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Aero Engineering 315 Lesson 17 High Lift Devices.

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1 Aero Engineering 315 Lesson 17 High Lift Devices

2 Homework #20 20.(BSBW A4.1) a.Consider a flying wing aircraft made using a NACA 2412 airfoil with a wing area of 250 ft 2, 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 10 6, what are C L and C D 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 C L in certain circumstances

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

7  The velocity at stall, V stall, occurs at C Lmax  Recall the definition of equivalent airspeed?  The minimum V e to avoid stall is Stall Velocity

8 V stall Problem You are landing your F-16 at Luke AFB with a density altitude of 6,000 feet. Your gross weight is 25,000 lbs. C Lmax is 1.2 and the whole aircraft planform area is 428 ft 2. What is your stalling velocity in knots? 2  S W V max C L Stall   V ( )(428)(1.2) 2(25,000) 2  S W V max C L e-Stall  SL  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 C L max Which lowers V stall Flaps improve visibility on final by creating an angle of incidence Landing speeds (1.3 V stall ) limited by braking, tires, runway distance and condition… Must dissipate KE (1/2mV 2 ) Take-off speed (1.2 V stall ) limited by max tire spin up speeds, runway length, thrust available…

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

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

12 Typical Flap Impact  (degrees) Anderson, J. D., Introduction to Flight, 4 th Edition, page 314 With flaps No flaps  = 0   = 50 0  = 15 0


14 Tornado - Slotted Flap

15 KC-10 Slotted Flap

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

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

18 F-16XL upper surface suction

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

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

30 Strake Vortices

31 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 no strake  C L Wing with strake

37 Next Lesson (18)…  Prior to Class Read 4.5, 4.6, 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  clcl clcl and C L Wing CLCL For  in radians

39 Calculating 3-D Lift and Drag Coefficients Determine Re c 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 per deg

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