thumb|A [[Laughing Gull with its wings extended in a
gull wing profile]]
thumb|right|[[Fixed-wing aircraft|Aircraft wing
planform shapes: a
swept wing KC-10 Extender (top)
refuels a trapezoid-wing
F-22 Raptor]]
A
wing is a surface used to produce
lift for
flight through the
air or another
gaseous or fluid medium. The wing shape is usually an
airfoil. The word originally referred only to the foremost
limbs of
birds, but has been extended to include the wings of
insects (see
insect wing),
bats,
pterosaurs, and
aircraft.
A wing's
aerodynamic quality is expressed as a
Lift-to-drag ratio. The lift generated by a wing at a given speed and
angle of attack can be 1-2
orders of magnitude greater than the
drag. 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.
Design features
Aircraft wings may feature some of the following:
- Trailing-edge devices such as flaps or flaperons (combination of flaps and ailerons)
- Ailerons (usually near the wingtips) to provide roll control
- Spoilers on the upper surface to disrupt lift and provide additional roll control
- Wing fences to keep flow attached to the wing by stopping boundary layer separation from spreading
- Winglets to keep wingtip vortices from increasing drag and decreasing lift
- 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
- Variable-sweep wing or 'swing wing' to allow outstretched wings for slow speed (i.e. take-off and landing) and swept back wings for high speed (usually supersonic) flight, such as the FB-111 and the F-14.
Science of wings
thumb|right|The wing of a landing [[BMI (airline)|BMI Airbus A319-100. The
slats at the
leading edge and the
flaps at the
trailing edge are extended.]]
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).
thumb|right| Internal mechanical construction of a generic mono spar wing. Black=solid, red=tube used for the spar, green=foam or wood or honeycomb or sheet metal used for the ribs. The leading edge gives torsional stiffness. The trailing can either have a flexible skin, which does not break under wing bending (bird-like) or have a stiff skin (made of carbon fiber or aluminum, jet-like) which is prevented from bucking by span-wise stringers.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.
In 1948
Francis Rogallo invented the fully limp flexible wing which ushered new possibilities for aircraft. Near in time
Domina Jalbert invented flexible un-sparred ram-air airfoiled thick wings. These two new branches of wings have been since extensively studied and applied in new branches of aircraft, especially altering the personal recreational aviation landscape.
thumb|right|A Mute swan spreads its wings.
The science of wings applies in other areas beyond conventional
fixed-wing aircraft, including:
- Kites which use a vast variety of wings.
- 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 100 mph.
- 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.
See also
