Aleading-edge extension (LEX) is a small extension to an aircraft wing surface, forward of theleading edge. The primary reason for adding an extension is to improve the airflow at highangles of attack and low airspeeds, to improve handling and delay the stall. A dog tooth can also improve airflow and reduce drag at higher speeds.
Aleading-edge slat is anaerodynamic surface running spanwise just ahead of the wing leading edge. It creates aleading edge slot between the slat and wing which directs air over the wing surface, helping to maintain smooth airflow at low speeds and highangles of attack. This delays thestall, allowing the aircraft to fly at a higher angle of attack. Slats may be made fixed, or retractable in normal flight to minimizedrag.
Adogtooth is a small, sharp zig-zag break in the leading edge of a wing. It is usually used on a swept wing, to generate avortex flow field to prevent separated flow from progressing outboard at high angle of attack.[1] The effect is the same as awing fence.[2] It can also be used on straight wings in adrooped leading edge arrangement.[citation needed]
Many high-performance aircraft use the dogtooth design, which induces a vortex over the wing to control boundary layer spanwise extension, increasing lift and improving resistance to stall. Some of the best-known uses of the dogtooth are in the stabilizer of theF-15 Eagle and the wings of theF-4 Phantom II,F/A-18 Super Hornet,CF-105 Arrow,F-8 Crusader, and theIlyushin Il-62. Where the dogtooth is added as an afterthought, as for example on theHawker Hunter and some variants of theQuest Kodiak, the dogtooth is created by adding an extension to the outer section of the leading edge.
A leading edge cuff (or wing cuff) is a fixedaerodynamic device employed on fixed-wingaircraft to introduce a sharp discontinuity in the leading edge of the wing in the same way as a dogtooth. It also typically has a slightly drooped leading edge to improve low-speed characteristics.
A leading-edge root extension (LERX) is a smallfillet, typically roughly triangular in shape, running forward from the leading edge of thewing 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 modernfighter aircraft, LERXes induce controlledairflow over the wing at highangles 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 adogfight or during takeoff and landing, the LERX generates a high-speedvortex that attaches to the top of the wing. The vortex action maintains the attachment of the airflow to the upper-wing surface well past the normalstall point at which the airflow separates from the wing surface, thus sustaining lift at very high angles.
LERX were first used on theNorthrop F-5 "Freedom Fighter" which flew in 1959,[3] and have since become commonplace on many combat aircraft. TheF/A-18 Hornet has especially large examples, as does theSukhoi Su-27 and theCAC/PAC JF-17 Thunder. The Su-27 LERX help make some advanced maneuvers possible, such as thePugachev's Cobra, theCobra Turn and theKulbit.
A long, narrow sideways extension to the fuselage, attached in this position, is an example of achine.
Leading-edge vortex controller (LEVCON) systems are a continuation of leading-edge root extension (LERX) technology, but with actuation that allows the leading edge vortices to be modified without adjusting the aircraft's attitude.[4] Otherwise they operate on the same principles as the LERX system to create lift augmenting leading edge vortices during highangle of attack flight.
This system has been incorporated in the RussianSukhoi Su-57 and IndianHAL LCA Navy.[5]
The LEVCONs actuation ability also improves its performance over the LERX system in other areas.When combined with thethrust vectoring controller (TVC), the aircraft controllability at extremeangles of attack is further increased, which assists in stunts which requiresupermaneuverability such asPugachev's Cobra.[dubious –discuss][citation needed] Additionally, on theSukhoi Su-57 the LEVCON system is used for increaseddeparture-resistance in the event of TVC failure at a post-stall attitude. It can also be used for trimming the aircraft, and optimizing the lift to drag ratio during cruise.
