GLIDER

nonpowered heavier-than-air craft capable of sustained flight. Though many men contributed to the development of the glider, the most famous pioneer was Otto Lilienthal (184896) of Germany, who, with his brother Gustav, began experiments in 1867 on the buoyancy and resistance of air. Lilienthal also investigated camber and wing sections and studied ways to increase the stability of the gliders he built, finally incorporating stabilizing tail surfaces. In 1891 he built his first man-carrying craft, with which he could take off by running downhill into the wind. In 1896 Octave Chanute, French-born American engineer, began designing gliders that were flown by others under his supervision. He discarded Lilienthal's method of securing control by a fixed rear fin with the horizontal tail parts freely hinging upward, and instead substituted a rudder and articulated (segmented) wings. Chanute's gliders were so stable that they made 2,000 flights without an accident. Orville and Wilbur Wright built their most successful early glider in 1902. Following experimentation they decided to use a vertical rudder that was movable in flight. They then added a horizontal elevator and combined their adjustable vertical rudder with a wing-warping mechanism that permitted them to move the trailing edges of the wings up and down. This perfect control made their gliding safe and allowed them to proceed to the powered airplane. Gliders being towed aloft by an airplane. To fly, a glider must be accelerated to flying speed, the speed at which wings generate enough lift to overcome the force of gravity. In most of the early gliders, flying speed was very low; normal practice was to fly into a wind so that the actual acceleration required was not great. Today's favoured launching techniques are the airplane tow (see photograph) and the automobile tow. The tow rope normally used is about 200 feet (60 m) long with a steel ring attached at each end, fitting the tow hooks of the towing vehicle and the glider. Gliders are also launched by shock-cord launching, which works on the principle of a slingshot, or by winch tow, which works like a giant fishing reel, with the glider attached to one end like a fish. While hang gliders usually are launched from a high point and descend, sailplane gliders can soar for hours on the lift from thermals and rising air due to rising terrain. Since 1935, gliders equipped with recording instruments have gained in reputation as tools for aeronautical and meteorological research. Gliders were widely used in World War II to carry troops. They, and sailplanes in particular, have become increasingly popular for recreational purposes and as vehicles for sports competition. also called Flying Phalanger, or Flying Possum, any of about six small phalangersmarsupial mammals of Australasiathat volplane from tree to tree like flying squirrels. Most have well-developed flaps of skin along the flanks; these become sails when the limbs are extended. An eastern Australian species, which feeds on nectar and insects, is the pygmy glider, or feathertail (Acrobates pygmaeus), only 15 cm (6 inches) in total length; it has narrow side flaps, and its 8-centimetre-long tail is stiffly haired laterallya feather that helps it to navigate. The 25-centimetre-long pen-tailed phalanger (Distoechurus pennatus) of New Guinea lacks the flaps; its tail is furry at the base but otherwise featherlike. The three species of lesser, or sugar, gliders (Petaurus) are 25 to 80 cm long. An example is the short-headed glider (P. breviceps) found from New Guinea to Tasmania; it is blue-gray with a dark centre stripe and has a long bushy tail. These animals can glide 55 m (180 feet). The greater glider (Schoinobates volans) of eastern Australia may be 105 cm long; it often glides 100 m or more. It has adapted to eating leaves and is sometimes classified with ring-tailed possums and the koala in a separate family, Phascolarctidae.