Profile Publications No. 142 The Short Stirling

Rare flying view o f the S.3I. Powered by four 90 h.p. Pobjoy Niagaras, the"m ini-Stirling" made its maiden flight on 19th September 1938, in great secrecy the pilot was John Lankester Parker. Rochester factory. This was the S.31, a fairly faithful miniature of the full-sized aircraft accommodating a pilot and observer in tandem. Slipstream effects were realistically reproduced, a retractable undercarriage was fitted and bomb doors could be opened to give an idea of their effect on the full-size aircraft. The S.31 used awing which was derived from that of the Scion Senior and was powered by four Pobjoy Niagara 111 seven-cylinder engines each developing 90 h.p. The maiden flight was made by Shorts' Chief Test Pilot, John Lankester Parker, from Rochester Airport on 19th September 1938, and was an occasion of great secrecy. Early test flights with the S.31 convinced Lankester Parker that the basic concept was good and on 21st October he flew the machine to the Aeroplane and Armament Experimental Establishment at Martlesham Heath where military test pilots were equally impressed by the aircraft’s handling properties. They asked, however, for an improvement in take-ofT performance as they could visualise a considerable increase in the all-up-weight of the full-sized aircraft The half-scale wooden S.31 prototype in its pre-war colours. The S.31 in warpaint. as military demands became greater. Their precise recommendation was for an increase of three degrees in the wing incidence which had been set at the optimum of 3+ degrees for minimum cruise drag. Unfortunately work on the Stirling production line had, by this time, reached a stage where such a modification was out of the question for reasons of both time and money so Shorts adopted a compromise solution of increasing the ground angle by three degrees through lengthening the undercarriage. This modification was also incorporated into the S.31 which, at the end of 1938, was re-engined with Pobjoy Niagara IVs which each developed 115 h.p. Trials of the S.31 revealed no need for further major modifications. There was some control difficulty with an aft e.g. and horn-balanced elevators were fitted. These were, in turn, replaced by a larger tailplane with normal elevators. As the last of the minor aerodynamic difficulties were being ironed out of the S.31 during the first months of 1939, so the construction of the two full- scale prototypes, L7600 and L7605, was nearing completion. Lankester Parker took L7600 into the air for the first time on 14th May 1939, and the aircraft handled satisfactorily throughout the twenty- minute test. Then came an incredible stroke of bad luck. As the Stirling landed one brake seized and the stalky undercarriage collapsed. The resulting damage caused the aircraft to be written off'. This was a set-back to the entire Stirling programme. The undercarriage was redesigned and strengthened but L7605 was not ready for flight testing until 3rd December 1939, when it made a successful half hour sortie with the undercarriage locked down. A second flight was made on Christmas Eve when the wheels were retracted and trials proceeded satis­factorily from then on. The maiden flight of N3635, the first production aircraft, took place five months later on 7th May. STIR LING CONSTRUCT ION The Stirling I was a mid-wing cantilever monoplane powered by four Bristol Hercules engines. Its wing 4
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