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 In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...

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

leading-edge slat Slats are aerodynamic surfaces on the leading edge of the wing of a fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. A higher coefficient of lift is produced as a result of angle of attack and speed, ...

is an

aerodynamic Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dyn ...

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

leading edge slot A leading-edge slot is a fixed aerodynamic feature of the wing of some aircraft to reduce the stall speed and promote good low-speed handling qualities. A leading-edge slot is a spanwise gap in each wing, allowing air to flow from below the wing ...

between the slat and wing which directs air over the wing surface, helping to maintain smooth airflow at low speeds and high

. 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

hawker hunter t7 blue diamond in planform arp

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 In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in th ...

flow field to prevent separated flow from progressing outboard at high angle of attack. The effect is the same as a

wing fence Wing fences, also known as boundary layer fences and potential fences are fixed aerodynamic devices attached to aircraft wings. Often seen on swept-wing aircraft, wing fences are flat plates fixed to the upper surfaces parallel to the wing ch ...

. 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 The McDonnell Douglas F-15 Eagle is an American twin-engine, all-weather tactical fighter aircraft designed by McDonnell Douglas (now part of Boeing). Following reviews of proposals, the United States Air Force selected McDonnell Douglas's ...

and the wings of the

F-4 Phantom II The McDonnell Douglas F-4 Phantom II is an American tandem two-seat, twin-engine, all-weather, long-range supersonic jet interceptor and fighter-bomber originally developed by McDonnell Aircraft for the United States Navy.Swanborough and Bow ...

F/A-18 Super Hornet The Boeing F/A-18E and F/A-18F Super Hornet are twin-engine, carrier-capable, multirole fighter aircraft variants based on the McDonnell Douglas F/A-18 Hornet. The F/A-18E single-seat and F/A-18F tandem-seat variants are larger and more a ...

CF-105 Arrow The Avro Canada CF-105 Arrow was a delta-winged interceptor aircraft designed and built by Avro Canada. The CF-105 held the promise of Mach 2 speeds at altitudes exceeding and was intended to serve as the Royal Canadian Air Force's (RCAF) ...

, F-8U Crusader, and the

Ilyushin Il-62 The Ilyushin Il-62 (russian: Илью́шин Ил-62; NATO reporting name: Classic) is a Soviet long-range narrow-body jetliner conceived in 1960 by Ilyushin. As successor to the popular turboprop Il-18 and with capacity for almost 200 pa ...

. Where the dogtooth is added as an afterthought, as for example on the

Hawker Hunter The Hawker Hunter is a transonic British 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 developed Rolls-R ...

and some variants of the

Quest Kodiak The Daher Kodiak (formerly Quest Kodiak) is an American utility aircraft designed by and originally manufactured by Quest Aircraft. Manufacturing was taken over by Daher in 2019 after its purchase of Quest Aircraft. The high-wing, unpressuri ...

, 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 is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...

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 (cut), a piece of meat *Fille ...

, typically roughly triangular in shape, running forward from the leading edge of the

wing root The wing root is the part of the wing on a fixed-wing aircraft or winged-spaceship that is closest to the fuselage,Peppler, I.L.: ''From The Ground Up'', page 9. Aviation Publishers Co. Limited, Ottawa Ontario, Twenty Seventh Revised Edition, 1996 ...

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 are fixed-wing military aircraft designed primarily for air-to-air combat. In military conflict, the role of fighter aircraft is to establish air superiority of the battlespace. Domination of the airspace above a battlefield ...

, LERXes induce controlled

airflow Airflow, or air flow, is the movement of air. The primary cause of airflow is the existence 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 a ...

over the wing at high

, 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 aerial battle between fighter aircraft conducted at close range. Dogfighting first occurred in Mexico in 1913, shortly after the invention of the airplane. Until at least 1992, it was a component in every majo ...

or during takeoff and landing, the LERX generates a high-speed

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 The Northrop F-5 is a family of supersonic light fighter aircraft initially designed as a privately funded project in the late 1950s by Northrop Corporation. There are two main models, the original F-5A and F-5B Freedom Fighter variants and t ...

"Freedom Fighter" which flew in 1959, and have since become commonplace on many combat aircraft. The

F/A-18 Hornet The McDonnell Douglas F/A-18 Hornet is an all-weather, twinjet, twin-engine, supersonic aircraft, supersonic, carrier-based aircraft, carrier-capable, Multirole combat aircraft, multirole combat aircraft, designed as both a Fighter aircraft, ...

has especially large examples, as does the

Sukhoi Su-27 The Sukhoi Su-27 (russian: Сухой Су-27; NATO reporting name: Flanker) is a Soviet-origin twin-engine supermaneuverable fighter aircraft designed by Sukhoi. It was intended as a direct competitor for the large US fourth-generation jet ...

and the

CAC/PAC JF-17 Thunder The CAC/PAC JF-17 Thunder ( ur , جے ایف-17 گرج), or FC-1 ''Xiaolong'' (), is a lightweight, single-engine, multi-role combat aircraft developed jointly by the Chengdu Aircraft Corporation (CAC) of China and the Pakistan Aeronautical ...

. The Su-27 LERX help make some advanced maneuvers possible, such as the

Pugachev's Cobra In aerobatics, the cobra maneuver (or just the ''cobra''), also called ''dynamic deceleration'', among other names (see Etymology), is a dramatic and demanding maneuver in which an airplane flying at a moderate speed abruptly raises its nose mom ...

, the Cobra Turn and the

Kulbit The "Kulbit" (also known as the "Frolov chakra") is an aerial maneuver developed by Russian pilots in which the aircraft performs an extremely tight loop, often not much wider than the length of the aircraft itself. It differs from the traditional ...

. A long, narrow sideways extension to the fuselage, attached in this position, is an example of a

chine A chine () is a steep-sided coastal gorge where a river flows to the sea through, typically, soft eroding cliffs of sandstone or clays. The word is still in use in central Southern England—notably in East Devon, Dorset, Hampshire and the Isl ...

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 In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...

flight. This system has been incorporated in the Russian

Sukhoi Su-57 The Sukhoi Su-57 (russian: Сухой Су-57; NATO reporting name: Felon) is a Twinjet, twin-engine stealth Multirole combat aircraft, multirole fighter aircraft developed by Sukhoi. It is the product of the PAK FA (russian: ПАК ФА, russ ...

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

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 aerodynamic techniques. Such maneuvers can involve controlled side-slipping or angles of attack beyond maximum lift. ...

such as

. Additionally, on the

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