The most important feature of Zeppelin's design was a rigid light-alloy skeleton, made of rings and longitudinal girders. The advantage of this design was that the aircraft could be much larger than non-rigid airships, which relied on a slight overpressure within the single pressure envelope to maintain their shape. The light alloys used for the structure (usually magnesium or aluminium alloys) enabled Zeppelins to lift heavier loads and be fitted with more engines and/or more powerful engines.
The basic form of the first Zeppelins was a long cylinder with tapered ends and complex multi-plane fins. During World War I, as a result of improvements by the rival firm Schütte-Lanz Luftschiffbau, the design was changed to the more familiar streamlined shape and empennage of cruciform fins used by almost all airships ever since. Within this outer envelope, several separate balloons, also known as "cells" or "gasbags", contained the lighter-than-air gas (usually hydrogen, but helium in Zeppelins operated by America). For most rigid airships the gasbags were made of many sheets of goldbeater's skin from the intestines of cows. About 200,000 were needed for a typical World War I Zeppelin. The sheets were joined together and folded into impermeable layers. Non-rigid airships often do not have multiple gas cells (though some Italian-built semi-rigid airships did).
Forward thrust was usually provided by several internal combustion engines, mounted in nacelles, or engine cars, attached to the structural skeleton. The Zeppelin company tended to use spark-ignition engines fuelled by Blaugas, a form of Naphtha, named after its inventor, Dr. Hermann Blau rather than its colour, which had the advantage of being stored in a gaseous state at roughly the same density as air, resolving issues of buoyancy and trim found when using liquid fuels. In comparison the British airship, R101, introduced diesel engines with the Beardmore Tornado to avoid using highly flammable petrol in hot climates; although these had a low power to weight ratio, limiting the payload of the weight conscious airships, as well as proving unreliable due to lack of development.
Apart from the fins, Zeppelins were also steered by adjusting and selectively reversing engine thrust.
A comparatively small compartment for passengers and crew was built into the bottom of the frame, but in large Zeppelins this was not the entire habitable space; they often carried crew or cargo internally for aerodynamic reasons.
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