aerostat(redirected from Envelope (lighter-than-air-craft))
Also found in: Dictionary.
an aircraft that is lighter than air. The lifting force of an aerostat is produced by a gas that is less dense than air—hydrogen or helium—contained in a casing, in conformity with Archimedes’ principle. A distinction is made between controlled (dirigible), noncontrolled or free-flight (with a spherical casing—spherical aerostats or balloons and stratostats), and captive (kite) aerostats. Variation in the flight altitude of a free aerostat is realized in the following manner: lift is achieved by reducing the mass of the aerostat by discarding part of the ballast (usually bags of sand); descent is accomplished by decreasing the lifting force through the release of part of the gas through a valve. The lift and descent of a captive aerostat are accomplished with a winch.
Free aerostats are used chiefly for sporting and research purposes. Radiosondes, rescue aerostats, pilot balloons, jumper halloons, stratostats, and automatic aerostats with telemetric, meteorological, and other equipment are examples of free aerostats. Automatic aerostats are used to investigate jet streams and the formation of cyclones, for photographing the earth’s surface, in the determination of the effect of cosmic radiation in the lower layers of the stratosphere on living organisms, and also as starting platforms for the launching of meteorological rockets and as a means of elevating telescopes. Captive aerostats are used for meteorological purposes (probing of the atmosphere), in the hauling of timber in mountainous regions that are otherwise inaccessible, and so on.
Barrage aerostats are used in military work for antiaircraft defense of military, industrial, and other objectives. When air attack threatens, the aerostats ascend into the air in specific combat arrangements (“winches in a line,” “winches in two lines,” “winches over an area”). Their action is calculated for the destruction or damage of enemy airplanes by collision with cables, aerostat casings, or explosive charges suspended on the cables. During the Great Patriotic War, barrage aerostats of 100–400 cu m in volume were successfully used in the antiaircraft defense systems of Moscow, Leningrad, and other cities. Single barrage aerostats ascended to an altitude of up to 2,500 m, double ones (two aerostats on one cable) up to 4,500 m. Observation aerostats are employed to observe the field of battle and to correct the firing of artillery. They have a suspended gondola for the crew and are equipped with a telephone connection to the ground. The volume of observation aerostats is 400–1,000 cu m and higher.
REFERENCESPolozov, N. P., and M. A. Sorokin. Vozdukhoplavanie. Moscow, 1940.
Stobrovskii, N. G. Nasha strana—rodina vozdukhoplavaniia. Moscow, 1954.