Airship

An airship, dirigible balloon or dirigible is a type of aerostat (lighter-than-air) aircraft that can navigate through the air flying under its own power. Aerostats use buoyancy from a lifting gas that is less dense than the surrounding air to achieve the lift needed to stay airborne.

In early dirigibles, the lifting gas was hydrogen, due to its high lifting capacity and ready availability. Still, its inherent flammability led to several fatal accidents, rendering hydrogen airships obsolete. The alternative lifting gas, helium, is not flammable, but is rare and relatively expensive. Significant amounts were first discovered in the United States and for a while helium was only available for airship usage in North America. Most airships built since the 1960s have used helium, though some have used hot air.

The bulk of an airship consists of the lighter-than-air envelope, which may either form the gasbag itself or contain some gas-filled cells. The engines, crew, and payload capacity necessary for the airship's operation are instead housed in the gondola, one or more enclosed platforms suspended below the envelope.

The main types of airship are non-rigid, semi-rigid, and rigid airships. Non-rigid airships, often called "blimps", rely solely on internal gas pressure to maintain the envelope shape. Semi-rigid airships maintain their shape by internal pressure, but have some form of supporting structure, such as a fixed keel, attached to it. Rigid airships have an outer structural framework that maintains the shape and carries all structural loads, while the lifting gas is contained in one or more internal gasbags or cells. Rigid airships were first flown by Count Ferdinand von Zeppelin, and the vast majority of rigid airships built were manufactured by the firm he founded, Luftschiffbau Zeppelin. As a result, rigid airships are often called zeppelins.

Airships were the first aircraft capable of controlled, powered flight and were most commonly used before the 1940s; their use declined as aeroplanes surpassed their capabilities. Their decline was accelerated by a series of high-profile accidents, including the 1930 crash and burning of the British R101 in France, the 1933 and 1935 storm-related crashes of the twin airborne aircraft carrier U.S. Navy helium-filled rigids, the USS Akron and USS Macon respectively, and the 1937 burning of the German hydrogen-filled Hindenburg. Since the 1960s, helium airships have been used where the ability to hover for extended periods outweighs the need for speed and manoeuverability, such as for advertising, tourism, camera platforms, geological surveys, and aerial observation.