Alphonse Pénaud, (born 1850, Paris, France—died October 1880, Paris), French aeronautical pioneer.
Pénaud was the son of an admiral but suffered from a degenerative hip condition that prevented his following a family tradition of service in the French navy. As early as 1870 he began to demonstrate the discoveries that would eventually establish his reputation as one of the most influential of 19th-century flying-machine pioneers. Early in his career, he built and flew a series of rotary wing and fixed-wing models and ornithopters powered by twisted rubber strands. His most significant contributions related to the stability of fixed-wing aircraft. In 1871 he designed and built a rubber-powered model featuring dihedral wings for lateral stability and a combined horizontal and vertical tail surface designed to provide a measure of inherent stability in pitch and yaw. Pénaud flew his planophore, as the model was known, in the Jardin des Tuileries in Paris on Aug. 18, 1871. The model completed a circular flight of approximately 40 metres (130 feet) in 11 seconds, providing the first public demonstration of genuine stability in a heavier-than-air machine.
In 1876 Pénaud published an extraordinarily advanced design for a streamlined amphibious aircraft featuring braced monoplane wings, a glazed canopy, a fully enclosed engine, a wheeled undercarriage, and something approaching a modern control system. Discouraged by his failure to find financial support for his research and by public ridicule of his ideas, he took his own life.