AC 65-15A - Airframe & Powerplant Mechanics - Airframe Handbook
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AC65-15A Airfrarne 4 Powerplant MECHANICS AIRFRAME HANDBOOK U.S. DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION TION
Transcript of AC 65-15A - Airframe & Powerplant Mechanics - Airframe Handbook
AC 65-15A - Airframe & Powerplant Mechanics - Airframe HandbookU.S. DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMIN~STRA TION
For sale by the U.S. Govemmcnt Prinling Office Superinrenclent of Documents, Mail Step: SSOP, WISIJin&ton, OC 20402-9328
ISBN 0-16-036209-1
PREFACE
This handbook was developed and first printed in 1972 as one of a series of three handbooks for persons preparing for certification as an airframe or powerplant mechanic. It i.s intended that this handbook will provide basic information on prin· ciples, fur.tlamentals and technical procedures in the subject matter areas relating to the airframe rating. It is designed to aid students enrolled in a formal course of instruction as well as the individual who is studying on his own. Since the knowl edge requirements for the airframe and powerplant ratings closely parallel each other in some subject areas, the chapters which discuss fire protection systems and electrical systems contain some material which is also duplicated in the Airframe and Powerplant Mechanics Powerplant Handbook, AC 65-12A.
This volume contains information on airframe construction features, assembly and rigging, fabric covering, structural repairs, and aircraft welding. The hand book also contains an explanation of the units which make up the various airframe systems.
Because there are so many different types of aircraft in use today, it is reason able to expect that differences exist in airframe components and systems. To avoid undue repetition, the practice of using representative systems and units is carried out throughout the handbook. Subject matter treatment is from a generalized point of view, and should be supplemented by reference to manufacturers' p~anuals or other textbooks if more detail is desired. This handbook is not intended to replace, substitute for, or supersede official regulations or the manufacturers' instructions.
Grateful acknowledgement is extended to the manufacturers of engines, pro pellers, and powerplant accessories for their cooperation in making material avail able for inclusion in this handbook.
Copyright material is used by special permission of the following organizations and may not be extracted or reproduced without permission of the copyright owner.
Monsanto Chemicals Co. Townsend Corporation
J. 0. King, Inc. Gravines, Inc. Walter Kidde DuPont De Nemours National Fire Protection Association
National Association of Fire Extinguisher Distributors
Flight Safety Foundation American Petroleum Institute Exxon Corporation Parker Hannifin Goodyear Tire and Rubber Co.
Firestone
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(R) Skydrol ® Fluids Cherry Rivets Acres Sleeves Acres Sleeves Fire Extinguishers Fire Extinguishers Fire Extinguishants Fire Extinguisher and Extinguishant Specifications Fire Extinguishers
Refueling Data Aviation Fuels Aviation Fuels Aircraft Fittings Aircraft Tires Aircraft Wheels Aircraft Brakes Aircraft Tires
Bendix Energy Controls
Puritan Equipment, Inc.
Aircraft Wheels Aircraft Brakes Plastics Portable Oxygen Generators in the DC-10 Air Conditioning Aircraft Tires Aircraft Wheels Aircraft Brakes Portable Oxygen Generators
The advancements in aeronautical technology dictate that an instructional hand· book must be under continuous review and brought up to date periodically to be valid. Flight Standards requested comments, from the certificated mechanic schools on the three handbooks. As a result, the handbooks have been updated to this extent: indicated errors have been corrected, new material has been added in the areas which were indicated as being deficient, and some material has bcc11 rearranged to improve the usefulness of the handbooks.
We would appreciate having errors brought to our attention, as well as receiv ing suggestions for improving the usefulness of the handbooks. Your comments and suggestions will be retained in our files until such time as the next revision will be accomplished.
Address all correspondence relating to these handbooks to:
U.S. Department of Transportation Federal Aviation Administration Flight Standards National Field Office P.O. Box 25082 Oklahoma City, Oklahoma 73125
The companion handbooks to AC 65-15A are the Airframe and Powerplant Mechanics General Handbook, AC 65-9A and the Airframe and Powerplant Me chanics Powerplant Handbook, AC 65-12A.
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CONTENTS
CO~E~S ------------------------------------------------------- v
CHAPTER 1. AIRCRAFT STRUCTURES
General ------------------------------------------------------- 1 Major Structural Stresses ---------------------------------------- 1 Fixed-Wing Aircraft -------------------------------------------- 2 Fu~lage ------------------------------------------------------ 2 Wing Structure ------------------------------------------------ 6 Nacelles or Pods ----------------------------------------------- 13 ED1pennage ---------------------------------------------------- 16 Flight Control Surfaces ------------------------------------------ 18 Landing Gear -------------------------------------------------- 23 Skin and Fairing ----------------------------------------------- 24 Access and Inspection Doors ------------~------------------------- 24 Helicopter Structures -------------------------------------------- 24
CHAPTER 2. ASSEMBLY AND RIGGING
General ------------------------------------------------------- 27 Theory of Flight ----------------------------------------------- 27 AerodynaJilics -------------------------------------------------- 27 The AtDlosphere ------------------------------------------------ 27 Pre~ure ------------------------------------------------------ 27 Den&ty ------------------------------------------------------- 28 HuDlidity ----------------------------------------------------- 28 Bernoulli's Principle and Subsonic Flow ---------------------------- 29
Motion ------------------------------------------------------- 29 Airfoils ------------------------------------------------------- 30 Center of Gravity ----------------------------------------------- 33 Thrust and Drag ----------------------------------------------- 33 Axes of an Aircraft --------------------------------------------- 35 Stability and Control -------------------------------------------- 35 Control ------------------------------------------------------- 39 Flight Control Surfaces ------------------------------------------ 40 Control Around the Longitudinal Axis ----------------------------- 41 Control Around the Vertical Axis --------------------------------- 44 Control Around the Lateral Axis ---------------------------------- 44
Tabs --------------------------------------------------------- 45 Boundary Layer Control Devices ---------------------------------- 48 Forces Acting on a Helicopter ------------------------------------ 49 Helicopter Axes of Flight ---------------------------------------- 55 High-Speed AerodynaDlics --------------------------------------- 56 Typical Supersonic. Flow Patterns --------------------------------- 59 AerodynaDlic Heating ------------------------------------------- 64 Flight Control SysteDls ------------------------------------------ 64 Hydraulic Operated Control SysteJils ------------------------------ 65
Cable Guides -------------------------------------------------- 66 Mechanical Linkage -------------------------------------------- 68
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CHAPTER 2. ASSEMBLY AND RIGGING-(Cont.)
Torque Tubes -------------------------------------------------- 68 Stops --------------------------------------------------------- 68 Control Surface Snubbers and Locking Devices ---------------------- 69 Aircraft Rigging ----------------------------------------------- 70 Rigging Checks ------------------------------------------------ 72 Adjustment of Control Surfaces ----------------------------------- 75 Helicopter Rigging --------------------------------------------- 77 Principles of Balancing or Re-balancing ---------------------------- 80 Re-balancing Procedures ---------------------------------------- 83 Methods------------------------------------------------------- 83
CHAPI'ER 3. AIRCRAFT FABRIC COVERING
Aircraft Fabrics ------------------------------------------------ 85 Miscellaneous Textile Materials ----------------------------------- 88
Seams -------------------------------------------------------- 89 Applying Covering --------------------------------------------- 91 Covering 1Vings ------------------------------------------------ 93 Covering Fuselages --------------------------------------------- 95 Ventilation, Drain, and Inspection Openings ------------------------ 95 Repair of Fabric Covers ----------------------------------------- 99 Replacing Panels in 1Ving Covers ---~----------------------------- 103 Re-covering Aircraft Surface with Glass Ooth ----------------------- 104 Causes of Fabric Deterioration ----------------------------------- 104 Checking Condition of Doped Fabric ------------------------------ 106 Testing Fabric Covering ----------------------------------------- 106 Strength Criteria for Aircraft Fabric ------------------------------ 107 Dopes and Doping---------------------------------------------- 107 Dope Materials ------------------------------------------------- 108 Aluminum-Pigmented Dopes ------------------------------------- 109 Temperature and Humidity Effects on Dope ------------------------ 109 Common Troubles in Dope Application ----------------------------- 109 Technique of Application ---------------------------------------- 110 Number of Coats Required --------------------------------------- 111
CHAPTER 4. AIRCRAFT PAINTING AND FINISHING
General ------------------------------------------------------- 113 Finishing Materials --------------------------------------------- 113 Paint Touchup ------------------------------------------------- 117 Identification of Paint Finishes ----------------------------------- 117 Paint Removal ---------~------------------------~-------------- 117 Restoration of Paint Finishes ------------------------------------- 118 Nitrocellulose Lacquer Finishes ----------------------------------- 118 Acrylic Nitrocellulose Lacquer Finish ------------------------------ 119 Epoxy Finishes ------------------------------------------------ 120 Fluorescent Finishes -------------------------------------------- 121 Enamcl Finishes ------------------------------------------------ 121 Paint System Compatibility -------------------------------------- 122 Methods of Applying Finishes ------------------------------------ 122 Preparation of Paint -------------------------------------------- 123
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Common Paint Troubles ----------------------------------------- 124 Painting Trim and Identification Numbers ------------------------- 125 Decalcomanias (Decals) ----------------------------------------- 125
CHAPTER 5. AIRCRAFT STRUCTURAL REPAIRS
Basic Principles of Sheet Metal Repair ---------------------------·:.: 127 General Structural Repair --------------------------------------- 129 Inspection of Damage ------------------------------------------- 130 Oassification of Damage ---------------------------------------- 131 Stresses in Structural Members ----------------------------------- 131 Special Tools and Devices for Sheet Metal -------------------------- 133 Metalworking Machines ----------------------------------------- 136 Forming Machines ---------------------------------------------- 141 Forming Operations and Terms ----------------------------------- 145 Making Straight Line Bends ------------------------------------- 146 Setback ------------------------------------------------------- 148 Making Layouts ------------------··----------------------------- 151 Hand Forming ------------------------------------------------- 155 Rivet Layout -------------------------------------------------- 164 Rivet Installation ----------------------------------------------- 166 Preparation of Rivet Holes --------------------------------------- 168 Driving Rive~ ------------------------------------------------- 173 Rivet Failures ------------------------------------------------- 175 Removing Rive~ ----------------------------------------------- 177 Special Rive~ -------------------------------------------------- 177 Self-Plugging (Friction Lock) Rivets ------------------------------ 178 Self-Plugging (Mechanical Lock) Rivets --------------------------- 181 Pull-Thru Rivets ----------------------------------------------- 184
Rivnu~ ------------------------------------------------------- 184 Dill Lok-Skrus and Lok-Rive~ ------------------------------------ 186 Deutsch Rivets ------------------------------------------------- 187 Hi-Shear Rivets ------------------------------------------------ 187 Specific Repair Types ------------------------------------------- 189 Structural Sealing ---------------------------------------------- 198 Metal Bonded Honeycomb --------------------------------------- 200 Construction Features ------------------------------------------- 201 Damage ------------------------------------------------------- 201 Repairs ------------------------------------------------------- 202 Repair Materials ----------------------------------------------- 205 Potted Compound Repair ---------------------------------------- 206 Glass Fabric Cloth Overlay Repairs ------------------------------- 208 One Skin .and Core Repair Procedures ----------------------------- 209 Plastics ------------------------------------------------------- 213 Transparent Plastics -------------------------------------------- 213 Storage and Protection ------------------------------------------ 214 Forming Plastics ----------------------------------------------- 215 Installation Procedures ------------------------------------------ 220 Laminated Plastics ---------------------------------------------- 221 Fiber Glass Componen~ ----------------------------------------- 221 Radomes ------------------------------------------------------ 223 Wooden Aircraft Structures -------------------------------------- 224 Inspection of Wooden Structures ---------------------------------- 224 Service and Repair of Wooden Structures -------------------------- 228
Glues --------------------------------------------------------- 230 Gluing -------------------------------------------------------- 232
CHAPTER 5. AIRCRAFT STRUCTURAL REPAIRS-(Cont.)
Spliced Joints -------------------------------------------------- 234 Plywood Skin Repairs -------- ·---------------------------------- 235 Spar and Rib Repair ------------------------------------------- 242 Bolt and Bushing Holes ----------------------------------------- 244 Rib Repairs --------------------------------------------------- 245
CHAPTER 6. AIRCRAFT WELDING
General ------------------------------------------------------- 247 Oxyacetylene Welding Equipment --------------------------------- 248 Welding Positions ---------------------------------------------- 255 Welded Joints -------------------------------------------------- 255 Expansion and Contraction of Metals ------------------------------ 257 Correct Forming of a Weld -------------------------------------- 258 Oxyacetylene Welding of Ferrous Metals --------------------------- 258 Welding Nonferrous Metals Using Oxyacetylene --------------------- 260
Titanium ------------------------------------------------------ 262 Cutting Metal Using Oxyacetylene -------------------------------- 263 Brazing Methods ----------------------------------------------- 264 Soft Soldering ------------------------------------------------- 265 Electric Arc Welding ------------------------------------------- 266 Welding Procedures and Techniques ------------------------------- 269 Welding of Aircraft Steel Structures ------------------------------ 276
CHAPTER 7. ICE AND RAIN PROTECTION
General ------------------------------------------------------- 285 Pneumatic Deicing Systems -------------------------------------- 286 Deicer Boot Construction ---------------------------------------- 287 Deicing System Components -------------------------------------- 288 Pneumatic Deicing System Maintenance --------------------------- 291 Thermal Anti-Icing Systems -------------------------------------- 293 Pneumatic System Ducting -------------------------------------- 296 Ground Deicing of Aircraft -------------------------------------- 299 Windshield Icing Control Systems --------------------------------- 300 Water and Toilet Drain Heaters ---------------------------------- 303 Rain Eliminating Systems --------------------------------------- 303 Maintenance of Rain Eliminating Systems -------------------------- 308
CHAPTER 8. HYDRAULIC AND PNEUMATIC POWER SYSTEMS
Aircraft Hydraulic Systems -------------------------------------- 309 Hydraulic Fluid ------------------------------------------------ 309 Types of Hydraulic Fluids --------------------------------------- 310 Phosphate Ester Base F1uids ------------------------------------- 311 Filters -------------------------------------------------------- 313 Basic Hydraulic System ----------------------------------------- 315 Reservoirs ----------------------------------------------------- .316 Pressure Regulation -------------------------------------------- 323 Actuating Cylinders -------------------------------------------- 328 Selector Valves ------------------------------------------------ 329 Aircraft Pneumatic Systems -------------------------------------- 331 Pneumatic System Components ----------------------------------- 334 Typical Pneumatic Power System --------------------------------- 338
CHAPTER 9. LANDING GEAR SYSTEMS
General ------------------------------------------------------- 341 Main Landing Gear Alignment, Support, Retraction ------------------ 348
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CHAPTER 9. LANDING GEAR SYSTEMS-(Cont.)
Emergency Extension Systems ------------------------------------ 351 Landing Gear Safety Devices ------------------------------------- 351 Nosewheel Steering System -------------------------------------- 354 Shimmy Dampers ---------------------------------------------- 356 Brake Systems ------------------------------------------------- 360 Brake Assemblies ----------------------------------------------~ 366 Inspection and Maintenance of Brake Systems ---------------------- 372 Aircraft Landing Wheels ---------------------------------------- 373 Aircraft Tires -------------------------------------------------- 377 Aircraft Tire Maintenance --------------------------------------- 379 Tire Inspection-Mounted On Wheel ------------------------------ 381 Tire Inspection-Tire Demounted --------------------------------- 382 Tube Inspection ------------------------------------------------ 384 Mounting and Demounting -------------------------------------- 385 Causes of Air Pressure Loss in Tubeless Aircraft Tires ---------------- 389
The Wheel ---------------------------------------------------- 390 Good Pressure Gage Practice ------------------------------------- 391 Repairing ----------------------------------------------------- 392 Operating and Handling Tips ------------------------------------ 394 Tube Repair --------------------------------------------------- 396 Sidewall.Jnflated Aircraft Tires ----------------------------------- 396 Tire Inspection Summary ---------------------------------------- 397 Antiskid System ------------------------------------------------ 399 Landing Gear System Maintenance -------------------------------- 400
CHAPTER 10. FIRE PROTECTION SYSTEMS
General ------------------------------------------------------- 407 Fire Detection Systems ------------------------------------------ 408 Types of Fires ------------------------------------------------- 411 Fire Zone Classification ----------------------------------------- 412 Extinguishing Agent Characteristics ------------------------------- 412 Fire Extinguishing Systems -------------------------------------- 417 Reciprocating Engine Conventional C02 System --------------------- 417 Turbojet Fire Protection System ---------------------------------- 419 Turbine Engine Fire Extinguishing System ------------------------- 420 Turbine Engine Ground Fire Protection ---------------------------- 422 Fire Detection System Maintenance Practices ----------------------- 423 Fire Detection System Troubleshooting ---------------------------- 425 Fire Extinguisher System Maintenance Practices -------------------- 425 Fire Prevention and Protection ----------------------------------- 429 Cockpit and Cabin Interiors -------------------------------------- 429 Smoke Detection Systems ---------------------------------------- 430
CHAPTER 11. AIRCRAFT ELECTRICAL SYSTEMS
General ------------------------------------------------------- 433 Lacing and Tying Wire Bundles ---------------------------------- 444 Cutting Wire and Cable ---------------------------------------- 446 Emergency Splicing Repairs ------------------------------------- 450 Connecting Terminal Lugs to Terminal Blocks ----------------------- 451 Bonding and Grounding ---------------------------------------- 452 Connectors ---------------------------------------------------- 452 Conduit ------------------------------------------------------- 457 Electrical Equipment Installation --------------------------------- 457 Aircraft Lighting Systems --------------------------------------- 459 Maintenance and Inspection o£ Lighting Systems -------------------- 464
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CHAPTER 12. AIRCRAFT INSTRUMENT SYSTEMS
Gener& ----------------------------------------------~-------- 469 ln~rument c~s ---------------------------------------------- 469 Di&s --------------------------------------------------------- 469 Range Markings ----------------------------------------------- 470 Instrument Pands ---------------------------------------------- 470 Repair of Aircrah ln~ruments ----------------------------------- 471 Aircraft Pressure Gages --------------------------------------- _ 471 Pitot-Static System --------------------------------------------- 474 Maintenance of Pitot-Static Systems ------------------------------- 481 Tum-and-Bank lndlcator ---------------------------------------- 482 Synchro-Type Remote Indicating Instruments ----------------------- 483 Remote-Indicating Fud and Oil Pressure Gages --------------------- 485 Capacitor-Type Fuel Quanity System ------------------------------ 485 Angle-of-Attack Indicator ---------------------------------------- 487 Tachometers --------------------------------------------------- 488 Synchroscope -------------------------------------------------- 491 Temperature Indicators ----------------------------------------- 491 Ratiometer Electric& Resistance Thermometer ---------------------- 497 Fuel Flowmeter Systems ----------------------------------------- 497 Gyroscopic Instruments ----------------------------------------- 499 Sources of Power for Gyro Operation ------------------------------ 501 Vacuum-Driven Attitude Gyros ----------------------------------- 504 Pressure-Operated Gyros ---------------------------------------- 506 Vacuum System Maintenance Practices ---------------------------- 506 Electric Attitude Indicator --------------------------------------- 507 Autopilot System ----------------------------------------------- 511 Basic Autopilot Components -------------------------------------- 513 Flight Director Systems ----------------------------------------- 518 Autopilot System Maintenance ------------------------------------ 516
CHAPTER 13. COMMUNICATIONS AND NAVIGATION SYSTEMS
Gener& ------------------------------------------------------- 519 Basic Radio Principles ------------------------------------------ 519 Basic Equipment Components ------------------------------------ 520 Power Supply ------------------------------------------------- 522 Communication Systems ----------------------------------------- 522 Airborne Navigation Equipment ---------------------------------- 524 VHF Omnirange Sy~em ---------------------------------------- 524 Instrument Landing System -------------------------------------- 525 Distance-Measuring Equipment ----------------------------------- 528 Automatic Direction Finders ------------------------------------- 529 Radar Beacon Transponder -------------------------------------- 530 Doppler Navigation Systems ------------------------------------- 530 Inertial Navigation System -------------------------------------- 531 Airborne Weather Radar System --------------------------------- 532 Radio Altimeter ------------------------------------------------ 533 Emergency Locator Transmitter (ELT) ---------------------------- 533 Installation of Communication and Navigation Equipment ------------- 534 Reducing Radio Interference ------------------------------------ 536 ln~&latoin of Aircraft Antenna Systems --------------------------- 537
CHAPTER 14. CABIN ATMOSPHERE CONTROL SYSTEM
Need for Oxygen ---------------------------------------------- 539 Com~tion of the Atmosphere ---------------------------------- 539 Pressur~ation -------------------------------------------------- 541 Air Conditioning and Pressurization Systems ----------------------- 543
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CHAPTER 14. CABIN ATMOSPHERE CONTROL SYSTEM-(Cont.)
Basic Requirements -------------------------------------------- 545 Sources of Cabin Pre~ure --------------------------------------- 545 Supercharger Instruments --------------------------------------- 549 Pre~urization Valves ------------------------------------------- 550 Cabin Pr~ure Control System ----------------------------------, . .,. 551 Air Distribution ----------------------------------------------- 556 Air Conditioning System ---------------------------------------- 558 Heating Systems ----------------------------------------------- 559 Combustion Heaters -------------------------------------------- 561 Maintenance of Combustion Heater Systems ------------------------ 564 Cooling Systems ------------------------------------------------ 565 Air Cycle Cooling System --------------------------------------- 565 Air Cycle System Component Operation --------------------------- 568 Electronic Cabin Temperature Control System ---------------------- 574 Electronic Temperature Control Regulator ------------------------- 575 Vapor Cycle System (Freon) ------------------------------------ 576 Freon System Components --------------------------------------- 577 Description of a Typical System --------------------------------- 580 Air Conditioning and Pr~urization System Maintenance ------------- 583 Cabin Pre~urization Operational Checks --------------------------- 585 Cabin Pr~urization Troubleshooting ----------------------------- 586 Oxygen Systems General ----------------------------------------- 587 Portable Oxygen Equipment ------------------------------------- 587 Smoke Protection Equipment ------------------------------------- 588 Oxygen Cylinders ---------------------------------------------- 588 Solid State Oxygen Systems ------------------------------------- 589 Oxygen Plumbing ---------------------------------------------- 591 Oxygen Valves ------------------------------------------------ 592 Regulators ----------------------------------------------------- 594 Oxygen System Flow Indicators ----------------------------------- 597 Pressure Gages ------------------------------------------------ 597 Oygen Masks -------------------------------------------------- 597 Servicing Gaseous Oxygen Systems ------------------------------- 598 Prevention of Oxygen Fires or Explosions ------------------------- 600
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GENERAL The airframe of a fixed-wing aircraft is generally
considered to consist of five principal units, the fuselage, wings, stabilizers, flight control surfaces, and landing gear. Helicopter airframes consist of the fuselage, main rotor and related gearbox, tail rotor (on helicopters with a single main rotor), and the landing gear.
The airframe components are constructed from a wide variety of materials and are joined by rivets, bolts, screws, and welding or adhesives. The air· craft components are composed of various parts called structural members (i.e., stringers, longerons, ribs, bulkheads, etc.). Aircraft structural members are designed to carry a load or to resist stress. A single member of the structure may be subjected to a combination of stresses. In most cases the struc tural members are designed to carry end loads rather than side loads: that is, to be subjected to tension or compression rather than bending.
Strength may be the principal requirement in cer· tain structures, while others need entirely different qualities. For example, cowling, fairing, and simi· lar parts usually are not required to carry the stresses imposed by flight or the landing loads. However, these parts must have such properties as neat appearance and streamlined shapes.
MAJOR STRUCTURAL STRESSES In designing an aircraft, every square inch of
wing and fuselage, every rib, spar, and even each metal fitting must be considered in relation to the physical characteristics of the metal of which it is made. Every part of the aircraft must be planned to carry the load to be imposed upon it. The determi· nation of such loads is called stress analysis. AI· though planning the design is not the function of the aviation mechanic, it is, nevertheless, important that he understand and appreciate the stresses in volved in order to avoid changes in the original design through improper repairs.
There are five major stresses to which all aircraft are subjected (figure 1-1):
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(1) Tension. (2) Compression. (3) Torsion. (4) Shear. (5) Bending.
CHAPTER 1 AIRCRAFT STRUCTURES
The term "stress" is often used interchangeably with the word "strain." Stress is an internal force of a substance which opposes or resists deforma· tion. Strain is the deformation of a material or substance. Stress, the internal force, can cause strain.
Tension (figure 1-1a) is the stress that resists a force that tends to pull apart. The engine pulls the aircraft forward, but air resistance tries to hold it back. The result is tension, which tries to stretch the aircraft. The tensile strength of a material is measured in p.s.i. (pounds per square inch) and is calculated by dividing the load (in pounds) re quired to pull the material apart by its cross-sec tional area (in square inches).
Compression (figure 1-1b) is the stress that res ists a crushing force. The compressive strength of a material is also measured in p.s.i. Compression is the stress that tends to shorten or squeeze aircraft parts.
Torsion is the stress that produces twisting (figure 1-1c). While moving the aircraft forward, the en· gine also tends to twist it to one side, but other aircraft components hold it on course. Thus, torsion is created. The torsional strength of a material is ita resistance to twisting or torque.
Shear is the stress that resists the force tending to cause one layer of a material to slide over an adjacent layer. Two riveted plates in tension (figure 1-1d) subject the rivets to a shearing force. Usually, the shearing strength of a material is either equal to or less than its tensile or compressive strength. Aircraft parts, especially screws, bolts, and rivets, are often subject to a shearing force.
Bending stress is a combination of compression and tension. The rod in figure 1-1e has been short· ened (compressed) on the inside of the bend and stretched on the outside of the bend.
(a) Tension
(b) Compression
FIGURE 1-1. Five stresses acting on an aircraft.
FIXED-WING AIRCRAFT The principal components of a single-engine, pro
peller-driven aircraft are shown in figure 1-2. Figure 1-3 illustrates the structural components
of a typical turbine powered aircraft. One wing and the empennage assemblies are shown exploded into the many components which, when assembled, form major structural units.
FUSELAGE The fuselage is the main structure or body of the
aircraft. It provides space for cargo, controls, acces sories, passengers, and other equipment. In single engine aircraft, it also houses the powerplant. In
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multi-engine aircraft the engin~ may either be in the fuselage, attached to the fuselage, or suspended from the wing structure. They vary principally in Jize and arrangement of the different compartments.
There are two general types of fuselage construc tion, the truss type, and the monocoque type. A truss is a rigid framework made up of members such as beams, struts, and bars to resist deforma tion by applied loads. The truss-framed fu.CJelage is generally covered with fabric.
Truss Type
The truss type fuselage frame (figure 1-4) is usually constructed of steel tubing welded together in such a manner that all members of the truss can carry both tension and compression loads. In some
.__--Propeller
aircraft, principally the light, single-engine models, truss fuselage frames are col18tructed of aluminum alloy and may be riveted or bolted into one piece, with cross-bracing achieved by using solid rods or tubes.
Monocoque Type
The monocoque (single shell) fuselage relies largely on the strength of the skin or covering to carry the primary stresses. The design may be di vided into three classes: (1) Monocoque, (2) semi· monocoque, or (3) reinforced shell. The true mono coque…
For sale by the U.S. Govemmcnt Prinling Office Superinrenclent of Documents, Mail Step: SSOP, WISIJin&ton, OC 20402-9328
ISBN 0-16-036209-1
PREFACE
This handbook was developed and first printed in 1972 as one of a series of three handbooks for persons preparing for certification as an airframe or powerplant mechanic. It i.s intended that this handbook will provide basic information on prin· ciples, fur.tlamentals and technical procedures in the subject matter areas relating to the airframe rating. It is designed to aid students enrolled in a formal course of instruction as well as the individual who is studying on his own. Since the knowl edge requirements for the airframe and powerplant ratings closely parallel each other in some subject areas, the chapters which discuss fire protection systems and electrical systems contain some material which is also duplicated in the Airframe and Powerplant Mechanics Powerplant Handbook, AC 65-12A.
This volume contains information on airframe construction features, assembly and rigging, fabric covering, structural repairs, and aircraft welding. The hand book also contains an explanation of the units which make up the various airframe systems.
Because there are so many different types of aircraft in use today, it is reason able to expect that differences exist in airframe components and systems. To avoid undue repetition, the practice of using representative systems and units is carried out throughout the handbook. Subject matter treatment is from a generalized point of view, and should be supplemented by reference to manufacturers' p~anuals or other textbooks if more detail is desired. This handbook is not intended to replace, substitute for, or supersede official regulations or the manufacturers' instructions.
Grateful acknowledgement is extended to the manufacturers of engines, pro pellers, and powerplant accessories for their cooperation in making material avail able for inclusion in this handbook.
Copyright material is used by special permission of the following organizations and may not be extracted or reproduced without permission of the copyright owner.
Monsanto Chemicals Co. Townsend Corporation
J. 0. King, Inc. Gravines, Inc. Walter Kidde DuPont De Nemours National Fire Protection Association
National Association of Fire Extinguisher Distributors
Flight Safety Foundation American Petroleum Institute Exxon Corporation Parker Hannifin Goodyear Tire and Rubber Co.
Firestone
iii
(R) Skydrol ® Fluids Cherry Rivets Acres Sleeves Acres Sleeves Fire Extinguishers Fire Extinguishers Fire Extinguishants Fire Extinguisher and Extinguishant Specifications Fire Extinguishers
Refueling Data Aviation Fuels Aviation Fuels Aircraft Fittings Aircraft Tires Aircraft Wheels Aircraft Brakes Aircraft Tires
Bendix Energy Controls
Puritan Equipment, Inc.
Aircraft Wheels Aircraft Brakes Plastics Portable Oxygen Generators in the DC-10 Air Conditioning Aircraft Tires Aircraft Wheels Aircraft Brakes Portable Oxygen Generators
The advancements in aeronautical technology dictate that an instructional hand· book must be under continuous review and brought up to date periodically to be valid. Flight Standards requested comments, from the certificated mechanic schools on the three handbooks. As a result, the handbooks have been updated to this extent: indicated errors have been corrected, new material has been added in the areas which were indicated as being deficient, and some material has bcc11 rearranged to improve the usefulness of the handbooks.
We would appreciate having errors brought to our attention, as well as receiv ing suggestions for improving the usefulness of the handbooks. Your comments and suggestions will be retained in our files until such time as the next revision will be accomplished.
Address all correspondence relating to these handbooks to:
U.S. Department of Transportation Federal Aviation Administration Flight Standards National Field Office P.O. Box 25082 Oklahoma City, Oklahoma 73125
The companion handbooks to AC 65-15A are the Airframe and Powerplant Mechanics General Handbook, AC 65-9A and the Airframe and Powerplant Me chanics Powerplant Handbook, AC 65-12A.
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CONTENTS
CO~E~S ------------------------------------------------------- v
CHAPTER 1. AIRCRAFT STRUCTURES
General ------------------------------------------------------- 1 Major Structural Stresses ---------------------------------------- 1 Fixed-Wing Aircraft -------------------------------------------- 2 Fu~lage ------------------------------------------------------ 2 Wing Structure ------------------------------------------------ 6 Nacelles or Pods ----------------------------------------------- 13 ED1pennage ---------------------------------------------------- 16 Flight Control Surfaces ------------------------------------------ 18 Landing Gear -------------------------------------------------- 23 Skin and Fairing ----------------------------------------------- 24 Access and Inspection Doors ------------~------------------------- 24 Helicopter Structures -------------------------------------------- 24
CHAPTER 2. ASSEMBLY AND RIGGING
General ------------------------------------------------------- 27 Theory of Flight ----------------------------------------------- 27 AerodynaJilics -------------------------------------------------- 27 The AtDlosphere ------------------------------------------------ 27 Pre~ure ------------------------------------------------------ 27 Den&ty ------------------------------------------------------- 28 HuDlidity ----------------------------------------------------- 28 Bernoulli's Principle and Subsonic Flow ---------------------------- 29
Motion ------------------------------------------------------- 29 Airfoils ------------------------------------------------------- 30 Center of Gravity ----------------------------------------------- 33 Thrust and Drag ----------------------------------------------- 33 Axes of an Aircraft --------------------------------------------- 35 Stability and Control -------------------------------------------- 35 Control ------------------------------------------------------- 39 Flight Control Surfaces ------------------------------------------ 40 Control Around the Longitudinal Axis ----------------------------- 41 Control Around the Vertical Axis --------------------------------- 44 Control Around the Lateral Axis ---------------------------------- 44
Tabs --------------------------------------------------------- 45 Boundary Layer Control Devices ---------------------------------- 48 Forces Acting on a Helicopter ------------------------------------ 49 Helicopter Axes of Flight ---------------------------------------- 55 High-Speed AerodynaDlics --------------------------------------- 56 Typical Supersonic. Flow Patterns --------------------------------- 59 AerodynaDlic Heating ------------------------------------------- 64 Flight Control SysteDls ------------------------------------------ 64 Hydraulic Operated Control SysteJils ------------------------------ 65
Cable Guides -------------------------------------------------- 66 Mechanical Linkage -------------------------------------------- 68
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CHAPTER 2. ASSEMBLY AND RIGGING-(Cont.)
Torque Tubes -------------------------------------------------- 68 Stops --------------------------------------------------------- 68 Control Surface Snubbers and Locking Devices ---------------------- 69 Aircraft Rigging ----------------------------------------------- 70 Rigging Checks ------------------------------------------------ 72 Adjustment of Control Surfaces ----------------------------------- 75 Helicopter Rigging --------------------------------------------- 77 Principles of Balancing or Re-balancing ---------------------------- 80 Re-balancing Procedures ---------------------------------------- 83 Methods------------------------------------------------------- 83
CHAPI'ER 3. AIRCRAFT FABRIC COVERING
Aircraft Fabrics ------------------------------------------------ 85 Miscellaneous Textile Materials ----------------------------------- 88
Seams -------------------------------------------------------- 89 Applying Covering --------------------------------------------- 91 Covering 1Vings ------------------------------------------------ 93 Covering Fuselages --------------------------------------------- 95 Ventilation, Drain, and Inspection Openings ------------------------ 95 Repair of Fabric Covers ----------------------------------------- 99 Replacing Panels in 1Ving Covers ---~----------------------------- 103 Re-covering Aircraft Surface with Glass Ooth ----------------------- 104 Causes of Fabric Deterioration ----------------------------------- 104 Checking Condition of Doped Fabric ------------------------------ 106 Testing Fabric Covering ----------------------------------------- 106 Strength Criteria for Aircraft Fabric ------------------------------ 107 Dopes and Doping---------------------------------------------- 107 Dope Materials ------------------------------------------------- 108 Aluminum-Pigmented Dopes ------------------------------------- 109 Temperature and Humidity Effects on Dope ------------------------ 109 Common Troubles in Dope Application ----------------------------- 109 Technique of Application ---------------------------------------- 110 Number of Coats Required --------------------------------------- 111
CHAPTER 4. AIRCRAFT PAINTING AND FINISHING
General ------------------------------------------------------- 113 Finishing Materials --------------------------------------------- 113 Paint Touchup ------------------------------------------------- 117 Identification of Paint Finishes ----------------------------------- 117 Paint Removal ---------~------------------------~-------------- 117 Restoration of Paint Finishes ------------------------------------- 118 Nitrocellulose Lacquer Finishes ----------------------------------- 118 Acrylic Nitrocellulose Lacquer Finish ------------------------------ 119 Epoxy Finishes ------------------------------------------------ 120 Fluorescent Finishes -------------------------------------------- 121 Enamcl Finishes ------------------------------------------------ 121 Paint System Compatibility -------------------------------------- 122 Methods of Applying Finishes ------------------------------------ 122 Preparation of Paint -------------------------------------------- 123
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Common Paint Troubles ----------------------------------------- 124 Painting Trim and Identification Numbers ------------------------- 125 Decalcomanias (Decals) ----------------------------------------- 125
CHAPTER 5. AIRCRAFT STRUCTURAL REPAIRS
Basic Principles of Sheet Metal Repair ---------------------------·:.: 127 General Structural Repair --------------------------------------- 129 Inspection of Damage ------------------------------------------- 130 Oassification of Damage ---------------------------------------- 131 Stresses in Structural Members ----------------------------------- 131 Special Tools and Devices for Sheet Metal -------------------------- 133 Metalworking Machines ----------------------------------------- 136 Forming Machines ---------------------------------------------- 141 Forming Operations and Terms ----------------------------------- 145 Making Straight Line Bends ------------------------------------- 146 Setback ------------------------------------------------------- 148 Making Layouts ------------------··----------------------------- 151 Hand Forming ------------------------------------------------- 155 Rivet Layout -------------------------------------------------- 164 Rivet Installation ----------------------------------------------- 166 Preparation of Rivet Holes --------------------------------------- 168 Driving Rive~ ------------------------------------------------- 173 Rivet Failures ------------------------------------------------- 175 Removing Rive~ ----------------------------------------------- 177 Special Rive~ -------------------------------------------------- 177 Self-Plugging (Friction Lock) Rivets ------------------------------ 178 Self-Plugging (Mechanical Lock) Rivets --------------------------- 181 Pull-Thru Rivets ----------------------------------------------- 184
Rivnu~ ------------------------------------------------------- 184 Dill Lok-Skrus and Lok-Rive~ ------------------------------------ 186 Deutsch Rivets ------------------------------------------------- 187 Hi-Shear Rivets ------------------------------------------------ 187 Specific Repair Types ------------------------------------------- 189 Structural Sealing ---------------------------------------------- 198 Metal Bonded Honeycomb --------------------------------------- 200 Construction Features ------------------------------------------- 201 Damage ------------------------------------------------------- 201 Repairs ------------------------------------------------------- 202 Repair Materials ----------------------------------------------- 205 Potted Compound Repair ---------------------------------------- 206 Glass Fabric Cloth Overlay Repairs ------------------------------- 208 One Skin .and Core Repair Procedures ----------------------------- 209 Plastics ------------------------------------------------------- 213 Transparent Plastics -------------------------------------------- 213 Storage and Protection ------------------------------------------ 214 Forming Plastics ----------------------------------------------- 215 Installation Procedures ------------------------------------------ 220 Laminated Plastics ---------------------------------------------- 221 Fiber Glass Componen~ ----------------------------------------- 221 Radomes ------------------------------------------------------ 223 Wooden Aircraft Structures -------------------------------------- 224 Inspection of Wooden Structures ---------------------------------- 224 Service and Repair of Wooden Structures -------------------------- 228
Glues --------------------------------------------------------- 230 Gluing -------------------------------------------------------- 232
CHAPTER 5. AIRCRAFT STRUCTURAL REPAIRS-(Cont.)
Spliced Joints -------------------------------------------------- 234 Plywood Skin Repairs -------- ·---------------------------------- 235 Spar and Rib Repair ------------------------------------------- 242 Bolt and Bushing Holes ----------------------------------------- 244 Rib Repairs --------------------------------------------------- 245
CHAPTER 6. AIRCRAFT WELDING
General ------------------------------------------------------- 247 Oxyacetylene Welding Equipment --------------------------------- 248 Welding Positions ---------------------------------------------- 255 Welded Joints -------------------------------------------------- 255 Expansion and Contraction of Metals ------------------------------ 257 Correct Forming of a Weld -------------------------------------- 258 Oxyacetylene Welding of Ferrous Metals --------------------------- 258 Welding Nonferrous Metals Using Oxyacetylene --------------------- 260
Titanium ------------------------------------------------------ 262 Cutting Metal Using Oxyacetylene -------------------------------- 263 Brazing Methods ----------------------------------------------- 264 Soft Soldering ------------------------------------------------- 265 Electric Arc Welding ------------------------------------------- 266 Welding Procedures and Techniques ------------------------------- 269 Welding of Aircraft Steel Structures ------------------------------ 276
CHAPTER 7. ICE AND RAIN PROTECTION
General ------------------------------------------------------- 285 Pneumatic Deicing Systems -------------------------------------- 286 Deicer Boot Construction ---------------------------------------- 287 Deicing System Components -------------------------------------- 288 Pneumatic Deicing System Maintenance --------------------------- 291 Thermal Anti-Icing Systems -------------------------------------- 293 Pneumatic System Ducting -------------------------------------- 296 Ground Deicing of Aircraft -------------------------------------- 299 Windshield Icing Control Systems --------------------------------- 300 Water and Toilet Drain Heaters ---------------------------------- 303 Rain Eliminating Systems --------------------------------------- 303 Maintenance of Rain Eliminating Systems -------------------------- 308
CHAPTER 8. HYDRAULIC AND PNEUMATIC POWER SYSTEMS
Aircraft Hydraulic Systems -------------------------------------- 309 Hydraulic Fluid ------------------------------------------------ 309 Types of Hydraulic Fluids --------------------------------------- 310 Phosphate Ester Base F1uids ------------------------------------- 311 Filters -------------------------------------------------------- 313 Basic Hydraulic System ----------------------------------------- 315 Reservoirs ----------------------------------------------------- .316 Pressure Regulation -------------------------------------------- 323 Actuating Cylinders -------------------------------------------- 328 Selector Valves ------------------------------------------------ 329 Aircraft Pneumatic Systems -------------------------------------- 331 Pneumatic System Components ----------------------------------- 334 Typical Pneumatic Power System --------------------------------- 338
CHAPTER 9. LANDING GEAR SYSTEMS
General ------------------------------------------------------- 341 Main Landing Gear Alignment, Support, Retraction ------------------ 348
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CHAPTER 9. LANDING GEAR SYSTEMS-(Cont.)
Emergency Extension Systems ------------------------------------ 351 Landing Gear Safety Devices ------------------------------------- 351 Nosewheel Steering System -------------------------------------- 354 Shimmy Dampers ---------------------------------------------- 356 Brake Systems ------------------------------------------------- 360 Brake Assemblies ----------------------------------------------~ 366 Inspection and Maintenance of Brake Systems ---------------------- 372 Aircraft Landing Wheels ---------------------------------------- 373 Aircraft Tires -------------------------------------------------- 377 Aircraft Tire Maintenance --------------------------------------- 379 Tire Inspection-Mounted On Wheel ------------------------------ 381 Tire Inspection-Tire Demounted --------------------------------- 382 Tube Inspection ------------------------------------------------ 384 Mounting and Demounting -------------------------------------- 385 Causes of Air Pressure Loss in Tubeless Aircraft Tires ---------------- 389
The Wheel ---------------------------------------------------- 390 Good Pressure Gage Practice ------------------------------------- 391 Repairing ----------------------------------------------------- 392 Operating and Handling Tips ------------------------------------ 394 Tube Repair --------------------------------------------------- 396 Sidewall.Jnflated Aircraft Tires ----------------------------------- 396 Tire Inspection Summary ---------------------------------------- 397 Antiskid System ------------------------------------------------ 399 Landing Gear System Maintenance -------------------------------- 400
CHAPTER 10. FIRE PROTECTION SYSTEMS
General ------------------------------------------------------- 407 Fire Detection Systems ------------------------------------------ 408 Types of Fires ------------------------------------------------- 411 Fire Zone Classification ----------------------------------------- 412 Extinguishing Agent Characteristics ------------------------------- 412 Fire Extinguishing Systems -------------------------------------- 417 Reciprocating Engine Conventional C02 System --------------------- 417 Turbojet Fire Protection System ---------------------------------- 419 Turbine Engine Fire Extinguishing System ------------------------- 420 Turbine Engine Ground Fire Protection ---------------------------- 422 Fire Detection System Maintenance Practices ----------------------- 423 Fire Detection System Troubleshooting ---------------------------- 425 Fire Extinguisher System Maintenance Practices -------------------- 425 Fire Prevention and Protection ----------------------------------- 429 Cockpit and Cabin Interiors -------------------------------------- 429 Smoke Detection Systems ---------------------------------------- 430
CHAPTER 11. AIRCRAFT ELECTRICAL SYSTEMS
General ------------------------------------------------------- 433 Lacing and Tying Wire Bundles ---------------------------------- 444 Cutting Wire and Cable ---------------------------------------- 446 Emergency Splicing Repairs ------------------------------------- 450 Connecting Terminal Lugs to Terminal Blocks ----------------------- 451 Bonding and Grounding ---------------------------------------- 452 Connectors ---------------------------------------------------- 452 Conduit ------------------------------------------------------- 457 Electrical Equipment Installation --------------------------------- 457 Aircraft Lighting Systems --------------------------------------- 459 Maintenance and Inspection o£ Lighting Systems -------------------- 464
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CHAPTER 12. AIRCRAFT INSTRUMENT SYSTEMS
Gener& ----------------------------------------------~-------- 469 ln~rument c~s ---------------------------------------------- 469 Di&s --------------------------------------------------------- 469 Range Markings ----------------------------------------------- 470 Instrument Pands ---------------------------------------------- 470 Repair of Aircrah ln~ruments ----------------------------------- 471 Aircraft Pressure Gages --------------------------------------- _ 471 Pitot-Static System --------------------------------------------- 474 Maintenance of Pitot-Static Systems ------------------------------- 481 Tum-and-Bank lndlcator ---------------------------------------- 482 Synchro-Type Remote Indicating Instruments ----------------------- 483 Remote-Indicating Fud and Oil Pressure Gages --------------------- 485 Capacitor-Type Fuel Quanity System ------------------------------ 485 Angle-of-Attack Indicator ---------------------------------------- 487 Tachometers --------------------------------------------------- 488 Synchroscope -------------------------------------------------- 491 Temperature Indicators ----------------------------------------- 491 Ratiometer Electric& Resistance Thermometer ---------------------- 497 Fuel Flowmeter Systems ----------------------------------------- 497 Gyroscopic Instruments ----------------------------------------- 499 Sources of Power for Gyro Operation ------------------------------ 501 Vacuum-Driven Attitude Gyros ----------------------------------- 504 Pressure-Operated Gyros ---------------------------------------- 506 Vacuum System Maintenance Practices ---------------------------- 506 Electric Attitude Indicator --------------------------------------- 507 Autopilot System ----------------------------------------------- 511 Basic Autopilot Components -------------------------------------- 513 Flight Director Systems ----------------------------------------- 518 Autopilot System Maintenance ------------------------------------ 516
CHAPTER 13. COMMUNICATIONS AND NAVIGATION SYSTEMS
Gener& ------------------------------------------------------- 519 Basic Radio Principles ------------------------------------------ 519 Basic Equipment Components ------------------------------------ 520 Power Supply ------------------------------------------------- 522 Communication Systems ----------------------------------------- 522 Airborne Navigation Equipment ---------------------------------- 524 VHF Omnirange Sy~em ---------------------------------------- 524 Instrument Landing System -------------------------------------- 525 Distance-Measuring Equipment ----------------------------------- 528 Automatic Direction Finders ------------------------------------- 529 Radar Beacon Transponder -------------------------------------- 530 Doppler Navigation Systems ------------------------------------- 530 Inertial Navigation System -------------------------------------- 531 Airborne Weather Radar System --------------------------------- 532 Radio Altimeter ------------------------------------------------ 533 Emergency Locator Transmitter (ELT) ---------------------------- 533 Installation of Communication and Navigation Equipment ------------- 534 Reducing Radio Interference ------------------------------------ 536 ln~&latoin of Aircraft Antenna Systems --------------------------- 537
CHAPTER 14. CABIN ATMOSPHERE CONTROL SYSTEM
Need for Oxygen ---------------------------------------------- 539 Com~tion of the Atmosphere ---------------------------------- 539 Pressur~ation -------------------------------------------------- 541 Air Conditioning and Pressurization Systems ----------------------- 543
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CHAPTER 14. CABIN ATMOSPHERE CONTROL SYSTEM-(Cont.)
Basic Requirements -------------------------------------------- 545 Sources of Cabin Pre~ure --------------------------------------- 545 Supercharger Instruments --------------------------------------- 549 Pre~urization Valves ------------------------------------------- 550 Cabin Pr~ure Control System ----------------------------------, . .,. 551 Air Distribution ----------------------------------------------- 556 Air Conditioning System ---------------------------------------- 558 Heating Systems ----------------------------------------------- 559 Combustion Heaters -------------------------------------------- 561 Maintenance of Combustion Heater Systems ------------------------ 564 Cooling Systems ------------------------------------------------ 565 Air Cycle Cooling System --------------------------------------- 565 Air Cycle System Component Operation --------------------------- 568 Electronic Cabin Temperature Control System ---------------------- 574 Electronic Temperature Control Regulator ------------------------- 575 Vapor Cycle System (Freon) ------------------------------------ 576 Freon System Components --------------------------------------- 577 Description of a Typical System --------------------------------- 580 Air Conditioning and Pr~urization System Maintenance ------------- 583 Cabin Pre~urization Operational Checks --------------------------- 585 Cabin Pr~urization Troubleshooting ----------------------------- 586 Oxygen Systems General ----------------------------------------- 587 Portable Oxygen Equipment ------------------------------------- 587 Smoke Protection Equipment ------------------------------------- 588 Oxygen Cylinders ---------------------------------------------- 588 Solid State Oxygen Systems ------------------------------------- 589 Oxygen Plumbing ---------------------------------------------- 591 Oxygen Valves ------------------------------------------------ 592 Regulators ----------------------------------------------------- 594 Oxygen System Flow Indicators ----------------------------------- 597 Pressure Gages ------------------------------------------------ 597 Oygen Masks -------------------------------------------------- 597 Servicing Gaseous Oxygen Systems ------------------------------- 598 Prevention of Oxygen Fires or Explosions ------------------------- 600
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GENERAL The airframe of a fixed-wing aircraft is generally
considered to consist of five principal units, the fuselage, wings, stabilizers, flight control surfaces, and landing gear. Helicopter airframes consist of the fuselage, main rotor and related gearbox, tail rotor (on helicopters with a single main rotor), and the landing gear.
The airframe components are constructed from a wide variety of materials and are joined by rivets, bolts, screws, and welding or adhesives. The air· craft components are composed of various parts called structural members (i.e., stringers, longerons, ribs, bulkheads, etc.). Aircraft structural members are designed to carry a load or to resist stress. A single member of the structure may be subjected to a combination of stresses. In most cases the struc tural members are designed to carry end loads rather than side loads: that is, to be subjected to tension or compression rather than bending.
Strength may be the principal requirement in cer· tain structures, while others need entirely different qualities. For example, cowling, fairing, and simi· lar parts usually are not required to carry the stresses imposed by flight or the landing loads. However, these parts must have such properties as neat appearance and streamlined shapes.
MAJOR STRUCTURAL STRESSES In designing an aircraft, every square inch of
wing and fuselage, every rib, spar, and even each metal fitting must be considered in relation to the physical characteristics of the metal of which it is made. Every part of the aircraft must be planned to carry the load to be imposed upon it. The determi· nation of such loads is called stress analysis. AI· though planning the design is not the function of the aviation mechanic, it is, nevertheless, important that he understand and appreciate the stresses in volved in order to avoid changes in the original design through improper repairs.
There are five major stresses to which all aircraft are subjected (figure 1-1):
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(1) Tension. (2) Compression. (3) Torsion. (4) Shear. (5) Bending.
CHAPTER 1 AIRCRAFT STRUCTURES
The term "stress" is often used interchangeably with the word "strain." Stress is an internal force of a substance which opposes or resists deforma· tion. Strain is the deformation of a material or substance. Stress, the internal force, can cause strain.
Tension (figure 1-1a) is the stress that resists a force that tends to pull apart. The engine pulls the aircraft forward, but air resistance tries to hold it back. The result is tension, which tries to stretch the aircraft. The tensile strength of a material is measured in p.s.i. (pounds per square inch) and is calculated by dividing the load (in pounds) re quired to pull the material apart by its cross-sec tional area (in square inches).
Compression (figure 1-1b) is the stress that res ists a crushing force. The compressive strength of a material is also measured in p.s.i. Compression is the stress that tends to shorten or squeeze aircraft parts.
Torsion is the stress that produces twisting (figure 1-1c). While moving the aircraft forward, the en· gine also tends to twist it to one side, but other aircraft components hold it on course. Thus, torsion is created. The torsional strength of a material is ita resistance to twisting or torque.
Shear is the stress that resists the force tending to cause one layer of a material to slide over an adjacent layer. Two riveted plates in tension (figure 1-1d) subject the rivets to a shearing force. Usually, the shearing strength of a material is either equal to or less than its tensile or compressive strength. Aircraft parts, especially screws, bolts, and rivets, are often subject to a shearing force.
Bending stress is a combination of compression and tension. The rod in figure 1-1e has been short· ened (compressed) on the inside of the bend and stretched on the outside of the bend.
(a) Tension
(b) Compression
FIGURE 1-1. Five stresses acting on an aircraft.
FIXED-WING AIRCRAFT The principal components of a single-engine, pro
peller-driven aircraft are shown in figure 1-2. Figure 1-3 illustrates the structural components
of a typical turbine powered aircraft. One wing and the empennage assemblies are shown exploded into the many components which, when assembled, form major structural units.
FUSELAGE The fuselage is the main structure or body of the
aircraft. It provides space for cargo, controls, acces sories, passengers, and other equipment. In single engine aircraft, it also houses the powerplant. In
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multi-engine aircraft the engin~ may either be in the fuselage, attached to the fuselage, or suspended from the wing structure. They vary principally in Jize and arrangement of the different compartments.
There are two general types of fuselage construc tion, the truss type, and the monocoque type. A truss is a rigid framework made up of members such as beams, struts, and bars to resist deforma tion by applied loads. The truss-framed fu.CJelage is generally covered with fabric.
Truss Type
The truss type fuselage frame (figure 1-4) is usually constructed of steel tubing welded together in such a manner that all members of the truss can carry both tension and compression loads. In some
.__--Propeller
aircraft, principally the light, single-engine models, truss fuselage frames are col18tructed of aluminum alloy and may be riveted or bolted into one piece, with cross-bracing achieved by using solid rods or tubes.
Monocoque Type
The monocoque (single shell) fuselage relies largely on the strength of the skin or covering to carry the primary stresses. The design may be di vided into three classes: (1) Monocoque, (2) semi· monocoque, or (3) reinforced shell. The true mono coque…
