View source for Leading-edge extension

{{Short description|Anti-stall control surface on aircraft}}
{{Use dmy dates|date=September 2020}}
[[File:Leadingedgeextensions annotated.svg|thumb|300px|Aircraft wing leading-edge extensions{{snd}}annotated]]
A '''leading-edge extension''' ('''LEX''') is a small extension to an aircraft wing surface, forward of the leading edge. The primary reason for adding an extension is to improve the airflow at high [[angle of attack|angles 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.
==Leading-edge slat==
[[File:Airfrance.a318-100.f-gugj.arp.jpg|thumb|[[Leading-edge slat]]s deployed on an [[Airbus A318-100]]]]
{{Main|Leading-edge slat}}
A [[leading-edge slat]] is an [[aerodynamic]] surface running spanwise just ahead of the wing leading edge. It creates a [[leading edge slot]] between the slat and wing which directs air over the wing surface, helping to maintain smooth airflow at low speeds and high [[angle of attack|angles of attack]]. This delays the [[stall (flight)|stall]], allowing the aircraft to fly at a higher angle of attack. Slats may be made fixed, or retractable in normal flight to minimize [[drag (physics)#drag in aerodynamics|drag]].
==Dogtooth extension==
[[File:hawker hunter t7 blue diamond in planform arp.jpg|thumb|Dog tooth on the wing of a [[Hawker Hunter]]]]
A '''dogtooth''' is a small, sharp zig-zag break in the leading edge of a wing. It is usually used on a swept wing, to generate a [[vortex]] flow field to prevent separated flow from progressing outboard at high angle of attack.<ref>''Effects of Wing-Leading-Edge Modifications on a Full-Scale, Low-Wing General Aviation Airplane'', Nasa TP 2011</ref> The effect is the same as a [[wing fence]].<ref>[http://www.flightglobal.com/pdfarchive/view/1959/1959%20-%203173.html A Two-seat Gnat Development for the R.A.F.] ''Flight'' 1959</ref> It can also be used on straight wings in a [[drooped leading edge]] arrangement.{{citation needed|date=August 2015|reason=Is that really a dog tooth and not a cuff?}}
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 the [[F-15 Eagle]] and the wings of the [[F-4 Phantom II]], [[F/A-18 Super Hornet]], [[CF-105|CF-105 Arrow]], [[Vought F-8 Crusader|F-8 Crusader]], and the [[Ilyushin Il-62]]. Where the dogtooth is added as an afterthought, as for example on the [[Hawker Hunter]] and some variants of the [[Quest Kodiak]], the dogtooth is created by adding an extension to the outer section of the leading edge.
==Leading-edge cuff==
[[File:DroopedLeadingEdgeCuff01.JPG|thumb|Experimental drooped leading-edge cuff on an [[American Aviation AA-1 Yankee]]]]
{{Main|Leading-edge cuff}}
A leading edge cuff (or wing cuff) is a fixed [[aerodynamics|aerodynamic]] device employed on fixed-wing [[aircraft]] 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.
==Leading-edge root extension==
[[File:FA18 LEX.jpg|thumb|Condensation vortex flows along the LERX of an [[McDonnell Douglas F/A-18 Hornet|F/A-18]]]]
A leading-edge root extension (LERX) is a small [[fillet (mechanics)|fillet]], 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]], LERXes induce controlled [[aerodynamics|airflow]] over the wing at high [[angle of attack|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 [[dogfight]] or during takeoff and landing, the LERX generates a high-speed [[vortex]] 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 normal [[stall (flight)|stall]] point at which the airflow separates from the wing surface, thus sustaining lift at very high angles.
LERX were first used on the [[Northrop F-5]] "Freedom Fighter" which flew in 1959,<ref>Green, W. and Swanborough, G.; ''The complete book of fighters'', Salamander, 1994</ref> and have since become commonplace on many combat aircraft. The [[F/A-18 Hornet]] has especially large examples, as does the [[Sukhoi Su-27]] and the [[CAC/PAC JF-17 Thunder]]. The Su-27 LERX help make some advanced maneuvers possible, such as the [[Pugachev's Cobra]], the [[Cobra Turn]] and the [[Kulbit]].
A long, narrow sideways extension to the fuselage, attached in this position, is an example of a [[chine (aircraft)|chine]].
==Leading-edge vortex controller==
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.<ref>{{cite web |last1=Lee |first1=Gwo-Bin |title=Leading-edge Vortices Control on a Delta Wing by Micromachined Sensors and Actuators |url=http://www.las.inpe.br/~jrsenna/AerospaceMEMS/Contr-Ensaios-voo/caltech1.pdf|publisher= American Institute of Aeronautics and Astronautics|access-date=18 October 2018}}</ref> Otherwise they operate on the same principles as the LERX system to create lift augmenting leading edge vortices during high [[angle of attack]] flight.
This system has been incorporated in the Russian [[Sukhoi Su-57]] and Indian [[HAL Tejas|HAL LCA Navy]].<ref>{{cite web |last1=Sweetman |first1=Bill |title=Sukhoi T-50 Shows Flight-Control Innovations |url=http://aviationweek.com/awin/sukhoi-t-50-shows-flight-control-innovations |website=Aviation Week |publisher=Aviation Week & Space Technology |access-date=18 October 2018}}</ref>
The LEVCONs actuation ability also improves its performance over the LERX system in other areas.
When combined with the [[thrust vectoring|thrust vectoring controller]] (TVC), the aircraft controllability at extreme [[angle of attack|angles of attack]] is further increased, which assists in stunts which require [[supermaneuverability]] such as [[Pugachev's Cobra]].{{dubious|date=September 2019}}{{citation needed|date=September 2019}} Additionally, on the [[Sukhoi Su-57]] the LEVCON system is used for increased [[Departure resistance|departure-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.
==See also==
* [[Index of aviation articles]]
* [[Canard (aeronautics)]]
* [[Strake (aviation)]]
* [[Vortex generator]]
==References==
{{Commons category|Leading-edge devices}}
{{Reflist}}
{{Aircraft components}}
{{DEFAULTSORT:Leading Edge Extension}}
[[Category:Aerospace engineering]]
[[Category:Aircraft aerodynamics]]
[[Category:Aircraft wing components]]
[[Category:Aircraft wing design]]