Editing Short Stirling (section)

===Prototypes===
The Air Ministry issued Shorts with contract number 672299/37, under which a pair of prototype S.29s was ordered.<ref name = "norris 3"/> However, prior to this, Shorts had decided to undertake a successful practice, which had been performed with the earlier Empire flying boat, in producing a half-scale version of the aircraft, known as the S.31 (also known internally as the M4 – as per the title on the tailfin), to prove the aerodynamic characteristics of the design.<ref name = "norris 3"/> The S.31, which was largely composed of wood, was powered by an arrangement of four [[Pobjoy Niagara]] engines and featured a retractable undercarriage, operable bomb-bay doors, and other measures to realistically represent the larger production aircraft. It was constructed at Short's [[Rochester, Kent|Rochester]] facility.<ref name = "norris 3 4">{{harvnb|Norris|1966|pp=3–4}}</ref>

[[File:Short S 31 Half Scale Stirling.jpg|thumb|left|The Short S.31 half-scale testbed used for aerodynamic tests of the Stirling design]]
On 19 September 1938, the S.31 conducted its [[maiden flight]], piloted by Shorts' Chief [[test pilot|Test Pilot]] [[John Lankester Parker|J. Lankester Parker]]. Impressed with its performance, on 21 October 1938, Parker flew the S.31 to [[RAF Martlesham Heath]], [[Suffolk]], where it was evaluated by the [[Aeroplane and Armament Experimental Establishment]] and received mostly favourable reviews.<ref name = "norris 4">{{harvnb|Norris|1966|p=4}}</ref> There was one notable criticism amongst the feedback from pilots, being that the length of the takeoff run was considered to be excessive and that improvements would be desirable. Fixing this required that the angle of the wing to be increased for takeoff; however, if the wing itself were<!-- subjunctive --> modified, the aircraft would fly with a nose-down attitude while cruising (as in the [[Armstrong Whitworth Whitley]]); making this change was also complicated by the fact that work on the production line had already reached an advanced stage. Thus, Shorts lengthened the undercarriage struts to tilt the nose up on take-off, leading to its spindly gear, which, in turn, contributed to many takeoff and landing accidents.<ref>{{Harvnb|Winchester|2005|p=49.}}</ref>

The S.31 also received the lengthened undercarriage to test this; subsequent trials found no need for further modification in this respect.<ref name = "norris 4"/> Other modifications made included the adoption of a larger tailplane with conventional [[Elevator (aeronautics)|elevator]]s to improve aft controllability. The sole S.31 was scrapped after a takeoff accident at [[RAF Stradishall]], Suffolk, in February 1944. Meanwhile, before either of the prototypes had flown, the Air Ministry had decided to order the S.29 into production "off the drawing board" in response to reports of further increases in strength on the part of the German [[Luftwaffe]].<ref name = "norris 3 4"/>

On 14 May 1939, the first S.29, which had by this point received the [[British military aircraft designation systems#Names|service name]] "Stirling" after the [[Stirling|Scottish city]], performed its first flight, but on landing, one of the brakes locked, causing the aircraft to slew off the runway and the landing gear to collapse. The resulting damage caused the first prototype to be written off.<ref name="norris 3"/><ref name="hallp5">{{harvnb|Hall|1998|p=5}}</ref><ref name="Story p30">{{harvnb|Bowyer|2002|p=30}}</ref> A resulting redesign of the undercarriage led to substantially stronger and heavier struts being installed upon the second prototype. On 3 December 1939, the second prototype made its maiden flight.<ref name = "norris 3"/>