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HiAlphaBasicsPres - Some High Alpha Aerodynamics W.H Mason...

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Slide 1 4/27/10 Some High Alpha Aerodynamics W.H. Mason Configuration Aerodynamics Class
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Slide 2 4/27/10 Issues in Hi- ± Aero General Aviation Prevention/recovery from spins Beware: Tail Damping Power Factor (TDPF) » Sometimes advocated for use in design » Has been shown to be inaccurate! Fighters Resistance to “departure” from controlled flight Carefree hi- ± air combat maneuvering » Fuselage pointing » Velocity vector rolls » Supermaneuverability » etc. Transports Control/prevention of pitchup and deep stall (the DC-9 case study)
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Slide 3 4/27/10 High Angle of Attack Aerodynamics are nonlinear - complicated component interactions (vortices) - depends heavily on WT data for analysis • Motion is highly dynamic - need unsteady aero • Exact requirements are still being developed • Keys issues (from a fighter designer’s perspective): - adequate nose down pitching moment to recover - roll rate at high alpha - departure avoidance - adequate yaw control power - the role of thrust vectoring
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Slide 4 4/27/10 The Hi- ± Story Longitudinal Typical unstable modern fighter ± 90° + - Cm Max nose up moment Max nose down moment Cm * Minimum Cm * allowable is an open question Issue of including credit for thrust vectoring Pinch often around ± ~ 30°-40° Suggested nose down req’t: Pitch accel in 1st sec: -0.25 rad/sec 2
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Slide 5 4/27/10 Example: F-16 NASA TP-1538, Dec. 1979 Found in flight, and also in tests at the NASA Full Scale Tunnel, other tunnels didn’t find this, and so the design was made with this “issue” An ± -limiter was put in the control system to prevent pilots from going above 28°
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Slide 6 4/27/10 The Hi- ± Story Directional
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Slide 7 4/27/10 Example: F-5 -0.0050 0.0000 0.0050 0.0100 -10° 10° 20° 30° 40° 50° C n ± ² , deg. Full Config., Tail Off Full Config., Vertical Tail On Forebody alone F-5 WT data: NASA TN D-7716 Sketch from NASA TN D-7716, 1974 Chine forebodies are even more effective! Above 30°, the directional stability comes entirely from the forebody!
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Slide 8 4/27/10 Forebody Vortices F-5A forebody, ± = 40°, ² = 5° NASA CR 4465, Aug. 1992 I’m looking for a better, color, figure At “high” angles of attack, vortices form over the forebody, producing additional forces, and often interacting with the rest of the airplane flowfield
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Slide 9 4/27/10 Illustration of Forebody Vortices and a “Fix” • Laser Light Sheet Video of the RFC forebody X-29 forebody Taken at the USAF Museum, WPAFB, Ohio • And Flow Asymmetries: - an amazing story - solve with nose strakes
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Slide 10 4/27/10 The Hi- ± Story Lateral Cl ± + - ² 90° “Stable” “Unstable” 0 Dihedral Effect (also due to sweep) Flow Separates on wing Drooping LE devices helps control severity
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Slide 11 4/27/10 Example: F-4 NASA TN D-7131, July 1973
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Slide 12 4/27/10 Example: F-16 Lateral/ Directional Control NASA TP-1538, Dec. 1979 Conventional aero control surfaces lose effectiveness at high angles of attack Control Effectiveness Change with alpha ± C n ± C l ± , deg ² r = 30° ² r = 30° ² a = -20° ² d = -5° ² a = -20° ² d = -5°
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Slide 13 4/27/10 A way to get yaw: differential canard
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