Aileron

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.

The name "aileron", from French, meaning "little wing", also refers to the extremities of a bird's wings used to control their flight. It first appeared in print in the 7th edition of Cassell's French-English Dictionary of 1877, with its lead meaning of "small wing". 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.

Ailerons had more or less completely supplanted other forms of lateral control, such as wing warping, by about 1915, well after the function of the rudder and elevator flight controls had been largely standardised. Although there were previously many conflicting claims over who first invented the aileron and its function, i.e., lateral or roll control, the flight control device was invented and described by the British scientist and metaphysicist Matthew Piers Watt Boulton in his 1864 paper On Aërial Locomotion. He was the first to patent an aileron control system in 1868.

Boulton's description of his lateral flight control system was "the first record we have of appreciation of the necessity for active lateral control as distinguished from [passive lateral stability].... With this invention of Boulton's we have the birth of the present-day three torque method of airborne control" as was praised by Charles Manly. This was also endorsed by C.H. Gibbs-Smith. Boulton's British patent, No. 392 of 1868, issued about 35 years before ailerons were "reinvented" in France, became forgotten and lost from sight until after the flight control device was in general use. Gibbs-Smith stated on several occasions that if the Boulton patent had been revealed at the time of the Wright brothers' legal filings, they might not have been able to claim priority of invention for the lateral control of flying machines. The fact that the Wright brothers were able to gain a patent in 1906 did not invalidate Boulton's lost and forgotten invention.

Ailerons were not used on manned aircraft until they were employed on Robert Esnault-Pelterie's glider in 1904, although in 1871 a French military engineer, Charles Renard, built and flew an unmanned glider incorporating ailerons on each side (which he termed 'winglets'), activated by a Boulton-style pendulum controlled single-axis autopilot device.

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. The French journal L'Aérophile then published photos of the ailerons on Esnault-Pelterie's glider which were included in his June 1905 article, and its ailerons were widely copied afterward.

The Wright brothers used wing warping instead of ailerons for roll control on their glider in 1902, and about 1904 their Flyer II was the only aircraft of its time able to do a coordinated banked turn. During the early years of powered flight the Wrights had better roll control on their designs than airplanes that used movable surfaces. From 1908, as aileron designs were refined it became clear that ailerons were much more effective and practical than wing warping. Ailerons also had the advantage of not weakening the airplane's wing structure as did the wing warping technique, which was one reason for Esnault-Pelterie's decision to switch to ailerons.