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Leading Edge Extensions

David Gallagher

Adam Entsminger

Will Graf

AOE 4124

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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

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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

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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

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Aerodynamic Advantages

• Higher

• Higher

• 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

LC

max,LC

Huenecke, Modern Combat Aircraft Design,1987

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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

http://www.eng.vt.edu/fluids/msc/gallery/vortex/baf18b.htmMedium/EC89-0096-149.jpg

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Implementation on Aircraft

F-16 Fighting Falconhttp://www.globalsecurity.org/military/systems/aircraft/images/f-16cj-981228-F-6082P-997.jpg

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Implementation on AircraftF-18 Hornet

http://globalsecurity.org/military/systems/aircraft/images/f-18-016.jpg

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Implementation on Aircraft

MiG-29 Fulcrumhttp://www.fas.org/nuke/guide/russia/airdef/mig-29_near_vertical.jpg

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Implementation on Aircraft

http://www.cafefoundation.org/aprs/localflow1.pdf

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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

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References• Background image:

http://www.dfrc.nasa.gov/gallery/photo/F-18HARV/Medium/EC89-0096-149.jpg

• Animated GIF: http://globalsecurity.org/military/systems/aircraft/f-18-pics.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. <http://aerodyn.org/HighSpeed/strakes.html>

• Wing. 24 Mar. 2004. <http://www.shaw.af.mil/20fw/weapons/wing.html>

• Seeley, Brian. Local Flow Control I. Aircraft Research Report. 24 Mar. 2004. <http://www.cafefoundation.org/aprs/localflow1.pdf>

• F-16 Fighting Falcon. 24 Mar. 2004. <http://www.globalsecurity.org/military/systems/aircraft/f-16-design.htm>

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Questions?