Short Stirling

Origins In the 1930s, the Royal Air Force (RAF) was interested primarily in twin-engined bombers. The aircraft should also be able to be used as a troop transport for 24 soldiers and be able to use catapult assistance for takeoff when heavily laden. Since it could be operating from limited "back country" airfields, it needed to lift off from a runway and be able to clear trees at the end, a specification with which most small aircraft would have a problem today. Aviation author Geoffrey Norris observed that the stringent requirements given in the specification for the prospective aircraft to be able to make use of existing infrastructure, specifically the specified maximum wingspan of 100 feet, adversely affected the Stirling's performance, such as its relatively low ceiling and its inability to carry anything larger than 500 lb bombs. In mid-1936, Specification B.12/36 was sent out to Supermarine, Boulton Paul, Handley Page, and Armstrong Whitworth. In August, the specification was issued to the rest of British industry. Shorts accepted this large amount of redesign work. The project had added importance due to the death of Supermarine's designer, Reginald Mitchell, which had generated doubt within the Air Ministry about the ability of Supermarine to deliver. Two prototypes were ordered from Shorts. The S.29 used the Sunderland's wing and it had to be reduced to less than In June 1937, the S.29 was accepted as the second string for the Supermarine Type 317 and formally ordered in October; Shorts and Supermarine were issued with instructions to proceed. On 19 September 1938, the S.31 conducted its maiden flight, piloted by Shorts' Chief Test Pilot 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. 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 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. The S.31 also received the lengthened undercarriage to test this; subsequent trials found no need for further modification in this respect. 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. In August 1940, series production of the Stirling commenced at the Rochester factory. Production of the Stirling was delayed by the ongoing bombing campaign of the Luftwaffe. The area, which included a number of major aviation firms, was heavily bombed in the opening days of the Battle of Britain, including one famous low-level raid by a group of Dornier Do 17s. A number of completed Stirlings were destroyed on the ground and the factories were heavily damaged, setting back production by almost a year. Some production was moved to Austin's Longbridge factory at Cofton Hackett just south of Birmingham, the Longbridge production line eventually produced nearly 150 Stirlings. From this point on, the Belfast factory became increasingly important, as it was thought to be well beyond the range of German bombers. However, Belfast and the aircraft factory were subjected to bombing by German aircraft during the Easter week of 1941. To meet the increased requirement for its aircraft during the war, satellite factories near Belfast were operated at Aldergrove and Maghaberry, producing 232 Stirlings between them. In 1940, bombing damaged Supermarine's factory at Woolston and the incomplete Type 316 prototypes. In November 1940, development of the 316 was formally cancelled, leaving the Stirling as the only B.12/36 design. The first few Stirling Mk.Is were furnished with Bristol Hercules II engines, but most were built with more powerful Hercules XI engines, instead. Total production of the bomber variants was 1759 aircraft, divided among four locations, as follows: • Short Brothers plant, Belfast: 261 Mk.I and 342 Mk.III • Short Brothers plant, Rochester, later relocated to the shadow factory of South Marston: 260 Mk.I and 276 Mk.III • Austin Motors plant, Longbridge: 181 Mk.I and 429 Mk.III Another 610 aircraft were built directly as Mk.IV and Mk.V transports/glider tugs. Proposed developments Even before the Stirling went into production, Short had improved on the initial design with the S.34 in an effort to meet specification B.1/39. It would have been powered by four Bristol Hercules 17 SM engines, optimised for high-altitude flight. The new design featured longer-span wings and a revised fuselage able to carry dorsal and ventral power-operated turrets each fitted with four 20 mm Hispano cannons; despite the obvious gains in performance and capability, the Air Ministry was not interested. In 1941, it was decided that the Stirling would be manufactured in Canada and an initial contract for 140 aircraft was placed. The S.37 was a fully-furnished transport aircraft that was capable of seating 30 passengers and was constructed to conform with civilian standards. A prototype, known as the Silver Stirling, was converted from a Mk.V aircraft; partly due to greater levels of interest being expressed for a more promising civilian version of the Handley-Page Halifax, the proposal met with little official interest. In 1941, Short proposed the development of a new variant of the Stirling, the S.36, which was nicknamed the "Super Stirling" in a company publication. ==Design==