Jump to content

User:Mr swordfish/Wing

From Wikipedia, the free encyclopedia
A laughing gull with its wings extended in the gull wing profile
Several aircraft wing planform shapes: a swept wing KC-10 Extender (top) refuels a trapezoidal-wing F-22 Raptor fighter plane

A wing is a surface that produces lift for flight through the atmosphere—or occasionally through another gaseous or fluid substance. An artificial wing is called an airfoil, which always have a distinctive cross-sectional shape.

The word "wing" for many centuries (reportedly[by whom?]) referred mainly to the foremost limbs of birds, but in recent centuries the word's meaning has extended to include wings of insects, bats, pterosaurs, and aircraft.

"Wing" can also mean an inverted airfoil on a race car that generates a downward force to increase traction. Various species of penguins and their close relatives (such as auks) of flightless birds are avid swimmers, and use use their (rather small) wings to swim through seawater.

A wing's aerodynamic quality is expressed as its lift-to-drag ratio. The lift a wing generates at a given speed and angle of attack can be one to two orders of magnitude greater than the total drag on the wing. A high lift-to-drag ratio requires a significantly smaller thrust to propel the wings through the air at sufficient lift.

Design features

[edit]

Aircraft wings may feature some of the following:

The aerodynamics of wings

[edit]
The wing of a landing BMI Airbus A319-100. The slats at its leading edge and the flaps at its trailing edge are extended.
The low pressure region over the wing of this A340 is clearly shown by the condensation it causes in the humid air

The design and analysis of the wings of aircraft (and of certain spaceplanes, such as the NASA Space Shuttle) is one of the principal applications of the science of aerodynamics. Aerodynamics is a branch of fluid mechanics, and the properties of the airflow around any moving object can - in principle - be found by solving the Navier-Stokes equations of fluid dynamics. However, except for simple geometries these equations are notoriously difficult to solve. Fortunately, simpler explanations can be described.

For a wing to produce "lift", its "leading edge" must be pointed at a correct angle (within a certain range) into the relative flow of air past the aircraft. When this occurs the wing deflects the airflow downwards, "turning" the air as it passes the wing. Since the wing exerts a force on the air to change it's direction, the air must exert a force on the wing, equal in size but opposite in direction. This force manifests itself as differing air pressures at different points on the surface of the wing.[1][2][4]

A region of lower-than-normal air pressure is generated over the top surface of the wing, with a higher pressure existing on the bottom of the wing. (See: airfoil) This higher pressure on the bottom of the wing is generally the normal atmospheric pressure, plus or minus a small percentage[citation needed]. These air pressure differences can be either measured directly using instrumentation or they can be calculated from the airspeed distribution using basic physical principles, including Bernoulli's Principle which relates changes in air speed to changes in air pressure.

The lower air pressure on the top of the wing generates a smaller downward force on the top of the wing than the upward force generated by the higher air pressure on the bottom of the wing. Hence, a net upward force acts on the wing. This force is called the "lift" generated by the wing.

The different velocities of the air passing by the wing, the air pressure differences, the change in direction of the airflow, and the lift on the wing are intrinsically one phenomenon. It is, therefore, possible to calculate lift from any of the other three. For example, the lift can be calculated from the pressure differences, or from different velocities of the air above and below the wing, or from the total momentum change of the deflected air. There are other approaches in fluid dynamics to solving these problems. All of these approaches will result in the same answers if done correctly. Given a particular wing and its velocity through the air, debates over which mathematical approach is the most convenient to use can be misperceived by novices as differences of opinion about the basic principles of flight.

For a more detailed coverage see lift (force).

Internal mechanical construction of a generic monospar wing. Black = solid, red = tube used for the spar, green = foam, wood, honeycomb, or sheet metal used for the ribs. The leading edge gives torsional stiffness. The trailing edge can either have a flexible skin, which does not break under wing bending (birdlike,) or have a stiff skin (made of carbon fiber, aluminum alloy, or titanium, aircraft-like), which is prevented from buckling by span-wise "stringers."
Flaps (green) are used in various configurations to increase the wing area and to increase the lift. In conjunction with spoilers (red), flaps maximize drag and minimize lift during the landing roll.

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 topside compared with the underside. Wings with this shape are normally used in subsonic flight and in sailing. However, for aerobatics, symmetrically-shaped wings (above and below) generate lift using a positive angle of attack to deflect air downward; for supersonic flight, aerofoils with complex asymmetrical shapes are used to minimise untoward differences between high- and low-speed flight. Symmetrical aerofoils are, in general, less efficient and lack the lift provided by cambered wings at the zero angle of attack[5] but are used in aerobatics, as they provide practical performance both upright and inverted.

Usually, aircraft wings have various devices, such as flaps and/or slats that the pilot uses to modify the shape and surface area of the wing 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.

A Mute Swan spreads its wings.

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

Structures with the same purpose as wings, but designed for use in liquid media, are generally called fins or hydroplanes, with hydrodynamics as the governing science, rather than aerodynamics. Applications of these arise in craft such as hydrofoils and submarines. Sailboats and sailing ships use both fins and wings.


See also

[edit]

References

[edit]
  1. ^ "...the effect of the wing is to give the air stream a downward velocity component. The reaction force of the deflected air mass must then act on the wing to give it an equal and opposite upward component." In: Halliday, David; Resnick, Robert, Fundamentals of Physics 3rd Edition, John Wiley & Sons, p. 378
  2. ^ "Lift from Flow Turning". NASA Glenn Research Center. Retrieved 2009-07-07.
  3. ^ Weltner, Klaus; Ingelman-Sundberg, Martin, Physics of Flight - reviewed
  4. ^ "The cause of the aerodynamic lifting force is the downward acceleration of air by the airfoil... "[3]
  5. ^ E. V. Laitone, Wind tunnel tests of wings at Reynolds numbers below 70 000, Experiments in Fluids 23, 405 (1997). doi:10.1007/s003480050128
[edit]