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The R31 class of British rigid airships was constructed in the closing months of World War I and comprised two aircraft, R31 and R32.
R31 was built on Schutte-Lanz lines with wooden girders. It had a length of 615 feet, a diameter of 66 feet and a capacity of 1,500,000 cubic feet.
They were designed by the Royal Corps of Naval Constructors – with assistance from a Herr Müller who had defected to Britain and previously worked for the Schütte-Lanz airship company – and built by Short Brothers at the Cardington airship sheds. The airship frame was made from spruce plywood laminated into girder sections, weatherproofed with varnish, and also fireproofed. These enclosed 21 gas bags. R31 was the largest British airship to fly before the end of the war, and the class remains the largest mobile wooden structures ever built.
As the airships were intended for fleet protection operations, they were to be fitted with defensive machine guns on top of the envelope, at the stern and in the gondolas. A 12-pounder gun was to be fitted in a special position centrally below the airship for use against U-boats. In the event, this armament was only fitted to R31, as R32 was only completed after the armistice with Germany.
It had also been intended to fit a bomb load of two 520 lb bombs and four 230 lb bombs. but with the end of hostilities these were never installed on either airship.
R31 made her first trial flight of two hours in July 1918 under the command of Squadron Leader W.C. Hinks. A top speed of 70 mph was achieved: well above the expected 50–55 mph and faster than any other airship then in service.
She was originally powered by six 275 hp (205 kW) Rolls-Royce Eagle engines, but in view of the performance and to reduce fuel consumption one was removed, reducing the maximum speed to a still satisfactory 65 mph; and similarly the R32 was built with six engines and later converted to a five-engine configuration.
The airship was finally commissioned on 6 November 1918, just before the armistice with Germany, after having spent four hours in the air. She set off again under the command of Squadron Leader Hincks for the airship base at East Fortune in Scotland. On the journey she encountered bad weather and it was feared that some of the plywood girders were failing, so she diverted to the airship base at Howden, East Riding of Yorkshire, for examination and repair. Unfortunately, the sheds had not been repaired after the R27 caught fire and the roof in particular leaked badly. This caused the glue holding the plywood together to deteriorate; as a result, the airship became un-airworthy and in February 1919 she was dismantled. The covering was removed and returned to Cardington and the frames sold for £200. As a final irony, these were broken up and sold for firewood but, because of the fireproofing treatment, they would not burn.