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Rigid Airships

 

The Graf Zeppelin LZ-127 the most successful rigid airship.

The rigid airship contained an internal framework constructed of a lightweight but strong material providing a rigid structure within which were the lifting gas cells; machinery; fuel and living/working space. A separate cover went over the outside of the framework to provide streamlining and weatherproofing.

In a typical rigid airship, the hull structure was built upon a row of coaxial circular transverse frames, each kept in shape by a diaphragm of wire bracing which also served to divide the hull internally into compartments, each housing a gasbag. Longitudinal girders connected the peripheries of these frames and were in turn stabilised against axial buckling by further light intermediate transverse frames, which had open centres to clear the gasbags. The intersecting girders and frames divided the outer shell into rectangular panels, each of which was then wire braced to confer adequate rigidity upon the whole assembly.

Despite its essential simplicity, this structure presented unprecedented problems in stress analysis at the design stage. Never before had such large space structures been contemplated within the context of a rigorous weight limitation allied to highly speculative loading requirements. New techniques for load analysis were developed, based upon iterative procedures that still form the basis of much computer methodology; in the absence of such devices at the time, however, teams of analysts had to toil with slide rules and drawing boards for weeks on end, like the hypothetical host of monkeys typing Shakespeare, to unravel the load distributions and wire tensions for the assumed flight cases. As the wire bracing threw virtually all the structural members into compression, important advances were also initiated in the design of light-weight compression girders.

In construction, as well as in analysis and design, the rigid airship framework was labour-intensive to a degree that might now be dismissed as economically prohibitive; welding techniques for light alloys were still not commercially applicable, so the complex and fragile girders had to be riveted at thousands of small joints, while the whole grid of wire-braced panels had finally to be tuned like some vast piano in pursuit of an optimum load distribution.

The first rigid airships were built in the early 1900s, most famously by Ferdinand Count von Zeppelin, whose success with the type led to the name Zeppelin becoming synonymous with the concept of large airships built around an internal skeleton. Rigid airships were used to create the first scheduled passenger air-routes before the First World War, but were then expropriated for military purposes to become the first bombers. Due to the use of hydrogen as a lifting gas, the rigid airships were relatively easy to destroy with aeroplanes and made spectacular victories. After 1918, rigid airships were used both for military purposes by the Americans, and for civilian passenger transport by the Zeppelin Company.

Rigid Airships made the first east-west crossing of the Atlantic Ocean, the first aerial circumnavigation of the globe and were planned by the British government to open air-routes to India, Canada and South America.

The British experiment with rigid airships, as a means of connecting the empire, took the form of a public/private competition. The competition was held to see who could build a more suitable vehicle for trans-imperial routes private industry of government departments. Tragically, this competition came to an inglorious conclusion after the loss of the government built R 101. Despite the successful flights of the privately built R-100, the government terminated the Imperial Airship programme, and forced the scrapping of R-100 .

The Germans continued to build Zeppelins up until 1939, with the very successful Graf Zeppelin LZ-127, the Hindenburg LZ-129 and the later Graf Zeppelin II LZ-130, operating a scheduled transatlantic service up to 1938. The use of Rigid Airships for passenger transport came to an end with the Hindenburg disaster of 1937. The last designs of the pre-war Zeppelin company were intended to use helium as a lifting gas, but America (at the time the only supplier of helium) declined to sell supplies to Nazi Germany. Subsequent development of the aeroplane during the Second World War meant that further construction of rigid airships became uneconomical.

The U.S. Navy experimented with Rigid Airships throughout the 1920s and 1930s, culminating in the construction of two airship aircraft carriers USS Akron and USS Macon, each carrying five scout planes. These were used as airborne scouts for the American Fleet, but the conventional Navy never accepted the concept, and the destruction of both airships in accidents terminated any further official interest in the programme.

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