Leading edge extension
Encyclopedia
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.
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.
A dogtooth is a small, sharp zig-zag double kink in the leading edge of a wing. On a swept wing, it is used is to generate a vortex
of air flowing backwards over the wing, reducing spanwise airflow.
Where the dogtooth 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.
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.
Later models of the English Electric Lightning
had the wing tip extended forwards to create a leading edge kink at approximately two-thirds span.
LERX are small fillet
s, typically roughly triangular in shape, running forward from the leading edge of the wing root
to a point along the fuselage.
On a modern fighter aircraft
they provide usable airflow
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 dog fight, the LERX generates a high-speed vortex
that attaches to the top of the wing. The vortex action maintains a smooth airflow over the wing surface well past the normal stall
point at which the airflow would otherwise break up, 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 Su-27 LERX help to make some advanced maneuvers possible, such as the Pugachev's Cobra
, the Cobra Turn
and the Kulbit
.
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. A standard leading edge extension joins to the fuselage at an angle while a chine is an extension of the curvature of the fuselage. Therefore chines avoid presenting corner reflector
s or vertical sides
to radars.
The F-22 Raptor
has chines that lead to the leading edge extensions that are blended into the engine air intakes.
Canards
can also help generate vortex lift over the main wings, but due to their poor stealth characteristics they have been replaced with chines in all fifth generation jet fighters except for the Chengdu J-20
.
Leading edge slats
A slatLeading edge slats
Slats are aerodynamic surfaces on the leading edge of the wings of 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, so by deploying slats an aircraft can fly at slower...
is a small aerofoil running spanwise just ahead of the wing leading edge. This creates a Leading edge slot
Leading edge slot
A leading edge slot is an 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 span-wise gap in each wing, allowing air to flow from below the wing to its upper surface...
between the slat and wing, which acts to allow the aircraft to fly at lower speeds.
Dogtooth extension
Vortex
A vortex is a spinning, often turbulent,flow of fluid. Any spiral motion with closed streamlines is vortex flow. The motion of the fluid swirling rapidly around a center is called a vortex...
of air flowing backwards over the wing, reducing spanwise airflow.
Where the dogtooth is added as an afterthought as for example with the Hawker Hunter
Hawker Hunter
The Hawker Hunter is a subsonic British jet aircraft developed in the 1950s. The single-seat Hunter entered service as a manoeuvrable fighter aircraft, and later operated in fighter-bomber and reconnaissance roles in numerous conflicts. Two-seat variants remained in use for training and secondary...
, the dogtooth is created by adding an extension to the outer span only of the leading edge.
Leading edge kink
Avro Vulcan
The Avro Vulcan, sometimes referred to as the Hawker Siddeley Vulcan, was a jet-powered delta wing strategic bomber, operated by the Royal Air Force from 1956 until 1984. Aircraft manufacturer A V Roe & Co designed the Vulcan in response to Specification B.35/46. Of the three V bombers produced,...
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.
Later models of the English Electric Lightning
English Electric Lightning
The English Electric Lightning is a supersonic jet fighter aircraft of the Cold War era, noted for its great speed and unpainted natural metal exterior finish. It is the only all-British Mach 2 fighter aircraft. The aircraft was renowned for its capabilities as an interceptor; Royal Air Force ...
had the wing tip extended forwards to create a leading edge kink at approximately two-thirds span.
Leading edge root extensions (LERX)
Fillet (mechanics)
In mechanical engineering, a fillet is a concave easing of an interior corner of a part design. A rounding of an exterior corner is called a "round" or a "chamfer".-Applications:...
s, typically roughly triangular in shape, running forward from the leading edge of the wing root
Wing root
The wing root is the part of the wing on a fixed-wing aircraft that is closest to the fuselage. On a simple monoplane configuration, this is usually easy to identify...
to a point along the fuselage.
On a modern fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
they provide usable airflow
Aerodynamics
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...
over the wing at high angles of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
, 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 dog fight, the LERX generates a high-speed vortex
Vortex
A vortex is a spinning, often turbulent,flow of fluid. Any spiral motion with closed streamlines is vortex flow. The motion of the fluid swirling rapidly around a center is called a vortex...
that attaches to the top of the wing. The vortex action maintains a smooth airflow over the wing surface well past the normal stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
point at which the airflow would otherwise break up, thus sustaining lift at very high angles.
F/A-18 Hornet
The McDonnell Douglas F/A-18 Hornet is a supersonic, all-weather carrier-capable multirole fighter jet, designed to dogfight and attack ground targets . Designed by McDonnell Douglas and Northrop, the F/A-18 was derived from the latter's YF-17 in the 1970s for use by the United States Navy and...
has especially large examples, as does the Sukhoi Su-27
Sukhoi Su-27
The Sukhoi Su-27 is a twin-engine supermanoeuverable fighter aircraft designed by Sukhoi. It was intended as a direct competitor for the large United States fourth generation fighters, with range, heavy armament, sophisticated avionics and high manoeuvrability...
. The Su-27 LERX help to make some advanced maneuvers possible, such as the Pugachev's Cobra
Pugachev's Cobra
In aerobatics, Pugachev's Cobra is a dramatic and demanding manoeuvre in which a plane flying at a moderate speed suddenly raises the nose momentarily to the vertical position and slightly beyond, before dropping it back to normal flight. It uses a potent engine thrust to maintain approximately...
, the Cobra Turn
Cobra Turn
The Cobra Turn is a fighter aircraft maneuver. It is a variation on the Pugachev's Cobra where the aircraft performs the pull-up, but instead of returning to level flight applies rudder or thrust vectoring and turns downward...
and the Kulbit
Kulbit
The "Kulbit" 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 is an example of post-stall maneuvering, a type of supermaneuverability...
.
Chines
SR-71 Blackbird
The Lockheed SR-71 "Blackbird" was an advanced, long-range, Mach 3+ strategic reconnaissance aircraft. It was developed as a black project from the Lockheed A-12 reconnaissance aircraft in the 1960s by the Lockheed Skunk Works. Clarence "Kelly" Johnson was responsible for many of the...
family. The chines contribute useful additional lift at supersonic speeds, as well as acting as LERX at low speeds. A standard leading edge extension joins to the fuselage at an angle while a chine is an extension of the curvature of the fuselage. Therefore chines avoid presenting corner reflector
Corner reflector
A corner reflector is a retroreflector consisting of three mutually perpendicular, intersecting flat surfaces, which reflects waves back directly towards the source, but shifted . Unlike a simple mirror, they work for a relatively wide-angle field of view. The three intersecting surfaces often have...
s or vertical sides
Specular reflection
Specular reflection is the mirror-like reflection of light from a surface, in which light from a single incoming direction is reflected into a single outgoing direction...
to radars.
The F-22 Raptor
F-22 Raptor
The Lockheed Martin/Boeing F-22 Raptor is a single-seat, twin-engine fifth-generation supermaneuverable fighter aircraft that uses stealth technology. It was designed primarily as an air superiority fighter, but has additional capabilities that include ground attack, electronic warfare, and signals...
has chines that lead to the leading edge extensions that are blended into the engine air intakes.
Canards
Canard (aeronautics)
In aeronautics, canard is an airframe configuration of fixed-wing aircraft in which the forward surface is smaller than the rearward, the former being known as the "canard", while the latter is the main wing...
can also help generate vortex lift over the main wings, but due to their poor stealth characteristics they have been replaced with chines in all fifth generation jet fighters except for the Chengdu J-20
Chengdu J-20
The Chengdu J-20 is a purported fifth-generation, stealth, twin-engine fighter aircraft prototype developed by Chengdu Aircraft Industry Group for the Chinese People's Liberation Army Air Force . In late 2010, the J-20 underwent high speed taxiing tests. The J-20 made its first flight on 11...
.
Aircraft using LEX
A few examples of aircraft with leading edge extensions are listed below.- EU
- Dassault RafaleDassault RafaleThe Dassault Rafale is a French twin-engine delta-wing multi-role jet fighter aircraft designed and built by Dassault Aviation. Introduced in 2000, the Rafale is being produced both for land-based use with the French Air Force and for carrier-based operations with the French Navy...
- Dassault Rafale
- China
- Shenyang J-13
- Chengdu J-9Chengdu J-9|...
- Su-30MKK/MK2
- JL-9
- L-15 Falcon
- China/Pakistan
- JF-17 ThunderJF-17 ThunderThe PAC JF-17 Thunder , or CAC FC-1 Xiaolong , is a light-weight, single-engine, multi-role combat aircraft developed jointly by the Chengdu Aircraft Industries Corporation of China, the Pakistan Air Force and the Pakistan Aeronautical Complex...
- JF-17 Thunder
- Sweden
- Saab JAS 39 Gripen
- Iran
- HESA Shafagh
- Russia/USSR
- Sukhoi Su-27Sukhoi Su-27The Sukhoi Su-27 is a twin-engine supermanoeuverable fighter aircraft designed by Sukhoi. It was intended as a direct competitor for the large United States fourth generation fighters, with range, heavy armament, sophisticated avionics and high manoeuvrability...
and derivatives, including the Sukhoi Su-34Sukhoi Su-34The Sukhoi Su-34 is a Russian twin-seat fighter-bomber. It is intended to replace the Sukhoi Su-24.- Beginnings and testing :The Su-34 had a somewhat muddied and protracted beginning...
and the Sukhoi Su-47Sukhoi Su-47The Sukhoi Su-47 Berkut , also designated S-32 and S-37 during initial development, was an experimental supersonic jet fighter developed by Sukhoi Aviation Corporation...
. - Mikoyan MiG-29Mikoyan MiG-29The Mikoyan MiG-29 is a fourth-generation jet fighter aircraft designed in the Soviet Union for an air superiority role. Developed in the 1970s by the Mikoyan design bureau, it entered service with the Soviet Air Force in 1983, and remains in use by the Russian Air Force as well as in many other...
- Sukhoi PAK FASukhoi PAK FAThe Sukhoi PAK FA is a twin-engine jet fighter being developed by Sukhoi OKB for the Russian Air Force. The Sukhoi T-50 is the prototype for PAK FA. The PAK FA is one of only a handful of stealth jet programs globally...
- on PAK-FA aircraft the part of the wing that includes the LERX is movable to control the airflow at high angles of attack, similar to a wing leading flap. - LEVCON (this is "active" control surface)
- Sukhoi Su-27
- USA/UK
- F-5 Freedom FighterF-5 Freedom FighterThe Northrop F-5A/B Freedom Fighter and the F-5E/F Tiger II are part of a family of widely-used light supersonic fighter aircraft, designed and built by Northrop...
- F-16 Fighting FalconF-16 Fighting FalconThe General Dynamics F-16 Fighting Falcon is a multirole jet fighter aircraft originally developed by General Dynamics for the United States Air Force . Designed as an air superiority day fighter, it evolved into a successful all-weather multirole aircraft. Over 4,400 aircraft have been built since...
and its unsuccessful competitor the YF-17 CobraYF-17 CobraThe Northrop YF-17 was a prototype lightweight fighter aircraft designed for the United States Air Force's Lightweight Fighter technology evaluation program. The LWF was initiated because many in the fighter community believed that aircraft like the F-15 Eagle were too large and expensive for... - F/A-18 HornetF/A-18 HornetThe McDonnell Douglas F/A-18 Hornet is a supersonic, all-weather carrier-capable multirole fighter jet, designed to dogfight and attack ground targets . Designed by McDonnell Douglas and Northrop, the F/A-18 was derived from the latter's YF-17 in the 1970s for use by the United States Navy and...
/Super Hornet - AV-8 Harrier II/RAF Harrier IIRAF Harrier IIThe British Aerospace/McDonnell Douglas Harrier II is a second-generation vertical/short takeoff and landing jet aircraft used previously by the Royal Air Force and, between 2006–2010, the Royal Navy. Derived from the McDonnell Douglas AV-8B Harrier II, which was a development of the Hawker...
- F-5 Freedom Fighter
- Civilian
- Quest KodiakQuest AircraftQuest Aircraft Company is an American aircraft manufacturing company located in Sandpoint, Idaho. Quest was started in 2001 to design and provide aircraft suitable for domestic and international humanitarian applications.-History:...
(Fixed Discontinuous Outboard Leading Edge Extension)
- Quest Kodiak