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, bats, pterosaurs, and aircraft.
See also Airfoils: Chord & Camber
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.
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.
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.
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.
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A fixed-wing aircraft, typically called an airplane, aeroplane or plane, is an aircraft capable of flight using forward motion that causes air to pass over its wings to generate lift. Planes include jet engine and propeller driven vehicles propelled forward by thrust, as well as unpowered aircraft (such as gliders). Fixed-wing aircraft are distinct from ornithopters in which lift is generated by blades and rotary-wing aircraft in which wings move relative to the aircraft.
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges (singular remex) while those on the tail are called rectrices (singular rectrix). Their primary function is to aid in the generation of both thrust and lift, thereby enabling flight. The flight feathers of some birds have evolved to perform additional functions, generally associated with territorial displays, courtship rituals or feeding methods. In some species, these feathers have developed into long showy plumes used in visual courtship displays, while in others they create a sound during display flights. Tiny serrations on the leading edge of their remiges help owls to fly silently (and therefore hunt more successfully), while the extra-stiff rectrices of woodpeckers help them to brace against tree trunks as they hammer. Even flightless birds still retain flight feathers, though sometimes in radically modified forms.
Insect wings are outgrowths of the insect exoskeleton that enable insects to fly. They are found on the second and third thoracic segments (the mesothorax and metathorax), and the two pairs are often referred to as the forewings and hindwings, respectively, though a few insects lack hindwings, even rudiments. Insect wings do not constitute appendages in technical parlance, as insects only have one pair of appendages per segment. The wings are strengthened by a number of longitudinal veins, which often have cross-connections that form closed "cells" in the membrane (extreme examples include Odonata and Neuroptera). The patterns resulting from the fusion and cross-connection of the wing veins are often diagnostic for different evolutionary lineages and can be used for identification to the family or even genus level in many orders of insects.
In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing. The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly, the landing and take-off speeds will be higher. The high wing loading also decreases maneuverability. The same constraints apply to birds and bats.
Wing clipping is the process of trimming a bird's primary flight feathers ("primaries") so that it is no longer fully-flighted.
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