page_title: Aerostat
section_title: Balloons
hierarchical_section_title: Aerostat / Types / Balloons
caption_attribution_description: 2006 Ojiya Balloon Festival (2006年おぢや風船一揆)
context_page_description: An aerostat is a lighter than air aircraft that gains its lift through the use of a buoyant gas. Aerostats include unpowered balloons and powered airships. A balloon may be free-flying or tethered. The average density of the craft is lower than the density of atmospheric air, because its main component is one or more gasbags, a lightweight skin containing a lifting gas to provide buoyancy, to which other components such as a gondola containing equipment or people are attached. Especially with airships, the gasbags are often protected by an outer envelope.
  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 the heavy aerodynes that primarily use aerodynamic lift which requires the movement of a wing surface through the surrounding air mass. The term has also been used in a narrower sense, to refer to the statically tethered balloon in contrast to the free-flying airship.
context_section_description: A balloon is an unpowered aerostat which has no means of propulsion and must be either tethered on a long cable or allowed to drift freely with the wind.
  Although a free balloon travels at the speed of the wind, it is travelling with the wind so to a passenger the air feels calm and windless. To change its altitude above ground it must either adjust the amount of lift or discard ballast weight. Notable uses of free-flying balloons include meteorological balloons and sport balloons.
  A tethered balloon is held down by one or more mooring lines or tethers. It has sufficient lift to hold the line taut and its altitude is controlled by winching the line in or out. A tethered balloon does feel the wind. A round balloon is unstable and bobs about in strong winds, so the kite balloon was developed with an aerodynamic shape similar to a non-rigid airship. Both kite balloons and non-rigid airships are sometimes called "blimps". Notable uses of tethered balloons include observation balloons and barrage balloons and notable uses of untethered balloons include espionage balloons and fire balloons.
caption: A free-flying hot air balloon
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