A wing is a type of fin that produces both lift and drag while moving through air. Wings are defined by two shape characteristics, an airfoil section and a planform. Wing efficiency is expressed as lift-to-drag ratio, which compares the benefit of lift with the air resistance of a given wing shape, as it flies. Aerodynamics is the study of wing performance in air.
Equivalent foils that move through water are found on Hydrofoil and foiling sailboats that lift out of the water at speed and on that use to point the boat upwards or downwards, while running submerged. Hydrodynamics is the study of foil performance in water.
Etymology and usage
The word "wing" from the Old Norse
vængr for many centuries referred mainly to the foremost limbs of
(in addition to the architectural aisle). But in recent centuries the word's meaning has extended to include lift producing appendages of
insect wing,
,
,
boomerangs,
Wingsail and
aircraft, or the airfoil on a race car.
[The Sports Car - Its design and performance,Colin Campbell,,p.180]
Aerodynamics
The design and analysis of the wings of aircraft is one of the principal applications of the science of
aerodynamics, which is a branch of
fluid mechanics. The properties of the airflow around any moving object can be found by solving the Navier-Stokes equations of
fluid dynamics. Except for simple geometries, these equations are difficult to solve.
Simpler explanations can be given.
For a wing to produce "lift", it must be oriented at a suitable angle of attack relative to the flow of air past the wing. 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 its direction, the air must exert a force on the wing, equal in size but opposite in direction. This force arises from different air pressures that exist on the upper and lower surfaces of the wing.["...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: ]["If the body is shaped, moved, or inclined in such a way as to produce a net deflection or turning of the flow, the local velocity is changed in magnitude, direction, or both. Changing the velocity creates a net force on the body" ]["The cause of the aerodynamic lifting force is the downward acceleration of air by the airfoil..." ]
Lower-than-ambient air pressure is generated on the top surface of the wing, with a higher-than ambient-pressure on the bottom of the wing. (See: airfoil) These air pressure differences can be either measured using a pressure-measuring device, or can be calculated from the airspeed using physics 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. This gives an upward force 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 different ways of describing how lift is produced so it is possible to calculate lift from any one 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. Fluid dynamics offers other approaches to solving these problems all which methods produce the same answer if correctly calculated. Given a particular wing and its velocity through the air, debates over which mathematical approach is the most convenient to use can be mistaken by those not familiar with the study of aerodynamics as differences of opinion about the basic principles of flight.
Cross-sectional shape
Wings with an asymmetrical cross-section are the norm in
subsonic flight. Wings with a symmetrical cross-section can also generate lift by using a positive angle of attack to deflect air downward. Symmetrical airfoils have higher stalling speeds than cambered airfoils of the same wing area
[E. V. Laitone, Wind tunnel tests of wings at Reynolds numbers below 70 000, Experiments in Fluids 23, 405 (1997). ] but are used in
aerobatic aircraft as they provide the same flight characteristics whether the aircraft is upright or inverted.
[The Design Of The Aeroplane,Darrol Stinton,,p.586] Another example comes from sailboats, where the sail is a thin sheet.
["...consider a sail that is nothing but a vertical wing (generating side-force to propel a yacht). ...it is obvious that the distance between the stagnation point and the trailing edge is more or less the same on both sides. This becomes exactly true in the absence of a mast—and clearly the presence of the mast is of no consequence in the generation of lift. Thus, the generation of lift does not require different distances around the upper and lower surfaces." Holger Babinsky How do Wings Work? Physics Education November 2003, PDF]
For flight speeds near the speed of sound (transonic flight), specific asymmetrical airfoil sections are used to minimize the very pronounced increase in drag associated with airflow near the speed of sound.[John D. Anderson, Jr. Introduction to Flight 4th ed page 271.] These airfoils, called supercritical airfoils, are flat on top and curved on the bottom.['Supercritical wings have a flat-on-top "upside down" look.' NASA Dryden Flight Research Center http://www.nasa.gov/centers/dryden/about/Organizations/Technology/Facts/TF-2004-13-DFRC.html]
Design features
Aircraft 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 or flaperons (combination of flaps and ailerons)
-
Winglets to keep wingtip vortices from increasing drag and decreasing lift
-
Dihedral, or a positive wing angle to the horizontal, increases spiral stability around the roll axis, whereas anhedral, or a negative wing angle to the horizontal, decreases spiral stability.
Aircraft wings may have various devices, such as flaps or slats, that the pilot uses to modify the shape and surface area of the wing to change its operating characteristics in flight.
-
(usually near the wingtips) to roll the aircraft
-
Spoilers on the upper surface to increase drag for descent and to reduce lift for more weight on wheels during braking
-
to help prevent flow separation in transonic flow
-
to keep flow attached to the wing by stopping boundary layer separation from spreading roll direction.
-
allow more aircraft storage in the confined space of the hangar of an aircraft carrier
-
Variable-sweep wing or "swing wings" that allow outstretched wings during low-speed flight (e.g., take-off, landing and loitering) and swept wing for high-speed flight (including supersonic flight), such as in the F-111 Aardvark, the F-14 Tomcat, the Panavia Tornado, the MiG-23, the MiG-27, the Tu-160 and the B-1B Lancer.
Types
Applications
Besides fixed-wing aircraft, applications for wing shapes include:
-
, which use wings ranging from fully flexible (, gliding ), flexible (framed sail wings), to rigid
-
Kite types, which use a variety of lifting surfaces
-
Flying model airplanes
-
, which use a rotating wing with a variable pitch angle to provide directional forces
-
, whose blades generate lift for propulsion.
-
The NASA Space Shuttle, which uses its wings only to glide during its descent to a runway. These types of aircraft are called .
-
Some racing cars, especially Formula One cars, which use upside-down wings (or ) to provide greater traction at high speeds
-
, which use sails as vertical wings with variable fullness and direction to move across water
Flexible wings
In 1948,
Francis Rogallo invented the fully limp flexible wing.
Domina Jalbert invented flexible un-sparred ram-air airfoiled thick wings.
In nature
Wings have
evolution multiple times in history: in
Insect wing,
(see
bird wing), mammals (see
), fish, reptiles (see
), and plants. Wings of birds, bats, and pterosaurs all evolved from existing limbs, however insect wings evolved as a completely separate structure.
Wings facilitated increased locomotion, dispersal, and diversification.
Various species of
and other flighted or
flightless bird water birds such as
,
,
,
,
eider duck and scoter ducks and diving
petrels are efficient underwater swimmers, and use their wings to propel through water.
See also
Natural world:
Aviation:
Sailing:
External links
