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The static buoyancy of airships in flight is not constant. It is therefore necessary to control the altitude of an airship by controlling its buoyancy: buoyancy compensation. ==Changes which have an effect on buoyancy== * Changes in air temperature (and thus the density of air) * Changes in lifting gas temperature (for example, the heating of the hull by the sun). * Accumulation of additional ballast (for example, precipitation or icing on the envelope) * Changes in ballast (for example, during a flight maneuver or the dropping of ballast) * Changes in weight of fuel on board, due to fuel consumption. This was a challenge especially in the large historic airships like the Zeppelins. For example, on a flight from Friedrichshafen to Lakehurst, the rigid airship LZ 126, built in 1923-24, used 23,000 kg gasoline and 1300 kg of oil (an average consumption of 290 kg/100 km). During the landing the airship had to release approximately 24,000 cubic meters of hydrogen to balance the ship before landing it. A Zeppelin of the size of the LZ 129 Hindenburg on a flight from Frankfurt am Main to Lakehurst consumed approximately 54 tonnes of diesel with a buoyancy equivalent of 48,000 cubic metres of hydrogen, which amounted to about a quarter of the lifting gas used at the start of the flight (200,000 cubic metres). After the landing, the jettisoned hydrogen was replaced with new hydrogen. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Buoyancy compensator (aviation)」の詳細全文を読む スポンサード リンク
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