These slides are written in very easy language this will help aeronautics students to understand Lift augmentation devices or High lift devices

1. LIFT AUGMENTATION
DEVICES
BY:
SUHAIL AHMED

3. Contents of Presentation
1. Purpose of High Lift Devices
2. Flaps
Trailing Edge Flaps
- Plain Flaps
- Split Flaps
- Slotted and Multiple Slotted Flaps
- Fowler Flaps
- Comparison of Trailing Edge flaps
- Cl max and stalling angles
- Drag, Lift/Drag Ratio
- Pitching and centre of pressure moment
- Change of Downwash
- Overall Pitch change

4. Contents of Presentation
Leading Edge High Lift Devices
- Leading Edge Flaps
- Kruger Flaps
- Variable Camber Leading Edge Flaps
- Effects of Leading Edge Flaps on Lift
- Leading Edge Slots/Slats
- Automatic Slots
- Disadvantages of Slots
- Drag and Pitching moment
Trailing + Leading Edge Devices together

5. Purpose of High Lift Devices
 To Reduce take off and landing distance
 Reduction in Stalling Speeds
 Lift Augmentation by increase in camber and related aspects
 If we revisit the formula: L = 1/2 ρ V2 x S x CL, we can
see that we have several ways to increase the lift for a given
wing. Speed (V), wing area (S) and the coefficient lift (CL) can
be varied for given angle of attack (AOA) to change lift. The
use of flaps will change the wing area and coefficient lift.
 Flaps – A hinged portion of leading of trailing edge of the wing.

6. Trailing Edge Flaps
1. Plain Flaps
 Simple Construction
 Good increase in Cl max
 High Drag, Mainly used on low speed aircrafts

7. Cl max and Stalling Angle
Effective angle of attack increases with
extension of trailing edge flaps

8. 2. Split Flaps
• The flaps are part of lower surface of trailing edge.
• The upper surface contour being un affected when flap is lowered
• or deployed.
• The split flaps give some more increase in lift as compare to plain flaps at
• low angle of attack .
 Split flaps gives slightly more lift at high angle of attack as upper camber
is not increased and separation is delayed.

9. 3. Slotted and Multiple 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.
• Re-energies the boundary layer. And it delays the separation of
airflow on upper surface.
• Slotted flaps gives a bigger increase in Clmax than plain or split
flap and much less drag
• Slotted flaps have more complex construction.

10. 4. Fowler Flaps

11. Fowler Flaps(Contd.)
 combined effect of increase in camber and
surface area
 the fowler flaps give the greatest increase in lift.
 It gives least drag because of the slots and
reduction in thickness: Chord ratio.
 However, the change in pitching moment is
greatest.

12. Comparison of Trailing Edge Flaps

13. Aerodynamic effects of flaps
 Increase in Drag due to trailing edge flaps
 Lift/Drag Ratio
 Pitching Moment
 Centre of Pressure Movement.
 Change of Downwash

14. Increase in Drag due to trailing edge flaps

15. Lift/Drag Ratio

16. LIFT/DRAG RATIO
 This ratio (L/D) is also reduced when full
flaps are extended. Normally, flap
settings between 0 - 25° will noticeably
increase lift more than drag, ideal for
take off. Flap settings beyond 25° will
increase drag much more than lift, ideal
for landing and steep approaches to
runways when there are obstacles in the
approach path.

17. Pitching Moment
Centre of Pressure Movement.
 Flaps extension will cause the CP to move aft
thus pitching the aircraft nose down.
 Flaps retraction will move the CP forward thus
pitching the aircraft nose up.

18. Change of Downwash
Tail plane effective angle of attach is
determined by the downwash of the wing.
Lowering flaps increases downwash thus
decreasing tail plane angle of attack. This
has a nose up pitching moment.

20. Leading Edge High Lift Devices
Two types:
Leading Edge Flaps
Leading Edge Slats and Slots

21. Leading Edge Flaps
(They Increase the camber of the leading edge)
Kruger Flaps
They are fitted at lower surface of wing leading
edge, rotated about their forward edge as shown in
the fig.

22. Variable camber leading edge flap
 They give better efficiency than Kruger Flaps by giving
better leading edge profile.

23. Effect of Leading edge Flaps on Lift

24. Leading Edge Slot
 It is a gap between the lower and upper surface of the
leading edge of the wing. It could be a fixed or a
moving part (Slat).
 When Slats are employed, they re-energize the
boundary layer

25. Effect of Slats/Slots on Lift

26. Automatic Slats
On some aircrafts slots are not controlled by the
pilot, but operate automatically their movement
depends on change in pressure occur around the
leading edge at low angle of attack the pressure
around the stagnation point keep the slat in
closed position. At high angle of attacks the
stagnation point moves underneath the leading
edge and suction pressure occur on the upper
surface of slat this pressure cause slat to move
forward and create the slot

27. Disadvantages of a Slat/Slot
 Much higher angle of attack is required to benefit from
the increased Cl max by the use of slat/slot. Visibility
could hamper by increased nose up pitch and landing
could be difficult.
Drag and Pitching Moment
 Compare to trailing edge devices, the drag and
pitching moment is small.

28. Trailing Edge + Leading Edge Devices
Most large aircraft employ both

29. THANK
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