Wing

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For some other uses of the word "wing" please see Wing (disambiguation).
A Laughing Gull on the beach in Atlantic City.
Wing shapes: a swept wing KC-10 Extender from Travis Air Force Base, California, refuels a delta wing F/A-22 Raptor.

A wing is a surface used to produce an aerodynamic force normal to the direction of motion by travelling in air or another gaseous medium, facilitating flight. It is a specific form of airfoil. The first use of the word was for the foremost limbs of birds, but has been extended to include other animal limbs and man-made devices.

A wing is an extremely efficient device for generating lift. Its aerodynamic quality, expressed as a Lift-to-drag ratio, can be up to 60 on some gliders and even more. This means that a significantly smaller thrust force can be applied to propel the wing through the air in order to obtain a specified lift.

Use

The most common use of wings is to fly by deflecting air downwards to produce lift, but upside-down wings are also commonly used as a way to produce downforce and hold objects to the ground (for example racing cars). A sailing boat moves by using its sails as wings to produce lift (in the horizontal plane) from the force of the wind.

Artificial wings

Terms used to describe aeroplane wings

  • Leading edge: the front edge of the wing
  • Trailing edge: the back edge of the wing
  • Span: distance from wing tip to wing tip
  • Chord: distance from wing leading edge to wing trailing edge, usually measured parallel to the long axis of the fuselage
  • Aspect ratio: ratio of span to standard mean chord
  • Aerofoil (or Airfoil in US English): the shape of the top and bottom surfaces when viewed as cross sections cut from leading edge to trailing edge.
  • Sweep angle: the angle between the perpendicular to the design centreline of the wing in the wing plane, and either the leading edge or 1/4 chord line.
  • Twist: gradual change of the airfoil (aerodynamic twist) and/or angle of incidence of the wing cross-sections (geometrical twist) along the span.

Design features

Aeroplane wings may feature some of the following:

  • A rounded (rarely sharp) leading edge cross-section
  • A sharp trailing edge cross-section
  • Leading-edge devices such as slats, slots, or extensions
  • Trailing-edge devices such as flaps
  • Ailerons (usually near the wingtips) to provide roll control
  • Spoilers on the upper surface to disrupt lift and additional roll control
  • Vortex generators to help prevent flow separation
  • Wing fences to keep flow attached to the wing
  • Dihedral, or a positive wing angle to the horizontal. This gives inherent stability in roll. Anhedral, or a negative wing angle to the horizontal, has a destabilising effect
  • Folding wings allow more aircarft to be carried in the confined space of the hangar of an aircraft carrier.

Wing types

  • Swept wings are wings that are bent back at some angle, instead of sticking straight out from the fuselage.
  • Forward-swept wings are high performance wings that are bent forward, the reverse of a traditional swept wing. Forward swept wings are also used in some two seat gliders.
  • Elliptical wings (technically wings with an elliptical lift distribution) are theoretically optimum for efficiency at subsonic speeds.
  • Delta wings have reasonable performance at subsonic and supersonic speeds and are good at high angles of attack.
  • Waveriders are efficient supersonic wings that take advantage of shock waves.
  • Rogallo wings are two hollow half-cones of fabric, one of the simplest wings to construct.
  • Swing-wings (or variable geometry wings) are able to move in flight to give the benefits of dihedral and delta wing. Although they were originally proposed by German aerodynamicists during the 1940s, they are currently only found on some military aircraft such as the Grumman F-14, Panavia Tornado, General Dynamics F-111, B-1 Lancer, Tupolev Tu-160, MiG-23 and Sukhoi Su-24.
  • Ring wings are optimally loaded closed lifting surfaces with higher aerodynamic efficiency than planar wings having the same aspect-ratios. Other non planar wing systems display an aerodynamic efficiency intermediate between ring wings and planar wings.
The wing of a landing Lufthansa Airbus A300B4-600

Science of wings

The science behind how wings work can be complex and is one of the principal applications of the science of aerodynamics. However at the simplest level, both the upper and lower surfaces of a wing produces lift by deflecting air downward, which propels the flying body upward with an equal and opposite force (see Newton's Third Law). The air is deflected downwards because of Bernoulli's principle. This relates the pressure of air to its local velocity. If the velocity of the air changes as it flows around an object, such as a wing, the pressure of the air also changes. The shape and the angle of attack of the wing causes the air to flow faster above the wing than below, and so the pressure above the wing is less than below the wing. This pressure difference causes a force, called lift that acts at right angles to the air-flow.

The science of wings applies in other areas beyond conventional fixed-wing aircraft, including:

  • Helicopters which use a rotating wing with a variable pitch or angle to provide a directional force
  • The space shuttle which uses its wings only for lift during its descent
  • Formula One cars which use upside-down wings to give cars greater adhesion at high speeds
  • Sailing boats which use sails as vertical wings with variable fullness and direction to move across water.

Structures with the same purpose as wings, but designed to operate in liquid media, are generally called fins or hydroplanes, with hydrodynamics as the governing science. Applications arise in craft such as hydrofoils and submarines. Interestingly sailing boats use both fins and wings.

Evolution of wings in animals

Biologists believe that animal wings evolved at least four separate times, an example of convergent evolution. Insect wings are believed to have evolved about 300 million years ago, pterosaur wings about 225 million years ago, bird wings about 150 million years ago, and bat wings about 55 million years ago. Wings in these groups are analogous structures because they evolved independently rather than being passed from a common ancestor. See also flight.

EVLOPS

A special aerodynamics technique is flying.

External links