A glider or sailplane is a type of glider aircraft used in the sport of gliding. It has rigid wings and an undercarriage. Some gliders, known as motor gliders, are also used for gliding and soaring, but have engines which can be used for extending a flight and, for some types, for take-off. Aircraft such as hang gliders and paragliders are foot-launched and so are described in separate articles, though their differences from sailplanes are covered below. Glider aircraft that are used for purposes other than recreation, for example for military purposes, do not soar.
Sports gliders benefit from creating the least drag for any given amount of lift, and this is best achieved with long, thin wings and a fully faired narrow cockpit. Aircraft with these features are able to climb efficiently in rising air and can glide long distances at high speed with a minimum loss of height in between.
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.
Gliding as a sport began in the 1920s. Initially the objective was to increase the duration of flights but soon pilots attempted cross-country flights away from the place of launch. Improvements in aerodynamics and in the understanding of weather phenomena have allowed greater distances at higher average speeds. Long distances are now flown using any of the main sources of rising air: ridge lift, thermals and lee waves. When conditions are favorable, experienced pilots can now fly hundreds of kilometres before returning to their home airfields; occasionally flights of more than 1,000 kilometres (621 mi) are achieved.
Some competitive pilots fly in races around pre-defined courses. These gliding competitions test pilots' abilities to make best use of local weather conditions as well as their flying skills. Local and national competitions are organized in many countries, and there are biennial World Gliding Championships. Techniques to maximize a glider's speed around the day's task in a competition have been developed, including the optimum speed to fly, navigation using GPS and the carrying of water ballast. If the weather deteriorates pilots are sometimes unable to complete a cross-country flight. Consequently they may need to land elsewhere, perhaps in a field, but motorglider pilots can avoid this by starting an engine.