Wing
From Wikipedia, the free encyclopedia
A wing is a surface used to produce lift and therefore flight, for travel in the air or another gaseous medium. The wing shape is usually an airfoil. The first use of the word was for the foremost limbs of birds, but has been extended to include the wings of insects, bats and pterosaurs and also man-made devices.
A wing is a device for generating lift. Its aerodynamic quality, expressed as a Lift-to-drag ratio, can be up to 60 on some gliders. 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.
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[edit] Uses
A common use of wings is in flight, using forward motion to create vertical lift, but wings are also used to produce downforce, as in racecars. A sail boat moves by using sails and a keel like a vertical wings to produce lift (in the horizontal plane).
[edit] Artificial wings
[edit] Terms related to aircraft wings
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Wing of a Boeing 737 |
Aircraft wing flaps small dsc06830.jpg
Flaps partially deployed |
Aircraft wing flaps full dsc06835.jpg
Full flaps |
Aircraft wing flaps full airbrakes dsc06838.jpg
Full flaps, with spoilers deployed. |
- 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 ¼ 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.
[edit] 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 aircraft to be carried in the confined space of the hangar of an aircraft carrier.
[edit] Wing types
- Swept wings are wings that are bent back at an angle, instead of sticking straight out from the fuselage.
- Forward-swept wings are bent forward, the reverse of a traditional swept wing. Forward swept wings have been used in some two seat gliders, and in the experimental X-29 and Sukhoi Su-47.
- Elliptical wings (technically wings with an elliptical lift distribution) are theoretically optimum for efficiency at subsonic speeds. A good example of this wing type can be seen on the British Supermarine Spitfire World War II fighter aircraft.
- Delta wings have reasonable performance at subsonic and supersonic speeds and are good at high angles of attack. For examples see the F-102, F-106, B-58, Avro Vulcan and Concorde.
- Waveriders are efficient supersonic wings that take advantage of shock waves. For an example, see the XB-70.
- Rogallo wings are two partial cone sections arranged with the apexes together and the convex side up. One of the simplest wings to construct using cloth or other membrane material and a frame.
- Variable geometry wings (or Swing-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 now only found on 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.
- Closed wings are optimally loaded closed lifting surfaces with higher aerodynamic efficiency than planar wings having the same aspect-ratios. Other nonplanar wing systems display an aerodynamic efficiency intermediate between closed wings and planar wings. Closed wings include annular wings, boxplanes, and joined wings.
- Oblique wing
- Flying wing
- Blended wing body
[edit] Science of wings
The science of wings is one of the principal applications of the science of aerodynamics.
In order for a wing to produce lift it has to be at a positive angle to the airflow. In that case a low pressure region is generated on the upper surface of the wing which draws the air above the wing downwards towards what would otherwise be a void after the wing had passed. On the underside of the wing a high pressure region forms accelerating the air there downwards out of the path of the oncoming wing. The pressure difference between these two regions produces an upwards force on the wing, called lift.
The pressure differences, the acceleration of the air and the lift on the wing are intrinsically one mechanism. It is therefore possible to derive the value of one by calculating another. For example lift can be calculated by reference to the pressure differences or by calculating the energy used to accelerate the air. Both approaches will result in the same answer if done correctly. Debates over which mathematical approach is the more convenient can be wrongly perceived as differences of opinion about the principles of flight and often create unnecessary confusion in the mind of the layman.
For a more detailed coverage see lift (force).
A common misconception is that it is the shape of the wing that is essential to generate lift by having a longer path on the top rather than the underside. This is not the case, thin flat wings can produce lift efficiently and aircraft with cambered wings can fly inverted as long as the nose of the aircraft is pointed high enough so as to present the wing at a positive angle of attack to the airflow.
The common aerofoil shape of wings is due to a large number of factors many of them not at all related to aerodynamic issues, for example wings need strength and thus need to be thick enough to contain structural members. They also need room to contain items such as fuel, control mechanisms and retracted undercarriage. The primary aerodynamic input to the wing’s cross sectional shape is the need to keep the air flowing smoothly over the entire surface for the most efficient operation. In particular, there is a requirement to prevent the low-pressure gradient that accelerates the air down the back of the wing becoming too great and effectively “sucking” the air off the surface of the wing. If this happens the wing surface from that point backwards becomes substantially ineffective.
The shape chosen by the designer is a compromise dependent upon the intended operational ranges of airspeed, angles of attack and wing loadings. Usually aircraft wings have devices, such as flaps, which allow the pilot to modify shape and surface area of the wing to be able to change its operating characteristics in flight.
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
- Some racing cars, especially Formula One cars, which use upside-down wings to give cars greater adhesion at high speeds over 100mph.
- 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. Sailing boats use both fins and wings.
[edit] Animal wings
Biologists believe that animal wings evolved at least four separate times, an example of convergent evolution.
- insect wings are believed to have evolved between 300 and 400 million years ago
- pterosaur wings at least 225 million years ago
- bird wings at least 150 million years ago
- 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.
[edit] See also
- Flight
- Bird flight
- Pinion (feather)
- Planform
- Wings in the enneagram
- Insect flight
- List of soaring birds
- Flying and gliding animals
[edit] External links
- Demystifying the Science of Flight - Audio segment on NPR's Talk of the Nation Science Friday
- NASA's explanations and simulations
- Advanced Topics in Aerodynamics Wings for all speeds
- Evolution of flight in animals
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