Leading%20Edge%20Extensions

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/mi
l02b.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/air
craft/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/ba
f18b.htmMedium/EC89-0096-149.jpg
7
Implementation on Aircraft
F-16 Fighting Falcon
http//www.globalsecurity.org/military/systems/air
craft/images/f-16cj-981228-F-6082P-997.jpg
8
Implementation on Aircraft
F-18 Hornet
http//globalsecurity.org/military/systems/aircraf
t/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/galler
  y/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.
  lthttp//aerodyn.org/HighSpeed/strakes.htmlgt
• Wing. 24 Mar. 2004. lthttp//www.shaw.af.mil/20fw/w
  eapons/wing.htmlgt
• Seeley, Brian. Local Flow Control I. Aircraft
  Research Report. 24 Mar. 2004.
  lthttp//www.cafefoundation.org/aprs/localflow1.pdf
  gt
• F-16 Fighting Falcon. 24 Mar. 2004.
  lthttp//www.globalsecurity.org/military/systems/ai
  rcraft/f-16-design.htmgt

13
Questions?