPs when access-ing weather information on the Internet.

RADAR WEATHER REPORTSRadar weather reports (SDs), derived from selectedradar locations are an excellent source of informationabout precipitation and thunderstorms. [Figure 9-50]The report describes the type, intensity, intensity trend,and height of the echo top of precipitation. [Figure 9-51] If the base of the precipitation is considered signif-icant, it is also included in the report. All heights arereported in hundreds of feet MSL.

PRINTED FORECASTSEveryday, National Weather Service Offices prepare avariety of forecasts using past weather observationsand computer modeling. Weather specialists developprinted forecasts for more than 2,000 forecasts for air-ports, over 900 route forecasts, which are intended forflight planning purposes. The printed forecasts pilotsneed to become familiar with include the aviation ter-minal forecast, aviation area forecast, and the windsand temperatures aloft forecast.

Pilot Weather Report Space Symbol=

3-Letter SA Identifier 1. UA UUARoutineReport

UrgentReport

2. /OVLocation:In relation to a NAVAID

3. /TM Time:Coordinated Universal Time

4. /FLAltitude/Flight Level:Essential for turbulence and icing reports

5. /TPAircraft Type:Essential for turbulence and icing reports

Items 1 through 5 are mandatory for all PIREPs

6. /SKSky Cover:Cloud height and coverage (scattered, broken,or overcast)

7. /WXFlight Visibility and Weather:Flight visibility, precipitation, restrictions tovisibility, etc.

8. /TATemperature (Celsius):Essential for icing reports

9. /WVWind:Direction in degrees and speed in knots

10. /TB

Turbulence:Turbulence intensity, whether the turbulenceoccurred in or near clouds, and duration ofturbulence

11. /ICIcing:Intensity and Type

12. /RMRemarks:For reporting elements not included or to clarifypreviously reported items

PIREP FORM

Figure 9-49. PIREP Form.

METAR KLAX 140651Z AUTO 14021G29KT 1SM R35L/4500V6000FT -RA BR BKN030

10/10 A2990 RMK AO2

Type ofReport

StationIdentifier

Time ofReport

WindInformation Visibility WeatherModifier

Temperature/Dewpoint

Altimeter Remarks

Figure 9-48.Typical Aviation Routine Weather Report (METAR) as generated in the United States.

9-35

TERMINAL AERODROME FORECASTThe terminal aerodrome forecast (TAF) is derived fromweather data and observations at a specific airport. It isa concise statement of expected weather conditionswithin a five statute mile radius of the center of the air-

port’s runway complex. Normally valid for a 24-hourperiod, TAFs are scheduled for dissemination fourtimes a day at 0000Z, 0600Z, 1200Z, and 1800Z. EachTAF contains the International Civil AviationOrganization (ICAO) station identifier, time and dateof issuance, valid period, and the body of the forecast.With a few exceptions, the coding used in a TAF issimilar to that found in a METAR.

The TAF for Pierre, South Dakota [Figure 9-52] wasissued on the eleventh day of the month at 1140Z. ThisTAF is valid from 1200Z to 1200Z on the 11-day of themonth. The first three digits of the surface wind fore-cast indicate direction and the following two indicatespeed in knots (KT). In this case, the winds are 130° at12 knots. P6SM indicates the visibility is forecast to begreater than 6 statute miles. BKN100 forecasts a bro-ken layer of clouds at 10,000 feet AGL. The temporary(TEMPO) change group is used when fluctuations of

Above SD report decoded as follows:

1. Location identifier and time of radar observation (Oklahoma City SD at 1935 UTC).

2. Echo pattern (LN in this example). The echo pattern or configuration may be one of the following: a. Line (LN) is a line of convective echoes with precipitation intensi ties that are heavy or greater, at least 30 miles long, at least 4 times as long as it is wide, and at least 25% coverage within the line. b. Area (AREA) is a group of echoes of similar type and not classified as a line. c. Cell (CELL) is a single isolated convective echo such as a rain shower.

3. Coverage, in tenths, of precipitation in the defined area (8/10 in this example).

4. Type and intensity of weather (thunderstorm [T] with very heavy rainshowers [RW++]).

5. Azimuth, referenced to true north, and range, in nautical miles (NM) from the radar site, of points defining the echo pattern (86/40 164/60 in this echo). For lines and areas, there will be two azimuth and range sets that define the pattern. For cells, there will be only one azimuth and range set. (See the examples that follow for elaboration of echo patterns.)

6. Dimension of echo pattern (20 NM wide in this example). The dimension of an echo pattern is given when azimuth and range define only the center line of the pattern. (In this example, “20W” means the line has a total width of 20 NM, 10 miles either side of a center line drawn from the points given in item “e” above.)

7. Cell movement (cells within line moving from 240 degrees at 25 knots in this example). Movement is only coded for cells; it will not be coded for lines or areas.

8. Maximum top and location (57,000 feet MSL on radial 159 degrees at 65 NM in this example). Maximum tops may be coded with the symbols “MT” or “MTS.” If it is coded with “MTS” it means that satellite data as well as radar information was used to measure the top of the precipitation.

9. The report is automated from WSR-88D weather radar data.

10. Digital section is used for preparing radar summary chart.

TLX 1935 LN 8 TRW++ 86/40 164/60 20W C2425 MTS 570 AT 159/65

AUTO ^MO1 NO2 ON3 PM34 QM3 RL2 =1. 2. 3. 4. 5. 6. 7. 8.

9. 10.

Location/Time CoverageEchoPattern

TypeIntensity

Intensity Trend

Azimuth &Rangeof Echo Echo

Dimensions

CellMovement

Maximum Top (MT)and Location

Remarks

Figure 9-50. Sample Radar Weather Report.

INTENSITY

Light

Moderate

Heavy

Very Heavy

Intense

Extreme

SYMBOL

-

(none)

+

++

X

XX

Figure 9-51. Intensity and intensity trend symbols.

9-36

wind, visibility, weather, or sky conditions are expectedto last for less than one hour at a time, and expected tooccur during less than half the time period. The fourdigits following the temporary code give the expectedbeginning and ending hours during which the condi-tions will prevail. In the example, reduced visibilitydue to mist is expected to prevail between 1200 hoursand 1400 hours. The from (FM) change group is usedto describe a rapid and significant change in the fore-cast weather that is expected to occur in less than anhour. When a gradual change in the forecast weatheris expected over a period of about 2-hours, thebecoming (BECMG) group is used. The probability-forecast group is used when there is less than a 50percent chance of thunderstorms or precipitation. In

the example, PROB40 indicates that between 0000Zand 0400Z there is a 40 to 50 percent chance of amoderate rain showers associated with a thunder-storm, 3 statute miles visibility, and broken cloudlayer at 3,000 feet AGL. The CB following the skycondition stands for cumulonimbus clouds.

AVIATION AREA FORECASTAn aviation area forecast (FA) covers general weatherconditions over several states or a known geographicalarea and is a good source of information for enrouteweather. It also helps determine the weather conditionsat airports, which do not have Terminal AerodromeForecasts. FAs are issued three times a day in the 48

Figure 9-52.Terminal Aerodrome Forecast.

TAF KPIR 111140Z 111212 13012KT P6SM BKN100 TEMPO 1214 5SM BR FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004 3SM TSRA BKN030CB FM0400 14008KT P6SM SCT040 BECMG 0810 32007KT=

MT

WY

COUT

AZ

ID

NM

NV

SLCSalt Lake City

HeadingSection

SLCC FA 141045SYNOPSIS AND CLDS/WXSYNOPSIS VALID UNTIL 150500CLDS/WX VALID UNTIL 142300... OUTLK VALID 142300-150500ID MT NV UT WY CO AZ NM

PrecautionaryStatements

SEE AIRMET SIERRA FOR IFR CONDS AND MTN OBSCN.TSTMS IMPLY PSBL SVR OR GTR TURBC SVR ICG LLWS AND IFR CONDS.

NON MSL HGTS ARE DENOTED BY AGL OR CIG.

Synopsis

SYNOPSIS...HIGH PRES OVER NERN MT CONTG EWD GRDLY. LOW PRES OVR AZ NM AND WRN TX RMNG GENLY STNRY. ALF...TROF EXTDS FROM WRN MT INTO SRN AZ RMNG STNRY.

VFR Cloudsand Weather

.ID MTFROM YXH TO SHR TO 30SE BZN TO 60SE PIH TO LKT TOYXC TO YXH.70-90 SCT-BKN 120-150. WDLY SCT RW-. TOPS SHWRS 180. OTLK...VFRRMNDR AREA...100-120. ISOLD RW- MNLY ERN PTNS AREA. OTLK...VFR.UT NV NM AZ80 SCT-BKN 150-200. WDLY SCT RW-/TRW-. CB TOPS 450. OTLK...VFR.WY COFROM BZN TO GCC TO LBL TO DVC TO RKS TO BZN.70-90 BKN-OVC 200. OCNL VSBY 3R-F. AFT 20Z WDLY SCT TRW-. CB TOPS 450. OTLK...MVFR CIG RW.

Figure 9-53. Aviation Area Forecast.

9-37

contiguous states, and amended as required. NWSoffices issue FAs for Hawaii and Alaska; however, theAlaska FA uses a different format. An additional spe-cialized FA may be issued for the Gulf of Mexico bythe National Hurricane Center in Miami, Florida.

The FA consists of several sections: a communicationsand product header section, a precautionary statementsection, and two weather sections (synopsis and VFRclouds and weather). Each area forecast covers an 18-hour period. [Figure 9-53]

COMMUNICATIONS AND PRODUCT HEADERSRefer to figure 9-53 for the following discussion. Inthe heading SLCC FA 141045, the SLC identifies theSalt Lake City forecast area, C indicates the productcontains clouds and weather forecast, FA means areaforecast, and 141045 is the date time group and indi-cates that the forecast was issued on the 14th day of themonth at 1045Z. Since these forecasts times arerounded to the nearest full hour, the valid time for thereport begins at 1100Z. The synopsis is valid until 18hours later, which is shown as the 15th 0500Z. Theclouds and weather section forecast is valid for 12-hour period, until 2300Z on the 14th. The outlook por-tion is valid for six hours following the forecast, from2300Z on the 14th to 0500Z on the 15th. The last lineof the header lists the states that are included in the SaltLake City forecast area.

Amendments to FAs are issued whenever the weathersignificantly improves or deteriorates based on thejudgment of the forecaster. An amended FA is identi-fied by the contraction AMD in the header along withthe time of the amended forecast. When an FA is cor-rected, the contraction COR appears in the heading,along with the time of the correction.

PRECAUTIONARY STATEMENTSFollowing the headers are three precautionary state-ments, which are part of all FAs. The first statementalerts the pilot to check the latest AIRMET Sierra,which describes areas of mountain obscuration whichmay be forecast for the area. The next statement is areminder that thunderstorms imply possible severe orgreater turbulence, severe icing, low-level wind shear,and instrument conditions. Therefore, when thunder-storms are forecast, these hazards are not included inthe body of the FA. The third statement points out thatheights, which are not MSL, are noted by the lettersAGL (above ground level) or CIG (ceiling). All heightsare expressed in hundreds of feet.

SYNOPSISThe synopsis is a brief description of the location andmovement of fronts, pressure systems, and circulationpatterns in the FA area over an l8-hour period. Whenappropriate, forecasters may use terms describing ceil-ings and visibility, strong winds, or other phenomena.

In the example, high pressure over northeasternMontana will continue moving gradually eastward. Alow-pressure system over Arizona, New Mexico, andwestern Texas will remain generally stationary. Aloft(ALF), a trough of low pressure extending from west-ern Montana into southern Arizona is expected toremain stationary.

VFR CLOUDS AND WEATHERThe VFR clouds and weather portion is usually severalparagraphs long and broken down by states or geo-graphical regions. It describes clouds end weather,which could affect VFR operations over an area of3,000 square miles or more. The forecast is valid for12 hours, and is followed by a 6-hour categorical out-look (18 hours in Alaska).

When the surface visibility is expected to be six statutemiles or less, the visibility and obstructions to visionare included the forecast. When precipitation, thunder-storms, and sustained winds of 20 knots or are fore-cast, they will be included in this section. The termOCNL (occasional) is used when there is a 50 percentor greater probability, but for less than 1/2 of the fore-cast period, of cloud or visibility conditions whichcould affect VFR flight. The area covered by showersor thunderstorms is indicated by the terms ISOLD (iso-lated), meaning single cells. WDLY SCT (widely scat-tered, less then 25 percent of the area), SCT or AREAS(25 to 54 percent of the area), and NMRS or WDSPRD(numerous or widespread, 55 percent or more of thearea).

The outlook follows the main body of the forecast, andgives a general description of the expected weatherusing the terms VFR, IFR, or MVFR (marginal VFR).A ceiling less than 1,000 feet and/or visibility less than3 miles is considered IFR. Marginal VFR areas arethose with ceilings from 1,000 to 3,000 feet and/or vis-ibility between 3 and 5 miles. Abbreviations are usedto describe causes of IFR or MVFR weather.

In the example shown above, the area of coverage inthe specific forecast for Wyoming and Colorado isidentified using three-letter designators. This areaextends from Bozeman, Montana to Gillette, Wyomingto Liberal, Kansas to Dove Creek, Wyoming toRocksprings, Wyoming, and back to Bozeman. Asmentioned previously under the header, the valid timebegins on the 14th day of the month at 1100Z for a 12-hour period. A broken to overcast cloud layer beginsbetween 7,000 to 9,000 feet MSL, with tops extendingto 20,000 feet. Since visibility and wind information isomitted, the visibility is expected to be greater than 6statute miles and the wind less than 20 knots. However,the visibility (VSBY) is forecast to be occasionally 3miles in light rain and fog (3R-F). After 2000Z, widelyscattered thunderstorms with light rain showers are

9-38

expected, with cumulonimbus (CB) cloud tops to45,000 feet. The 6-hour categorical outlook covers theperiod from 2300Z on the 14th to 0500 on the 15th. Theforecast is for marginal VFR weather due to ceilings(CIG) and rain showers (RW).

CONVECTIVE OUTLOOK CHARTThe convective outlook chart (AC), is a two-panel chartthat forecasts general thunderstorm activity for thevalid period of the chart. ACs describe areas in whichthere is a risk of severe thunderstorms. Severe thunder-storm criteria include winds equal to or greater than 50knots at the surface or hail equal to or greater than 3/4inch in diameter, or tornadoes. Convective outlooks areuseful for planning flights within the forecast period.Both panels of the convective outlook chart qualify therisk of thunderstorm activity at three levels, as well asareas of general thunderstorm activity.

Slight (SLGT)—implies well-organized severe thun-derstorms are expected but in small numbersand/or low coverage.

Moderate (MDT)—implies a greater concentration ofsevere thunderstorms, and in most cases greatermagnitude of severe weather.

High (HIGH)—means a major severe weather outbreakis expected, with a greater coverage of severeweather with a likelihood of violent tornadoesand/or damaging high winds.

General thunderstorm activity is identified on the chartby a solid line with an arrowhead at one end. This indi-cated that the area of general thunderstorm activity isexpected to the right of the line from the direction ofthe arrowhead.

The left panel [Figure 9-54] describes specific areas ofprobable thunderstorm activity for day-1 of the out-look. The day-1 panel is issued five times daily, start-ing a 0600Z and is valid from 1200Z that day until

1200Z the day after. The other issuance times are1300Z, 1630Z, 2000Z, and 0100Z and are valid until1200Z the day after the original issuance day.

The right panel [Figure 9-55] is the day-2 chart, it isissued twice daily. The initial issue is 0830Z standardtime, 0730Z daylight time and is updated at 1730Z.The valid time of the chart is from 1200Z followingthe original issue of the day-1 chart until 1200Z of thenext day. For example, if the day-1 chart is issued onMonday it is valid until 1200Z on Tuesday, subse-quently the day-2 chart is valid from 1200Z Tuesdayuntil 1200Z on Wednesday.

WINDS AND TEMPERATURES ALOFT FORECASTA winds and temperatures aloft forecast (FD) providesan estimate of wind direction relation to true north,wind speed in knots and the temperature in degreesCelsius for selected altitudes. Depending on the sta-tion elevation, winds and temperatures are usuallyforecast for nine levels between 3,000 and 39,000 feet.Information for two additional levels (45,000 foot and53,000 foot) may be requested from a FSS briefer orNWS meteorologist but is not included on an FD.[Figure 9-56]

The heading begins with the contraction FD, followedby the four-letter station identifier. The six digits arethe day of the month and the time of the transmission.The next two lines indicate the time of the observationand the valid time for the forecast. In the example, theobservation was taken on the 15th day of the month at1200Z, is valid at 1800Z, and is intended to be usedbetween 1700Z and 2100Z on the same day.

The first two numbers indicate the true direction fromwhich the wind is blowing. For example, 1635-08indicates the wind is from 160° at 35 knots and thetemperature is –8°C. Determining the wind directionand speed and temperature requires interpolationbetween two levels. For instance, to determine theFigure 9-54. Day-1 panel of the Convective Outlook Chart.

Figure 9-55. Day-2 panel of the Convective Outlook Chart.

9-39

wind direction and speed for a flight at 7,500 feet overHill City (HLC), a good estimate of the wind at 7,500feet is 190° at 10 knots with a temperature of -2C.

Wind speed between 100 and 199 knots are encoded,so direction and speed can be represented by four dig-its. This is done by adding 50 to the two-digit winddirection; and subtracting 100 from the velocity. Forexample, a wind of 270° at 101 knots is coded as 7701(27 + 50 = 77 for wind direction and 101 – 100 = 0l forwind speed). A code of 9900 indicates light and vari-able winds (less than five knots). However, windspeeds of 200 knots or more are encoded as 199.

It is important to note that temperatures are not fore-cast for the 3,000-foot level or for any level within2,500 feet of the station elevation. Likewise, windgroups are omitted when the level is within 1,500 feetof the station elevation. For example, the station eleva-tion at Denver (DEN) is over 5,000 feet, so the fore-cast for the lower two levels is omitted.

TRANSCRIBED WEATHER BROADCASTSA transcribed weather broadcast (TWEB) containsrecorded weather information concerning expected

sky cover, cloud tops, visibility, weather, and obstruc-tions to vision in a route format. This information istransmitted over selected navigation aids such as veryhigh frequency omni-directional ranges (VORs) andnon-directional radio beacons (NDBs). At some loca-tions, the information is only broadcast locally and islimited to items, such as the hourly weather for thetransmitting station and up to five adjacent stations,local NOTAM information, the local TAF, and poten-tial hazardous conditions.

When a TWEB is available along a route of flight, it isparticularly useful for timely in-flight weather infor-mation. At some locations, telephone access to therecording is also available (TEL-TWEB), providing anadditional source of preflight information. The tele-phone numbers for this service are listed in the A/FD.A circled “T” inside the communication boxes ofselected NDBs and VORs on National AeronauticalCharting Office (NACO) enroute and sectional chartsidentifies the TWEB availability. In the regions wherethere has been high utilization of TWEB, the FSS putsthe TWEB on a recording called TelephoneInformation Briefing Service (TIBS). It can beaccessed prior to flight by calling 1-800-WX-BRIEF,then choosing TIBS from the menu.

FD KWBC 151640

BASED ON 151200Z DATA

VALID 151800Z FOR USE 1700-2100Z TEMPS NEG ABV 24000

FD 3000 6000 9000 12000 18000 24000 30000

ALA 2420 2635-08 2535-18 2444-30 245945

AMA 2714 2725+00 2625-04 2531-15 2542-27 265842

DEN 2321-04 2532-08 2434-19 2441-31 235347

HLC 1707-01 2113-03 2219-07 2330-17 2435-30 244145

D

Figure 9-56. Winds and Temperatures Aloft Forecast.

9-40

APPENDIX A—KEY FOR TAF AND METAR

10-1

Soaring flight, maintaining or gaining altitude ratherthan slowly gliding downward, is the reason mostglider pilots take to the sky. After learning to stay aloftfor two or more hours at a time, the urge to set off crosscountry often overcomes the soaring pilot. The goal isthe same whether on a cross-country or a local flight—to use available updrafts as efficiently as possible. Thisinvolves finding and staying within the strongest partof the updraft. This chapter covers the basic soaringtechniques.

In the early 1920s, soaring pilots discovered the abilityto remain aloft using updrafts caused by wind deflectedby the very hillside from which they had launched. Thisallowed time aloft to explore the air. Soon afterward,they discovered thermals in the valleys adjacent to thehills. In the 1930s, mountain waves, which were notyet well understood by meteorologists, were discov-ered leading pilots to make the first high altitudeflights. Thermals are the most commonly used type oflift for soaring flight, since they can occur over flat ter-rain and in hilly country. Therefore, we will begin withthermal soaring techniques.

As a note, glider pilots refer to rising air as lift. This isnot the lift generated by the wings as was discussed inChapter 3—Aerodynamics of Flight. The use of thisterm may be unfortunate, but in reality it rarely causesconfusion when used in the context of updrafts. Thischapter refers to lift as the rising air within an updraftand sink as the descending air in downdrafts.

THERMAL SOARINGWhen locating and utilizing thermals for soaring flight,called thermalling, glider pilots must constantly beaware of any nearby lift indicators. Successful ther-malling requires several steps: locating the thermal,entering the thermal, centering the thermal, and finallyleaving the thermal. Keep in mind that every thermal isunique in terms of size, shape, and strength.

In the last chapter, we learned that if the air is moistenough and thermals rise high enough, cumulus clouds,or Cu (pronounced ‘q’) form. Glider pilots seek Cu intheir developing stage, while the cloud is still beingbuilt by a thermal underneath it. The base of the Cushould be sharp and well defined. Clouds that have afuzzy appearance are likely well past their prime andwill probably have little lift left or even sink as thecloud dissipates. [Figure 10-1]

Judging which clouds have the best chance for a goodthermal takes practice. On any given day, the lifetimeof an individual Cu can differ from previous days, so itbecomes important to observe their lifecycle on a par-ticular day. A good looking Cu may already be dissipat-ing by the time you reach it. Soaring pilots refer to suchCu as rapid or quick cycling, meaning they form,mature, and dissipate in a short time. The lifetime ofCu often varies during a given day as well; quickcycling Cu early in the day will often become wellformed and longer lived as the day develops.

Figure 10-1. Photographs of (A) mature cumulus likely producing good lift, and (B) dissipating cumulus.

A B

Courtesy of NCAR

10-2

Sometimes Cu cover enough of the sky that seeing thecloud tops becomes difficult. Hence, glider pilotsshould learn to read the bases of Cu. Generally, a darkarea under the cloud base indicates a deeper cloud;therefore, a higher likelihood of a thermal underneath.Also, several thermals can feed one cloud, and it isoften well worth the deviation to those darker areasunder the cloud. At times, an otherwise flat cloud baseunder an individual Cu has wisps or tendrils of cloudhanging down from it, producing a particularly activearea. Cloud hanging below the general base of a Cuindicate that that air is more moist, and hence morebuoyant. Note the importance of distinguishing fea-tures under Cu that indicate potential lift from virga.Virga is rain or snow from the cloud base that is not yetreaching the ground and often signals that the friendlyCu has grown to cumulus congestus or thunderstorms.[Figure 10-2] Another indicator that one area of Cumay provide better lift is a concave region under anotherwise flat cloud base. This indicates air that isespecially warm, and hence more buoyant, whichmeans stronger lift. This can cause problems for theunwary pilot, since the lift near cloud base often dra-matically increases, for instance from 400 to 1,000(fpm). When trying to leave the strong lift in the con-cave area under the cloud, pilots can find themselvesclimbing rapidly with cloud all around—another goodreason to abide by required cloud clearances.

After a thermal rises from the surface and reaches theConvective Condensation Level (CCL), a cloudbegins to form. At first, only a few wisps form. Thenthe cloud grows to a cauliflower shape. The initialwisps of Cu in an otherwise blue (cloudless) sky indi-cate where an active thermal is beginning to build acloud. When crossing a blue hole (a region anywherefrom a few miles to several dozen miles of cloud-freesky in an otherwise Cu-filled sky), diverting to an ini-tial wisp of Cu is often worthwhile. On some days,when only a few thermals are reaching the CCL, theinitial wisps may be the only cloud markers around.The trick is to get to the wisp when it first forms, inorder to catch the thermal underneath.

Lack of Cu does not necessarily mean lack of thermals.If the air aloft is cool enough and the surface tempera-

ture warms sufficiently, thermals will form whether ornot enough moisture exists for cumulus formation.These blue or dry thermals, as they are called, can bejust as strong as their Cu-topped counterparts. Gliderpilots can find blue thermals, without Cu markers, bygliding along until stumbling upon a thermal. With anyluck, other blue thermal indicators exist, making thesearch less random.

One indicator of a thermal is another circling glider.Often the glint of the sun on wings is all you will see,so finding other gliders thermalling requires keeping agood lookout, which glider pilots should be doing any-way. Circling birds are also good indicators of thermalactivity. Thermals tend to transport various aerosols,such as dust, upward with them. When a thermal risesto an inversion it disturbs the stable air above it andspreads out horizontally, thus depositing some of theaerosols at that level. Depending on the sun angle andthe pilot’s sunglasses, haze domes can indicate drythermals. If the air contains enough moisture, hazedomes often form just before the first wisp of Cu.

On blue, cloudless days, gliders and other airborneindicators are not around to mark thermals. In suchcases, you must pay attention to clues on the ground.First, think about your previous flight experiences. It isworth noting where thermals have been found previ-ously since certain areas tend to be consistent thermalsources. Remember that weather is fickle, so there isnever a guarantee that a thermal will exist in the sameplace. In addition, if a thermal has recently formed, itwill take time for the sun to reheat the area before thenext thermal is triggered. Glider pilots new to a soaringlocation should ask the local pilots about favoredspots—doing so might save the cost of a tow. Gliderpilots talk about house thermals, which are simplythermals that seem to form over and over in the samespot or in the same area.

Stay alert for other indicators, as well. In drier climates,dust devils mark thermals triggering from the ground.In hilly or mountainous terrain, look for sun-facingslopes. Unless the sun is directly overhead, the heatingof a sun-facing slope is more intense than that over

Figure 10-2. Photographs of (A) cumulus congestus, (B) cumulonimbus (Cb), (C) virga.

A B C

10-3

streets, a joyous sight when they lie along a cross-coun-try course line. [Figure 10-4]

In lighter wind conditions, consideration of thermaldrift is still important, and search patterns shouldbecome “slanted.” For instance, in Cu-filled skies,glider pilots need to search upwind of the cloud to finda thermal. How far upwind depends on the strength ofthe wind, typical thermal strength on that day, and dis-tance below cloud base (the lower the glider, the fur-ther upwind the gliders needs to be). Add to this thefact that wind speed does not always increase at a con-stant rate with height, and/or the possibility that winddirection also can change dramatically with height, andthe task can be challenging.

Wind speed and direction at cloud base can be esti-mated by watching the cloud shadows on the ground.With all the variables, it is sometimes difficult to esti-mate exactly where a thermal should be. Pay attentionto where thermals appear to be located in relation toclouds on a given day, and use this as the search crite-ria for other clouds on that day. If approaching Cu fromthe downwind side, expect heavy sink near the cloud.Head for the darkest, best defined part of the cloudbase, then continue directly into the wind. Dependingon the distance below cloud base, just about the time ofpassing upwind of the cloud, fly right into the lift form-ing the cloud. If approaching the cloud from a cross-wind direction (for instance, heading north withwesterly winds), try to estimate the thermal locationfrom others encountered that day. If only reduced sinkis found, there may be lift nearby, so a short leg upwindor downwind may locate the thermal.

Of course, thermals drift with the wind on blue days aswell, and similar techniques are required to locate ther-mals using airborne or ground-based markers. Forinstance, if heading toward a circling glider but at a

adjacent flat terrain because the sun’s radiation strikesthe slope at more nearly right angles. [Figure 10-3]Also, cooler air usually pools in low-lying areasovernight; therefore, it takes longer to heat up duringthe morning. Finally, slopes often tend to be drier thansurrounding lowlands, and hence tend to heat better.Given the choice, it usually pays to look to the hills forthermals first.

Whether soaring over flat or hilly terrain, some expertssuggest taking a mental stroll through the landscape tolook for thermals. Imagine strolling along the groundwhere warmer areas would be found. For instance,walking from shade into an open field the air suddenlywarms. A town surrounded by green fields will likelyheat more than the surrounding farmland. Likewise, ayellowish harvested field will feel warmer than an adja-cent wet field with lush green vegetation. Wet areastend to use the sun’s radiation to evaporate the mois-ture rather than heat the ground. Thus, a field with arocky outcrop might produce better thermals. Rockyoutcrops along a snowy slope will heat much more effi-ciently than surrounding snowfields. Though this tech-nique works better when at lower altitudes, it can alsobe of use at higher altitudes in the sense of avoidingcool-looking areas, such as a valley with many lakes.

Wind also has important influences not only on thermalstructure, but on thermal location as well. Strong windsat the surface and aloft often break up thermals, mak-ing them turbulent and difficult or impossible to workat all. Strong shear can break thermals apart and effec-tively cap their height even though the local soundingindicates that thermals should extend to higher levels.On the other hand, as discussed in Chapter 9—SoaringWeather, moderately strong winds without too muchwind shear will sometimes organize thermals into long

Sun's Rays

Sun's Rays

Small Area -Strong Heating

Large Area -Weaker Heating

Figure 10-3. Sun’s rays are concentrated in a smaller area ona hillside than on adjacent flat ground.

Figure 10-4. Photograph of cloud streets.

10-4

thousand feet lower, estimate how much the thermal istilted in the wind and head for the most likely spotupwind of the circling glider. [Figure 10-5] When inneed of a thermal, pilots might consider searching on aline upwind or downwind once abeam the circlingglider. This may or may not work; if the thermal is abubble rather than a column, the pilot may be belowthe bubble. It is easy to waste height while searching insink near one spot, rather than leaving and searchingfor a new thermal. Remember that a house thermal willlikely be downwind of its typical spot on a windy day.Only practice and experience enable glider pilots toconsistently find good thermals.

As a note, cool stable air can also drift with the wind.Avoid areas downwind of known stable air, such aslarge lakes or large irrigated regions. On a day with Cu,stable areas can be indicated by a big blue hole in anotherwise Cu-filled sky. If the area is broad enough, adetour upwind of the stabilizing feature might be inorder. [Figure 10-6]

When the sky is full of Cu, occasional gliders aremarking thermals, and dust devils move across thelandscape, the sky becomes glider pilot heaven. If glid-ing in the upper part of the height band, it is best tofocus on the Cu, and make choices based on the bestclouds. Sometimes lower altitudes will cause gliderpilots to go out of synch with the cloud. In that circum-stance, use the Cu to find areas that appear generallyactive, but then start focusing more on ground-basedindicators, like dust devils, a hillside with sunshine onit, or a circling bird. When down low, accept weakerclimbs. Often the day cycles again, and hard work isrewarded.

When searching for lift, use the best speed to fly, thatis, best L/D speed plus corrections for sink and any

wind. This technique allows glider pilots to cover themost amount of ground with the available altitude.

Once a thermal has been located, enter it properly, so asnot to lose it right away. The first indicator of a nearbythermal is often, oddly enough, increased sink. Next apositive G-force will be felt, which may be subtle orobvious depending on the thermal strength. The “seat-of-the-pants” indication of lift is the quickest, and is farfaster than any variometer, which has a small lag.Speed should have been increased in the sink adjacentto the thermal, hence as the positive G-force increases,reduce speed to between L/D and minimum sink. Notethe trend of the variometer needle (should be anupswing) or the audio variometer going from the droneto excited beeping, and at the right time in the antici-pated lift, begin the turn. If everything has gone per-fectly, the glider will roll into a coordinated turn, at justthe right bank angle, at just the right speed, and be per-fectly centered perfectly. In reality, it rarely works thatwell.

Figure 10-5.Thermal tilt in shear that (a) does not change with height, and that (b) increases with height.

Lake

Figure 10-6. Blue hole in a field of cumulus downwind of alake.

10-5

Before going further, what vital step was left out of theabove scenario? CLEAR BEFORE TURNING! The var-iometer is hypnotic upon entering lift, especially atsomewhat low altitudes. This is exactly where pilotsforget that basic primary step before any turn—lookingaround first. An audio variometer helps avoid this.

To help decide which way to turn, determine whichwing is trying to be lifted. For instance, when enteringthe thermal and the glider is gently banking to the right,CLEAR LEFT, then turn left. A glider on its own tendsto fly away from thermals. [Figure 10-7] As the gliderflies into the first thermal, but slightly off center, thestronger lift in the center of the thermal banks the gliderright, away from the thermal. It then encounters thenext thermal with the right wing toward the center andis banked away from lift to the left, and so on. Avoidletting thermals bank the glider even slightly.Sometimes the thermal-induced bank is subtle, so belight on the controls and sensitive to the air activity. Atother times there is no indication on one wing oranother. In this case, take a guess, CLEAR, then turn.As a note, new soaring pilots often get in the habit ofturning in a favorite direction, to the extreme of notbeing able to fly reasonable circles in the other direc-tion. If this happens, make an effort to thermal in theother direction half the time—being proficient in eitherdirection is important, especially when thermallingwith traffic.

Optimum climb is achieved when proper bank angleand speed are used after entering a thermal. The shal-lowest possible bank angle at minimum sink speed is

ideal. Thermal size and associated turbulence usuallydo not allow this. Large-size, smooth, and well-behaved thermals can be the exception in some parts ofthe country. Consider first the bank angle. The glider’ssink rate increases as the bank angle increases.However, the sink rate begins to increase more rapidlybeyond about a 45° bank angle. Thus, a 40° comparedto a 30° bank angle may increase the sink rate less thanthe gain achieved from circling in the stronger lift nearthe center of the thermal. As with everything else, thistakes practice, and the exact bank angle used willdepend on the typical thermal, or even a specific ther-mal, on a given day. Normally bank angles in excess of50° are not needed, but exceptions always exist. It maybe necessary, for instance, to use banks of 60° or so tostay in the best lift. Thermals tend to be smaller atlower levels and expand in size as they rise higher.Therefore, a steeper bank angle is required at loweraltitudes, and shallower bank angles can often be usedwhile climbing higher. Remain flexible with techniquesthroughout the flight.

If turbulence is light and the thermal is well-formed,use the minimum sink speed for the given bank angle.This should optimize the climb because the glider’ssink rate is at its lowest, and the turn radius is smaller.As an example, for a 30° bank angle, letting the speedincrease from 45 to 50 knots increases the diameter ofthe circle by about 100 feet. In some instances, this canmake the difference between climbing or not. Somegliders can be safely flown several knots below mini-mum sink speed. Even though the turn radius issmaller, the increased sink rate may offset any gainachieved by being closer to strong lift near the thermalcenter.

There are two other reasons to avoid thermallingspeeds that are too slow: the risk of a stall and lack ofcontrollability. Distractions while thermalling canincrease the risk of an inadvertent stall and include, butare not limited to: studying the cloud above or theground below (for wind drift, etc.), quickly changingbank angles without remaining coordinated while cen-tering, thermal turbulence, or other gliders in the ther-mal. Stall recovery should be second nature, so that ifthe signs of an imminent stall appear while thermalling,recovery is instinctive. Depending on the stall charac-teristics of the particular glider or in turbulent thermals,a spin entry is always possible. Glider pilots shouldcarefully monitor speed and nose attitude at lower alti-tudes. Regardless of altitude, when in a thermal withother gliders below, maintain increased awareness ofspeed control and avoid any stall/spin scenario.Controllability is a second, though related, reason forusing a thermalling speed greater than minimum sink.The bank angle may justify a slow speed, but turbu-lence in the thermal may make it difficult or impossibleto maintain the desired quick responsiveness, espe-

Figure 10-7. Effect of glider being allowed to bank on its ownwhen encountering thermals.

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cially in aileron control, in order to properly remain inthe best lift. Using sufficient speed will ensure that thepilot, and not the thermal turbulence, is controlling theglider.

Soaring pilots’ opinions differ regarding how long towait after encountering lift and before rolling into thethermal. Some pilots advocate flying straight until thelift has peaked. Then, they start turning, hopefully backinto stronger lift. It is imperative not to wait too longafter the first indication that the thermal is decreasingfor this maneuver. Other pilots favor rolling into thethermal before lift peaks, thus avoiding the possibilityof losing the thermal by waiting too long. Turning intothe lift too quickly will cause the glider to fly back outinto sink. There is no one right way; the choice dependson personal preference and the conditions on a givenday. Timing is everything and practice is key.

Usually upon entering a thermal, the glider is in lift forpart of the circle and sink for the other part. It is rare toroll into a thermal and immediately be perfectly cen-tered. The goal of centering the thermal is to determinewhere the best lift is and move the glider into it for themost consistent climb. One centering technique isknown as the “270° correction.” [Figure 10-8] In thiscase, the pilot rolls into a thermal and almost immedi-ately encounters sink, an indication of turning thewrong way. Complete a 270° turn, straighten out for afew seconds, and if lift is encountered again, turn backinto it in the same direction. Avoid reversing the direc-tion of turn. The distance flown while reversing turns ismore than seems possible and can lead away from thelift completely. [Figure 10-9]

Often stronger lift exists on one side of the thermal thanon the other, or perhaps the thermal is small enoughthat lift exists on one side and sink on the other, therebypreventing a climb. There are several techniques andvariations to centering. One method involves payingclose attention to where the thermal is strongest, forinstance, toward the northeast or toward some featureon the ground. To help judge this, note what is underthe high wing when in the best lift. On the next turn,adjust the circle by either straightening or shallowingthe turn toward the stronger lift. Anticipate things a bitand begin rolling out about 30° before actually headingtowards the strongest part. This allows rolling backtoward the strongest part of the thermal rather than fly-ing through the strongest lift and again turning awayfrom the thermal center. Gusts within the thermal cancause airspeed indicator variations; therefore, avoid“chasing the ASI.” Paying attention to the nose attitudehelps pilots keep their focus outside the cockpit. Howlong a glider remains shallow or straight depends onthe size of the thermal. [Figure 10-10]

Other variations include the following. [Figure 10-11]

1. Shallow the turn slightly (by maybe 5° or 10°)when encountering the weaker lift, then asstronger lift is encountered again (feel the posi-tive g, variometer swings up, audio variometerstarts to beep) resume the original bank angle. Ifshallowing the turn too much, it is possible to flycompletely away from the lift.Figure 10-8.The 270° centering correction.

Figure 10-9. Possible loss of thermal while trying to reversedirections of circle.

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2. Straighten or shallow the turn for a few seconds60° after encountering the weakest lifts or worstsink indicated by the variometer. This allows forthe lag in the variometer since the actual worstsink occurred a couple of seconds earlier thanindicated. Resume the original bank angle.

3. Straighten or shallow the turn for a few secondswhen the stronger seat-of-the-pants surge is felt.Then resume the original bank. Verify with thevariometer trend (needle or audio).

For the new glider pilots, it is best to become profi-cient using one of the above methods first, and then

experiment with other methods. As an additional note,thermals often deviate markedly from the conceptualmodel of concentric gradients of lift increasing evenlytoward the center. For instance, it sometimes feels as iftwo (or more) nearby thermal centers exist, makingcentering difficult. Glider pilots must be willing toconstantly adjust, and re-center the thermal to maintainthe best climb.

In addition to helping pilots locate lift, other gliderscan help pilots center a thermal as well. If a nearbyglider seems to be climbing better, adjust the turn to flywithin the same circle. Similarly, if a bird is soaringclose by, it is usually worth turning toward the soaringbird. Along with the thrill of soaring with a hawk oreagle, it usually leads to a better climb.

Collision avoidance is of primary importance whenthermalling with other gliders. The first rule calls forall gliders in a particular thermal to circle in the samedirection. The first glider in a thermal establishes thedirection of turn and all other gliders joining the ther-mal should turn in the same direction. Ideally, two glid-ers in a thermal at the same height or nearly so shouldposition themselves across from each other so they canbest maintain visual contact. [Figure 10-12] Whenentering a thermal, strive to do so in a way that will notinterfere with gliders already in the thermal, and aboveall, in a manner that will not cause a hazard to othergliders. An example, of a dangerous entry, is pullingup to bleed off excess speed in the middle of a crowdedthermal. A far safer technique is to bleed off speedbefore reaching the thermal and joining the thermal ata “normal” thermalling speed. Collision avoidance, notoptimum aerodynamic efficiency, is the priority whenthermalling with other gliders. Announcing to the other

Lake

Shift CircleToward Lake

Lift Strongest WhenHigh Wing PointsToward Lake

Figure 10-10. Centering by shifting the circle turn towardstronger lift.

Shallowthen Steepen

Do notShallow

Too MuchLowestVariometerIndication-Wait 60¡

LowestVariometerIndication Surge of Lift

Felt Here

1. 2. 3.

Figure 10-11. Other centering corrections.

10-8

glider(s) on the radio when entering the thermalenhances collision avoidance. [Figure 10-12]

Different types of gliders in the same thermal may havedifferent minimum sink speeds, and it may be difficultto remain directly across from another glider in a ther-mal. Avoid putting yourself in a situation where youcannot see the other glider, or the other glider cannotsee you. Radio communication is helpful. Too muchtalking clogs the frequency, and may make it impossi-ble for a pilot to broadcast an important message. Donot fly directly above or below another glider in a ther-mal since differences in performance, or even minorchanges in speed can lead to larger than expected alti-tude changes. If you lose sight of another glider in athermal and cannot establish position via a radio call,leave the thermal. After 10 or 20 seconds, come backaround to rejoin the thermal, hopefully with better traf-

fic positioning. It cannot be stressed enough that colli-sion avoidance when thermalling is a priority! Mid-aircollisions can sometimes be survived but only with agreat deal of luck. Unsafe thermalling practices notonly endangers your own safety but that of your fellowglider pilots. [Figure 10-13]

Leaving a thermal properly can also save you somealtitude. While circling, scan the full 360° of sky witheach thermalling turn. This first allows the pilot to con-tinually check for other traffic in the vicinity. Second, ithelps the pilot analyze the sky in all directions in orderto decide where to go for the next climb. It is better todecide where to go next while still in lift rather thanlosing altitude in sink after leaving a thermal. Exactlywhen to leave depends on the goals for the climb—whether the desire is to maximize altitude for a longglide or leave when lift weakens in order to maximizetime on a cross-country flight. In either case, be readyto increase speed to penetrate the sink often found onthe edge of the thermal, and leave the thermal in a man-ner that will not hinder or endanger other gliders.

The preceding pages describe techniques for locatingthermals, as well as entering, centering, and leavingthermals. Exceptions to normal or typical thermals arenumerous. For instance, instead of stronger sink at theedge of a thermal, weak lift sometimes continues for adistance after leaving a thermal. Glider pilots should bequick to adapt to whatever the air has to offer at the

A

B

1

1

2

23

3

5

4

5

4

Figure 10-12. Proper positioning with two gliders at the samealtitude. Numbers represent each glider’s position at thattime.

Figure 10-13. When thermalling, avoid flying in anotherglider’s blind spot, or directly above or below another glider.

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time. Just as the mechanics of simply flying the gliderbecome second nature with practice, so do thermallingtechniques. Expect to land early because anticipatedlift was not there on occasion—it is part of the learningcurve.

If thermal waves are suspected, climb in the thermalnear cloud base, then head toward the upwind side ofthe Cu. Often, only very weak lift, barely enough toclimb at all, is found in smooth air upwind of the cloud.Once above cloud base and upwind of the Cu, climbrates of a few hundred fpm can be found. Climbs canbe made by flying back and forth upwind of an individ-ual Cu, or by flying along cloud streets if they exist. Ifno clouds are present, but waves are suspected, climbto the top of the thermal and penetrate upwind in searchof smooth, weak lift. Without visual clues, thermalwaves are more difficult to work. Thermal waves aremost often stumbled upon as a pleasant surprise whentheir presence is furthest from the pilot’s mind.

RIDGE AND SLOPE SOARINGEfficient slope soaring (also called ridge soaring) isfairly easy; simply fly in the updraft along the upwindside of the ridge (see Figure 9-20). The horizontal dis-tance from the ridge will vary with height above theridge, since the best lift zone tilts upwind with heightabove the ridge. Even though the idea is simple, trapsexist for both new and expert glider pilots. Obtaininstruction when first learning to slope soar.

Avoid approaching from the upwind side perpendicu-larly to the ridge. Instead, approach the ridge at a shal-lower angle, so that a quick egress away from the ridgeis possible should lift not be contacted. While flyingalong the ridge, a crab angle is necessary to avoid drift-ing too close to the ridge or, if gliding above the ridge,

to avoid drifting over the top into the lee-side down-draft. For the new glider pilot, crabbing along the ridgemay be a strange sensation, and it is easy to becomeuncoordinated while trying to point the nose along theridge. This is both inefficient and dangerous, since itleads to a skid toward the ridge. [Figure 10-14]

In theory, to obtain the best climb, it is best to slopesoar at minimum sink speed. However, flying thatslowly may be unwise for two reasons. First, minimumsink speed is relatively close to stall speed, and flyingclose to stall speed near terrain has obvious dangers.Second, maneuverability at minimum sink speed maybe inadequate for proper control near terrain, especiallyif the wind is gusty and/or thermals are present. Whengliding at or below ridge top height, fly faster than min-imum sink speed—how much faster depends on theglider, terrain, and turbulence. When the glider is atleast several hundred feet above the ridge and shiftingupwind away from it in the best lift zone, reduce speed.If in doubt, fly faster!

Slope soaring comes with several procedures to enablesafe flying and to allow many gliders on the sameridge. The rules are:

1. make all turns away from the ridge;

2. do not fly directly above or below another glider;

3. pass another glider on the ridge side, anticipatingthat the other pilot will make a turn away fromthe ridge; and

4. the glider with its right side to the ridge has theright of way. [Figure 10-15]

15 Kt 15 Kt

Increased Radiusof Turn With Wind

Ridge

Safer, AngledApproach, ThenSet Crab Angle

Normal Radiusof Turn - No Wind

Strong Lee-side Sink

Figure 10-14. Flying with a wind increases the turn radius over the ground, so approach the ridge at a shallow angle.

10-10

These procedures deserve some comment.

Procedure #1: A turn toward the ridge is dangerous,even if gliding seemingly well away from the ridge.The ground speed on the downwind portion of the turnwill be difficult to judge properly, and striking the ridgeis a serious threat. Even if above the ridge, it will beeasy to finish the turn downwind of the ridge in heavysink.

Procedure #2: Gliders spaced closely together in thevertical are in each other’s blind spots. A slight changein climb-rate between the gliders can lead to a colli-sion.

Procedure #3: Sometimes the glider to be passed is soclose to the ridge that there is inadequate space to passbetween the glider and the ridge. In that case, eitherturn back in the other direction (away from the ridge) iftraffic permits, or fly upwind away from the ridge andrejoin the slope lift as traffic allows. When soaring out-side of the United States, be aware that this rule maydiffer.

Procedure #4: Federal Aviation Regulations call for air-craft approaching head-on to both give way to the right.A glider with the ridge to the right may not have roomto move in that direction. The glider with its left side tothe ridge should give way. When piloting the gliderwith its right side to the ridge, make sure the approach-ing glider sees you and is giving way in plenty of time.In general, gliders approaching head-on are difficult tosee; therefore, extra vigilance is needed to avoid colli-sions while slope soaring.

If the wind is at an angle to the ridge, bowls or spursextending from the main ridge can create better lift onthe upwind side and sink on the downwind side. If at ornear the height of the ridge, it may be necessary todetour around the spur to avoid the sink, then drift backinto the bowl to take advantage of the better lift. Afterpassing such a spur, do not make abrupt turns towardthe ridge (Rule #1), and as always, consider what thegeneral flow of traffic is doing. If soaring hundreds offeet above a spur, it may be possible to fly over it and

1 2

3 4

Figure 10-15. Ridge rules.

10-11

increase speed in any sink. This requires caution, sincea thermal in the upwind bowl, or even an imperceptibleincrease in the wind, can cause greater than anticipatedsink on the downwind side. Always have an escaperoute or, if in any doubt, detour around. [Figure 10-16]

It is not uncommon for thermals to exist with slope lift.Indeed, slope soaring can often be used as a “save”when thermals have temporarily shut down. Workingthermals from slope lift requires special techniques.When a thermal is encountered along the ridge, a seriesof S-turns can be made into the wind. Drift back to thethermal after each turn if needed and, of course, nevercontinue the turn to the point that the glider is turningtoward the ridge. Speed is also important, since it iseasy to encounter strong sink on the sides of the ther-mal. It is very likely that staying in thermal lift throughthe entire S-turn is not possible. The maneuver takespractice, but when done properly, a rapid climb in thethermal can be made well above the ridge crest, wherethermalling turns can begin. Even when well above theridge, caution is needed to ensure the climb is not tooslow as to drift into the lee-side sink. Before trying S-turns make sure it will not interfere with other trafficalong the ridge. [Figure 10-17]

A second technique for catching thermals when slopesoaring is to head upwind away from the ridge. Thisworks best when Cu mark potential thermals and aidetiming. If no thermal is found, the pilot should cut thesearch short while still high enough to dash back down-wind to the safety of the slope lift. [Figure 10-18]

As a final note, caution is also needed to avoid obstruc-tions when slope soaring. These primarily includewires, cables, and power lines, all of which are very

difficult to see. Aeronautical charts show high-tensiontowers that, of course, have many wires between them.Soaring pilots familiar with the area should be able toprovide useful information on any problems with thelocal ridge.

Sink

Lift

Figure 10-16. Avoid sink on the downwind side of spurs bydetouring around them.

Figure 10-17. One technique for catching a thermal fromridge lift.

Figure 10-18. Catching a thermal by flying upwind away fromthe slope lift.

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WAVE SOARINGAlmost all high-altitude flights are made using moun-tain lee waves. As covered in Chapter 9—SoaringWeather, lee wave systems can contain tremendous tur-bulence in the rotor, while the wave flow itself is usu-ally unbelievably smooth. In more recent years, the useof lee waves for cross-country soaring has lead toflights exceeding 1,500 miles, with average speedsover 100 mph. [Figure 10-19]

PREFLIGHT PREPARATIONThe amount of preflight preparation depends on theheight potential of the wave itself. Let us assume thatthe pilot is planning a flight above 18,000 feet MSLduring the winter. (Pilots planning wave flights tomuch lower altitudes can reduce the list of preparationitems accordingly.)

For flights above 14,000 feet MSL, the CFRs state thatrequired crewmembers must use supplemental oxygen.Pilots must be aware of their own physiology; how-ever, it may be wise to use oxygen at altitudes wellbelow 14,000 feet MSL. In addition, signs of hypoxiashould be known. The U.S. Air Force in cooperationwith the FAA provides a one-day, high-altitude orien-tation and chamber ride for civilian pilots. The experi-ence is invaluable for any pilot contemplating highaltitude soaring and is even required by many clubsand operations as a prerequisite. Before any waveflight, it is important to be thoroughly familiar with thespecific oxygen system that will be used, as well as itsadequacy for potential heights. The dangers of oxygendeprivation should not be taken lightly. At around20,000 feet MSL pilots might have only 10 minutes of“useful consciousness.” By 30,000 feet MSL, the time-frame for “useful consciousness” decreases to oneminute or less! For planned flights above 25,000 feetMSL, an emergency oxygen back-up or bailout bottleshould be carried.

Proper clothing is a must since temperatures of –30° to–60°C may be encountered at altitude. Proper prepara-tion for the cold is especially difficult since tempera-tures on the ground are often pleasant on wave soaringdays. Sunshine through the canopy keeps the upperbody amazingly warm for a time, but shaded legs andfeet quickly become cold. Frostbite is a very realthreat. After an hour or two at such temperatures, eventhe upper body can become quite cold. Layered, loose-fitting clothing aides in insulating body heat. Eitherwool gloves or light fitting gloves with mittens overthem work best for the hands. Mittens make tasks suchas turning radio knobs difficult. For the feet, two orthree pair of socks (inner silk, outer wool) with an insu-lated boot is recommended.

Within the continental United States, Class A airspacelies between 18,000 and 60,000 feet MSL (FL 180 toFL 600). Generally, flights in Class A must be con-ducted under Instrument Flight Rules (IFR). However,several clubs and glider operations have establishedso-called “Wave Windows”. These are special areas,arranged in agreement with Air Traffic Control (ATC),in which gliders are allowed to operate above 18,000feet MSL under VFR operations. Wave windows havevery specific boundaries. Thus, to maintain this privi-lege, it is imperative to stay within the designated win-dow. On any given day, the wave window may beopened to a specific altitude during times specified byATC. Each wave window has its own set of proceduresagreed upon with ATC. All glider pilots should becomefamiliar with the procedures and required radio fre-quencies.

True Airspeed (TAS) becomes a consideration athigher altitudes. To avoid the possibility of flutter,some gliders require a reduced indicated never-exceedspeed as a function of altitude. For instance, at sealevel the POH for one common two-seat glider, theVNE, is 135 knots. However, at 19,000 feet MSL it isonly 109 knots. Study the glider’s POH carefully forany limitations on indicated airspeeds.

There is always the possibility of not contacting thewave. Sink on the downside of a lee wave can behigh—2,000 fpm or more. In addition, missing thewave often means a trip back through the turbulentrotor. The workload and stress levels in either case canbe high. To reduce the workload, it is a good idea tohave minimum return altitudes from several locationscalculated ahead of time. In addition, plan for someworse case scenarios. For instance, consider what off-field landing options are available if the planned mini-mum return altitude proves inadequate.

A normal preflight of the glider should be performed.In addition, check the lubricant that has been used oncontrol fittings. Some lubricants can become very stiff

Rotor Cloud

Cap Cloud

LenticularClouds

Figure 10-19. Rotor and cap clouds with lenticulars above.

10-13

when cold. Also, check for water from melting snow ora recent rain in the spoilers or dive brakes. Freezingwater in the spoilers or drive brakes at altitude canmake them difficult to open. Checking the spoilers ordive brakes occasionally during a high climb helpsavoid this problem. A freshly charged battery is recom-mended, since cold temperatures can reduce batteryeffectiveness. Check the radio and accessory equip-ment, such as a microphone in the oxygen mask even ifit is not generally used. As mentioned, the oxygen sys-tem is vital. Other specific items to check depend onthe system being used. A checklist such as PRICE isoften helpful. The acronym PRICE stands for:

• Pressure—Check pressure in the oxygen bottle.

• Regulator—Check at all settings.

• Indicator—Check flow meters or flow-indicatorblinkers.

• Connections—Check for solid connections, pos-sible leaks, cracks in hoses, etc.

• Emergency—Check that the system is full andproperly connected.

A briefing with the towpilot is even more importantbefore a wave tow. Routes, minimum altitudes, rotoravoidance (if possible), anticipated tow altitude, andeventualities should the rotor become too severe, areamong topics that are best discussed on the groundprior to flight.

After all preparations are complete, it is time to get inthe glider. Some pilots may be using a parachute for thefirst time on wave flights, so make sure you are famil-iar with its proper fitting and use. The parachute fits ontop of clothing that is much bulkier than for normalsoaring, so the cockpit can suddenly seem quitecramped. It will take several minutes to get settled andorganized. Make sure radio and oxygen are easilyaccessible. If possible, the oxygen mask should be inplace, since the climb in the wave can be very rapid. Atthe very least, the mask should be set up so that it isready for use in a few seconds. All other gear (e.g., mit-tens, microphone, maps, barograph, etc.) should besecurely stowed in anticipation of the rotor. Check forfull, free rudder movement, since footwear is likelylarger than what you normally use. In addition, giventhe bulky cold-weather clothing, check to make surethe canopy clearance is adequate. The pilot’s head hasbroken canopies in rotor turbulence so seat and shoul-der belts should be tightly secured. This may be diffi-cult to achieve with the extra clothing and accessories,but take the time to make sure everything is secure.There will not be time to attend to such matters oncethe rotor is encountered.

GETTING INTO THE WAVEThere are two possibilities for getting into the wave:soaring into it or being towed directly into it. Threemain wave entries while soaring are: thermalling intothe wave, climbing the rotor, and transitioning into thewave from slope soaring.

At times, an unstable layer at levels below the moun-taintop is capped by a strong, stable layer. If other con-ditions are favorable, the overlying stable layer maysupport lee waves. On these days, it is sometimes pos-sible to largely avoid the rotor and thermal into thewave. Whether lee waves are suspected or not, near thethermal top the air may become turbulent. At this point,attempt a penetration upwind into smooth wave lift. Aline of cumulus downwind of and aligned parallel tothe ridge or mountain range is a clue that waves may bepresent. [Figure 10-20]

Another possibility is to tow into the upside of therotor, then climb the rotor into the wave. This can berough, difficult, and prone to failure. The technique isto find a part of the rotor that is going up and try to stayin it. The rotor lift is usually stationary over the ground.Either “figure-8” in the rotor lift to avoid driftingdownwind, fly several circles with an occasionalstraight leg, or fly straight into the wind for several sec-onds until lift diminishes. Then circle to reposition inthe lift. Which choice works depends on the size of thelift and the wind strength. Since rotors have rapidlychanging regions of very turbulent lift and sink, simpleairspeed and bank angle control can become difficult.This wave-entry technique is not for new pilots.

Depending on the topography near the soaring site, itmay be possible to transition from slope lift into a leewave that is created by upwind topography as shown inFigure 9-27. In this case, climb as high as possible inslope lift, then penetrate upwind into the lee wave.When the lee waves are in phase with the topography,it is often possible to climb from slope to wave liftwithout the rotor. At times, the glider pilot may notrealize wave has been encountered until they find liftsteadily increasing as they climb from the ridge.Climbing in slope lift and then turning downwind toencounter possible lee waves produced downwind of

Figure 10-20.Thermalling into wave.

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the ridge is generally not recommended. Even with atailwind, the lee-side sink can put the glider on theground before the wave is contacted.

Towing into the wave can be accomplished by eithertowing ahead of the rotor or through the rotor. Avoidingthe rotor completely will generally increase the towpi-lot’s willingness to perform future wave tows. If possi-ble, tow around the rotor and then directly into thewave lift. This may be feasible if the soaring site islocated near one end of the wave-producing ridge ormountain range. A detour around the rotor may requiremore time on tow, but it’s well worth the diversion.[Figure 10-21]

Often, a detour around the rotor is not possible and atow directly through the rotor is the only route to thewave. The rotor turbulence is, on rare occasion, onlylight. However, moderate to severe turbulence is usu-ally encountered. The nature of rotor turbulence differsfrom turbulent thermal days, with sharp, chaotic hori-zontal and vertical gusts along with rapid accelerationsand decelerations. At times, the rotor can become sorough that even experienced pilots may elect to remainon the ground. Any pilot inexperienced in flyingthrough rotors should obtain instruction beforeattempting a tow through rotor.

When towing through a rotor, being out of position isnormal. Glider pilots must maintain position horizon-

tally and vertical as best they can. Pilots should also beaware that an immediate release may be necessary atany time if turbulence becomes too violent. Slack-pro-ducing situations are common, due to a rapid decelera-tion of the towplane. The glider pilot must react quicklyto slack if it occurs and recognize that slack is about tooccur and correct accordingly. The vertical positionshould be the normal high-tow. Any tow position that islower than normal runs the risk of the slack line com-ing back over the glider. On the other hand, care shouldbe taken to tow absolutely no higher than normal toavoid a forced release should the towplane suddenlydrop. Gusts may also cause an excessive bank of theglider, and it may take a moment to roll back to level.Full aileron and rudder deflection, held for a few sec-onds, is sometimes needed.

Progress through the rotor is often indicated by notingthe trend of the variometer. General down swings arereplaced by general upswings, usually along withincreasing turbulence. The penetration into the smoothwave lift can be quick, in a matter of few seconds,while at other times it can be more gradual. Note anylenticulars above—a position upwind of the cloudshelps confirm contact with the wave. If in doubt, tow afew moments longer to be sure. Once confident abouthaving contacted the wave lift, make the release. Ifheading more or less crosswind, the glider shouldrelease and fly straight or with a crab angle. If flyingdirectly into the wind, the glider should turn a few

Slope Lift

Wave Sink

Wave Lift

Rotor Cloud

Wave Sink

Figure 10-21. If possible, tow around the rotor directly into the wave.

10-15

degrees to establish a crosswind crab angle. The goal isto avoid drifting downwind and immediately lose thewave. After release, the towplane should descendand/or turn away to separate from the glider. Possiblenon-standard procedures need to be briefed with thetowpilot before takeoff. [Figures 10-22 and 10-23]

FLYING IN THE WAVEOnce the wave has been contacted, the best techniquesfor utilizing the lift depends on the extent of the lift(especially in the direction along the ridge or mountainrange producing the wave) and the strength of the wind.The lift may initially be weak. In such circumstances,be patient and stay with the initial slow climb. Patienceis usually rewarded with better lift as the climb contin-

ues. At other times, the variometer may be pegged at1,000 fpm directly after release from tow.

If the wind is strong enough (40 knots or more), findthe strongest portion of the wave and point into thewind, and adjust speed so that the glider remains in thestrong lift. The best lift will be found along the upwindside of the rotor cloud or just upwind of any lenticu-lars. In the best-case scenario, the required speed willbe close to the glider’s minimum sink speed. In quitestrong winds, it may be necessary to fly faster thanminimum sink to maintain position in the best lift.Under those conditions, flying slower will allow theglider to drift downwind (fly backwards over theground!) and into the down side of the wave. This canbe a costly mistake since it will be difficult to penetrate

VariometerIndicationss

Wave-Steady Lift

UpwindSide

DownwindSide

RotR or

Foehn Cloud

Release

SmoothWave

Tow Path

TurbulentRotor

Figure 10-22. Variometer indications during the penetration into the wave.

Wave Lift

Rotor Cloud

StrongWind

ModerateWind

Figure 10-23. Possible release and separation on a wave tow.

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back into the strong headwind. When the lift is strong,it is easy to drift downwind while climbing intostronger winds aloft, so it pays to be attentive to theposition relative to rotor clouds or lenticulars. If noclouds exist, special attention is needed to judge winddrift by finding nearby ground references. It may benecessary to increase speed with altitude to maintainposition in the best lift. Often the wind is strong, butnot quite strong enough for the glider to remain station-ary over the ground, so that the glider slowly movesupwind out of the best lift. If this occurs, turn slightlyfrom a direct upwind heading, drift slowly downwindinto better lift, and turn back into the wind before drift-ing too far. [Figure 10-24]

Oftentimes, the wave lift is not perfectly stationaryover the ground since small changes in wind speedand/or stability can alter the wavelength of the lee wavewithin minutes. If lift begins to decrease while climb-ing in the wave, one of these things has occurred: theglider is nearing the top of the wave, the glider hasmoved out of the best lift, or the wavelength of the leewave has changed. In any case, it is time to explore thearea for better lift, and it is best to search upwind first.Searching upwind first allows the pilot to drift down-wind back into the up part of the wave if he or she iswrong. Searching downwind first can make it difficultor impossible to contact the lift again if sink on thedownside of the wave is encountered. In addition, cau-tion is needed to avoid exceeding the glider’s maneu-vering speed or rough-air redline, since a penetrationfrom the down side of the wave may put the glider backin the rotor. [Figure 10-25]

If the winds are moderate (20 to 40 knots), and thewave extends along the ridge or mountain range for afew miles, it is best to fly back and forth along the wave

lift while crabbing into the wind. This technique is sim-ilar to slope soaring, using the rotor cloud or lenticularas a reference. All turns should be into the wind toavoid ending up on the down side of the wave or backinto the rotor. Once again, it is easy to drift downwindinto sink while climbing higher and searching for bet-ter lift should be done upwind first. When making anupwind turn to change course 180°, remember that theheading change will be less, depending on the strengthof the wind. Note the crab angle needed to stay in lifton the first leg, and assume that same crab angle aftercompleting the upwind turn. This will prevent theglider from drifting too far downwind upon complet-ing the upwind turn. With no cloud, ground referencesare used to maintain the proper crab angle, and avoiddrifting downwind out of the lift. While climbinghigher into stronger winds, it may become possible totransition from crabbing back and forth to a stationaryupwind heading. [Figure 10-26]

Weaker winds (15 to 20 knots) sometimes require dif-ferent techniques. Lee waves from smaller ridges canform in relatively weak winds, on the order of only 15knots. Wave lift from larger mountains will rapidlydecrease when climbing to a height where winds aloftdiminish. As long as the lift area is big enough, use atechnique similar to that used in moderate winds. Nearthe wave top, there sometimes remains only a smallarea that still provides lift. In order to attain the maxi-mum height; fly shorter “figure-8” patterns within theremaining lift. If the area of lift is so small that consis-tent climb is not possible, a series of circles can beflown with an occasional leg into the wind to avoiddrifting too far downwind. Another possibility is anoval-shaped pattern—fly straight into the wind in lift,and as it diminishes, fly a quick 360° turn to reposi-

Wave Lift

Wave Crest

Wave Sink

StrongWind

Glider SpeedEquals

Wind Speed

Glider SpeedGreater ThanWind Speed Glider Speed

Less ThanWind Speed

Figure 10-24. Catching a thermal by flying upwind away fromthe slope lift.

Search UpwindFirst

TurbulentRotor

Figure 10-25. Search upwind first to avoid sink behind thewave crest or the rotor.

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tion. These last two techniques do not work as well inmoderate winds, and not at all in strong winds since itis too easy to end up downwind of the lift and intoheavy sink. [Figure 10-27]

In the discussion thus far, we have assumed a climb inthe primary wave. It is also possible to climb in the sec-ondary or tertiary lee wave (if they exist on a givenday) and then penetrate into the next wave upwind. Thesuccess of this depends on wind strength, clouds, theintensity of sink downwind of wave crests, and the per-formance of the glider. Depending on the heightattained in the secondary or tertiary lee wave, a tripthrough the rotor of the next wave upwind is a distinctpossibility. Caution is needed if penetrating upwind athigh speed. The transition into the downwind side ofthe rotor can be as abrupt as on the upwind side, sospeed should be reduced at the first hint of turbulence.In any case, expect to lose surprising amounts of alti-

tude while penetrating upwind through the sinking sideof the next upwind wave. [Figure 10-28]

If a quick descent is needed or desired, the sink down-wind of the wave crest can be used. Sink can easily betwice as strong as lift encountered upwind of the crest.Eventual descent into downwind rotor is also likely.Sometimes the space between a rotor cloud and over-lying lenticulars is inadequate and a transition down-wind cannot be accomplished safely. In this case, acrosswind detour may be possible if the wave is pro-duced by a relatively short ridge or mountain range. Ifclouds negate a downwind or crosswind departurefrom the wave, a descent on the upwind side of thewave crest will be needed. Spoilers or dive brakes maybe used to descend through the updraft, followed by atransition under the rotor cloud and through the rotor.A descent can be achieved by moving upwind of a verystrong wave lift if spoilers or dive brakes alone do notallow a quick enough descent. A trip back through therotor is at best unpleasant. At worst it can be dangerousif the transition back into the rotor is done with toomuch speed. In addition, strong wave lift and lift onthe upwind side of the rotor may make it difficult tostay out of the rotor cloud. This wave descent requires

Band of Wave Lift

Lift Weakens -Turn BackInto Wind

DownwindTurn Leads toStrong Sink

or Rotor

Figure 10-26. Proper crabbing to stay in lift and effects ofupwind turn (correct) or downwind turn (incorrect).

WeakWind

S - Turns withSlight Drift to

Stay in Weak Lift

Upwind Legwith a 360°

Turn

Series ofCircles with an

Upwind Leg

Figure 10-27.Techniques for working lift near the top of the wave in weak winds.

PrimaryWave

SecondaryWave

TertiaryWave

Figure 10-28. Possible flight path while transitioning fromthe tertiary into the secondary and then into the primary.

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a good deal of caution and emphasizes the importanceof an exit strategy before climbing too high in thewave, keeping in mind that conditions and clouds canrapidly evolve during the climb.

Some of the dangers and precautions associated withwave soaring have already been mentioned. Those andothers are summarized below.

• If any signs of hypoxia appear, check the oxygensystem and immediately begin a descent to loweraltitudes below which oxygen is not needed. Donot delay!

• Eventually, regardless of how warmly you aredressed, it will become cold at altitude. Descendwell before it becomes uncomfortably cold.

• Rotor turbulence can be severe or extreme.Caution is needed on tow and when transitioningfrom smooth wave flow (lift or sink) to rotor.Rotors near the landing area can cause strongshifting surface winds—20 or 30 knot. Windshifts up to 180° sometimes occur in less than aminute at the surface under rotors.

• Warm, moist exhaled air can cause frost on thecanopy, restricting vision. Opening air vents mayalleviate the problem or prolong frost formation.Clear-vision panels may also be installed. Iffrosting cannot be controlled, descend beforefrost becomes a hazard.

• In “wet” waves, those associated with a greatdeal of cloud, beware of the gaps closing beneaththe glider. If trapped above cloud, a benign spiralmode is an option, but only if this mode has beenpreviously explored and found stable for yourglider.

• Know the time of actual sunset. At legal sunset,bright sunshine is still found at 25,000 feet whilethe ground below is already quite dark. Even atan average 1,000 fpm descent it takes 20 minutesto lose 20,000 feet.

SOARING CONVERGENCE ZONESConvergence zones are most easily spotted whencumulus clouds are present. They appear as a singlestraight or curved cloud street, sometimes well definedand sometimes not, for instance when a wind field asin Figure 9-30(B) causes the convergence. The edge ofa field of cumulus can mark convergence between amesoscale air mass that is relatively moist and/orunstable from one that is much drier and/or more sta-ble. Often the cumulus along convergence lines have abase lower on one side than the other, similar to Figure9-33.

With no cloud present, a convergence zone is some-times marked by a difference in visibility across it,

which may be subtle or distinct. When there are noclues in the sky itself, there may be some on theground. If lakes are nearby, look for wind differenceson lakes a few miles apart. A lake showing a winddirection different than the ambient flow for the daymay be a clue. Wind direction shown by smoke canalso be an important indicator. A few dust devils, orbetter, a short line of them, may indicate the presenceof ordinary thermals vs. those triggered by conver-gence. Spotting the subtle clues takes practice andgood observational skills, and is often the reason a fewpilots are still soaring while others are already on theground.

The best soaring technique for this type of lift dependson the nature of the convergence zone itself. Forinstance, a sea-breeze front may be well-defined andmarked by “curtain” clouds, in which case the pilot canfly straight along the line in fairly steady lift. A weakerconvergence line often produces more lift than sink, inwhich case the pilot must fly slower in lift and faster insink. An even weaker convergence line may just act asfocus for more-frequent thermals, in which case normalthermal techniques are used along the convergence line.Some combination of straight legs along the line withan occasional stop to thermal is often used.

Convergence zone lift can at times be somewhat turbu-lent, especially if air from different sources is mixing,such as along a sea-breeze front. The general roughnessmay be the only clue of being along some sort of con-vergence line. There can also be narrow and rough (butstrong) thermals within the convergence line. Workthese areas like any other difficult thermals—steeperbank angles and more speed for maneuverability.

COMBINED SOURCES OF UPDRAFTSFinally, lift sources have been categorized into fourtypes: thermal, slope, wave, and convergence. Often,more than one type of lift exists at the same time. Forinstance, thermals with slope lift, thermalling into awave, convergence zones enhancing thermals, thermalwaves, and wave soaring from slope lift were all con-sidered. In mountainous terrain, it is possible for allfour lift types to exist on a single day. The glider pilotneeds to remain mentally nimble to take advantage ofvarious pieces of rising air during the flight.

Nature does not know that it must only produce risingair based on these four lift categories. Sources of liftthat do not fit one of the four lift types discussed prob-ably exist. For instance, there have been a few reportsof pilots soaring in travelling waves, the source ofwhich was not known. At some soaring sites it is some-times difficult to classify the type of lift. This shouldnot be a problem—simply work the mystery lift asneeded, then ponder its nature after the flight.

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A cross-country flight is defined as one in which theglider has flown beyond gliding distance from the localsoaring site. Cross-country soaring seems simpleenough in theory, but in reality, it requires a great dealmore preparation and decision making than local soar-ing flights. Items that must be considered during cross-country flights are how good are the thermals ahead,and will they remain active? What are the landing pos-sibilities? Which airport along the course has a runwaythat is favorable for the prevailing wind conditions?What effect will the headwind have on the glide? Whatis the best speed to fly in sink between thermals?

Flying cross-country using thermals is the basis of thischapter. A detailed description of cross-country usingridge or wave lift is beyond the scope of this chapter.

FLIGHT PREPARATION AND PLANNINGAdequate soaring skills form the basis of the pilot’spreparation for cross-country soaring. Until the pilothas flown several flights in excess of two hours and canlocate and utilize thermals consistently, the pilot shouldfocus on improving those skills before attemptingcross-country flights.

Any cross-country flight may end in an off-field land-ing, so short-field landing skills are essential. Theselandings should be practiced on local flights by settingup a simulated off-field landing area. Care is needed toavoid interfering with the normal flow of traffic duringsimulated off-field landings. The first few simulatedlandings should be done with an instructor, and severalshould be done without the use of the altimeter.

The landing area can be selected from the ground, butthe best training is selecting one from the air. Landingarea selection training and simulated approaches tothese areas using a self-launch glider or other poweredaircraft is a good investment if one is available.

Once soaring skills have been honed, pilots need to beable to find their position along a route of flight. ASectional Aeronautical Chart, or sectional for short, is amap soaring pilots use during cross-country flights.They are updated every 6 months and contain generalinformation, such as topography, cities, major andminor roads and highways, lakes, and other featuresthat may stand out from the air, such as a ranch in an

Figure 11-1. Sample area from a Sectional Aeronautical Chart.

otherwise featureless prairie. In addition, sectionalsshow the location of private and public airports, air-ways, restricted and warning areas, and boundaries andvertical limits of different classes of airspace.Information on airports includes field elevation, orien-tation and length of all paved runways, runway light-ing, and radio frequencies in use. Each sectionalfeatures a comprehensive legend. A detailed descrip-tion of the sectional chart is found in the Pilot’sHandbook of Aeronautical Knowledge, FAA-H-8083-25. Figure 11-1 shows a sample sectional chart.

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The best place to become familiar with sectional chartsis on the ground. It is instructive to fly some “virtual”cross-country flights in various directions from thelocal soaring site. In addition to studying the terrain(hills, mountains, large lakes) that may effect the soar-ing along the route, study the various lines and sym-bols. What airports are available on course? Do anyhave a control tower? Can all the numbers and symbolsfor each airport be identified? If not, find them on thelegend. Is there Class B, C, or D airspace enroute? Arethere any restricted areas? Are there airways along theflight path? Once comfortable with the sectional fromground study, it can be used on some local flights topractice locating features within a few miles of thesoaring site.

Any cross-country flight may end with a landing awayfrom the home soaring site, so pilots and crews shouldbe prepared for the occurrence prior to flight.Sometimes an aerotow retrieve can be made if theflight terminates at an airport; however, trailerretrieval is more typical. Both the trailer and tow vehi-cle need a “preflight” before departing on the flight.The trailer should be roadworthy and set up for thespecific glider. Stowing and towing a glider in an inap-propriate trailer can lead to damage. The crew shouldbe familiar with procedures for towing and backing along trailer. The tow vehicle should be strong and sta-ble enough for towing. Both radio and telephone com-munication options should be discussed with theretrieval crew.

Before any flight, obtain a standard briefing from theAutomated Flight Service Station (AFSS). As dis-cussed in Chapter 9—Soaring Weather, the briefer sup-plies general weather information for the plannedroute, as well as any NOTAMs, AIRMETs, orSIGMETs, winds aloft, an approaching front, or areasof likely thunderstorm activity. Depending on theweather outlook, beginners may find it useful to dis-cuss options with more experienced cross-countrypilots at their soaring site.

Many pilots have specific goals in mind for their nextcross-country flight. Several options should be plannedahead based on the area and different weather scenar-ios. For instance, if the goal is a closed-course 300 kmflight, several likely out and return or triangle coursesshould be laid out ahead of time, so that on the specificday, the best task can be selected based on the weatheroutlook. There are a number of final details that needattention on the morning of the flight, so special itemsshould be organized and readied the day before theflight.

Lack of preparation can lead to delays, which maymean not enough of the soaring day is left to accom-plish the planned flight. Even worse, poor planning

leads to hasty last minute preparation and a rush tolaunch—critical safety items can then be missed easily.

Inexperienced and experienced pilots alike should usechecklists for various phases of the cross-country prepa-ration in order to organize details. When properly used,checklists can help avoid oversights, such as sectionalsleft at home, barograph not turned on before take-off.Checklists also aid in making certain that safety of flightitems are checked or accomplished, such as all assem-bly items are accomplished, and checked, oxygenturned on, drinking water in the glider, etc. Examples ofchecklists include the following.

• Items to take to the gliderport (food, water,battery, charts, barograph).

• Assembly (follow the Glider Flight Manual/Pilot’sOperating Handbook [GFM/POH] and add itemsas needed).

• Pre-launch (water, food, charts, glide calculator,oxygen on, sunscreen, cell phone).

• Pre-take-off checklist itself.

Being better organized before the flight leads to lessstress during the flight, thus enhancing flight safety.

PERSONAL AND SPECIAL EQUIPMENTMany items not required for local soaring are neededfor cross-country flights. Pilot comfort and physiologyis even more important on cross-country flights sincethese flights often last longer than local flights. An ade-quate supply of drinking water is essential to avoiddehydration. Many pilots use the backpack drinkingsystem with readily accessible hose and bite-valve thatis often used by bicyclists. This system is easily stowedbeside the pilot, allowing frequent sips of water. Arelief system also may be needed on longer flights.Cross-country flights can last anywhere from two toeight hours or more, so food of some kind is also a goodidea.

Several items should be carried in case there is an off-field landing. (For more details, see Chapter 8—Abnormal and Emergency Procedures.) First, a systemfor securing the glider is necessary, as is a land-out kitfor the pilot. The kit will vary depending on the popu-lation density and climate of the soaring area. Forinstance, in the Great Basin in the United States, a safelanding site may be many miles from the nearest roador ranch house. Since weather is often hot and dry dur-ing the soaring season, extra water and food should beadded items. Carrying good walking shoes is a goodidea as well. A cell phone may prove useful for land-outs in areas with sparse telephone coverage. Some

11-3

pilots elect to carry an Emergency Locator Transmitter(ELT) in remote areas in case of mishap during an off-field landing.

Cross-country soaring requires some means of measur-ing distances to calculate glides to the next source oflift or the next suitable landing area. Distances can bemeasured using a sectional chart and navigational plot-ter with the appropriate scale, or by use of GlobalPositioning System (GPS). If GPS is used, a sectionaland plotter should be carried as a backup. A plotter maybe made of clear plastic with a straight edge on the bot-tom marked with nautical or statute miles for a sec-tional scale on one side and World Aeronautical Chart(WAC) scale on the other. On the top of the plotter is aprotractor or semicircle with degrees marked for meas-uring course angles. A small reference index hole islocated in the center of the semicircle. [Figure 11-2]

Glide calculations must take into account any head-wind or tailwind, as well as speeds to fly through vary-ing sink rates. Tools range widely in their level ofsophistication, but all are based on the performancepolar for the particular glider. The simplest glide aide isa table showing altitudes required for distance vs. wind,which can be derived from the polar. To avoid a tablewith too many numbers, which could be confusing,some interpolation is often needed. Another option is acircular glide calculator as shown in Figure 11-3. Thistool allows the pilot to read the altitude needed for anydistance and can be set for various estimated head-winds and tailwinds. Circular glide calculators alsomake it easy to determine whether you are actuallyachieving the desired glide, since heavy sink or astronger-than-estimated headwind can cause you tolose more height with distance than was indicated bythe calculator. For instance, the settings in Figure 11-3indicate that for the estimated 10-knot headwind, 3,600feet is required to glide 18 miles. After gliding 5 miles,you should still have 2,600 feet. Note that this onlygives the altitude required to make the glide. You must

also add the ground elevation and an altitude cushionto set up the pattern.

In addition to a glide calculator, a MacCready ring onthe variometer allows the pilot to easily read the speedto fly for different sink rates. MacCready rings are spe-cific to the type of glider and are based on the glider per-formance polar.(See Chapter 4–Flight Instruments for adescription of the MacCready ring.) Accurately flyingthe correct speed in sinking air, while flying slower inlift, can extend the achieved glide considerably.

Many models of electronic glide calculators now exist.Often coupled with an electronic variometer, theydisplay the altitude necessary for distance and windas input by the pilot. In addition, many electronicglide calculators feature speed-to-fly functions thatindicate whether the pilot should fly faster or slower.Most electronic speed-to-fly directors include audioindications, so the pilot can keep eyes outside thecockpit. The pilot should have manual backups forelectronic glide calculators and speed-to-fly directorsin case of a low battery or other electronic systemfailure.

Figure 11-2. Navigational plotter.

Figure 11-3. Circular glide calculator.

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Other equipment may be needed to verify soaring per-formance for Federation Aeronautique Internationale(FAI) badge or record flights. These include turn-pointcameras, barographs, and GPS flight recorders. Forcomplete descriptions of these items, as well as badgeor record rules, check the Soaring Society of Americaweb site (www.ssa.org).

Finally, a notepad or small leg-attached clipboard onwhich to make notes before and during the flight isoften handy. Notes prior to flight could include weatherinformation like winds aloft forecasts or distancebetween turn points. In flight, noting takeoff and starttime, as well as time around any turn points, is useful togauge average speed around the course.

NAVIGATION Airplane pilots navigate by pilotage (flying by ref-erence to ground landmarks) or dead reckoning(computing a heading from true airspeed and wind,then estimating time needed to fly to a destination).Glider pilots use pilotage since they generally cannotremain on a course line over a long distance and do notfly one speed for any length of time. Nonetheless, it is

important to be familiar with the concepts of dead reck-oning since a combination of the two methods is some-times needed.

USING THE PLOTTERMeasuring distance with the plotter is accomplished byusing the straight edge. Use the Albuquerque sectionalchart and measure the distance between Portales Airport(Q34) and Benger Airport (Q54), by setting the plotterwith the zero mark on Portales. Read the distance of 47NM to Benger. Make sure to set the plotter with the sec-tional scale if using a sectional chart (as opposed to theWAC scale), otherwise the measurement will be off bya factor of two. [Figure 11-4]

The true heading between Portales and Benger can bedetermined by setting the top of the straightedge alongthe course line, then slide it along until the index hole ison a line of longitude intersecting the course line. Readthe true heading on the outer scale, in this case, 48°. Theouter scale should be used for headings with an easterlycomponent. If the course were reversed, flying from

Figure 11-4. Measuring distance using the navigational plotter.

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Benger to Portales, use the inner scale, for a westerlycomponent, to find 228°. [Figure 11-5]

A common error when first using the plotter is to readthe course heading 180° in error. This error is easy tomake by reading the scale marked W (270°) instead ofthe scale marked E (090°). For example, the coursefrom Portales to Benger is towards the northeast, so theheading should be somewhere between 30° and 60°,therefore the true heading of 48° is reasonable.

Calculating heading and groundspeed when there is acrosswind component along the course can be done byusing the wind triangle. [Figure 11-6] Suppose thecourse is 50°, the true airspeed (TAS) is 70 knots, andthe wind at cruise altitude is 190° at 20 knots. On a sheetof paper, draw a line representing north-south. Mark a

reference point midway along the north-south line, anddraw a line along 50° using the plotter and label it Cfor course. Designate the original point along thenorth-south line as point A. Next, using either the WACor sectional scale on the plotter, draw a line from thereference point A along 190°. Make this line 20 mileslong and label it W for wind. Mark the end of the linepoint B. Set the 0-mile mark on the plotter straightedgeat point B and rotate the plotter until the 70-mile markintersects line C. The heading can be obtained from thenew line (label it H) and is found to be 61°. Thegroundspeed is determined by measuring the distancepoint B and where the H line intersects line C and isfound to be 84 knots.

Construction of the wind triangle is useful if cruising ina self-launch glider under power at a constant indicated

Figure 11-5. Navigational plotter.

11-6

speed and altitude. This also assumes the winds at alti-tude do not change along the course, which is reason-able for a course of 100 miles or so. For longerdistances, winds aloft may change along the course.Normal soaring flight involves glides that vary in alti-tude (so the winds will vary), drifting off course whilethermalling, deviations from course to follow the bestlift, and frequent speed variations for lift and sink. Sothe wind triangle is of limited use on soaring flights,and usually glider pilots simply estimate the crab angleneeded for a given crosswind component. It is a usefulexercise to devise a few scenarios and note the crabangle needed for varying airspeeds. For instance, cruis-ing 60 knots will require about 20° of crab with a 20knot direct crosswind, while only 15° is needed for thesame crosswind cruising at 80 knots.

A SAMPLE CROSS COUNTRY FLIGHTFor training purposes, plan a triangle course starting atPortales Airport (Q34), with turn points at BengerAirport (Q54), and the town of Circle Back. As part ofthe preflight preparation, draw the course lines for thethree legs. Using the plotter, determine the true heading

for each leg, then correct for variation and make writ-ten note of the magnetic heading on each leg. Use 9°easterly variation as indicated on the sectional chart(subtract easterly variations, and add westerly varia-tions). For the first leg, the distance is 47 NM with atrue heading of 48° (39° magnetic), the second leg is 38NM at 178° true (169° magnetic) and the third leg is 38NM at 282° true (273° magnetic). [Figure 11-7]

Assume the base of the cumulus is forecast to be 11,000MSL, and the winds aloft indicate 320° at 10 knots at9,000 MSL and 330° at 20 knots at 12,000 MSL. Makewritten note of the winds aloft for reference during theflight. Mentally note the estimated crab angle neededto remain on course along each leg. For instance, thefirst leg will have almost a direct crosswind from theleft; on the second leg, a weaker crosswind componentfrom the right; while the final leg will be almostdirectly into the wind. Knowing courses and approxi-mate headings aids the navigation and helps avoidinggetting lost, even though deviations to stay with thebest lift are often needed. During the flight, if the skyahead shows several equally promising cumulus

Figure 11-6. Construction of the wind triangle.

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clouds, choosing the one closest to the course linemakes the most sense.

As further preflight preparation, study the course linealong each leg for expected landmarks. For instance,the first leg follows highway and parallel railroadtracks for several miles before the highway turns north.The town of Clovis should become obvious on the left.Note the Class D airspace around Cannon Air ForceBase (AFB) just west of Clovis—this could be an issueif better clouds lead to a north of course track. Also,with the northwesterly flow, it is possible to be cross-ing the path of aircraft on a long final approach to the

northwest-southeast runway. Note that Clovis Airport(CVN) has parachute activity—be aware that they willdrop upwind of the airport if they are active. Next thetowns of Bovina and then Friona should come intoview. The proximity of the Texico VOR near Bovinaindicates that alertness needs to be taken for power traf-fic in the vicinity. The second leg has fewer landmarks.After about 25 miles, the town of Muleshoe and the air-port will be straddled. Note that the Reese 1 MOA cov-ers part of this leg of the flight and the next leg. Thedimensions of the MOA can be found on the sectionalchart, and the AFSS should be consulted concerningthe active times of this airspace. Approaching the sec-

Figure 11-7. Cross-country triangle.

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ond turn point it is easy to confuse the towns of CircleBack and Needmore. The clues are the position ofCircle Back relative to a 466 feet AGL obstruction(south and east) and the lack of a road that heads northout of Needmore. Landmarks on the third leg includepower transmission lines, Coyote Lake (possibly dry),Salt Lake, the small town of Arch and a major roadcoming south out of Potales. About eight miles fromPortales a VOR airway is crossed.

After a thorough preflight of the glider and all theappropriate equipment is stowed or in position for usein flight, it is time to go fly. Once in the air and oncourse, try to verify the winds aloft. Use pilotage toremain as close to the course line as soaring conditionspermit. If course deviations become necessary, stayaware of the location of the course line to the next turnpoint. For instance, the cu directly ahead indicates lift,but the one 30° off course indicates possibly even morelift, it may be better not to deviate. If the cu left ofcourse indicates a possible area of lift compared to theclouds ahead and only requires a 10° off course devia-tion, proceed towards the lift. Knowing the presentlocation of the glider and where the course line islocated is important for keeping situational awareness.

Sometimes it is necessary to determine an approximatecourse once already in the air. Assume a few miles beforereaching the town of Muleshoe, on the second leg, theweather ahead is not as forecast and has deteriorated—there is now a shower at the third turn point (Circle Back).Rather than continuing on to a certain landing in the rain,the decision is made to cut the triangle short and try toreturn directly to Portales. Measure and find that Portalesis about 37 miles away, and the estimated true heading isabout 240°. Correct for variation (9° east) for a compassheading of about 231°. The northwesterly wind is almost90° to the new course and requires a 10° or 20° crab tothe right, so a compass heading between 250° and 270°should work, allowing for some drift in thermal climbs.With practice, the entire thought process should take littletime.

The sky towards Portales indicates favorable lift condi-tions. However, the area along the new course includessand hills, an area that may not have good choices foroff-field landings. It may be a good idea to fly moreconservatively until beyond this area and then back towhere there are suitable fields for landing. Navigation,evaluation of conditions ahead, and decision-makingare required until arrival back at Portales or until a safeoff-field landing is completed.

NAVIGATION USING GPSThe GPS navigation systems are available as smallhand-held units. (See Chapter 4—Flight Instrumentsfor information on GPS and electronic flight comput-ers.) Some pilots prefer to use existing flight computers

for final glide and speed-to-fly information and add ahand-held GPS for navigation. A GPS system makesnavigation easier. A GPS unit will display distance andheading to a specified point, usually found by scrollingthrough an internal database of waypoints. Many GPSunits also continuously calculate and display groundspeed. If TAS is also known, the headwind componentcan be calculated from the GPS by subtracting groundspeed from TAS. Many GPS units also feature a mov-ing map display that shows past and present positionsin relation to various prominent landmarks like air-ports. These displays can often be zoomed in and out tovarious map scales. Other GPS units allow you to marka spot for future reference. This feature can be used tomark the location of a thermal before going into a turnpoint, with the hopes that the area will still be activeafter rounding the turn point.

One drawback to GPS units is their attractiveness—itis easy to be distracted by the unit at the expense offlying the glider and finding lift. This can lead to adangerous habit of focusing too much time inside thecockpit rather than scanning outside for traffic. Likeany electronic instrument, GPS units can fail, so it isimportant to have a backup for navigation, such as asectional and plotter.

CROSS–COUNTRY TECHNIQUESThe number one rule of safe cross-country soaring isnever allow the glider to be out of glide range of a suit-able landing area. The alternate landing area may be anairport or a farmer’s field. If thermalling is required justto make it to a suitable landing area, safe cross-countryprocedures are not being practiced.

Before venturing beyond gliding distance from thehome airport, thermalling and cross-country techniquescan be practiced using small triangles or other shortcourses. Three examples are shown in Figure 11-8. Thelength of each leg depends on the performance of theglider, but they are typically small, around 5 or 10miles each. Soaring conditions do not need to beexcellent for these practice tasks but should not be soweak that it is difficult just to stay aloft. On a goodday, the triangle may be flown more than once.Besides locating, entering, and centering thermals oncourse, altitude needed to glide to each turnpointshould be determined using a manual or electronicglide calculator with corrections for wind on each leg.If other airports are nearby, practice finding andswitching to their communication frequency and lis-tening to local traffic. As progress is made along eachleg of the triangle, frequently cross check the altitudeneeded to return to the home airport and abandon thecourse if needed. Setting a minimum altitude of 1,500feet or 2,000 feet AGL to arrive back at the home siteadds a margin of safety. Every landing after a soaringflight should be an accuracy landing.

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Determining winds aloft while en route can be diffi-cult. Often an estimate is the best that can be achieved.A first estimate is obtained from winds aloft forecasts

provided by the AFSS. Once aloft, estimate wind speedand direction from the track of cumulus shadows overthe ground, keeping in mind that the winds at cloudlevel are often different than those at lower levels. Oncloudless days, obtain an estimate of wind by notingdrift while thermalling. If the estimate was for head-wind of 10 knots but you seem to lose more height onglides than the glide calculator indicates, the headwindestimate may be too low and needs to be adjusted.When flying with GPS, determine wind speed fromTAS by simple subtraction. Some flight computersautomatically calculate the winds aloft while other GPSsystems estimate winds by calculating the drift afterseveral thermal turns.

It is important to develop skill in quickly determiningaltitude needed for a measured distance using one ofthe glide calculator tools. For instance, while on across-country flight you are over a good landing spotand the next good landing site is a distance of 12 milesinto a 10-knot headwind. [Figure 11-9] The glide cal-culator shows that 3,200 feet is needed to accomplishthe glide. Add 1,500 feet above ground to allow timeto set up for an off-field landing if necessary, to makethe total needed 4,700 feet. The present height isonly 3,800 feet, not high enough to accomplish the12-mile glide, but still high enough to start alongcourse. Head out adjusting the speed based on theMacCready ring or other speed director. After twomiles with no lift, altitude is almost 3,300 feet, stillnot high enough to glide the remaining 10 miles, buthigh enough to turn back to the last landing site. After

Figure 11-9. Example of a flight profile during a cross-country flight.

Figure 11-8. Examples of practice cross country courses

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almost 4 miles, a 4-knot thermal is encountered at about2,700 feet and you are able to climb to 4,300 feet.During the climb, the downwind drift of the thermalmoves the glider back on course approximately a half-mile. Now there is almost 9 miles to glide to the nextlanding spot, and a check of the glide calculator indi-cates 2,400 feet needed for the glide into the 10 knotheadwind, plus 1,500 feet at the destination, for a totalof 3,900 feet. Now there is 400 feet above the mini-mum glide with a margin to plan the landing.

In the previous example, had the thermal topped at3,600 feet (instead of 4,300 feet) there would not beenough altitude to glide the 9 miles into the 10-knotheadwind. However, there would be enough height tocontinue further on course in hopes of finding more liftbefore needing to turn downwind back to the previouslanding spot. Any cross-country soaring flight involvesdozens of decisions and calculations such as this. Inaddition, safety margins may need to be more conser-vative if there is reason to believe the glide may notwork as planned, for example, other pilots reportingheavy sink along the intended course.

On any soaring flight there is an altitude when a deci-sion must be made to cease attempts to work thermalsand commit to a landing. This is especially true ofcross-country flights in which landings are often inunfamiliar places and feature additional pressures likethose discussed in Chapter 8—Abnormal andEmergency Procedures. It is even more difficult oncross-country flights to switch the mental process fromsoaring to committing to a landing. For beginners, analtitude of 1,000 feet AGL is a recommended minimumto commit to landing. A better choice is to pick a land-ing site by 1,500 feet AGL, which still allows time tobe ready for a thermal while further inspecting theintended landing area. The exact altitude where thethought processes should shift from soaring to landingpreparation depends on the terrain. In areas of theMidwest in the United States, landable fields may bepresent every few miles, allowing a delay in field selec-tion to a lower altitude. In areas of the desert southwestor the Great Basin, landing sites may be 30 or moremiles apart, so focusing on a landing spot must begin atmuch higher altitudes above the ground.

Once committed in the pattern, do not try to thermalaway again. Accidents occur due to stalls or spins fromthermalling attempts in the pattern. Other accidentshave occurred as pilots drifted away from a safe landingspot while trying to thermal from low altitudes. Whenthe thermal dissipated, the pilot was too far beyond thesite to return for a safe landing. It is easy to fall into thistrap! In all the excitement of preparing for an off-fieldlanding, do not forget a pre-landing checklist.

A common first cross-country flight is a 50-kilometer(32 statute miles) straight distance flight with a landing

at another field. The distance is short enough that itcan be flown at a leisurely pace on an average soaringday and also qualifies for part of the FAI Silver Badge.Prepare the course well and find out about all avail-able landing areas along the way. Get to the soaringsite early so there is no rush in the preflight prepara-tions. Once airborne, take time to get a feel for theday’s thermals. If the day looks good enough andheight is adequate to set off on course, go!Committing to a landing away from the home field forthe first time is difficult. The first landing away fromthe home field, whether the goal was reached or not, isa notable achievement.

SOARING FASTER AND FARTHEREarly cross-country flights, including small practicetriangles within gliding range of the home field, areexcellent preparation and training for longer cross-country flights. The FAI Gold Badge requires a 300-km (187 statute miles) cross-country flight, which canbe straight out distance or a declared triangle or outand return flight. An average cross-country speed of20 or 30 MPH may have been adequate for a 32-mileflight, but that average speed is too slow on most daysfor longer flights. Flying faster average cross-countryspeeds also allows for farther soaring flights.

Improvement of cross-country skills comes primarilyfrom practice, but reviewing theory as experience isgained is also important. A theory or technique thatinitially made little sense to the beginner will have realmeaning and significance after several cross-countryflights. Post-flight self-critique is a useful tool toimprove skills.

In the context of cross-country soaring, flying fastermeans achieving a faster average ground speed. Thesecret to faster cross-country lies in spending less timeclimbing and more time gliding. This is achieved by onlyusing the better thermals and spending more time in lift-ing air and less time in sinking air. Optimum speedsbetween thermals are given by MacCready ring theoryand/or speed-to-fly theory, and can be determinedthrough proper use of the MacCready speed ring orequivalent electronic speed director.

On most soaring days there is an altitude range,called a height band, in which the thermal strengthis at a maximum. Height bands can be defined as theoptimum altitude range in which to climb and glideon a given day. For instance, thermals in the lowest3,000 feet AGL may be 200-300 fpm, then increaseto 500 fpm up to 5,000 feet AGL and again weakenbefore topping out at 6,000 feet AGL. In this case,the height band would be 2,000 feet deep between3,000 feet and 5,000 feet AGL. Staying within theheight band gives the best (fastest) climbs. Avoidstopping for weaker thermals while within the height

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band unless there is a good reason. On another day,thermals may be strong from 1,000 feet to 6,000 feetAGL before weakening, which would suggest aheight band 5,000 feet deep. In this case, however,depending on thermal spacing, terrain, pilot experi-ence level, and other factors, the height band wouldbe 2,000 feet or 3,000 feet up to 6,000 feet AGL.Avoid continuing on to the lower bounds of strongthermals (1,000 feet AGL) since failure to find a ther-mal there gives no extra time before committing to alanding. [Figure 11-10]

Determining the top of the height band is a matter ofpersonal preference and experience, but a rule ofthumb puts the top at an altitude where thermals dropoff to 75 percent of the best achieved climb. If maxi-mum thermal strength in the height band is 400 fpm,leave when thermals decrease to 300 FPM for morethan a turn or two. The thermal strength used to deter-mine the height band should be an average achievedclimb. Many electronic variometers have an averagefunction that display average climb over specific timeintervals. Another technique involves simply timingthe altitude gained over 30 seconds or 1 minute.

Theoretically, the optimum average speed is attained ifthe MacCready ring is set for the achieved rate-of-

climb within the height band. To do this, rotate the ringso that the index mark is at the achieved rate of climb(for instance 400 fpm) rather than at zero (the settingused for maximum distance). A series of climbs andglides gives the optimum balance between spendingtime climbing and gliding. The logic is that on strongerdays, the extra altitude lost by flying faster betweenthermals is more than made up in the strong lift duringclimbs. Flying slower than the MacCready setting doesnot make the best use of available climbs. Flying fasterthen the MacCready setting uses too much altitudebetween thermals; it then takes more than the optimumamount of time to regain the altitude.

Strict use of the MacCready ring assumes that the nextthermal is at least as strong as that set on the ring andcan be reached with the available altitude. Efforts tofly faster must be tempered with judgement when con-ditions are not ideal. Factors which may require depar-ture from the MacCready ring theory include terrain(extra height needed ahead to clear a ridge), distance tothe next landable spot, or deteriorating soaring condi-tions ahead. If the next thermal appears to be out ofreach before dropping below the height band, eitherclimb higher, glide more slowly, or both.

To illustrate the use of speed-to-fly theory, assumethere are four gliders at the same height. Ahead arethree weak cumulus clouds, each produced by 200-fpmthermals, then a larger cumulus with 600 fpm under itas in Figure 11-11 on the next page.

• Pilot #1 sets his ring to 600 fpm for the antici-pated strong climb under the large cumulus, buthis aggressive approach has him on the groundbefore reaching the cloud.

• Pilot #2 sets his ring for 200 fpm and climbsunder each cloud until resetting the ring to 600fpm after climbing under the third weak cumu-lus, in accordance with strict speed-to-fly theory.

• Pilot #3 is conservative and sets his ring to zerofor the maximum glide.

• Pilot #4 calculates the altitude needed to glide tothe large cumulus using an intermediate settingof 300 fpm, and finds she can glide to the cloudand still be within the height band.

By the time Pilot #4 has climbed under the large cumu-lus, she is well ahead of the other two airborne pilotsand is relaying retrieve instructions for Pilot #1. Thisexample illustrates the science and art of faster cross-country soaring. The science is provided by speed-to-fly theory, while the art involves interpreting andmodifying the theory for the actual conditions.Knowledge of speed-to-fly theory is important as a

Figure 11-10. Example of the height band.

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foundation. How to apply the art of cross-country soar-ing stems from practice and experience.

The height band changes during the day. On a typicalsoaring day, thermal height and strength often increasesrapidly during late morning, then both remain some-what steady for several hours during the afternoon. Theheight band rises and broadens with thermal height.Sometimes the top of the height band is limited by thebase of cumulus clouds. Cloud base may slowlyincrease by thousands of feet over several hours, inwhich case the height band also increases over severalhours. Thermals often “shut off” rapidly late in the day,so a good rule of thumb is to stay higher late in the day.[Figure 11-12]

It is a good idea to stop and thermal when at or near thebottom of the height band. Pushing too hard can lead toan early off-field landing. At best, pushing too hardleads to lost time at lower altitudes because you are try-ing to climb away in weak lift.

Another way to increase cross-country speed is to avoidturning at all! A technique known as dolphin flight canbe used to cover surprising distances on thermal dayswith little or no circling. The idea is to speed up in sinkand slow down in lift while only stopping to circle inthe best thermals. The speed-to-fly between lift areas isbased on the appropriate MacCready setting. This tech-nique is effective when thermals are spaced relativelyclose together, as occurs along a cloud street.

As an example, assume two gliders are flying under acloud street with frequent thermals and only weak sinkbetween thermals. Glider #1 conserves altitude and

stays close to cloud base by flying best L/D throughweak sink. To stay under the clouds, he is forced to fly

Figure 11-11. Examples of glides achieved for different MacCready ring settings.

Figure 11-12. Thermal height and height band (shaded) vs.time of day.

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faster in areas of lift, exactly opposite of flying fast insink, slow in lift. Glider #2 uses the conditions moreefficiently by flying faster in the sink and slower in lift.In a short time, Glider #2 has gained distance on Glider#1. At the end of the cloud street, one good climbquickly puts Glider #2 near cloud base and well aheadof Glider #1. [Figure 11-13]

On an actual cross-country flight, a combination of dol-phin flight and classic climb and glide is frequentlyneeded. In a previous example, the two pilots whodecided not to stop and circle in the weaker thermalswould still benefit from dolphin flight techniques in thelift and sink until stopping to climb in the strong lift.

SPECIAL SITUATIONS

COURSE DEVIATIONSDiversion on a soaring cross-country flight is the normrather than the exception. Some soaring days supplyfair-weather cumulus evenly-spaced across all quad-rants, but even these days cycle and it is beneficial todeviate toward stronger lift. Deviations of 10° or lessadd little to the total distance and should be used with-out hesitation to fly toward better lift. Even deviationsup to 30° are well worthwhile if they lead toward betterlift and/or avoid suspected sink ahead. The sooner thedeviation is started, the less total distance will be cov-ered during the deviation. [Figure 11-14]

Figure 11-13. Advantage of proper speed to fly under a cloud street.

Figure 11-14. Effect of starting course deviations at different times. White arrows show extra distance and indicate the benefitof early course deviations.

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Deviations of 45° or even 90° may be needed to avoidpoor conditions ahead. An example might be a largecloudless area or a shaded area where cumulus havespread out into stratus clouds. Sometimes deviations inexcess of 90° are needed to return to active thermalsafter venturing into potentially dead air.

Deviations due to poor weather ahead should be under-taken before the flight becomes unsafe. For instance, ifcloud bases are lowering and showers developing,always have the option for a safe, clear landing areabefore conditions deteriorate too far. It is very easy toleave one safe landing site hoping to beat weather tothe next, only to have both spots go below VFR duringthe glide. Thunderstorms along the course are a specialhazard, since storm outflow can affect surface windsfor many miles surrounding the storm. Do not count onlanding at a site within 10 miles of a strong thunder-storm—sites further removed are safer. Thunderstormsahead often warrant large course deviations, even up to180° (i.e., retreat to safety).

LOST PROCEDURESNavigation has become far easier with the advent ofGPS. Since GPS systems are not 100 percent free fromfailure, pilots must still be able use the sectional chartand compass for navigation. It is important to have analternate plan in the event of becoming lost.

As discussed earlier, preflight preparation can help inavoiding becoming lost. Spend some time studying thesectional chart for airports or other notable landmarksalong the route.

If still lost after some initial searching, try to remaincalm. The first priority is to make sure there is a suit-able landing area within gliding distance. Then, if pos-sible, try to find lift, even if it is weak, and climb. Thisbuys time and gives a wider view of the area. Next, tryto estimate the last known position, the course flown,and any possible differences in wind at altitude. Forinstance, maybe the headwind is stronger then antici-pated and not as far along the course as expected. Tryto pin point the present position from an estimate of thedistance traveled for a given period of time and con-firm it with visible landmarks by reference to the sec-tional chart. For instance, if at point X, averagingabout 50 knots, heading north for about 30 minutes,should put you at point Y. Look again at the sectionalchart for landmarks that should be nearby point Y, thensearch the ground for these landmarks. Thermallingwhile searching has the added advantage of allowing awider area of scan while circling.

Once a landmark is located on the sectional and on theground, confirm the location by finding a few othernearby landmarks. For instance, if that is a town below,then the highway should curve like the one shown on

the chart. Does it? If lost and near a suitable landingarea, make certain not to leave the area until certain ofyour location. Airport runways sometimes providevaluable clues. The airport name is often painted righton the runway. Failing that, the runway orientationitself may indicate the airport.

If all efforts fail, attempt a radio call to other soaringpilots in the area. A description of what is below andnearby may bring help from a fellow pilot more famil-iar with the area.

CROSS–COUNTRY USING ASELF-LAUNCHING GLIDERA self-launch glider can give the pilot much morefreedom in exchange for a more complex and expen-sive aircraft. First, a self-launch glider allows the pilotto fly from airports without a towplane or towpilot.Second, the engine can be used to avoid off-field land-ings and extend the flight. In theory, when low in aself-launcher, simply start the engine and climb tothe next source of lift. This second advantage haspitfalls and dangers of its own and has lead to manyaccidents due to engine failure and/or improperstarting procedures. Engines on self-launch glidersare generally not quite as reliable as those on air-planes and are susceptible to special problems. Forinstance, in the western United States, summer ther-mals often extend to altitudes where the air is cold.The self-launch engine can become cold soaked,after several hours of flight and may take more timeto start or may fail to start altogether.

Over reliance on the engine may result in a falsesense of security. This can lead pilots to glide overunlandable terrain, something they might not nor-mally do. If the engine then fails just when neededmost, the pilot has no safe place to land. Some acci-dents have occurred when the engine starting systemwas actually fully functional, but in the rush to startthe engine to avoid landing, the pilot did not performa critical task, such as switching the ignition on.Other accidents have occurred when the engine didnot start right away, and while trying to solve thestarting problem, the pilot flew too far from a suit-able landing area. For self-launch gliders with anengine that stows in the fuselage behind the cockpit,the added drag of an extended engine can reduce theglide ratio by 50 to 75 percent![Figure 11-15]

The critical decision height to commit to an enginestart on a self-launch glider is typically higher than theminimum to commit to landing of a non-poweredglider. This is due to a combination of time needed toactually start the engine and extra drag during thestarting process. It may take anywhere from 200 feetto 500 feet of altitude to extend and start the engine.Whereas a pure glider may commit to landing at 1,000

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feet AGL, the self-launch pilot will likely opt for 1,500feet AGL, depending on the glider and landing optionsshould the engine fail. In this sense, the self-launchglider becomes more restrictive.

Cross-country flight can also be done under power witha self-launching glider, or a combination of poweredand soaring flight. For some self-launch gliders, themost efficient distance per gallon of fuel is achieved bya maximum climb under power followed by a power-off glide. Check the GFM/POH for recommendations.

Another type of glider features a sustainer engine.These engines are not powerful enough to self-launchbut are able to keep the glider airborne if lift fails. Thesustainer engine is typically less complex to operatethan their self-launch counterparts, and can eliminatethe need for a time-consuming retrieve. Pilots flyingwith a sustainer are susceptible to the same pitfalls astheir self-launch counterparts.

HIGH–PERFORMANCE GLIDER OPERATIONS AND CONSIDERATIONSExtended cross-country flights have been made in rela-tively low-performance gliders. However, on any givensoaring day, a glider with a 40-to-1 glide ratio will beable to fly farther and faster than one with 20-to-1,assuming the pilots in each have similar skill levels.Often a glider pilot looks for more performance in aglider to achieve longer and faster cross-country flights.

High-performance gliders are usually more complexand somewhat more difficult to fly, but they vary con-siderably. Current Standard Class gliders (15-meterwingspan and no flaps) are easy to assemble and newertypes are comparatively easier to fly. On the other endof the spectrum, Open Class gliders (unlimitedwingspan with flaps) can feature wingspans of 24

meters or more with wings in four sections. The expe-rience required to fly a high-performance glider cannot be quantified simply in terms of a pilot’s totalglider hours. Types of gliders flown (low- and high-performance) must be considered.

Most high-performan ce gliders are single-seat. If atwo-seat, high-performance glider is available, thepilot should obtain some instruction from an author-ized flight instructor before attempting to fly a single-seat high-performance glider for the first time. Beforeflying any single-seat glider, pilots should thoroughlyfamiliarize themselves with the GFM/POH, includingimportant speeds, weight and balance issues, and alloperating systems in the glider GFM/POH such aslanding gear, flaps, and wheel-brake location.

As mentioned, most high-performance gliders are com-plex. Almost all have retractable landing gear, so pilotsmust make certain that “landing gear down” is on theirpre-landing checklist. Most landing-gear handles are onthe right side of the cockpit, but a few are on the leftside, so caution is required when reaching for a handleto make sure it is not flaps or airbrakes. A common erroris to neglect to retract the landing gear and then mistak-enly retract it as part of the pre-landing checklist. A gear-up landing in a glider usually only causesembarrassment and minor damage. The distancebetween the pilot and the runway with the landing gearup is minimal, however, providing no real “cushioning”protection for the pilot in case of a hard landing.

Many high-performance gliders have flaps. A fewdegrees of positive flap can be used when thermalling,and some gliders have 30° or more positive flap set-tings for slower landing speeds. Flaps can be set to 0°for relatively slow-speed glides, while negative flapsettings are available for glides at faster speeds. The

Figure 11-15. Effect on the glide ratio of the engine being extended but not running.

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GFM/POH and glider polar provide recommended flapsettings for different speeds, as well as maximumspeeds allowed for different flap settings. A few high-performance gliders have no airbrakes and use onlylarge positive flap settings for landing. This systemallows for steep approaches but can be unconfortablefor a pilot who has only used spoilers or divebrakes forlanding. A thorough ground briefing is required.

Many high-performance gliders have longer wingspansthat require special care to avoid ground loops on take-off or landing. Runway lights and other obstructionsnear the runway can become a problem. If a wingtipstrikes the ground before the glider has touched down,a cartwheel is a possibility, leading to extensive dam-age and serious injury. Gliders with long wings oftenhave speed restrictions for dive-brake use to avoidsevere bending loads at the wingtips.

The feel of the controls on high-performance gliders islight, and pilot-induced oscillations (PIOs) occur easilywith the sensitive elevator. Elevator movements usingthe wrist only, while the forearm rests on the thigh, canaid in avoiding PIOs.

Some high-performance gliders have only one center-of-gravity (CG) tow hook either ahead of the landinggear or in the landing gear well. If the CG hook iswithin the landing gear well, retracting the gear on towinterferes with the towrope. Even if the glider has anose hook, retracting the gear on tow is not recom-mended, since the handle is usually on the right cockpitside and switching hands to raise the gear can lead tolose of control on tow. A CG hook, as compared to anose hook, makes a crosswind take-off more difficultsince the glider can weathervane into the wind moreeasily. In addition, a CG hook makes the glider moresusceptible to “kiting” on take-off, especially if the fly-ing CG is near the aft limit. This can present a seriousdanger to the towpilot.

Most high-performance gliders are built from compos-ites, instead of metal or wood, with a gelcoat finish.The gelcoat is susceptible to damage from exposure toultraviolet radiation (UV) from the sun as well as pro-longed exposure to moisture. At some soaring sites,pilots can keep the glider assembled in a hanger, butmore frequently, the composite glider is rigged beforeflying and derigged after flying. The transition tohigh-performance gliders necessitates developmentof checklists and discipline during glider assemblyand disassembly. Other considerations for gelcoatcare include extreme cold soaking. There is evidencethat flying a composite glider with a gelcoat finish tovery high and cold altitudes followed by a quickdescent to warmer levels can seriously reduce the lifeof the gelcoat. Composite gliders appear to be moresusceptible to flutter than metal gliders. Flutter is a

function of true airspeed, thus the GFM/POH of com-posite gliders sometimes present a table of the indi-cated VNE for different heights. For instance, a populartwo-seat composite glider shows 135 knots as the sealevel VNE, 128 knots at 10,000 feet MSL, 121 knots at13,000 feet MSL, etc. Read the GFM/POH carefullyand abide by the limits.

Many high-performance gliders have the capability ofadding water ballast. A heavier glider has a higherminimum sink rate and speed; thus it has a larger cir-cling radius. A glider with water ballast achieves thesame glide ratio but at a higher speed than the sameglider without water ballast. To maximize averagecross-country speed on a day with strong thermals,water ballast can be used. The gain in speed betweenthermals outweighs the lost time due to slightly slowerclimbs with water ballast. If thermals are weak, ballastshould not be used. If strong thermals become weakthe water ballast can be dumped. In any case, waterballast should be dumped before landing becauseheavy wings are more difficult to keep level on theground roll and a hard landing is more likely to lead todamage with a heavier glider. Dump times vary but aretypically between two and five minutes.

Water ballast is carried in the wings in built-in tanks orwater bags. The latter works well but has been knownto have problems with leaks. Filling and dumping sys-tems vary from glider to glider, and it is vital to befamiliar with the ballast system as described in theGFM/POH. Filling without proper venting can lead tostructural damage. Care must be taken to ensure thatboth wings are filled with the same amount of water. Ifone wing has a few extra gallons, it can be lead toground loops and loss of control on take-off, especiallyin the presence of a crosswind.

Water unfortunately expands when going from liquidto solid state. The force of the water ballast freezingcan be enough to split composite wing skins. If antici-pating flying at levels where the temperature might bebelow 0°C, follow the GFM/POH recommended addi-tive to avoid freezing.

Some gliders have a small ballast tank in the tail aswell as ballast in the wings. Tail ballast is an effectivemeans to adjust for a CG that is too far forward. Itshould be used with caution, however, since the posi-tion of the tail ballast tank gives it a long arm aft of theempty CG. A careless calculation can lead to too muchwater in the tail tank and a flying CG that is aft of thelimits.

CROSS–COUNTRY USING OTHER LIFT SOURCESMany world distance and speed records have been bro-ken using ridge or wave lift. Under the right conditions,

11-17

these lift sources can extend for hundreds of miles fromsunrise to sunset. Ridge or wave lift is often more con-sistent than thermals, allowing long, straight stretchesat high speed.

Cross-country on ridge lift poses some special prob-lems and considerations. Often the best lift is veryclose to the ridge crest where the air can be quite tur-bulent. Great concentration is needed over severalhours close to terrain in rough conditions for longerflights. On relatively low ridges, for instance in theeastern United States; ridge lift may not extend veryhigh, so the pilot is never too far from a potential off-field landing. These are not conditions for the begin-ning cross-country pilot. In milder conditions, gaps inthe ridge may require thermalling to gain enoughheight to cross the gap. Ridge lift can provide a placeto temporarily wait for thermals to generate. Forinstance, if cumulus have spread out to form a stratuslayer shading the ground and eliminating thermals, awind facing slope can be used to maintain soaringflight until the sun returns to regenerate thermals.

Wave lift can also provide opportunities for longand/or fast cross-country flights. Most record flights

have been along mountain ranges with flights in excessof 2,000 km having been flown in New Zealand andalong the Andes. In the United States, speed records havebeen set using the wave in the lee of the Sierra NevadaMountains. In theory, long-distance flights could also bemade by climbing high in wave then gliding with a strongtailwind to the next range downwind for another climb.Special consideration to pilot physiology (cold, oxygen,etc.) and airspace restrictions are needed when consider-ing a cross-country flight using wave.

Convergence zones can also be used to enhance cross-country speed. Even if the convergence is not a con-sistent line but merely acts as a focus for thermals,dolphin flight is often possible, making glides overlong distances possible without thermalling. Whenflying low, awareness of local, small-scale conver-gence can help the pilot find thermal triggers to helpthem climb back to a comfortable cruising height.

It is possible to find ridge, thermal, wave, and evenconvergence lift during one cross-country flight.Optimum use of the various lift sources requires men-tal agility but makes for an exciting and rewardingflight.

11-18

A

ABSOLUTE ALTITUDE, 4-7ACUTE FATIGUE, 1-14ADVECTION, 9-5 ADVERSE YAW, 3-12, 7-23AERODYNAMICS, 3-1AERONAUTICAL CHARTS, 11-1

sectional, 11-1WAC, 11-3

AERONAUTICAL DECISION MAKING, 1-2AERONAUTICAL INFORMATION MANUAL

(AIM), 9-26AEROTOW EMERGENCIES, 7-4AEROTOW LAUNCH, 7-1

launch procedures, 7-2AILERONS, 2-2AIR DENSITY, 3-2AIRFOIL, 3-1AIR MASSES, 9-4, 9-11AIRMET, 9-37, 11-2AIRSPACE, 11-2AIRSPEED, 4-1, 4-2

true, 4-2indicated, 4-2minimum control, 4-3, 4-4, 7-26placard, 5-5. 5-6maneuvering, 4-3L/D Speed, 4-3, 5-5minimum sink, 4-3, 5-5aero tow, 4-3ground launch, 4-3flaps extended, 4-3never exceed, 4-3indicator, 4-1calibrated, 4-2

AIRSPEED CONTROL, 7-26ALCOHOL, 1-15ALTIMETER, 4-4ALTITUDE, 4-7, 5-1

indicated, 4-7true, 4-7absolute, 4-7pressure, 4-7density, 4-7

AMPLITUDE, 9-20ANGLE OF ATTACK, 3-1, 3-14

ANGLE OF BANK, 3-11ANGLE OF INCIDENCE, 3-1ANXIETY, 1-6AREA FORECAST, 9-36ARM, 5-10ASPECT RATIO, 3-7ASSEMBLY TECHNIQUES, 6-1ASYMMETRICAL AIRFOIL, 3-1ATMOSPHERE, 9-1ATMOSPHERIC PRESSURE, 5-1ATMOSPHERIC STABILITY, 9-4, 9-6ATMOSPHERIC SOUNDINGS, 9-4ATTITUDE, 4-16ATTITUDE INDICATOR, 4-16AUTO LAUNCH PROCEDURES, 7-11AUTO-ROTATION, 7-31AUTO TOW, 7-2AUTOMATED FLIGHT SERVICE STATION, 9-25,11-2AVIATION AREA FORECAST, 9-36AVIATION ROUTINE WEATHER REPORT, 9-33AVIATION WEATHER SERVICES, 9-25AWARDS, 11-4, 11-5AXES, 3-8

BBAILOUT, 10-12BALLAST, 5-5, 5-13BANK ANGLE, 3-11BAROGRAPH, 11-2BASE LEG, 7-35BASIC FLIGHT MANEUVERS, 7-22BERNOULLI’S PRINCIPLE, 3-3BEST GLIDE (L/D) AIRSPEED, 5-5, 7-34BOXING THE WAKE, 7-10

CCALCULATOR, 11-3

I-1

I-2

CALIBRATED AIRSPEED (CAS), 4-2CAS (CALIBRATED AIRSPEED), 4-2CAMBER, 3-1CAP CLOUD, 9-22CARBON MONOXIDE POISONING, 1-13CENTER OF GRAVITY, 5-11CENTER OF PRESSURE, 3-1CENTRIFUGAL FORCE, 3-11CENTRIPETAL FORCE, 3-11CG, 3-8, 5-11CHART SYMBOLS, 11-1CHORD LINE, 3-1CHRONIC FATIGUE, 1-14CLEARING TECHNIQUES, 10-5CLOUDS, 10-1

cumulonimbus, 9-13cumulus, 10-1lenticular, 10-12

CLOUD FORMATION, 10-1CLOUD STREETS, 9-11CONVECTION, 9-5CONVECTIVE CONDENSATION LEVEL (CCL), 9-10CONVECTIVE OUTLOOK CHART, 9-37CONVENTIONAL TAIL, 2-4CONVERGENCE, 9-4, 9-23, 10-18, 11-17CRITICAL ANGLE OF ATTACK, 3-14CROSS-COUNTRY PLANNING, 11-1CROSS-COUNTRY PREPARATION, 11-1CROSS-COUNTRY PROFILE, 11-6CROSS-COUNTRY SOARING, 11-1CROSSWIND LANDING, 7-36CROSSWIND TAKEOFF, 7-3, 7-15, 7-18CUMULONIMBUS CLOUDS, 10-2CUMULUS CLOUDS, 10-1CUMULUS CONGESTUS, 9-13

DDATUM, 4-7DEAD RECKONING, 11-4DECISION MAKING PROCESS, 1-3DEFINITIONS, 5-10DEHYDRATION, 1-14DENSITY, 9-2DENSITY ALTITUDE, 5-1DIHEDRAL, 3-7DISORIENTATION, 1-12DIVE BRAKES, 2-2DOWNDRAFTS, 9-14DOWNWIND LANDING, 7-38DOWNWIND LEG, 7-35DRAG, 3-4

induced drag, 3-4parasite drag, 3-4total drag, 3-5

DROGUE CHUTE, 8-15DRUGS, 1-15DRY ADIABAT, 9-6DRY ADIABATIC LAPSE RATE (DALR), 9-6DUATS, 9-26DUST DEVILS, 10-2DYNAMIC PRESSURE, 3-6

EEFAS, 9-39EARS, 1-11ELECTRONIC FLIGHT COMPUTERS, 4-9ELEVATOR, 2-3EMERGENCY OXYGEN, 8-18EMERGENCY PROCEDURES, 7-4

aerotow, 7-4ground launch, 7-16self-launching glider, 7-22

EMPENNAGE, 2-3ENROUTE FLIGHT ADVISORY SERVICE, 9-39ENTRY LEG, 7-35

F

FATIGUE, 1-14chronic, 1-14acute, 1-14skill, 1-14

FEDERAL AVIATION REGULATIONS, 1-2FINAL APPROACH, 7-35FLAPS, 2-2

plain, 2-2slotted, 2-2fowler, 2-2negative, 2-2

FLAPS EXTENDED SPEED, 4-3FLIGHT COMPUTER, 4-9FLIGHT CONTROLS, 2-2FLIGHT MANUALS, 5-5FLUTTER, 3-10FREEZING RAIN, 9-31FRONTAL WEATHER, 9-28FUSELAGE, 2-1

GG-FORCES, 4-17G-METER, 4-17GEOGRAPHIC COORDINATES, 4-10

latitude, 4-10longitude, 4-10

I-3

GLIDER INDUCED OSCILLATIONS, 8-5GLIDING TURNS, 3-11, 3-12GRAVEYARD SPIRAL, 1-13GRAVITY, 3-8GROUND CREW PROCEDURES, 6-1GROUND EFFECT, 3-14GROUND HANDLING, 6-2,GROUND LAUNCH PROCEDURES, 7-11

auto tow, 7-12auto pulley tow, 7-14winch launch, 7-12

GUST-INDUCED OSCILLATIONS, 8-4GYROSCOPIC, 4-15

instruments, 4-15, 4-16principles, 4-15

HHAIL, 9-13HAZARDOUS ATTITUDES, 1-6HEATSTROKE, 1-15HEADING INDICATOR, 4-16HIGH DENSITY ALTITUDE 5-2HIGH DRAG DEVICES, 2-2HIGH LIFT DEVICES, 2-2HIGH TOW, 7-7HOUSE THERMALS, 10-2HUMAN FACTORS, 1-2HYPERVENTILATION, 1-11HYPOXIA, 1-10

IIAS (INDICATED AIRSPEED), 4-2IMPACT PRESSURE, 4-1INCLINOMETER, 4-14INDICATED AIRSPEED (IAS), 4-2INDICATED ALTITUDE, 4-7INERTIA, 3-11INVERSION, 9-3ISOHUMES, 9-32ISOPLETH, 9-32ISOTHERM, 9-32

LLANDING GEAR, 2-4LANDINGS, 7-21

crosswind, 7-3downwind, 7-38off-field, 8-9

LANDMARKS, 11-7

LAPSE RATE, 9-3LATERAL AXIS, 3-8LATITUDE, 4-10LAUNCH EQUIPMENT, 7-12LAUNCH EQUIPMENT INSPECTION, 6-2LAUNCH PROCEDURES, AEROTOW, 7-7LAUNCH SIGNALS, 7-1

aerotow, 7-1ground, 7-12

L/D SPEED, 5-5, 7-34LENTICULAR CLOUDS, 9-22LIFT, 3-2LIFT SOURCES, 10-18

convergence, 10-18slope lift, 10-10thermal lift, 10-1wave lift, 10-12

LIFT-TO-DRAG (L/D) RATIO, 5-5, 5-6LIMIT LOAD, 4-3LOAD FACTOR, 3-11

flight envelope, 5-10LONGITUDE, 4-10LONGITUDINAL AXIS, 3-8LOW DENSITY ALTITUDE, 5-2LOW LEVEL SIGNIFICANT WEATHER

PROGNOSTIC CHART, 9-28LOW TOW, 7-7

MMAGNETIC COMPASS, 4-11

deviation, 4-12variation, 4-12errors, 4-12, 4-13lag, 4-13, 4-14

MAGNETIC NORTH POLE, 4-11MAGNETIC DEVIATION, 4-12MAGNETIC VARIATION, 4-12MALFUNCTIONS, 8-10, 8-11, 8-12, 8-13, 8-14, 8-15,

8-16, 8-17MANEUVERS, 7-22MANEUVERING SPEED, 4-3MEDICAL FACTORS, 1-10MESOSCALE CONVECTIVE SYSTEMS (MCS), 9-15MICROBURSTS, 9-14MIDDLE EAR PROBLEMS, 1-11MILITARY OPERATIONS AREA, 9-26MILITARY TRAINING ROUTES, 9-26MINIMUM CONTROL AIRSPEED, 7-26MINIMUM SINK SPEED, 5-6, 7-33MIXING RATIO, 9-9MOISTURE, 5-2MOMENT, 5-11MOTION SICKNESS, 1-13

I-4

MOUNTAIN SOARING, 10-12MOUNTAIN WAVES, 10-1, 10-12MULTI-CELL THUNDERSTORM, 9-14

NNAVIGATION, 11-4

pilotage, 11-4checkpoints, 11-7dead reckoning, 11-4radio navigation, 11-8plotter, 11-4

NAVIGATION PLOTTER, 11-4NETTO, 4-9,NORTH POLE, 4-11NOTAMS, 9-26

OOBSCURED SKY, 9-28, 9-29OCCLUDED FRONTS, 9-27OFF-FIELD LANDINGS, 8-7OXYGEN, 8-15

systems, 8-15OXYGEN DURATION, 6-4

PPARACHUTES, 7-32, 8-18PERFORMANCE INFORMATION, 5-6PERFORMANCE SPEEDS, 5-6, 5-7, 5-8

L/D ratio, 5-5, 5-6, 5-7minimum sink, 5-5, 5-6, 5-7, 5-8curves, 5-5, 5-6, 5-7

PERFORMANCE MANEUVERS, 7-22PERSONAL EQUIPMENT, 11-2

preflight inspection, 11-2PHYSIOLOGICAL TRAINING, 1-11PILOT REPORTS, 9-34PILOTAGE, 11-4PILOT–INDUCED OSCILLATIONS, 8-1PIREP, 9-34PITCH, 3-1PITOT-STATIC SYSTEM, 4-1PLACARD SPEEDS, 5-5, 5-6PLOTTER, 11-3POLARS, 5-6PORPOISING, 8-1POWER FAILURE, 8-7POWERPLANT, 2-4POSITIVE CONTROL CHECK, 6-4PRECESSION, 4-15PRECIPITATION, 9-29, 9-31

drizzle, 9-31

freezing rain, 9-31hail, 9-31ice pellets, 9-31rain, 9-31snow, 9-31thunderstorms, 9-31

PREFLIGHT AND GROUND OPERATIONS, 6-4inspection, 6-4

PRELAUNCH CHECKS, 6-4PRESSURE, 9-2PRESSURE ALTITUDE, 5-1PRESSURE LAPSE RATE, 9-3PSYCHOLOGICAL ASPECTS, 1-14

RRADAR SUMMARY CHART, 9-28RADAR WEATHER REPORTS, 9-34RADIANT ENERGY, 9-1RADIO EQUIPMENT, 4-9RADIO NAVIGATION, 11-8RADIUS OF TURN, 3-12RAIN, 9-29, 9-31RATE-OF-CLIMB, 5-5RATE OF TURN, 3-12REGULATIONS, 1-2RELATIVE WIND, 3-1RELEASE FAILURE, 7-9RIDGE AND SLOPE SOARING, 10-9RIDGE LIFT, 10-10RIGIDITY IN SPACE, 4-15RISK MANAGEMENT, 1-4ROLL, 2-2ROLL-IN, 7-24ROLL-OUT, 7-24ROTOR, 9-22RUDDER, 2-3

SSAFETY LINKS, 6-3SAILPLANE, 1-1SATURATED ADIABATIC LAPSE RATE (SALR), 9-7SCUBA DIVING, 1-16SECTIONAL CHARTS, 11-1SELF-LAUNCH GLIDERS, 1-1, 7-18, 7-19, 7-20, 7-21, 7-22SELF-LAUNCH TAKEOFF, 7-18SIGMET, 11-2SITUATIONAL AWARENESS, 1-9SKIDS, 7-24SKILL FATIGUE, 1-14SLACK LINE, 7-10

I-5

SLIPS, 3-12, 7-36forward, 3-13, 7-37side, 3-13, 7-37turning, 7-23 7-25

SLOPE SOARING, 9-18SLOW FLIGHT, 7-26SNOW, 9-29, 9-31SOARING TECHNIQUES, 10-1SPATIAL DISORIENTATION, 1-12SPEED-TO-FLY, 5-6SPEED RING, 4-8SPIN, 3-14, 7-31SPIRAL DIVES, 7-25SPOILERS, 2-2SQUALL LINE, 9-15STABILATOR, 2-3STABILITY, 3-8

atmospheric, 9-6directional, 3-10dynamic, 3-9lateral, 3-10longitudinal, 3-9negative, 3-8neutral, 3-8positive, 3-8static, 3-8

STALL, 3-14, 7-26, 7-27STALL SPEED, 3-11, 3-14STANDARD ATMOSPHERE, 5-1STATIC PRESSURE, 4-1STATIC STABILITY, 3-8STEEP TURNS, 7-25STRAIGHT GLIDES, 7-22STRESS, 1-13STRESS MANAGEMENT, 1-7SUPERCELL, 9-14SURFACE ANALYSIS CHART, 9-27

TT-TAIL, 2-4TAKEOFF, 7-2, 7-11, 7-18TAS (TRUE AIRSPEED), 4-2TEMPERATURE, 5-2, 9-2TEMPERATURE INVERSION, 9-3TEMPERATURE LAPSE RATE, 9-3TERMINAL AERODROME FORECAST, 9-34THERMAL, 9-4, 10-4, 10-5THERMAL ACTIVITY, 10-1, 10-2, 10-3THERMAL INDEX, 9-9THERMAL PRODUCTION, 10-1, 10-2, 10-3THERMAL SOARING, 9-4, 10-4, 10-5, 10-6, 10-7THERMAL WAVES, 9-12THERMODYNAMIC DIAGRAM, 9-8THRUST, 3-8THUNDERSTORM, 9-13

TIEDOWN, 6-2TOTAL ENERGY COMPENSATORS, 4-8TOWING, 7-2

aerotow, 7-2TOWHOOK, 2-4, 6-3, 7-11, 8-14TOW POSITIONS, 7-7TOW RELEASE, 7-9, 7-11TOWRINGS, 6-3TOWROPE, 6-2TOW SPEEDS, 7-12TRAFFIC PATTERNS, 7-34, 7-35TRAILERING, 6-1TRANSCRIBED WEATHER BROADCAST, 9-39TRIM DEVICES, 2-3TRUE AIRSPEED (TAS), 4-2TRUE ALTITUDE, 5-1TURBULENCE, 3-14TURN COORDINATION, 3-12TURN COORDINATOR, 4-16TURNING FLIGHT, 3-11, 7-22

drag in turns, 7-23radius of turn, 7-23, 7-24rate of turn, 7-23, 7-24stall speed in turns, 3-11

TURNS ON TOW, 7-7TWEB, 9-39

UUPDRAFTS, 9-13

VV-TAIL, 2-4VARIOMETER, 4-7

electric, 4-8total energy, 4-8

VERTICAL AXIS, 3-8VG DIAGRAM, 5-10

WWAKE, 7-7WASHOUT, 3-7,WATER VAPOR, 9-1WAVE FORMATION, 9-20, 10-13WAVELENGTH, 9-20, 10-13WAVE SOARING, 9-20, 10-12WAVE WINDOWS, 10-12WEAK LINK, 6-3WEATHER, 9-25WEATHER BRIEFINGS, 9-25WEATHER CHARTS, 9-27

I-6

WEATHER DEPICTION CHART, 9-27WEATHER HAZARDS, WEATHER REPORTS AND FORECASTS, 9-27WEIGHT, 3-8, 5-4WEIGHT AND BALANCE, 5-8, 5-10, 5-11, 5-12, 5-13

graph, 5-12, 5-13,WHEEL BRAKES, 2-4WINCH LAUNCH, 7-12WINCH TOW, 7-12WIND, 5-3

WIND TRIANGLE, 11-5WINDS AND TEMPERATURES ALOFT, 9-26, 9-30

forecast, 9-30, 9-38WING PLANFORM, 3-6WINGWALKERS, 6-2

WORKLOAD MANAGEMENT, 1-8WORLD AERONAUTICAL CHARTS, 11-3

Y

I-7

YAW, 3-8, 3-10adverse yaw, 3-12, 7-23

YAW STRING, 4-14

ADVECTION—The transport ofan atmospheric variable due tomass motion by the wind. Usuallythe term as used in meteorologyrefers only to horizontal transport.

AILERONS—The hinged portionof the trailing edge of the outerwing used to bank or roll aroundthe longitudinal axis.

AIR DENSITY—The mass of airper unit volume.

AIRFOIL—The surfaces on aglider that produce lift.

AIR MASS—A widespread massof air having similar characteristics(e.g., temperature), which usu-ally helps to identify the sourceregion of the air. Fronts are dis-tinct boundaries between airmasses.

AMPLITUDE—In wave motion,one half the distance between thewave crest and the wave trough.

ANGLE OF ATTACK—Theangle formed between the relativewind and the chord line of thewing.

ANGLE OF INCIDENCE—Theangle between the chord line ofthe wing and the longitudinal axisof the glider. The angle of inci-dence is built into the glider by themanufacturer and cannot beadjusted by the pilot’s movementsof the controls.

ASPECT RATIO—The ratio be-tween the wing span and the meanchord of the wing.

BEST GLIDE SPEED (BESTL/D SPEED)—The airspeed thatresults in the least amount of alti-tude loss over a given distance.This speed is determined from theperformance polar. The manufac-turer publishes the best glide (L/D)airspeed for specified weights andthe resulting glide ratio. For exam-ple, a glide ratio of 36:1 meansthat the glider will lose 1 foot of alti-tude for every 36 feet of forwardmovement in still air at this air-speed.

CAMBER—The curvature of awing when looking at a cross sec-tion. A wing has upper camber onits top surface and lower camberon its bottom surface.

CAP CLOUD—Also called afoehn cloud. These are cloudsforming on mountain or ridge topsby cooling of moist air rising on theupwind side followed by warmingand drying by downdrafts on thelee side.

CENTERING—Adjusting circleswhile thermalling to provide thegreatest average climb.

CENTER OF PRESSURE—The point along the wing chord linewhere lift is considered to be con-centrated.

CENTRIFUGAL FORCE—Theapparent force occurring in curvilin-ear motion acting to deflect objectsoutward from the axis of rotation.For instance, when pulling out of adive, it is the force pushing youdown in your seat.

ASYMMETRICALAIRFOIL—One in which the uppercamber differs from the lower cam-ber.ATMOSPHERIC SOUNDING—A measure ofatmo-spheric variables aloft, usu-ally pressure, temperature, humid-ity, and wind.

ATMOSPHERICSTABILITY—Describes a state inwhich an air parcel will resist verti-cal displacement, or once dis-placed (for instance by flow over ahill) will tend to return to its originallevel.

BAILOUT BOTTLE—Small oxy-gen cylinder connected to the oxy-gen mask supplying severalminutes of oxygen. It can be usedin case of primary oxygen systemfailure or if an emergency bailoutat high altitude became necessary.

BALLAST—Term used todescribe any system that addsweight to the glider. Performanceballast employed in some glidersincreases wing loading usingreleasable water in the wings (viaintegral tanks or water bags).This allows faster average cross-country speeds. Trim ballast isused to adjust the flying CG, oftennecessary for light-weight pilots.Some gliders also have a smallwater ballast tank in the tail foroptimizing flying CG.

BAROGRAPH—Instrument forrecording pressure as a function oftime. Used by glider pilots to verifyflight performance for badge orrecord flights.

G-1

G-2

CENTRIPETAL FORCE—Theforce in curvilinear motion actingtoward the axis of rotation. Forinstance, when pulling out of adive, it is the force that the seatexerts on the pilot to offset the cen-trifugal force.

CHORD LINE—An imaginarystraight line drawn from the lead-ing edge of an airfoil to the trailingedge.CLOUD STREETS—Parallel rowsof cumulus clouds. Each row can beas short as 10 miles or as long as a100 miles or more.

COLD SOAKED—Condition ofa self-launch or sustainer enginemaking it difficult or impossible tostart in flight due to long-timeexposure to cold temperatures.Usually occurs after a long soaringflight at altitudes with cold temper-atures, e.g., a wave flight.

CONVECTION—Transport andmixing of an atmospheric variabledue to vertical mass motions (e.g.,updrafts).

CONVECTIVE CONDENSAT-ION LEVEL (CCL)—The level atwhich cumulus will form from sur-face-based convection. Under thislevel, the air is dry adiabatic, andthe mixing ratio is constant.

CONVENTIONAL TAIL—Aglider design with the horizontalstabilizer mounted at the bottom ofthe vertical stabilizer.

CONVERGENCE—A netincrease in the mass of air over a specified

area due to horizontal wind speedand/or direction changes. Whenconvergence occurs in lower lev-els, it is usually associated withupward air motions.

CONVERGENCE ZONE—Anarea of convergence, sometimesseveral miles wide, at other times

sure remain constant, in order toattain saturation with respect towater.

DIHEDRAL—The angle at whichthe wings are slanted upward fromthe root to the tip.

DIURNAL EFFECTS—A dailyvariation (may be in temperature,moisture, wind, cloud cover, etc.)especially pertaining to a cyclecompleted within a 24-hour period,and which recurs every 24 hours.

DOLPHIN FLIGHT—Straightflight following speed-to-fly theory.Glides can often be extended andaverage cross-country speedsincreased by flying faster in sink andslower in lift without stopping to cir-cle.

DOWNBURST—A strong, con-centrated downdraft, often associ-ated with a thunderstorm. Whenthese reach the ground, theyspread out, leading to strong andeven damaging surface winds.

DRAG—The force that resists themovement of the glider throughthe air.

DRY ADIABAT—A line on a ther-modynamic chart representing arate of temperature change at thedry adiabatic lapse rate.

DRY ADIABATIC LAPSE RATE(DALR)—The rate of decrease oftemperature with height of unsatu-rated air lifted adiabatically (notheat exchange). Numerically thevalue is 3°C or 5.4°F per 1,000feet.

DUST DEVIL—A small vigorouscirculation that can pick up dust orother debris near the surface toform a column hundreds or eventhousands of feet deep. At theground, winds can be strongenough to flip an unattended gliderover on its back. Dust devils markthe location where a thermal isleaving the ground.

very narrow. These zones oftenprovide organized lift for manymiles along the convergencezone, for instance, a sea-breezefront.

CRITICAL ANGLE OF ATTACK—Angle of attack, typi-cally around 18°, beyond which astall occurs. The critical angle ofattack can be exceeded at any air-speed and at any nose attitude.

CROSS COUNTRY—In soaring,any flight out of gliding range of thetake-off airfield. Note that this isdifferent than the definitions in theCFRs for meeting the experiencerequirements for various pilot cer-tificates and/or ratings.

CUMULUS CONGESTUS—Acumulus cloud of significant verti-cal extent and usually displayingsharp edges. In warm climates,these sometimes produce precipi-tation. Also called towering cumu-lus, these clouds indicate thatthunderstorm activity may soonoccur.

CUMULONIMBUS (CB)—Alsocalled thunderclouds, these aredeep convective clouds with a cir-rus anvil and may contain any ofthe characteristics of a thunder-storm: thunder, lightning, heavyrain, hail, strong winds, turbulence,and even tornadoes.

DEAD RECKONING—Naviga-tion by computing a heading fromtrue airspeed and wind, then esti-mating time needed to fly to a des-tination.

DENSITY ALTITUDE—Pres-sure altitude corrected for nonstan-dard temperature variations.Performance charts for many oldergliders are based on this value.

DEWPOINT (OR DEWPOINTTEMPERATURE)—The temper-ature to which a sample of air mustbe cooled, while the amount ofwater vapor and barometric pres-

G-3

DYNAMIC STABILITY—Aglider’s motion and time requiredfor a response to static stability.

ELEVATOR—Attached to theback of the horizontal stabilizer,the elevator controls movementaround the lateral axis.

EMPENNAGE—The tail group ofthe aircraft usually supporting thevertical stabilizer and rudder, aswell as the horizontal stabilizerand elevator, or on some aircraft,the V-Tail.

FLAPS—Hinged portion of thetrailing edge between the aileronsand fuselage. In some glidersailerons and flaps are intercon-nected to produce full-span “flap-erons.” In either case, flapschange the lift and drag on thewing.FLUTTER—Resonant conditionleading to rapid, unstable oscilla-tions of part of the glider structure(e.g., the wing) or a control surface(e.g., elevator or aileron). Flutterusually occurs at high speeds andcan quickly lead to structural fail-ure.

FORWARD SLIP—A slide usedto dissipate altitude without increas-ing the glider’s speed, particularly ingliders without flaps or with inopera-tive spoilers.

GLIDER—A heavier-than-air air-craft that is supported in flight bythe dynamic reaction of the airagainst its lifting surfaces, andwhose free flight does not dependon an engine.

GRAUPEL—Also called soft hailor snow pellets, these are white,round or conical ice particles 1/8 to1/4 inch diameter. They often formas a thunderstorm matures andindicate the likelihood of lightning.

Meteorological Conditions(VMC). Gliders rarely fly in IMCdue to instrumentation and air traf-fic control requirements.

INVERSION—Usually refers toan increase in temperature withheight, but may also be used forother atmospheric variables.

ISOHUMES—Lines of equal rel-ative humidity.

ISOPLETH—A line connectingpoints of constant or equal value.

ISOTHERM—A contour line ofequal temperature.

KATABATIC—Used to describeany wind blowing down slope.

KINETIC ENERGY—Energy dueto motion, defined as one half masstimes velocity squared.

LAPSE RATE—The decreasewith height of an atmospheric vari-able, usually referring to tempera-ture, but can also apply topressure or density.LATERAL AXIS—An imaginarystraight line drawn perpendicularly(laterally) across the fuselage andthrough the center of gravity. Pitchmovement occurs around the lat-eral axis, and is controlled by theelevator.

LENTICULAR CLOUD—Smooth, lens-shaped cloudsmarking mountain-wave crests.They may extend the entire lengthof the mountain range producingthe wave and are also called waveclouds or lennies by glider pilots.

LIFT—Produced by the dynamiceffects of the airstream acting onthe wing, lift opposes the down-ward force of weight.

LIMIT LOAD—The maximum

GROUND EFFECT—A reduc-tion in induced drag for the sameamount of lift produced. Within onewingspan above the ground, thedecrease in induced drag enablesthe glider to fly at a slower air-speed. In ground effect, a lowerangle of attack is required to pro-duce the same amount of lift.

HEIGHT BAND—The altituderange in which the thermals arestrongest on any given day.Remain-ing with the height bandon a cross-country flight shouldallow the fastest average speed.

HOUSE THERMAL—A thermalthat forms frequently in the sameor similar location.

HUMAN FACTORS—The studyof how people interact with theirenvironments. In the case of gen-eral aviation, it is the study of howpilot performance is influenced bysuch issues as the design of cock-pits, the function of the organs ofthe body, the effects of emotions,and the interaction and communi-cation with the other participants ofthe aviation community, such asother crewmembers and air trafficcontrol personnel.

INDUCED DRAG—Drag that isthe consequence of developing liftwith a finite-span wing. It can berepresented by a vector thatresults from the differencebetween total and vertical lift.

INERTIA—The tendency of amass at rest to remain at rest, or ifin motion to remain in motion,unless acted upon by some exter-nal force.

INSTRUMENTMETEOROLOGICALCONDITIONS (IMC)—Meteor-ological conditions expressed interms of visibility, distance fromcloud, and ceiling less than theminimum specified for Visual

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load, expressed as multiples ofpositive and negative G (force ofgravity), that an aircraft can sus-tain before structural damagebecomes possible. The load limitvaries from aircraft to aircraft.

LOAD FACTOR—The ratio ofthe load supported by the glider’swings to the actual weight of theaircraft and its contents.

LONGITUDINAL AXIS—Animaginary straight line runningthrough the fuselage from nose totail. Roll movement occurs aroundthe longitudinal axis, and is con-trolled by the ailerons.

MESOSCALE CONVECTIVESYSTEM (MCS)—A large clusterof thunderstorms with horizontaldimensions on the order of 100miles. MCSs are sometimesorganized in a long line of thunder-storms (e.g., a squall line) or as arandom grouping of thunder-storms. Individual thunderstormswithin the MCS may be severe.

MICROBURST—A small-sizeddownburst of 2.2 nautical mile orless horizontal dimension.

MINIMUM SINK AIRPSEED—Airspeed, as determined by theperformance polar, at which theglider will achieve the lowest sinkrate. That is, the glider will lose theleast amount of altitude per unit oftime at minimum sink airspeed.

MIXING RATIO—The ratio of themass of water vapor to the massof dry air.

MULTI-CELLTHUNDERSTORM—A group orcluster of individual thunderstormcells, with varying stages of devel-opment. These storms are oftenself propagating and may last forseveral hours.

PARASITE DRAG—Drag

due to any form of electromagneticradiation, for instance, from thesun.

RADIUS OF TURN—The amountof horizontal distance an aircraftuses to complete a turn.

RATE OF TURN—The amountof time it takes for a glider to turn aspecified number of degrees.

RELATIVE WIND—The airflowcaused by the motion of the air-craft through the air. Relativewind, also called relative airflow isopposite and parallel to the direc-tion of flight.

ROTOR—A turbulent circulationunder mountain-wave crests, tothe lee side and parallel to themountains creating the wave.Glider pilots use the term rotor todescribe any low-level turbulentflow associated with mountainwaves.

ROTOR STREAMING—A phe-nomenon that occurs when the airflow at mountain levels may besufficient for wave formation, butbegins to decrease with altitudeabove the mountain. In this case,the air downstream of the moun-tain breaks up and becomes turbu-lent, similar to rotor, with no leewaves above.

RUDDER—Attached to the backof the vertical stabilizer, the ruddercontrols movement about the ver-tical axis.SAILPLANE—A glider used fortraveling long distances andremaining aloft for extended peri-ods of time.

SATURATED ADIABATICLAPSE RATE(SALR)—The rateof temperature decrease withheight of saturated air. Unlike thedry adiabatic lapse rate (DALR),the SALR is not a constant numer-ical value but varies with tempera-ture.

caused by any aircraft surface,which deflects or interferes withthe smooth airflow around the air-plane.

PILOTAGE—Navigational tech-nique based on flight by referenceto ground landmarks.

PILOT-INDUCEDOSCILLATION (PIO)—Rapidoscillations caused by the pilot’sover-controlled motions. PIOs usu-ally occur on takeoff or landingswith pitch sensitive gliders and insevere cases can lead to loss ofcontrol or damage.

PITCH ATTITUDE—The angleof the longitudinal axis relative tothe horizon. Pitch attitude servesas a visual reference for the pilotto maintain or change airspeed.

PITOT-STATIC SYSTEM—Powers the airspeed altimeter andvariometer by relying on air pres-sure differences to measure gliderspeed, altitude, and climb or sinkrate.

PLACARDS—Small statementsor pictorial signs permanently fixedin the cockpit and visible to thepilot. Placards are used for oper-ating limitations (e.g., weight orspeeds) or to indicate the positionof an operating lever (e.g., landinggear retracted or down andlocked).

PRECIPITABLE WATER—Theamount of liquid precipitation thatwould result if all water vapor werecondensed.

PRESSURE ALTITUDE—Theheight above the standard pressurelevel of 29.92 in. Hg. It is obtainedby setting 29.92 in the barometricpressure window and reading thealtimeter.

RADIANT ENERGY—Energy

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SELF-LAUNCH GLIDER—Aglider equipped with an engine,allowing it to be launched under itsown power. When the engine isshut down, a self-launch glider dis-plays the same characteristics asa non-powered glider.

SIDE SLIP—A slip in which theglider’s longitudinal axis remainsparallel to the original flight pathbut in which the flight pathchanges direction according to thesteepness of the bank.

SLIP—A descent with one winglowered and the glider’s longitudi-nal axis at an angle to the flightpath. A slip is used to steepen theapproach path without increasingthe airspeed, or to make the glidermove sideways through the air,counteracting the drift resultingfrom a crosswind.

SPEED TO FLY—Optimumspeed through the (sinking or rising)air mass to achieve either the fur-thest glide or fastest average cross-country speed depending on theobjectives during a flight.

SPIN—An aggravated stall thatresults in the glider descending ina helical, or corkscrew, path.

SPOILERS—Devices on the topsof wings to disturb (spoil) part ofthe airflow over the wing. Theresulting decrease in lift creates ahigher sink rate and allows for asteeper approach.

SQUALL LINE—A line of thun-derstorms often located along orahead of a vigorous cold front.Squall lines may contain severethunderstorms. The term is alsoused to describe a line of heavyprecipitation with an abrupt windshift but no thunderstorms, assometimes occurs in associationwith fronts.

STABILATOR—A one-piece hor-izontal stabilizer used in lieu of anelevator.

forming a T.

THERMAL—A buoyant plume orbubble of rising air.

THERMAL INDEX (TI)—For anygiven level is the temperature ofthe air parcel having risen at thedry adiabatic lapse rate (DALR)subtracted from the ambient tem-perature. Experience has shownthat a TI should be -2 for thermalsto form and be sufficiently strongfor soaring flight.

THERMAL WAVE—Waves, oftenbut not always marked by cloudstreets, that are excited by con-vection disturbing an overlying sta-ble layer. Also called convectionwaves.

THERMODYNAMIC DIAGRAM—A chart presentingisopleths of pressure, tempera-ture, water vapor content, as wellas dry and saturated adiabats.Various forms exist, the most com-monly used in the United Statesbeing the Skew-T/Log-P.

THRUST—The forward force thatpropels a powered glider throughthe air.

TOTAL DRAG—The sum of par-asite and induced drag.

TOWHOOK—A mechanism all-owing the attachment and releaseof a towrope on the glider or tow-plane. On gliders, it is locatednear the nose or directly ahead ofthe main wheel. Two types oftowhooks commonly used in glid-ers are manufactured by Tost andSchweizer.

TRIM DEVICES—Any devicedesigned to reduce or eliminatepressure on the control stick.When properly trimmed, the glidershould fly at the desired airspeedwith no control pressure from thepilot (i.e., “hands off”). Trim mech-anisms are either external tabs on

STABILITY—The glider’s abilityto maintain a uniform flight condi-tion and return to that conditionafter being disturbed.

STALL—Condition that occurswhen the critical angle of attack isreached and exceeded. Airflowbegins to separate from the top ofthe wing, leading to a loss of lift. Astall can occur at any pitch attitudeor airspeed.

STANDARD ATMOSPHERE—A theoretical vertical distribution ofpressure, temperature and densityagreed upon by international con-vention. It is the standard used,for instance, for aircraft perform-ance calculations. At sea level,the standard atmosphere consistsof a barometric pressure of 29.92inches of mercury (in. Hg.) or1013.2 millibars, and a tempera-ture of 15°C (59°F). Pressure andtemperature normally decrease asaltitude increases. The standardlapse rate in the lower atmos-phere for each 1,000 feet of alti-tude is approximately 1 in. Hg. and2°C (3.5°F). For example, thestandard pressure and tempera-ture at 3,000 feet mean sea level(MSL) is 26.92 in. Hg. (29.92 - 3)and 9°C (15°C - 6°C).

STATIC STABILITY—The initialtendency to return to a state ofequilibrium when disturbed fromthat state.

SUPERCELL THUNDERSTORM—A large,powerful type of thunderstorm thatforms in very unstable environ-ments with vertical and horizontalwind shear. These are almostalways associated with severeweather, strong surface winds,large hail, and/or tornadoes.

T-TAIL—A type of glider with thehorizontal stabilizer mounted onthe top of the vertical stabilizer,

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the elevator (or stabilator) or asimple spring-tension system con-nected to the control stick.

TRUE ALTITUDE—The actualheight of an object above meansea level.

V-TAIL—A type of glider with twotail surfaces mounted to form a V.

V-Tails combine elevator and rud-der movements.

VARIOMETER—Sensitive rateof climb or descent indicator thatmeasures static pressure betweenthe static ports and an externalcapacity. Variometers can bemechanical or electrical and canbe compensated to eliminate unre-alistic indications of lift and sink

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due to rapid speed changes.

VERTICAL AXIS—An imaginarystraight line drawn through thecenter of gravity and perpendicu-lar to the lateral and longitudinalaxes. Yaw movement occursaround the vertical axis and iscontrolled by the rudder.

VISUAL METEOROLOGICALCONDITIONS (VMC)—Meteor-ological conditions expressed interms of visibility, distance fromcloud, and ceiling equal to or bet-ter than a specified minimum.VMC represents minimum condi-tions for safe flight using visualreference for navigation and traf-fic separation. Ceilings and visi-bility below VMC constitutesInstrument Meteorolog-icalConditions (IMC).

WASHOUT—Slight twist built intowards the wingtips, designed toimprove the stall characteristics ofthe wing.

WATER VAPOR—Water presentin the air while in its vapor form. Itis one of the most important ofatmospheric constituents.WAVE LENGTH—The distancebetween two wave crests or wavetroughs.

WAVE WINDOW—Special areasarranged by Letter of Agreementwith the controlling ATC whereingliders may be allowed to fly underVFR in Class A Airspace at certaintimes and to certain specified alti-tudes.

WEIGHT—Acting vertically throughthe glider’s center of gravity, weightopposes lift.

WIND TRIANGLE Navigationalcalculation allowing determinationof true heading with a correction

for crosswinds on course.