A rigid airship is a type of airship (or dirigible) in which the envelope is supported by an internal framework rather than by being kept in shape by the pressure of the lifting gas within the envelope, as in blimps (also called pressure airships) and semi-rigid airships. Rigid airships are often commonly called Zeppelins, though this technically refers only to airships built by the Luftschiffbau Zeppelin company.
In 1900, Count Ferdinand von Zeppelin successfully performed the maiden flight of his first airship; further models quickly followed. Prior to the First World War, Germany was a world leader in the field, largely attributable to the work of von Zeppelin and his Luftschiffbau Zeppelin company. During the conflict, rigid airships were tasked with various military duties, which included their participation in Germany's strategic bombing campaign. Numerous rigid airships were produced and employed with relative commercial success between the 1900s and the late 1930s. The heyday of the rigid airship was abruptly ended by the destruction of the Hindenburg by fire on 6 May 1937. The disaster not only destroyed the biggest zeppelin in the world, but the film caused considerable reputation damage to rigid airships in general. Several nations had ended military rigid airship programs after serious accidents earlier in the decade, but widespread public safety concerns in the wake of the Hindenburg disaster led several nations to permanently ground their existing rigid airships and scrap them in subsequent years.
Construction and operation Rigid airships consist of a structural framework usually covered in doped fabric containing a number of gasbags or cells containing a lifting gas. In the majority of airships constructed before the Second World War, highly flammable hydrogen was used for this purpose, resulting in many airships such as the British R101 and the German Hindenburg being lost in catastrophic fires. The inert gas helium was used by American airships in the 1920s and 1930s; it is also used in all modern airships.
Airships rely on the difference in density between the lifting gas and the surrounding air to stay aloft. Typically airships start a flight with their gasbags inflated to about 95% capacity: as the airship gains height the lifting gas expands as the surrounding atmospheric pressure reduces. As the surrounding atmospheric pressure decreases, the lifting gas expands, displacing ambient air. When the entire envelope is filled with expanded lifting gas, the aircraft is at its pressure height, which is generally the maximum operational ceiling. At this point, excess expanding gas must either be vented or the airship must descend so that the lifting gas can contract and ambient air brought back into the hull.
Airships can also generate a certain amount of aerodynamic lift by using their elevators to fly in a nose-up attitude. Similarly, by flying nose-down, down-force can be generated: this may be done to prevent the airship rising above its pressure height.
History
Early history By 1874, several people had conceived of a rigid dirigible (in contrast to non-rigid powered airships which had been flying since 1852). The Frenchman Joseph Spiess had patented a rigid airship design in 1873 but failed to get funding.Dooley A.174 citing Hartcup p89 Another such individual was the German Count Ferdinand von Zeppelin, who had outlined his thoughts of a rigid airship in diary entries from 25 March 1874 through to 1890 when he resigned from the military.Dooley A.175
The concept of a metal-clad dirigible airship was again explored in the late 1800s by Russian rocket theorist Konstantin Eduardovich Tsiolkovsky.Von A. Kosmodemyansky, X. Danko. 2000. Konstantin Tsiolkovsky His Life and Work The Minerva Group, Inc., . He wrote that since his teens (in the early 1870s) "the idea of the all-metal aerostat has never left my mind" and by 1891 he had produced detailed designs of a variable volume corrugated metal envelope airship that did not need ballonets.
David Schwarz had thought about building an airship in the 1880s and had probably started design work in 1891: by 1892, he had started construction.Dooley A.183 However, Schwarz's all-aluminium airship would not perform any test flights until after his death in 1897. Schwarz had secured help in its construction from the industrialist Carl Berg and the Prussian Airship Battalion; there was an exclusive contract in place between Schwarz and Berg, thus Count Zeppelin was obliged to reach a legal agreement with Schwarz's heirs to obtain aluminium from Carl Berg, although the two men's designs were different and independent from each other: the Schwarz design lacked the separate internal gasbags that characterise rigid airships.Dooley A.184-A.196 Using Berg's aluminium, von Zeppelin was able to start building his first airship, the LZ 1, in 1898.Robinson 1973 p. 23.
First practical rigid airships
During July 1900, Ferdinand von Zeppelin completed LZ 1. Constructed in a floating shed on Lake Constance, it was 128.02 m (420 ft) long, 11.73 m (38 ft 6 in) in diameter with a volume of 11,298 m3 (399,000 ft 3) and was powered by a pair of 11 kW (14 hp) Daimler engines. The first flight, lasting 20 minutes, was made on 2 July, but ended with the airship being damaged. After repairs and modifications, two further flights were conducted in October 1900.Robinson 1973, pp. 23–24. However, these initial experiments failed to attract any investors, and Count Zeppelin did not complete his next design, LZ 2, until 1906. This performed only a single flight on 17 January 1906, during which both engines failed and the zeppelin was compelled to conduct a forced landing in the Allgäu mountains; it was subsequently damaged beyond repair by a storm.Robinson 1973, p. 29. Undeterred, Zeppelin quickly completed another airship with a largely similar design, the LZ 3, and put it into flight.Brooks 1992, p. 34.
LZ 3 proved to have performed sufficiently to interest the German Army, who opted to purchase and operate it as the Z I until 1913. Even so, the German Army observed that they required an airship that would be capable of flying for 24 hours. As this was beyond the capability of LZ 3, it was decided to design and construct a larger craft, LZ 4. This was 136 m (446 ft) long, 12.95 m (42 ft 6 in) in diameter and powered by two Daimler engines delivering a total of 156 kW (210 hp).Robinson 1973, p. 331. LZ 4 first flew on 20 June 1908, and on 1 July made a spectacular 12 hour cross-country flight during which it was flown over Switzerland to Zürich and then back to Lake Constance. The 24-hour trial was started on 4 August, but was interrupted by the failure of one of the engines. It was moored near Echterdingen in order to make repairs but a storm arose, causing it to break away from its moorings, after which it was blown into some trees and caught fire.Robinson 1973, pp. 34-35. The disaster took place in front of an estimated 40 to 50 thousand spectators, and produced an extraordinary wave of nationalistic support for von Zeppelin's work. Unsolicited donations from the public poured in: enough had been received within 24 hours to rebuild the airship, and the eventual total was over 6 million marks were donated, finally giving Count Zeppelin a sound financial base for his experiments.Robinson 1973, p. 41.
Seven zeppelins were operated by DELAG, the first airline in the world. DELAG was founded at the suggestion of Alfred Colsman, the business manager of Zeppelin Luftschiffbau, seeking to capitalise on the German public's enthusiastic interest in the zeppelin by permitting them onboard passenger-carrying airships as a commercial venture; von Zeppelin distanced himself from this commercialisation, reportedly regarding such efforts to have been a vulgar tradesman's enterprise.Robinson 1973, p. 52. Commencing such flights in 1910, DELAG was initially limited to offering pleasure cruises in the vicinity of the existing zeppelin bases.Robinson 1973, p. 55.
DELAG soon received more capable zeppelins, such as the LZ 10 Schwaben, which would carry a total of 1,553 paying passengers during its career, which involved not only pleasure flights but a number of long-distance flights to destinations such as Frankfurt, Düsseldorf, and Berlin.Robinson 1973, p. 59. The company's airships were also used by the Imperial German Navy for crew training, with the Navy crews operating passenger flights.Robinson 1973, p. 61. By July 1914, one month prior to the start of the First World War, DELAG's Zeppelins had transported a total of 34,028 passengers on 1,588 commercial flights; over these trips, the fleet had accumulated 172,535 kilometres across 3,176 hours of flight."Zeppelin-Wegbereiter des Weltluftverkehrs", 1966. Commercial operations came to an abrupt end in Germany due to the outbreak of the First World War, after which DELAG's airships were taken over by the German Army for wartime service.
During 1911, the first rigid airship produced by the German Schütte-Lanz company was flown. Designed by the naval architect Johann Schütte, the Schütte-Lanz introduced a number of technical innovations. The shape of the hull was more streamlined than the early Zeppelin craft, the hulls of which were cylindrical for most of their length, simplifying construction at the expense of aerodynamic efficiency. Other Schütte-Lanz innovations included the use of an axial cable running the length of the airship to reduce additional stressing caused by the partial deflation of a single gasbag, the introduction of venting tubes to carry any hydrogen vented to the top of the ship and simplified cruciform tail surfaces.
The British Royal Navy took an early interest in rigid airships and ordered His Majesty's Airship No. 1 in 1909 from Vickers Limited at Barrow-in-Furness. It was 512 ft (156.06 m) long with two Wolseley engines. It was completed in 1911 but broke in two before its first flight and was scrapped.Patrick Abbott and Nick Walmsley, British Airships in Pictures: An Illustrated History, House of Lochar 1998, (pp.20–21) This caused a temporary halt to British airship development, but in 1913 an order was placed for HMA No. 9r. Due to various factors, including difficulties in acquiring the necessary materials, it was not completed until April 1917.Higham 1961, pp. 347-348.
France's only rigid airship was designed by Alsatian engineer Joseph Spiess and constructed by Société Zodiac at the Aérodrome de Saint-Cyr-l'École. It had a framework of hollow wooden spars braced with wire, and was given the name Zodiac XII but had the name SPIESS painted along the side of the envelope. It was 113 m (370 ft 9 in) long, with a diameter of 13.5 m (44 ft 3 in) and was powered by a single Chenu 200 hp engine that drove two propellers. It first flew on 13 April 1913, but it became clear that it was underpowered and required more lift, so it was lengthened to 140 m (459 ft 4 in) to accommodate three more gas cells and a second engine was added. Spiess then presented the airship to the French government as a gift. After further trials it was not accepted by the French military, because their view was that smaller non-rigid types would be more effective. The Spiess airship seems to have been broken-up in 1914.
First World War