What is a Glider?

GLIDER [glider] kind of aircraft resembling an aeroplane but having at most a tiny auxiliary power plant and generally no means of propulsion at all. The typical contemporary glider has relatively narrow wings and a streamlined body. The unpowered variant is launched by an elastic shock cord, a rope, or a cable, tied to the front of the glider and pushed by a launching crew, a winch, a tow vehicle, or a tow aircraft. Gliders may be trailed behind aircraft over considerable distances. The motorised variant can take off and ascend on its own. The glider combines gravity and updrafts of air to keep it flying; slope soaring depends on wind rising off dunes or slopes, while thermal soaring exploits convection currents in the air. In soaring the glider is repeatedly steered into updrafts to reach heights as high as 46,000 ft (14,000 m) (14,000 m). It may then glide down through air that is not rising. In a powered glider the engine may be switched on to keep the glider afloat when there are no updrafts. A sailplane, a glider which is constructed specifically for soaring and prolonged flight, may go as far as 500 mi (800 km) in this way. The standard flying controls of a glider consist of a pedal to operate the rudders and a control stick to manipulate the elevators and ailerons. Otto and Gustav Lilienthal of Germany performed the first successful piloted glider flight in 1891. The Lilienthals demonstrated the superiority of curved over flat surfaces in flight and encouraged others to make glider experiments, at least until Otto’s death in a glider crash in 1896. At the beginning of the 20th cent. the Wright brothers created and flew several gliders. They developed land skids, wing warping, and other advances that define present-day gliders. In World War II troop-transport gliders were utilised for airborne invasions. The gliders were launched and hauled by cargo planes to the invasion area, where they were released. Early gliders were launched from hills or by jogging forward; the aircraft maintained stability while in flight by the pilot’s changing body weight. These approaches have been revived in contemporary hang gliding, a development based on NASA studies with flexible-wing gliders in the 1950s. The hang glider, using nylon or Kevlar stretched over an aluminium frame, can reach an altitude of 20,000 ft (6,100 m) and remain aloft up to 15 hours; in 1979 five hang glider pilots flew their machines (equipped with auxiliary engines) across the United States. A paraglider is a parachutelike airfoil composed of nylon and Mylar from which the pilot is held by a sequence of cables. Paraglider pilots must “kite” —raise the airfoil into the air by sprinting and exploiting the wind—before throwing themselves from a cliff or the like.

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