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gliding

The art of using air currents to fly unpowered aircraft. Technically, gliding involves the gradual loss of altitude; gliders designed for soaring flight (utilizing air rising up a cliff face or hill, warm air rising as a thermal above sun-heated ground, and so on) are known as sailplanes.

Soaring

There are three main methods of gaining height after launch: air currents, thermals, and thunderstorms. Air currents follow the contours of the land below them, and though in relation to the air itself the sailplane is losing height, the wind blowing up the side of a hill may enable it to gain more height than it is losing. By circling in a thermal, the glider can soar upwards for many hundreds of metres. By using the ascending currents in or near thunderstorms even greater heights can be attained.

Long cross-country flights

These are usually accomplished by the use of thermals. The glider first gains height in a thermal, then glides, gradually losing height, to the next thermal, where the process is repeated. By this method, which requires great skill and judgement of weather conditions, sailplanes may fly several hundred kilometres.

Launching

A sailplane must be given an intitial impetus by an external force in order for it to reach a speed sufficient to keep it in the air. Launching may be by rubber catapult from a hilltop (in the UK, the only remaining site for catapult launches is Long Mynd in Shropshire), by aircraft tow (the towing cable is released by the glider pilot when sufficient height has been gained), or by winch launching where the glider is attached to a winch with a reel of wire (when the wire is retracted the glider is launched like a kite). Once in the air, speed is maintained by depressing the nose and thus losing height in relation to the surrounding air.

History

Gliding played an important part in the development of flight. Pioneers include George Cayley, Otto Lilienthal, Octave Chanute (1832-1910), and the Wright brothers, the last-named perfecting gliding technique in 1902.

Because of the ban on military flying, gliding made great progress in Germany between the two world wars. In World War II, towed gliders were used by the Germans in Crete and the Allies at Arnhem, the Netherlands, to provide additional carrying capacity for troops and equipment. These transport gliders were expendable and could be landed in open country away from airfields, and the troops required no special training such as is necessary for parachutists.

The height record of 14,102 m/46,266 ft was established on 17 February 1986 in California by R R Harris, and the distance record of 1,460.8 km/907.7 mi on 25 April 1972 by H W Grosse.

The sport of hang-gliding was developed in the 1970s.

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