Sir George Cayley (1773-1857), English flight pioneer and aerodynamicist. Cayley spent much of his life engaged in his own experiments, devoting himself to the study of flight. In 1808, he built and flew a large glider, thought to be the first heavier-than-air machine ever flown. He built and tested a variety of designs, including flapping- wing ornithopters, and bi- and triplanes. He realised that stability and control were derived from the horizontal and vertical surfaces of an aircraft's tail, and that a lightweight propeller could be used to power an aircraft. In 1853, his coachman flew across a valley in one of his gliders, the first manned glider flight.