Glider (sailplane)

A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding (also called soaring). This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplanes are aerodynamically streamlined and so can fly a significant distance forward for a small decrease in altitude. In North America the term 'sailplane' is also used to describe this type of aircraft. In other parts of the English-speaking world, the word 'glider' is more common. Gliders benefit from producing very low drag for any given amount of lift, and this is best achieved with long, thin wings, a slender fuselage and smooth surfaces with an absence of protuberances. Aircraft with these features are able to soar – climb efficiently in rising air produced by thermals or hills. In still air, sailplanes can glide long distances at high speed with a minimum loss of height in between. Sailplanes have rigid wings and either skids or undercarriage. In contrast hang gliders and paragliders use the pilot's feet for the start of the launch and for the landing. These latter types are described in separate articles, though their differences from sailplanes are covered below. Sailplanes are usually launched by winch or aerotow, though other methods, auto tow and bungee, are occasionally used. These days almost all gliders are sailplanes, but in the past many gliders were not. These types did not soar. They were simply engine-less aircraft towed by another aircraft to a desired destination and then cast off for landing. The prime example of non-soaring gliders were military gliders (such as those used in the Second World War). They were often used just once and then usually abandoned after landing, having served their purpose. Motor gliders are gliders with engines which can be used for extending a flight and even, in some cases, for take-off. Some high-performance motor gliders (known as "self-sustaining" gliders) may have an engine-driven retractable propeller which can be used to sustain flight.