As early as 1868, Englishman Matthew Piers Watt Boulton patented a system of lateral flight control involving what would later be called ailerons. Wrote historian C.H. Gibbs-Smith in his 1960 book, The Aeroplane, this was “…one of the most remarkable inventions…of aeronautical history, which was immediately lost sight of.”
During the late 19th and early 20th centuries, Charles Renard, Alphonse Pénaud, and Louis Mouillard either described horizontal control surfaces on the trailing edge of wings or incorporated them into experimental craft. Gibbs-Smith insisted that these were air brakes, however, intended to increase the drag on one wing to control yaw, not roll.
In the mid- to late 1800s, Jean-Marie LeBris, John Montgomery, Clement Ader, D.D. Wells, Edson F. Gallaudet, and Hugo Mattullath all suggested some form of what would become known as wing warping, or applied it to unmanned kites or a full-scale machine. None were successful at using the technique to achieve active control, nor did they envision combining wing warping with a rudder to counteract differential drag or to achieve coordinated turns— an essential feature of Wilbur and Orville Wright’s patent. The Wrights were the first to successfully employ such a system on piloted gliders and powered aircraft. The Wrights and their lawyer, Harry Toulmin, crafted the patent to include lateral control achieved by mechanical means other than wing warping, but which relied on the principles they were claiming legal protection for. From Patent 821,393: “[O]ur invention is not limited to [wing warping], since any construction whereby the angular relations of the lateral margins of the aeroplanes [wings] may be varied in opposite directions with respect to the normal planes of…aeroplanes comes within the scope of our invention.”
The essential idea was to obtain lateral control by varying the lift on either wing. The mechanical means of achieving that end are secondary.
In every instance, the courts that heard arguments involving the Wright patent ruled in favor of the brothers, affirming the view that ailerons were among the “other means” of achieving lateral control for which the Wrights deserved legal protection.
French experimenter Robert Esnault-Pelterie moved from wing warping to ailerons, French for “little wings,” in 1904. In his design, the two surfaces were placed between the two wings, forward of the leading edge. “The warping of the surfaces, preferred by the Wright brothers and used on our aircraft,” he said in a January 1905 talk before the Aéro-Club de France, “gives good enough results for the maintenance of transverse equilibrium, but…may, in our opinion, cause excessive strains on the wiring, and so we fear breakages…which cannot occur with the ordinary rigid [trussed] system…. We therefore choose to abandon warping. [T]o…control lateral balance, we…employed at the front two independent horizontal rudders (“deux gouvernails horizontaux”), one placed in front toward the end of each wing…attached to a steering device within reach of…the operator…. The arrangement gave satisfaction, although…not as powerful as…wing-warping….”
In December 1906, the editor of L’Aérophile described the pivoting control surfaces mounted in the outer bays of Alberto Santos Dumont’s 14-bis as “gouvernails auxiliares.” In reporting the flight of the Aerial Experiment Association’s White Wing in upstate New York in May 1908, L’Aérophile described the wingtip control surfaces as being “like those of Robert Esnault-Pelterie.” L’Aérophile did not use the word “aileron” until July 1908.