A glider, also called a sailplane, is an unpowered airplane which, once launched by air or ground towing, or by using a winch, is kept aloft by its light, aerodynamic design and the skill of the pilot in exploiting "thermals" and other rising air currents. George Cayley built his first model glider in 1804 and in 1853 he persuaded his coachman to undertake a short glide – the first manned heavier-than-air flight. Otto Lilienthal made many successful flights in his hang-gliders (planes in which the pilot hangs underneath and controls the flight by altering his body position, hence moving the craft's center of gravity) from 1891 until his death in a gliding accident in 1896. Later, the Wright brothers developed gliders in which control was achieved by moving control surfaces, as a prelude to their experiences with powered flight.