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 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

A leading-edge slat is an

aerodynamic Aerodynamics () is the study of the motion of atmosphere of Earth, air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an ...

surface running spanwise just ahead of the wing leading edge. It creates a

leading edge slot A leading-edge slot is a fixed aerodynamics, aerodynamic feature of the wing of some aircraft to reduce the Stall (flight), stall speed and promote good low-speed handling qualities. A leading-edge slot is a spanwise gap in each wing, allowing ai ...

between the slat and wing which directs air over the wing surface, helping to maintain smooth airflow at low speeds and high angles of attack. This delays the 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.

Dogtooth extension

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. The effect is the same as a wing fence. It can also be used on straight wings in a drooped leading edge arrangement. 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 Arrow, F-8 Crusader, and the Ilyushin Il-62. Where the dogtooth is added as an afterthought, as for example on the

Hawker Hunter The Hawker Hunter is a transonic British jet propulsion, jet-powered fighter aircraft that was developed by Hawker Aircraft for the Royal Air Force (RAF) during the late 1940s and early 1950s. It was designed to take advantage of the newly dev ...

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

A leading edge cuff (or wing cuff) is a fixed

device employed on fixed-wing

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

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

A leading-edge root extension (LERX) is a small

fillet Fillet may refer to: *Annulet (architecture), part of a column capital, also called a fillet *Fillet (aircraft), a fairing smoothing the airflow at a joint between two components *Fillet (clothing), a headband *Fillet (heraldry), diminutive of the ...

, 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 Fighter aircraft (early on also ''pursuit aircraft'') are military aircraft designed primarily for air-to-air combat. In military conflict, the role of fighter aircraft is to establish air supremacy, air superiority of the battlespace. Domina ...

, LERXes induce controlled

airflow Airflow, or air flow, is the movement of air. Air behaves in a fluid manner, meaning particles naturally flow from areas of higher pressure to those where the pressure is lower. Atmospheric air pressure is directly related to altitude, temperat ...

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

dogfight A dogfight, or dog fight, is an air combat manoeuvring, aerial battle between fighter aircraft that is conducted at close range. Modern terminology for air-to-air combat is air combat manoeuvring (ACM), which refers to tactical situations requir ...

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 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, 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 Sukhoi Su-27 (; NATO reporting name: Flanker) is a Soviet Union, Soviet-origin twinjet, twin-engine supersonic Supermaneuverability, supermaneuverable fighter aircraft designed by Sukhoi. It was intended as a direct competitor for the lar ...

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.

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. 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 LCA Navy. The LEVCONs actuation ability also improves its performance over the LERX system in other areas. When combined with the thrust vectoring controller (TVC), the aircraft controllability at extreme angles of attack is further increased, which assists in stunts which require

supermaneuverability Supermaneuverability is the capability of fighter aircraft to execute tactical maneuvers that are not possible with purely Supermaneuverability#Aerodynamic maneuverability vs supermaneuverability, aerodynamic techniques. Such maneuvers can inv ...

such as Pugachev's Cobra. Additionally, on the Sukhoi Su-57 the LEVCON system is used for increased 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.

References