Also found in: Dictionary, Thesaurus, Medical, Acronyms, Wikipedia.
glider, type of aircraft resembling an airplane but having at most a small auxiliary propulsion plant and usually no means of propulsion at all. The typical modern glider has very slender wings and a streamlined body. The unpowered variety is launched by an elastic shock cord, a rope, or a cable, attached to the front of the glider and pulled by a launching crew, a winch, a tow car, or a tow plane. Gliders can be towed behind airplanes over great distances. The powered variety can take off and climb on its own.
The glider uses gravity and updrafts of air to keep it flying; slope soaring relies on wind rising off dunes or hillsides, while thermal soaring exploits convection currents in the air. In soaring the glider is repeatedly maneuvered through updrafts to reach altitudes as high as 46,000 ft (14,000 m). It can then glide down through air that is not rising. In a powered glider the engine can be turned on to keep the glider aloft when there are no updrafts. A sailplane, a glider which is built especially for soaring and sustained flight, can travel as much as 500 mi (800 km) in this manner. The usual flight controls in a glider consist of a pedal to operate the rudders and a control stick to operate the elevators and ailerons.
Otto and Gustav Lilienthal of Germany made 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 constructed and flew many gliders. They introduced land skids, wing warping, and other improvements that characterize present-day gliders. In World War II troop-transport gliders were used for aerial invasions. The gliders were launched and towed by cargo aircraft to the invasion area, where they were released.
Early gliders were launched from hills or by running forward; the machine maintained stability while in flight by the pilot's shifting body weight. These techniques have been resurrected in modern hang gliding, a development based on NASA experiments with flexible-wing gliders in the 1950s. The hang glider, with nylon or Kevlar stretched over an aluminum frame, can reach an altitude of 20,000 ft (6,100 m) and stay aloft up to 15 hours; in 1979 five hang glider pilots flew their machines (fitted with auxiliary motors) across the United States. A paraglider is an parachutelike airfoil made of nylon and Mylar from which the pilot is suspended by a series of ropes. Paraglider pilots must “kite”—raise the airfoil into the air by running and using the wind—before launching themselves from a cliff or the like.
See T. L. Knauff, Glider Basics from First Flight to Solo (1982); D. Piggott, Gliding (5th ed. 1987).
an unpowered aircraft that is heavier than air. A glider moves forward by gravity. In calm air its flight path follows a line of constant descent at some angle to the horizon (the gliding angle) and is based on the same physical laws as the flight of an airplane. When there are rising air currents, soaring —the flight of a glider without loss of altitude or even with gains in altitude—becomes possible. Modern gliders are classified according to the number of seats as single-seaters, two-seaters, and multiseaters. They are categorized by function as trainers, semi-trainers, and performance-type machines. Single-seater performance-type gliders may compete in the standard class, which allows a wingspan up to 15 m, or the open class, which places no restrictions on wingspan.
The first glider was constructed and tested by the French sea captain J. Le Bris in 1868. Using a horse-drawn carriage (on which the glider rested) as a launcher, he succeeded in making glider flights of up to 30 m. In the late 19th and early 20th centuries a large number of short gliding descents from hills were carried out. Through these descents man learned to control the flight of a glider. In the period 1891–96 the German O. Lilienthal became the first to make a large number of glider flights over distances up to 250 m in hang gliders. Such gliders were controlled by shifting the craft’s center of gravity by moving the pilot’s body in the desired direction.
The engineer P. Pilcher in Great Britain and the engineer O. Chanute and the brothers O. Wright and W. Wright in the United States followed in Lilienthal’s path. The successful glider flights of the Wright brothers in the years 1901–03 enabled them to construct an airplane, which was a somewhat enlarged copy of their gliders; this plane was used in 1903 for the first powered flight. By 1908, hang-glider flights became common. The balance method of control was later replaced by aircraft-type rudder controls. In 1913 in the Crimea the Russian designer S. P. Dobrovol’skii became the first in Russia to make soaring flights lasting approximately 5 min in a biplane glider with a rudder. In Dobrovol’skii’s glider the pilot flew in a sitting position.
In the USSR, glider construction expanded in the 1920’s and 1930’s. Designers included K. K. Artseulov, G. F. Groshev, V. I. Emel’ianov, S. V. Il’iushin, B. N. Sheremetev, and A. S. Iakovlev. During World War II (1939–45) multiseater towed gliders for the transport of soldiers and equipment across the front lines were built in the USSR, the United States, Great Britain, Germany, and Japan. The seven-seater A-7, designed by O. K. Antonov, and the 11-seater Gr-29, designed by V. K. Gribovskii, were used during the Great Patriotic War (1941–45). The 18-seater Iakov Alksnis, designed by B. D. Urlapov and constructed in Moscow in 1932, was the first towed glider in the world for airborne troops.
In the early 1970’s performance-type gliders and glider techniques were greatly improved. This made it possible to achieve record flights at altitudes of up to 14 km over distances greater than 1,000 km. In the USSR well-known designers of modern gliders include O. K. Antonov, the design team of the Kazan Aviation Institute B. O. Karvialis, B. I. Oshkinis, and V. F. Spivak. Z. Mowakowski and J. Niespala are among the best-known designers in Poland, as is H. Holinghaus in the Federal Republic of Germany.
The gliders of the 1920’s had a wooden frame. They differed little in appearance, size, principles of control, and location of the pilot from airplanes of the same period, but they weighed much less. Glider design subsequently underwent significant change, leading to an increase in aerodynamic efficiency (the ratio of wing lift to drag) and in the wing aspect ratio (the ratio of wingspan to wing depth) and also to a decrease in the minimum descent rate to 0.5 m per sec. A laminated wing profile with a characteristic camber in the rear surfaces came into use. Because the pilot was now placed in a cockpit in a legs-forward, reclining position and the cockpit was covered by a transparent canopy that did not protrude beyond the fuselage contours, the maximum cross section of the fuselage, or midsection, could be sharply reduced. A single-wheel retractable landing gear has been introduced. Dural and fiberglass serve as the primary structural materials for modern gliders; wood is used less often.
Gliders are launched in various ways. In the 1930’s a shock cord was used, and the glider was launched like a stone from a slingshot. Beginning in 1931, Soviet glider pilots mastered the method of launching a glider by towing it behind an airplane. Since then, the towed start, generally to an altitude of 600 m, has become the rule for performance-type gliders. The winch tow, in which a steel cable and a winch powered by an internal-combustion engine propel the craft to altitudes of 200–300 m, has become the main method of launching without the aid of an airplane. Power gliders with auxiliary engines for independent takeoff also became popular in the 1960’s.
Modern gliders have the following performance standards: maximum lift-drag ratio, 40–53; wingspan, to 29 m; wing aspect ratio, 20–36; wing loading, 250–350 newtons per sq m; rate of descent, 0.4–0.8 m per sec; flying speed (for maximum aerodynamic efficiency), 80–100 km/hr; and maximum speed, 220–250 km/hr.
REFERENCESP’etsukh, A. I. Kryl’ia molodezhi. Mosow, 1954.
Sheremetev, B. N. Planery. Moscow, 1959.
Kostenko, I. K., O. A. Sidorov, and B. N. Sheremetev. Zarubezhnye planery. Moscow, 1959.
Zamiatin, V. M. Planery i planerizm. Moscow, 1974. (Bibliography.) Keedus, Ü. Purilend. Tallinn, 1962.
Skarbiński, A., and W. Stafiej. Projektowanie i konstrukcja szybowców. Warsaw, 1965.
Podręcznik pilota szybowcowego. Warsaw, 1967.
I. K. KOSTENKO