Two Young Girls Posing With The Old Airplane

Propulsion
Unpowered
• Gliders
Heavier-than-air unpowered aircraft such as gliders (i.e. sailplanes), hang gliders and paragliders, and other gliders usually do not employ propulsion once airborne. Take-off may be by launching forwards and downwards from a high location, or by pulling into the air on a tow-line, by a ground-based winch or vehicle, or by a powered "tug" aircraft. For a glider to maintain its forward air speed and lift, it must descend in relation to the air (but not necessarily in relation to the ground). Some gliders can 'soar'- gain height from updrafts such as thermal currents. The first practical, controllable example was designed and built by the British scientist and pioneer George Cayley, who many recognise as the first aeronautical engineer.