Differential ailerons

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

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 assive 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.Bullmer 2009, p. 20.

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.

By 1911 most biplanes used ailerons rather than wing warping—by 1915 ailerons had become almost universal on monoplanes as well. The U.S. Government, frustrated by the lack of its country's aeronautical advances in the years leading up to World War I, enforced a patent pool effectively putting an end to the Wright brothers patent war. The Wright company quietly changed its aircraft flight controls from wing warping to the use of ailerons at that time as well.

Other early aileron designers

Others who were previously thought to have been the first to introduce ailerons included:

* American John J. Montgomery included spring-loaded trailing edge flaps on his second glider (1885): these were operable by the pilot as ailerons. In 1886 his third glider design used rotation of the entire wing rather than just a trailing edge portion for roll control. By his own accounts all of these changes in addition to his use of an elevator for pitch control provided "entire control of the machine in the wind, preventing it from upsetting."
* 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.

* 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, which was later copied by the U.S. aeronautical pioneer Glenn Curtiss the same year, with the AEA ''June Bug''.
* Henry Farman's ailerons on his 1909 Farman III