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An aerostat (From Greek ἀήρ aer (air) + στατός statos (standing) through French) is a craft that remains aloft primarily through the use of buoyant lighter than air gases, which impart lift to a vehicle with nearly the same overall density as air. Aerostats include free balloons, airships, and moored balloons. An aerostat's main structural component is its envelope, a lightweight skin containing a lifting gas[1][2] to provide buoyancy, to which other components are attached. One of the most recent deployments of an aerostat was seen at the opening ceremony of the nineteenth 2010 Commonwealth Games, held in Delhi, India. The aerostat used in the ceremony was the largest in the world.
Aerostats are so named because they use "aerostatic" lift which is a buoyant force that does not require movement through the surrounding air mass. This contrasts with aerodynes that primarily use aerodynamic lift which requires the movement of at least some part of the aircraft through the surrounding air mass.
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There are two distinct senses for the scope of term aerostat. In the broader sense, the term refers to all systems that remain aloft primarily using aerostatic buoyancy. In the narrower sense, the term is used to refer to the most common type of aerostat which is the moored balloons. This article uses the term in its broader sense. For the narrower sense, see moored balloon.
Systems that are connected to the surface via one or more tethers. In contrast to the other types of aerostats, moored balloons are non-free flying. A notable example of moored balloons are barrage balloons. Some moored balloons obtain aerodynamic lift via the contours of their envelope or through the use of fins. Moored balloons are also used for sight seeing and advertising. Aerophile SA has made the first one in 1994 and have sold so far more than 50 of them in 25 countries becoming the world's largest lighter than air carrier ever with 300 000 passengers flown every year.
A trademarked name given to a patented combination of a helium balloon and a kite to form a single, aerodynamically sound tethered aircraft, that exploits both wind and helium for its lift. The attached balloon is generally oblate-spheroid in shape although this is not essential. A Helikite is not a moored balloon, because a Helikite is not a balloon. A Helikite is a tethered aerostat. The US Customs classifies a Helikite as "other non-powered aircraft" not as balloons. The British Civil Aviation Authority's Air Navigation Order gives Helikites its own classification as "Helikites" as opposed to "kites" and "balloons". A Helikite is not just a kite because Helikites fly in nil wind and kites need wind to fly. A Helikite is not just a balloon because Helikites can fly even if weighed down to be heavier than air whereas balloons will never fly if heavier than air. A Helikite is a new type of tethered aerostat with its own official classification. Trials have shown that Helikites fly to greater altitudes than tethered balloons and in far higher winds. They stay stationary and steady in the air in more conditions and for longer than any other type of aerostat. If the word aerostat comes from the greek "aer" + "statos" then Helikites are a pure form of aerostat.
Free-flying buoyant aircraft that move by being carried along by the wind. Types of free balloons include hot air balloons and gas balloons.
Free-flying buoyant aircraft that can be propelled and steered. Some airships obtain aerodynamic lift via the shape of their envelope or through the addition of fins or other shape. These types of craft are called hybrid airships.