1. Lesson 17 High Lift Devices
Aero Engineering 315
Lesson 17 High Lift Devices

2. Homework #20
(BSBW A4.1)
Consider a flying wing aircraft made using a NACA 2412 airfoil with a wing area of 250 ft2, a wing span of 50 ft, and a span efficiency factor of 0.9.
If the aircraft is flying at 6 deg angle of attack and a Reynolds number of approximately 9 x 106, what are CL and CD for the flying wing?
b. If the flying wing is flying at sea level, standard day at V¥ = 280 ft/s, how much lift and drag is it experiencing?

3. NACA 2412

4. High Lift Device Objectives
Calculate stall velocity
Describe typical high lift devices and their purpose
Flaps, strakes, BL control, powered/blown lift and thrust vectoring
Draw the effects of flaps and boundary layer control devices on lift and drag curves

5. High-Lift Devices
Method to improve CL in certain circumstances

6. For straight level unaccelerated flight (SLUF)
Velocity for lift
Remember our forces?
If Lift = Weight, then , and
the velocity to maintain lift is
For straight level unaccelerated flight (SLUF)
Lift
Thrust
Drag
Weight
So, to fly slower at a given altitude you either jettison wt or increase CL

7. Stall Velocity The velocity at stall, Vstall, occurs at CLmax
Recall the definition of equivalent airspeed?
The minimum Ve to avoid stall is

8. Vstall Problem 2 = S W V C r 2 = S W V C rSL = V = V = V = V
You are landing your F-16 at Luke AFB with a density altitude of
6,000 feet. Your gross weight is 25,000 lbs. CLmax is 1.2 and the whole
aircraft planform area is 428 ft2. What is your stalling velocity in knots? 2 = S W V
max C L
Stall r 2 = S W V
max C L
e-Stall
rSL = V
Stall
( )(428)(1.2)
2(25,000) = V
e-Stall
( )(428)(1.2)
2(25,000) = V
Stall
221 ft/sec = 131 KTAS = V
e-Stall
202 ft/sec = 120 KEAS

9. Why High-Lift Devices? Low camber good for high speed
A/C needs to operate at low speeds also!
High lift devices allow increase in CLmax
Which lowers Vstall
Flaps improve visibility on final by creating an angle of incidence
Landing speeds (1.3 Vstall) limited by braking, tires, runway distance and condition…
Must dissipate KE (1/2mV2)
Take-off speed (1.2 Vstall) limited by max tire spin up speeds, runway length, thrust available…

10. Trailing Edge Flaps
Plain flap
Split flap
Slotted flap
Fowler flap

11. Effect of Flaps on Lift and Drag Curves
Wing with Flap C C D
Wing with Flap L
Basic Wing Section
Basic Wing Section C a L

12. Typical Flap Impact d d = 500 With flaps d = 150 No flaps d = 0
a (degrees)
Anderson, J. D., Introduction to Flight, 4th Edition, page 314

14. Tornado - Slotted Flap

15. KC-10 Slotted Flap

16. Adding flaps gives higher CLmax
Anderson, J. D., Introduction to Flight, 4th Edition, page 315

17. Leading Edge Devices and Boundary Layer Control
Leading-edge flap
by upper surface suction
Fixed slot
Boundary Layer Control
by tangential blowing
Slat

18. F-16XL upper surface suction

19. Boundary layer control devices affect lift curve like higher Rec
Wing with Leading-Edge Flap or Slat
or Boundary Layer Control C L
Basic Wing Section a

20. Powered (blown) lift
Internally Blown Flap

21. Powered (blown) lift
Externally Blown Flap

22. C-17 externally blown flap

23. Powered (blown) lift
Upper-Surface Blowing
Example: YC-14

24. YC-14 - Upper Surface Blown Flap

25. Powered (vectored) lift
Vectored Thrust

26. AV-8B -- Vectored Thrust

27. C-130 JATO - Vectored Thrust

28. Strakes Energize the flow over the wing, delaying separation
Cause more lift (especially at high AOA) due to lower pressure inside vortex
Increase the amount of lifting surface
Cause lift curve to rotate up and extend

29. Strakes
Strakes

30. Strakes
Strakes
Strake Vortices

31. F-16 Strakes

32. F-16 Strakes

33. F-16 vortex rollup sequence

34. F/A-18 leading-edge extensions (strakes)

35. F-18 HARV LEX effects

36. Effect of strakes on lift curve
Wing with strake C L
Wing with no strake a

37. Next Lesson (18)… Prior to Class In Class Read 4.5, 4.6, 3.5.10
Complete all problems through #21
In Class
Discuss how lift and drag of an aircraft differ from that of a wing
Discuss the aircraft drag polar

38. To get numbers (i.e. 3-D wing lift and drag), we need the 3-D lift-curve slope
Airfoil a cl
cla
and CL
Wing
CLa
For a in radians

39. Calculating 3-D Lift and Drag Coefficients
per deg
Determine Rec
Find 3-D lift curve slope
( from chart)
Find 3-D lift coefficient
( from chart)
Find induced drag coeff.
Find profile drag coeff.
(c from chart)
L=0 d  c l