Slide #1.

Leading Edge Extensions David Gallagher Adam Entsminger Will Graf AOE 4124 3/26/2004 1
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Slide #2.

Outline • • • • • • • Physical Description How does it work? Aerodynamic Advantages Aerodynamic Disadvantages Implementation on Aircraft Conclusions References http://www.eng.vt.edu/fluids/msc/gallery/vortex/mil02b.htm 3/26/2004 2
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Slide #3.

Physical Description • • • • • Combination of less sweptback wing (better low-speed properties, greater flap effectiveness) and delta wing (better stall characteristics) Leading edge can be straight or curved Must always have a sharp leading edge Small aspect ratio High sweep angle http://www.globalsecurity.org/military/systems/aircraft/f-16-pics.htm 3/26/2004 3
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Slide #4.

How does it work? • • • • • At low angles of attack, the LEX has little effect At higher angles of attack a vortex, formed from the leading edge of the LEX, flows over the wing. The vortex helps to energize the upper surface boundary layer, delaying separation. LEX vortex stabilizes wing leading edge vortex and prevents it from separating LEX vortex and wing leading edge vortex exist side by side and support each other Huenecke, Modern Combat Aircraft Design,1987 3/26/2004 4
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Slide #5.

Aerodynamic Advantages • • • • • Higher C L Higher C L , max Better maneuverability, especially during turns in aerial combat Smaller wing for same lift – YF-17 showed 50% increase in max lift for just 10% more wing area – F-16 was able to reduce wing size and save about 500 lbs in weight Reduced transonic lift center shift, giving lower supersonic trim drag at high g 3/26/2004 Huenecke, Modern Combat Aircraft Design,1987 5
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Slide #6.

Aerodynamic Disadvantages • • • • Tendency to cause pitchup at high angles of attack Increased drag at low angles of attack Structural fatigue of vertical stabilizers buffeted by flowfield When angle of attack becomes sufficiently large and vortex breakdown progresses ahead of wing trailing edge, aerodynamic advantages deteriorate significantly; BL blowing helps to prevent this 3/26/2004 6 http://www.eng.vt.edu/fluids/msc/gallery/vortex/baf18b.htmMedium/EC89-0096-149.jpg
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Slide #7.

Implementation on Aircraft F-16 Fighting Falcon http://www.globalsecurity.org/military/systems/aircraft/images/f-16cj-981228-F-6082P-997.jpg 3/26/2004 7
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Slide #8.

Implementation on Aircraft F-18 Hornet http://globalsecurity.org/military/systems/aircraft/images/f-18-016.jpg 3/26/2004 8
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Slide #9.

Implementation on Aircraft MiG-29 Fulcrum http://www.fas.org/nuke/guide/russia/airdef/mig-29_near_vertical.jpg 3/26/2004 9
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Slide #10.

Implementation on Aircraft http://www.cafefoundation.org/aprs/localflow1.pdf 3/26/2004 10
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Slide #11.

Conclusions • Leading edge extensions are more beneficial for combat fighter aircraft because these aircraft are more often in the flight conditions where a leading edge extension is most useful, such as high angle of attack maneuvers • However, strakes (as shown in the previous slide) are used on some general aviation aircraft to reduce the abruptness of stall onset and provide better landing capabilities • Leading edge extensions have their drawbacks, including pitchup at high angles of attack, and should only be used when additional maneuverability is necessary 3/26/2004 11
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Slide #12.

References • • • • • • • • • Background image: http://www.dfrc.nasa.gov/gallery/photo/F18HARV/Medium/EC89-0096-149.jpg Animated GIF: http://globalsecurity.org/military/systems/aircraft/f-18pics.htm Huenecke, Klaus. Modern Aircraft Design. Maryland: Naval Institute Press, 1987. Whitford, Ray. Fundamentals of Fighter Design. England: Airlife Publishing, 2000. Bertin, John. Aerodynamics for Engineers. New Jersey: Prentice Hall, 2002. Filippone, High Speed Aerodynamics. 24 Mar. 2004. Wing. 24 Mar. 2004. Seeley, Brian. Local Flow Control I. Aircraft Research Report. 24 Mar. 2004. F-16 Fighting Falcon. 24 Mar. 2004. 3/26/2004 12
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Slide #13.

Questions? 3/26/2004 13
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