Wing

For some other uses of the word "wing" please see Wing (disambiguation).

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. 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.

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).

Artificial wings

Wing shapes: a swept wing KC-10 Extender from Travis Air Force Base, California, refuels a delta wing F/A-22 Raptor.

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

Design features

Aeroplane wings may feature some of the following:

• A rounded 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
• 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. As the aircraft rolls, the lower wing generates more lift than the upper, rolling the aircraft back into the level position. Anhedral, or a negative wing angle to the horizontal has a destabilising effect.
• Swept wings are good for high-speed aircraft. The wing is at an angle to the airflow, so that the effective flow speed across the wing chord is lower.

Wing types

• 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.
• 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 fighter aircraft such as the Grumman F-14, Panavia Tornado, and General Dynamics F-111.
• 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.

Science of wings

At the simplest level, 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). Bernoulli's principle has traditionally been used to explain the functioning of a wing in terms of differing pressure above and below the wing, but this model can often be misleading or depend on false assumptions. See Coanda effect for an alternative explanation of how a wing produces lift.

The amount of lift produced by a wing increases with the angle of attack (the angle between the onset flow and the chord line) but this relationship ends once the stall angle is reached. At this angle the airflow starts to separate from the upper surface, and any further increase in angle of attack gives no more lift (it will in fact dramatically reduce) and gives a large increase in drag.

Wing design can be complex and is one of the principal applications of the science of aerodynamics.

• A helicopter uses a rotating wing with a variable pitch or angle to provide a directional force.
• The space shuttle uses its wings only for lift during its descent.

Structures with the same purpose as wings, but designed to operate in liquid media, are generally called fins, with hydrodynamics as the governing science.

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.

External links

• Coanda Effect: Understanding Why Wings Work (http://jef.raskincenter.org/published/coanda_effect.html)
• An Excellent treatment of why and how wings generate lift (http://www.av8n.com/how/)
• Demystifying the Science of Flight (http://www.npr.org/templates/story/story.php?storyId=3875411) - Audio segment on NPR's Talk of the Nation Science Friday
• Advanced Topics in Aerodynamics (http://aerodyn.org/Wings/) Wings for all speeds
• Evolution of flight (http://www.nurseminerva.co.uk/adapt/evolutio.htm) in animalsbg:Крило

da:Vinge de:Tragfläche es:Ala (aeronáutica) fr:Voilure it:Ala (aeronautica) nl:Vleugel (vliegtuig) ja:翼 zh:机翼