SCIENCE OF AERONAUTICSAND

ENGINEERING EDUCATIONAL TECHNICS

Presented by :-CH. PURUSHOTHAM

Aeronautical Engineering

Lift Augmentationor

High Lift Devices (Flaps)

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Contents Introduction -- High Lift Systems

FlapsTrailing edge Devices

1. plain flap2. split flap3. Slotted flaps4. Double-Slotted Fowler Flap5. Triple-slotted Flap 6. Fowler flap7. Zap flap8. Junkers flap9. Blown flaps

Leading edge Devices SLATS AND SLOTS

OperationLift Augmentation Effects On CL

High Lift Systems -- IntroductionA wing designed for efficient high-speed flight is often quite different from one designed solely for take-off and landing. Take-off and landing distances are strongly influenced by aircraft stalling speed, with lower stall speeds requiring lower acceleration or deceleration and correspondingly shorter field lengths. It is always possible to reduce stall speed by increasing wing area, but it is not desirable to cruise with hundreds of square feet of extra wing area (and the associated weight and drag), area that is only needed for a few minutes. Since the stalling speed is related to wing parameters by: It is also possible to reduce stalling speed by reducing weight, increasing air density, or increasing wing CLmax . The latter parameter is the most interesting. One can design a wing airfoil that compromises cruise efficiency to obtain a good CLmax , but it is usually more efficient to include movable leading and/or trailing edges so that one may obtain good high speed performance while achieving a high CLmax at take-off and landing. The primary goal of a high lift system is a high CLmax; however, it may also be desirable to maintain low drag at take-off, or high drag on approach. It is also necessary to do this with a system that has low weight and high reliability.

This is generally achieved by incorporating some form of trailing edge flap and perhaps a leading edge device such as a slat.

Flaps

Trailing edge Devices

1. plain flap2. split flap3. Slotted flaps4. Double-Slotted Fowler Flap5. Fowler flap6. Zap flap7. Junkers flap8. Blown flaps

50% Increase CLMAX Critical Angle 12o

plain flap

The plain flap changes camber to increase lift, but its effect is limited by additional flow separation which occurs when it is deflected. The additional separation occurs because the upper surface of the deflected flap experiences a stronger adverse pressure gradient

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SPLIT FLAP

split flap

The split flap deflects only the underside of the trailing edge so that, while it creates a great deal of pressure drag, it avoids the strong adverse pressure gradient on its upper surface and therefore keeps the flow attached slightly longer. This gives the split flap slightly greater lift.

65% Increase CLMAX Critical Angle 16o

SLOTTED FLAP

Slotted flaps

A Slotted flaps have a gap or slot in them to allow faster-moving air from the lower surface to flow over the upper surface. The higher-energy air from the slot gives the boundary layer more energy to fight the adverse pressure gradient and delay separation

Double-Slotted Fowler FlapModern high lift systems are often quite

complex with many elements and multi-bar linkages. Here is a double-slotted flap system as used on a DC-8. For some time Douglas resisted the temptation to use tracks and resorted to such elaborate 4-bar linkages. The idea was that these would be more reliable. In practice, it seems both schemes are very reliable. Current practice has been to simplify the flap system and double (or even single) slotted systems are often preferred.

Triple-slotted Flap A type of trailing-edge wing flap used on

some of the larger, high-performance airplanes. Triple-slotted flaps extend from the trailing edge of a wing in three sections. The trailing edge of one section forms a duct with the leading edge of the section behind it to force air down over the top of the flap. Triple-slotted flaps prevent the airflow from separating from the surface of the flap when they are fully extended.

FOWLER FLAP

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Fowler flap

The Fowler flap moves aft to increase the wing area before deflecting downward to increase camber. Fowler flaps usually have one or more slots to increase their effectiveness.

Zap FLAP

Zap flap

The leading edge of the flap is mounted on a track, while a point at mid chord on the flap is connected via an arm to a pivot just above the track. When the flap's leading edge moves aft along the track, the triangle formed by the track, the shaft and the surface of the flap (fixed at the pivot) gets narrower and deeper, forcing the flap down.

Junkers flap

A slotted plain flap where the flap is fixed below the trailing edge of the wing, rotating about its forward edge, and usually part of the Junkers Doppelflügel, or "double-wing" style of wing trailing edge control surfaces (including the ailerons), which hung just below and behind the wing's fixed trailing edge. When not in use, it has more drag than other types, but is more effective at creating additional lift than a plain or split flap, while retaining their mechanical simplicity.

THE BLOWN FLAP

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Blown flaps

Blown flaps also known as Boundary Layer Control Systems, are systems that blow engine air over the upper surface of any of the previously mentioned types of flap to improve lift characteristics. Two types exist - the original type blew air out of channels or holes in the surface of the flap, while newer systems simply blow engine exhaust over the top of the flap. These require ample reserves of power and are maintenance intensive thus limiting their use, but they provide lots of lift at low airspeeds.

SLATS AND SLOTS

Leading edge Devices

SLOTS AND SLATS

Slats: are auxiliary airfoils fitted to the leading edge of the wing. At high angles of attack, they automatically move out ahead of the wing. The angle of attack of the slat being less than that of the main plane, there is a smooth airflow over the slat which tends to smooth out the eddies forming over the wing. Slats are usually fitted to the leading edge near the wing tips to improve lateral control.

Slots: are passageways built into the wing a short distance from the leading edge in such a way that, at high angles of attack, the air flows through the slot and over the wing, tending to smooth out the turbulence due to eddies.

AUTOMATIC SLAT

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Automatic Slat

The slat lies flush with the wing leading edge until reduced aerodynamic forces allow it to extend by way of aerodynamics when needed. Sometimes referred to as Handley-Page slats

Fixed Slat

Fixed Slat The slat is permanently extended.

This is sometimes used on specialist low-speed aircraft (these are referred to as slots) or when simplicity takes precedence over speed.

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SLOT

A leading edge slot is a fixed aerodynamic feature of the wing of some aircraft to reduce the stall speed and promote good low-speed handling qualities. A leading edge slot is a span-wise gap in each wing, allowing air to flow from below the wing to its upper surface. In this manner they allow flight at higher angles of attack and thus reduce the stall speed.

“DROOP SNOOT”FLAP

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droop or droop nose

A droop or droop nose is a type of high-lift device found on the wings of some aircraft. Droops are similar to leading-edge slats, but with the difference that the entire leading edge section rotates downwards, whereas a slat is a panel that moves away from a wing leading edge when it is deployed.

Krueger flaps 

Krueger flaps are lift enhancement devices that may be fitted to the leading edge of an aircraft wing. Unlike slats or drooped leading edges, the main wing upper surface and its nose is not changed. Instead, a portion of the lower wing is rotated out in front of the main wing leading edge.

KRUGER FLAP

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•To increase lift at low speed

•Increase camber increase lift

OperationThe chord of the slat is typically only a few percent of the

wing chord. The slats may extend over the outer third of the wing, or they may cover the entire leading edge. Many early aerodynamicists, including Ludwig Prandtl believed that slats work by inducing a high energy stream to the flow of the main airfoil thus re-energizing its boundary layer and delaying stall . In reality, the slat does not give the air in the slot high velocity (it actually reduces its velocity) and also it cannot be called high-energy air since all the air outside the actual boundary layers has the same total heat.

boundary layer separation on bluff body

boundary layer separation on blunt body

To avoid the boundary layer separation Due to High lift devices

LIFT AUGMENTATION EFFECTS ON CL

Relative Airflow

Chord

Basic ‘Clean’ Situation

α

EFFECT OF FLAP

Relative AirflowChord

Flap Lowered

α

Basic ‘Clean’ Situation

Effective Increase in AoA

EFFECT OF FLAP

EFFECT OF FLAPFlap Lowered

α

Maintaining the Same Lift

Effective Increase in AoATo obtain the same CL the Attitude is Lowered to Reduce the AoA

Cl Max

AT STALL: WEIGHT = LIFT = CLMAX ½ρ V2

STALL S

Critical Angle

Without Flap

AoA

CL

EFFECT OF FLAP

AT STALL: WEIGHT = LIFT = CLMAX ½ρ V2

STALL SIF THIS IS THIS IS

CONSTANT MORE LESS

Critical Angle

With FlapCl Max More

AoA

CL

Nose lowerat Stall

Without Flap

Cl Max

EFFECT OF FLAP

EFFECTS ON CL

α

CL

BASIC AEROFOIL SECTION

BASIC AEROFOIL SECTION

α

CL

BASIC AEROFOIL SECTIONTRAILING EDGE FLAP

TRAILING EDGE FLAP

EFFECTS ON CL

α

CL

BASIC AEROFOIL SECTION

LEADING EDGE FLAP

EFFECTS ON CLLEADING EDGE FLAP

α

CL

BASIC AEROFOIL SECTION

SLAT OR SLOT

EFFECTS ON CLSLAT

α

CL

BASIC AEROFOIL SECTIONTRAILING EDGE FLAPLEADING EDGE FLAPSLAT OR SLOT

EFFECTS ON CL

Adding flaps gives higher CLmax

CLmax

Anderson, J. D., Introduction to Flight, 4th Edition, page 315

FlapsBut, what about Drag?

Flaps 30oFlaps 90oFlaps 60o

Flap

30o

60o

90o

Drag

Small Inc

Large Inc

V Large Inc

Lift

Large Inc

Small Inc

No Sig Inc

Conclusion1. Clear understanding the High lift Devices and its operational

working principle2. Several technology research and development efforts exist to

integrate the functions of flight control systems such as ailerons, elevators, flaps, and flaperons into wings to perform the aerodynamic purpose with the advantages of less: mass, cost, drag, inertia (for faster, stronger control response), complexity (mechanically simpler, fewer moving parts or surfaces, less maintenance), and radar cross section for stealth.

To invent an airplane is nothing. To build one is something. But to fly is

everything.

- Otto Lilienthal

Thank you..

SCIENCE OF AERONAUTICSAND

ENGINEERING EDUCATION TECHNICS