Vortex lift is that portion of

lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people or goods ** Paternoster lift, a type of lift using a continuous chain of cars which do not stop ** Patient lift, or Hoyer lift, mobile ...

due to the action of leading edge vortices. It is generated by wings with highly sweptback, sharp, leading edges (beyond 50 degrees of sweep) or highly-swept wing-root extensions added to a wing of moderate sweep. It is sometimes known as non-linear lift due to its rapid increase with angle of attack. and controlled separation lift, to distinguish it from conventional lift which occurs with attached flow.

How it works

Vortex lift works by capturing

vortices 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 ...

generated from the sharply swept leading edge of the wing. The vortex, formed roughly parallel to the leading edge of the wing, is trapped by the airflow and remains fixed to the upper surface of the wing. As the air flows around the leading edge, it flows over the trapped vortex and is pulled in and down to generate the lift. A straight, or moderate sweep, wing may experience, depending on its airfoil section, a leading-edge stall and loss of lift, as a result of flow separation at the leading edge and a non-lifting wake over the top of the wing. However, on a highly-swept wing leading-edge separation still occurs but instead creates a vortex sheet that rolls up above the wing producing spanwise flow beneath. Flow not entrained by the vortex passes over the top of the vortex and reattaches to the wing surface. The vortex generates a high negative pressure field on the top of the wing. Vortex lift increases with angle of attack (AOA) as seen on lift~AOA plots which show the vortex, or unattached flow, adding to the normal attached lift as an extra non-linear component of the overall lift. Vortex lift has a limiting AoA at which the vortex bursts or breaks down.

Applications

Four basic configurations which have used vortex lift are, in chronological order, the 60-degree delta wing; the ogive delta wing with its sharply-swept leading edge at the root; the moderately-swept wing with a leading-edge extension, which is known as a hybrid wing; and the sharp-edge forebody, or vortex-lift strake. Wings which generate vortex lift have been used on delta-winged research aircraft such as the

Convair XF-92A The Convair XF-92 (re-designated from XP-92 in 1948) was an American, delta wing, first-generation jet prototype. Originally conceived as a point-defence interceptor, the design was later used purely for experimental purposes and only one wa ...

and Fairey Delta 2. Early delta wing fighters such as the Convair F-102, the F-106 and Century Series contemporaries such as Dassault's deltas had cambered leading edges that were blunt and did not generate significant vortexes. The

Concorde The Aérospatiale/BAC Concorde () is a retired Franco-British supersonic airliner jointly developed and manufactured by Sud Aviation (later Aérospatiale) and the British Aircraft Corporation (BAC). Studies started in 1954, and France and t ...

supersonic airliner had sharp leading edges. Wings with vortex lift over the inboard section are the moderate-sweep wings with an easily identified LERX used on high-manoeuvrability combat aircraft, such as 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 ...

and

McDonnell Douglas F/A-18 Hornet The McDonnell Douglas F/A-18 Hornet is an all-weather, twin-engine, supersonic, carrier-capable, multirole combat aircraft, designed as both a fighter and attack aircraft (hence the F/A designation). Designed by McDonnell Douglas (now par ...

. Vortex lift sharp forebody strakes are used on the

General Dynamics F-16 Fighting Falcon The General Dynamics F-16 Fighting Falcon is a single-engine multirole fighter aircraft originally developed by General Dynamics for the United States Air Force (USAF). Designed as an air superiority day fighter, it evolved into a success ...

. File:Akaflieg DM 1.jpg, Lippisch DM-1 test glider, 64-degree delta which demonstrated vortex lift in wind tunnel when modified with sharp leading edge at NASA Langley Research Center in 1946 File:Eclipse program QF-106 aircraft in flight, view from tanker.jpg, F-106 , a 60-degree delta: an early example with leading edge flow separation File:Concorde on Bristol.jpg,

showing its ogive delta wing with high sweep angle at wing root: a highly developed shape with controlled flow separation File:J-3005.jpg,

a wing with moderate sweep: an early application of vortex lift using a LERX File:F-16 June 2008.jpg,

vortices from sharp-edged wide forebody stabilize flow over entire aircraft including outboard wing

Benefits and shortcomings

Vortex lift provides high lift with increasing AoA at landing speeds and in manoeuvring flight. A high AoA needed to meet landing requirements has, in the past, restricted pilot visibility and led to design complications to accommodate a drooping nose, as in the case of the Fairey Delta 2 and

. For moderate swept wings the addition of a LERX reduces wave drag and improves turning performance and enables a far wider range of flying attitudes. The use of vortex lift is restricted by vortex breakdown or bursting and an inherent instability in yaw . There is considerable drag due to increased lift production and loss of leading edge suction that is part of normal attached flow round a leading edge.

Among animals

Animals such as

hummingbird Hummingbirds are birds native to the Americas and comprise the biological family Trochilidae. With about 361 species and 113 genera, they occur from Alaska to Tierra del Fuego, but the vast majority of the species are found in the tropics ar ...

s, and bats that eat pollen and nectar, are able to hover. They produce vortex lift with the sharp

leading edge The leading edge of an airfoil surface such as a wing is its foremost edge and is therefore the part which first meets the oncoming air.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 305. Aviation Supplies & Academics, ...

s of their wings and change their wing shapes and curvatures to create stability in the lift.

References

{{DEFAULTSORT:Vortex Lift Aerodynamics Vortices

How it works

Applications

Benefits and shortcomings

Among animals

See also

References