Balloons and dirigibles
Airships (the name comes from “lighter-than-air ships”) often comprise a balloon envelope filled with either hot air or helium, which are lighter than air and will raise the craft off the ground (1 m3 of helium will lift 1 kg). Helium and hot-air balloons go where the wind goes; the pilot can vary the altitude in search of more favourable wind but cannot change direction. A dirigible airship is a hot-air or gas balloon equipped with motors and propellers; dirigibles can choose their direction of travel and can reach an average speed of 80 kph in calm air.
Airships were widely used during the first half of the 20 th century. The Zeppelin company operated a regular transatlantic airship service, carrying about a hundred people between Germany and the United States. After the Hindenburg exploded on landing at Lakehurst (New Jersey) in 1937 (it was filled with hydrogen, which is inflammable in contact with air), airships gradually disappeared from the skies.
Airships today and tomorrow
These days, airships are filled with helium, an inert gas that involves no risk of explosion. Most airships are used as advertising supports or for tourism but there are plans to use them for technical and environmental surveillance (high-tension lines, pipelines, etc). Studies are under way for an airship capable of carrying significant payloads (up to 30 metric tons).