Aerostat
From Wikipedia, the free encyclopedia
The term aerostat has two meanings. In the first, broader sense, it includes all lighter than air aircraft.
The term "aerostat" comes from the fact that buoyancy is technically said to provide "aerostatic" lift in that the force upwards arises without movement through the surrounding air mass. This contrasts with aerodynamic lift which requires the movement of at least some part of the aircraft through the surrounding air mass.
The second, narrower and more technical usage refers only to moored balloons. This article focuses on the narrower use of the term. For a discussion of the other types of buoyant aircraft, see balloon (aircraft), airship, and lighter than air.
Thus, in the narrower sense, an aerostat is a tethered or moored balloon often shaped like an airship and usually filled with helium. Aerostats differ from airships and balloons in that airships and balloons are both free flying whereas aerostats are tied to the ground.
Tethered aerostats come in three forms. 1) Traditional sausage shaped (i.e. blimp shaped) with fins to stabilise them but relying upon helium alone for lift. 2)Simple round balloons relying on helium alone but without stabilisation. 3) Helikites, that utilise both helium and wind if it is available. A Helikite has a kite attached directly to its oblate-spheroid balloon to stabilise it and to create a single aerodynamic structure for wind lift. Helikites can fly in higher winds than other types of aerostat and to greater altitude.
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[edit] Applications
The barrage balloons of World War I and World War II were examples of aerostats. Today, aerostats are used for lifting: cameras; radio antennas;electro-optical sensors; radio-relay equipment and advertising banners - often for long durations. Aerostats are also used for position marking and bird control work.
Surveillance aerostats have been used in the 2004 American occupation of Iraq. Utilizing a high-tech optics system to detect and observe enemies from miles away and have been used accompanying foot patrols in Baghdad.
The USGS uses aerostats to carry equipment to places where conventional aircraft cannot go, such as above an erupting volcano. Aerostats are ideal as they can easily remain more or less in one place, are less likely to be damaged by volcanic ash, and are less expensive to operate than a helicopter.
[edit] Aerostats in science fiction
Aerostats are commonly used in science fiction, though they are often envisioned as having a vacuum based displacement rather than helium; doing such appears to require the construction of a very large craft or the use of super-strong rigid materials. Aerostats of fiction are typically not tied to the ground, but rather remain stationary through the use of propulsion systems and internal sensors and controls.
