Leading edge extension
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A leading edge extension is a small extension to an aircraft wing surface, forward of the leading edge. Different kinds of extensions have been used for different reasons.
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[edit] Leading edge slats
A slat is a small aerofoil running spanwise just ahead of the wing leading edge. This creates a Leading edge slot between the slat and wing, which acts to allow the aircraft to fly at lower speeds.
[edit] Dogtooth extension
A dogtooth is a small, sharp zig-zag double kink in the leading edge of a wing. On a swept wing, it is used is to generate a vortex of air flowing backwards over the wing, reducing spanwise airflow.
Where the dogtooth is added as an afterthought as for example with the Hawker Hunter and some variants of the Quest Kodiak, the dogtooth is created by adding an extension to the outer span only of the leading edge.
[edit] Leading edge kink
The Avro Vulcan prototypes had a delta wing with a straight leading edge. To cure handling problems, a shallow triangular extension was added to the outer leading edge, giving the planform of a compound delta having three leading edge sections at different angles, with kinks between the sections.
Later models of the English Electric Lightning had the wing tip extended forwards to create a leading edge kink at approximately two-thirds span.
[edit] Leading edge root extensions
Leading edge root extensions (LERX) are small fillets, typically roughly triangular in shape, running forward from the leading edge of the wing root to a point along the fuselage. These are often called simply leading edge extensions (LEX), although they are not the only kind. To avoid ambiguity, this article uses the term LERX.
On a modern fighter aircraft they provide usable airflow over the wing at high angles of attack, so delaying the stall and consequent loss of lift. In cruising flight the effect of the LERX is minimal. However at high angles of attack, as often encountered in a dog fight, the LERX generates a high-speed vortex that attaches to the top of the wing. The vortex action maintains a smooth airflow over the wing surface well past the normal stall point at which the airflow would otherwise break up, thus sustaining lift at very high angles.
LERX were first used on the Northrop F-5 "Freedom fighter" which flew in 1959,[1] and have since become commonplace on many combat aircraft. The F/A-18 Hornet has especially large examples, as does the Sukhoi Su-27. The Su-27 LERX help to make some advanced maneuvers possible, such as the Pugachev's Cobra, the Cobra Turn and the Kulbit.
[edit] Aircraft using LERX
A few examples of aircraft with leading edge root extensions are listed below.
- China
- China/Pakistan
- Iran
- Russia/USSR
- Sukhoi Su-27 and derivatives, including the Sukhoi Su-34 and the Sukhoi Su-47.
- Mikoyan MiG-29
- Sukhoi PAK FA - on PAK-FA aircraft the part of the wing that includes the LERX is movable to control the airflow at high angles of attack, similar to a wing leading flap. - LEVCON (this is "active" control surface)
- USA/UK
- F-5 Freedom Fighter
- F-16 Fighting Falcon and its unsuccessful competitor the YF-17 Cobra
- F/A-18 Hornet/Super Hornet
- AV-8 Harrier II/RAF Harrier II
[edit] Chines
A chine is a long extension of the wing root along the forward fuselage, first seen on the Lockheed SR-71 Blackbird family. The chines contribute useful additional lift at supersonic speeds, as well as acting as LERX at low speeds. A standard leading edge extension joins to the fuselage at an angle while a chine is an extension of the curvature of the fuselage. Therefore chines avoid presenting corner reflectors or vertical sides to radars.[2]
The F-22 Raptor has chines that lead to the leading edge extensions that are blended into the engine air intakes.[3]
Canards can also help generate vortex lift over the main wings, but due to their poor stealth characteristics they have been replaced with chines in all fifth generation jet fighters except for the Chengdu J-20.[4]
[edit] See also
[edit] References
- ^ Green, W. and Swanborough, G.; The complete book of fighters, Salamander, 1994
- ^ Rebecca Grant (political expert) "The Radar Game" Mitchell Institute, 2010
- ^ The beams, made of composite material, also provide an attachment point for the F-22's chine, a fuselage edge that provides smooth aerodynamic blending into the intakes and wings.
- ^ Canards
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