Aileron - WikiHQ

thumb|right

thumb|right|An aircraft "rolling" or "banking", with its ailerons

thumb|An aileron and roll trim tab of a [[light aircraft]]

An aileron (French for 'little wing' or 'fin') is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around the aircraft's longitudinal axis), which normally results in a change in flight path due to the tilting of the lift vector. Movement around this axis is called rolling or banking.

Considerable controversy exists over credit for the invention of the aileron. The Wright brothers and Glenn Curtiss fought a years-long legal battle over the Wright patent of 1906, which described a method of wing-warping to achieve lateral control. The brothers prevailed in several court decisions which found that Curtiss's use of ailerons violated the Wright patent. Ultimately, the First World War compelled the U.S. Government to legislate a legal resolution. A much earlier aileron concept was patented in 1868 by British scientist Matthew Piers Watt Boulton, based on his 1864 paper On Aërial Locomotion.

History

thumb|left|upright|Boulton's 1864 paper, "On Aërial Locomotion" describing several designs including ailerons

The name "aileron", from French, meaning "little wing", also refers to the extremities of a bird's wings used to control their flight. In the context of powered airplanes it appears in print about 1908. Prior to that, ailerons were often referred to as rudders, their older technical sibling, with no distinction between their orientations and functions, or more descriptively as horizontal rudders (in French, gouvernails horizontaux). Among the earliest printed aeronautical use of 'aileron' was that in the French aviation journal L'Aérophile of 1908.

The pioneering U.S. aeronautical engineer Octave Chanute published descriptions and drawings of the Wright brothers' 1902 glider in the leading aviation periodical of the day, L'Aérophile, in 1903. This prompted Esnault-Pelterie, a French military engineer, to build a Wright-style glider in 1904 that used ailerons in lieu of wing warping.

New Zealander Richard Pearse reputedly made a powered flight in a monoplane that included small ailerons as early as 1902, but his claims are controversial—and sometimes inconsistent—and, even by his own reports, his aircraft were not well controlled.

thumb|right|A 1912 [[Farman HF.20 biplane with single acting ailerons hinged from the rear spar. The ailerons hang down when at rest and are pushed up into position when flying by the force of the air, being pulled down by cable to provide control.]]

In 1906, Alberto Santos-Dumont's 14-bis was one of the earliest (if not the earliest) engine-powered, aileron-equipped aircraft to fly, as it was modified to have added octagonal-planform interplane ailerons in its outermost wing bays on November 12 of that year for its concluding flight sessions at the Chateau de Bagatelle's grounds; but those roll control surfaces were not true "trailing-edge" ailerons hinged directly to the wing panels' framework—for the 14-bis, these were instead pivoted around a horizontal axis centred on the forward outboard interplane struts, and protruded forward past the wings' leading edges - said to be very much like those on Robert Esnault-Pelterie's 1904 biplane glider design.
On May 18, 1908, engineer and aircraft designer Frederick Baldwin, a member of the Aerial Experiment Association headed by Alexander Graham Bell, flew their first aileron-controlled aircraft, the AEA White Wing, the same year, with the AEA June Bug.
Henry Farman's ailerons on his 1909 Farman III were the first to resemble ailerons on modern aircraft as they were hinged directly to the wing planform structure, and thus were viewed as having a reasonable claim as the ancestor of the modern-day aileron. at nearly the same time for his methods of wing warping. Both the Wright Brothers patent and Montgomery's patent were reviewed and approved by the same patent examiner at the United States Patent Office, William Townsend. At the time Townsend indicated that both methods of wing warping were invented independently and were sufficiently different to each justify their own patent award.

Multiple U.S. court decisions favoured the expansive Wright patent, which the Wright Brothers sought to enforce with licensing fees starting from $1,000 per airplane, One of the disadvantages of this setup was a greater tendency to yaw than even with basic interconnected ailerons. some designs of early aircraft used "wingtip" ailerons, where the entire wingtip was rotated to achieve roll control as a separate, pivoting roll-control surface—the AEA June Bug used a form of these, with both the experimental German Fokker V.1 of 1916 and the earlier versions of the Junkers J 7 all-duralumin metal demonstrator monoplane using them—the J 7 led directly to the Junkers D.I all-duralumin metal German fighter design of 1918, which had conventionally hinged ailerons. The main problem with this type of aileron is the dangerous tendency to stall if used aggressively, especially if the aircraft is already in danger of stalling, hence the use primarily on prototypes, and their replacement on production aircraft with more conventional ailerons.

Frise ailerons

thumb|right|With a Frise-type aileron, when pressure is applied to the control wheel, or control stick, the aileron that is being raised pivots on an offset hinge. This projects the leading edge of the aileron into the airflow and creates drag.

Engineer Leslie George Frise (1897–1979) of the Bristol Aeroplane Company developed an aileron shape that is pivoted at about its 25 to 30% chord line and near its bottom surface [http://www.flightglobal.com/pdfarchive/view/1943/1943%20-%202340.html], in order to decrease stick forces as aircraft became faster during the 1930s. When the aileron is deflected up (to make its wing go down), the leading edge of the aileron starts to protrude below the underside of the wing into the airflow beneath the wing. The moment of the leading edge in the airflow helps to move up the trailing edge, which decreases the stick force. The down moving aileron also adds energy to the boundary layer. The edge of the aileron directs air flow from the underside of the wing to the upper surface of the aileron, thus creating a lifting force added to the lift of the wing. This reduces the needed deflection of the aileron. Both the Canadian Fleet Model 2 biplane of 1930 and the 1938 popular US Piper J-3 Cub monoplane possessed Frise ailerons as designed and helped introduce them to a wide audience.

A claimed benefit of the Frise aileron is the ability to counteract adverse yaw. To do so, the leading edge of the aileron has to be sharp or bluntly rounded, which adds significant drag to the upturned aileron and helps counterbalance the yaw force created by the other aileron turned down. This can add some unpleasant, nonlinear effect and/or potentially dangerous aerodynamic vibration (flutter). Adverse yaw moment is basically countered by aircraft yaw stability and also by the use of differential aileron movement.

The Frise-type aileron also forms a slot, so air flows smoothly over the lowered aileron, making it more effective at high angles of attack. Frise-type ailerons may also be designed to function differentially. Like the differential aileron, the Frise-type aileron does not eliminate adverse yaw entirely. Coordinated rudder application is still needed when ailerons are applied. This helps reduce the likelihood of a wing tip stall when aileron deflections are made at high angles of attack. In addition, the consequent differential in drag reduces adverse yaw (as also discussed above). The idea is that the loss of lift associated with the up aileron carries no penalty while the increase in lift associated with the down aileron is minimized. The rolling couple on the aircraft is always the difference in lift between the two wings. A designer at de Havilland invented a simple and practical linkage and their de Havilland Tiger Moth classic British biplane became one of the best-known aircraft, and one of the earliest, to use differential ailerons.

Roll control without ailerons

Wing warping

On the earliest Pioneer Era aircraft, such as the Wright Flyer and the later, 1909-origin Blériot XI and Etrich Taube, lateral control was effected by twisting the outboard portion of the wing so as to increase or decrease lift by changing the angle of attack. This had the disadvantages of stressing the structure, being heavy on the controls, and of risking stalling the side with the increased angle of attack during a maneuver. By 1916, most designers had abandoned wing warping in favor of ailerons. Researchers at NASA and elsewhere have been taking a second look at wing warping again, although under new names. The NASA version is the X-53 Active Aeroelastic Wing while the United States Air Force tested the Adaptive Compliant Wing.

Combinations with other control surfaces

thumb|A USAF F-16 displaying its rear tailerons, which move independently of each other to provide both pitch and roll control. Note the different attack angles visible.

A control surface that combines an aileron and flap is called a flaperon. A single surface on each wing serves both purposes: Used as an aileron, the flaperons left and right are actuated differentially; when used as a flap, both flaperons are actuated downwards. When a flaperon is actuated downward (i.e., used as a flap), there is enough freedom of movement left to be able to still use the aileron function.
Some aircraft have used differentially controlled spoilers or spoilerons to provide roll instead of conventional ailerons. The advantage is that the entire trailing edge of the wing may be devoted to flaps, providing better low speed control. The Northrop P-61 Black Widow used spoilers in this manner, in conjunction with full span zap flaps and some modern airliners use spoilers to assist the ailerons.
On delta-winged aircraft, the ailerons are combined with the elevators to form an elevon.
Several modern fighter aircraft may have no ailerons on their wings but provide roll control with an all moving horizontal tailplane. When horizontal tailplane stabilators can move differentially to perform the roll control function of ailerons, as they do on some modern fighter aircraft, they are termed "tailerons" or "rolling tails". Tailerons additionally permit wider flaps on the aircraft's wings.
Aileron struts combined movable surfaces with an airfoil shaped wing strut. Acting in the propeller slipstream increased their effectiveness, although their mechanical advantage is lowered due to the inboard location.

References

Footnotes

Citations

Bibliography

Bullmer, Joe. The WRight Story: The True Story of the Wright Brothers' Contribution to Early Aviation, CreateSpace Independent Publishing Platform, , , 2009.
Casey, Louis S. Curtiss, The Hammondsport Era, 1907–1915, New York: Crown Publishers, 1981, pp. 12–15, , .
Parkin, John H. Bell and Baldwin: Their Development of Aerodromes and Hydrodromes at Baddeck, Nova Scotia, Toronto: University of Toronto Press, 1964.

External links

NASA Glenn Research Center aileron article with Java demo and more pictures