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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.

Contents

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.

Dogtooth extension

Dog tooth on the wing of a Hawker Hunter

A dogtooth is a small, sharp kink in the leading edge of a wing. On a swept wing, it is used is to generate a jet of air flowing backwards over the wing, reducing spanwise airflow.

Where the dog tooth is added as an afterthought as for example with the Hawker Hunter, the dogtooth is created by adding an extension to the outer span only of the leading edge.

Leading edge kink

Kinked leading edge of an Avro Vulcan

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.

Leading edge root extensions (LERX)

Flow visualization smoke marks vortex flows along an F/A-18's LERX

LERX are fillets or strakes, typically roughly triangular in shape, running from the leading edge of the wing root to a point near the cockpit along the fuselage. They tend to be fairly small in span, extending out less than a metre.

On a modern fighter aircraft they provide usable airflow over the wing at high angles of attack. In cruising flight the effect of the LERX is minimal. However: when the angle of attack increases, as in a dog fight, the LERX starts to generate a high-speed vortex that remains attached to the top of the wing. Due to the effects described by Bernoulli's principle the wing therefore has a low pressure zone on top, and continues to generate lift past the normal stall point. The F/A-18 Hornet has especially large examples, as does the Sukhoi Su-27. Early prototypes of the Su-27 crashed due to poorly designed LERX, causing it to freeze at angles of attack above 5 degrees. This has since been overcome. In fact, the LERX help to make possible advanced maneuvers such as the Pugachev's Cobra, the Cobra Turn and the Kulbit.

Chines

Chines along the fuselage of a SR-71 Blackbird

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.

The F-22 Raptor has chines that lead to the leading edge extensions that are blended into the engine air intakes.[1]

Canards can also help generate vortex lift over the main wings, but due to their poor stealth characteristics they have been replaced with chines and LEX in fifth generation jet fighters.[2]

Aircraft using LEX

A few examples of aircraft with leading edge extensions are listed below.

  • Civilian
    • Quest Kodiak (Fixed Discontinuous Outboard Leading Edge Extension)

See also

References

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