A Zeppelin is a type of rigid airship named after the German Count Ferdinand von Zeppelin (German pronunciation: ) who pioneered rigid airship development at the beginning of the 20th century. Zeppelin's notions were first formulated in 1874 and developed in detail in 1893. They were patented in Germany in 1895 and in the United States in 1899. After the outstanding success of the Zeppelin design, the word zeppelin came to be commonly used to refer to all rigid airships. Zeppelins were first flown commercially in 1910 by Deutsche Luftschiffahrts-AG (DELAG), the world's first airline in revenue service. By mid-1914, DELAG had carried over 10,000 fare-paying passengers on over 1,500 flights. During World War I the German military made extensive use of Zeppelins as bombers and scouts, killing over 500 people in bombing raids in Britain.
The defeat of Germany in 1918 temporarily slowed down the airship business. Although DELAG established a scheduled daily service between Berlin, Munich, and Friedrichshafen in 1919, the airships built for this service eventually had to be surrendered under the terms of the Treaty of Versailles, which also prohibited Germany from building large airships. An exception was made allowing the construction of one airship for the US Navy, which saved the company from extinction. In 1926 the restrictions on airship construction were lifted and with the aid of donations from the public, work was started on the construction of LZ 127 Graf Zeppelin. This revived the company's fortunes, and during the 1930s the airships Graf Zeppelin and the larger LZ 129 Hindenburg operated regular transatlantic flights from Germany to North America and Brazil. The Art Deco spire of the Empire State Building was originally designed to serve as a mooring mast for Zeppelins and other airships, although it was found that high winds made this impossible and the plan was abandoned. The Hindenburg disaster in 1937, along with political and economic issues, hastened the demise of the Zeppelins.
The principal feature of Zeppelin's design was a fabric-covered rigid metal framework made up from transverse rings and longitudinal girders containing a number of individual gasbags. 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 framework of most Zeppelins was made of duralumin (a combination of aluminum and copper as well as two or three other metals— its exact content was kept a secret for years). Early Zeppelins used rubberised cotton for the gasbags, but most later craft used goldbeater's skin, made from the intestines of cattle.
The first Zeppelins had long cylindrical hulls with tapered ends and complex multi-plane fins. During World War I, following the lead of their rivals Schütte-Lanz Luftschiffbau, the design changed to the more familiar streamlined shape with cruciform tail surfaces, as used by almost all later airships.
They were propelled by several engines, mounted in gondolas or engine cars, which were attached to the outside of the structural framework. Some of these could provide reverse thrust for manoeuvring while mooring.
Early models had a comparatively small externally mounted gondola for passengers and crew which was attached to the bottom of the frame. This space was never heated (fire outside of the kitchen was considered too risky) so passengers during trips across the North Atlantic or Siberia were forced to bundle themselves in blankets and furs to keep warm and were often miserable with the cold.
By the time of the Hindenburg, several important changes had taken place: the passenger space had been relocated to the interior of the overall vessel, passenger rooms were insulated from the exterior by the dining area, and forced-warm air could be circulated from the water that cooled the forward engines, all of which made traveling much more comfortable though it deprived passengers of views from the windows of their berths which had been a major attraction on the Graf Zeppelin: on both the older and newer vessels, the external viewing windows were often opened during flight. The flight ceiling was so low that no pressurization of the cabins was necessary, though the Hindenburg did maintain a pressurized air-locked smoking room (no flame allowed, however— one electric lighter was maintained permanently inside the room).