Gliders

Gliders or sailplanes are aircraft designed for unpowered flight. Most gliders are intended for use in the sport of gliding and so have high aerodynamic efficiency. Lift-to-drag ratios may exceed 70 to 1. After launch, the energy for sustained gliding flight is obtained through the skillful exploitation of rising air in the atmosphere. Glider flights of thousands of kilometers at average speeds over 200 km/h have been achieved. The glider is most commonly launched by a tow-plane or by a winch. Some gliders, called motor gliders, are equipped with engines (often retractable) and some are capable of self-launching. Military gliders have been used in war to deliver assault troops, and specialized gliders have been used in atmospheric and aerodynamic research. The most numerous class of gliders are hang gliders; hang gliders generally are slower, less massive, and less expensive than sailplanes; hang gliders are generally categorized into a default use of the term "hang glider" for hang gliders that have considerable stiffening and the fully-flexible non-sparred-winged hang gliders called "paragliders".