Leading Edge Extensions

1. Leading Edge Extensions David Gallagher Adam Entsminger Will Graf AOE 4124

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. 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

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

5. 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 Huenecke, Modern Combat Aircraft Design,1987

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

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

8. Implementation on Aircraft F-18 Hornet http://globalsecurity.org/military/systems/aircraft/images/f-18-016.jpg

9. Implementation on Aircraft MiG-29 Fulcrum http://www.fas.org/nuke/guide/russia/airdef/mig-29_near_vertical.jpg

10. Implementation on Aircraft http://www.cafefoundation.org/aprs/localflow1.pdf

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

12. 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>

13. Questions?