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Aero Engineering 315

Aero Engineering 315. Lesson 17 High Lift Devices. Homework #20. (BSBW A4.1) 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.

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Aero Engineering 315

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

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

  8. 2 W 2 W = = V V rSL r e-Stall S Stall S C C L L max max 2(25,000) 2(25,000) = = V V Stall e-Stall (.001987)(428)(1.2) (.002377)(428)(1.2) = = 202 ft/sec = 120 KEAS 221 ft/sec = 131 KTAS V V e-Stall Stall Vstall 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. CLmax is 1.2 and the whole aircraft planform area is 428 ft2. What is your stalling velocity in knots?

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

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

  13. Tornado - Slotted Flap

  14. KC-10 Slotted Flap

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

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

  17. F-16XL upper surface suction

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

  19. Powered (blown) lift Internally Blown Flap

  20. Externally Blown Flap Powered (blown) lift

  21. C-17 externally blown flap

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

  23. YC-14 - Upper Surface Blown Flap

  24. Vectored Thrust Powered (vectored) lift

  25. AV-8B -- Vectored Thrust

  26. C-130 JATO - Vectored Thrust

  27. 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

  28. Strakes Strakes

  29. Strakes Strakes Strake Vortices

  30. F-16 Strakes

  31. F-16 Strakes

  32. F-16 vortex rollup sequence

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

  34. F-18 HARV LEX effects

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

  36. Next Lesson (18)… • Prior to 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

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

  38. 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 c l d Calculating 3-D Lift and Drag Coefficients

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