MAE 3241: AERODYNAMICS AND FLIGHT MECHANICS - PowerPoint PPT Presentation

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MAE 3241: AERODYNAMICS AND FLIGHT MECHANICS

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  1. MAE 3241: AERODYNAMICS ANDFLIGHT MECHANICS Examples of Dihedral, Anhedral, Adverse Yaw and Leading Edge Extensions April 15, 2011 Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk

  2. DIHEDRAL • Dihedral, d, is upward angle from horizontal in a fixed-wing aircraft from root to tip, as viewed from directly in front of aircraft • Purpose of positive dihedral is to confer stability in roll axis d

  3. ZERO DIHEDRAL, STEADY LEVEL FLIGHT L W

  4. ZERO DIHEDRAL ROLL L Fy Vside W

  5. POSITIVE DIHEDRAL, STEADY LEVEL FLIGHT L W

  6. POSITIVE DIHEDRAL ROLL Wing is at positive angle of attack relative to incoming wind L Fy Vside W

  7. SUMMARY

  8. SUMMARY

  9. ANHEDRAL • Anhedral required to keep aircraft from becoming too stable • Significant anhedral often seen on aircraft with a high mounted wing • High mounted wing is above center of mass which confers roll stability due to pendulum effect, so additional dihedral is not required

  10. DIHEDRAL ( BOEING 737) and ANHEDRAL (BAE 146)

  11. C-5 GALAXY EXAMPLE

  12. POLYHEDRAL • McDonnell Douglas F-4 Phantom II is one such example, unique among fighters for having dihedral wingtips • Added after prototype flight testing (original prototype of F-4 had a flat wing) showed need to correct some unanticipated roll instability - angling the wingtips, which were already designed to fold up for carrier operations, was more practical solution than re-engineering entire wing

  13. EXAMPLE: ADVERSE YAW

  14. EXAMPLE: F-18 VORTEX FENCES

  15. WHY LEADING EDGE EXTENSIONS? • Idea is generate vortex that interacts with rest of wing • Vortex speeds up flow of air over a wing and allow a plane to reach a higher angle of attack than it would be able to otherwise • Also causes drag

  16. CFD EXAMPLE OF LEADING EDGE EXTENSIONS

  17. CFD EXAMPLE OF LEADING EDGE EXTENSIONS

  18. VORTEX FROM LEADING EDGE EXTENSIONS

  19. VORTEX FROM LEADING EDGE EXTENSIONS Vortex Burst

  20. SUMMARY OF FIX • Solution was to implemented LEX fence • Fence is essentially another vortex generator itself • Fence creates a second unsteady vortex that interacts with main vortex created by leading edge extension • Interaction strengthens rotation of main vortex so that vortex bursting is eliminated near vertical tail • Repair was so effective that it not only solved tail buffet problem but fence also allows F-18 to reach even higher angles of attack

  21. ADDITIONAL FIX