page_title: Short Sperrin
section_title: Design
hierarchical_section_title: Short Sperrin / Design
caption_attribution_description: A Short SA.4 Sperrin (serial VX158) at the Farnborough Airshow in 1956.
context_page_description: The Short SA.4 Sperrin was a British jet bomber design of the early 1950s, built by Short Brothers and Harland of Belfast. It first flew in 1951. From the onset, the design had been viewed as a fall-back option in case the more advanced strategic bomber aircraft, then in development to equip the Royal Air Force's nuclear-armed V bomber force, experienced delays; the Sperrin was not put into production because these swept-wing designs, such as the Vickers Valiant, were by then available.
  As their usefulness as an interim bomber aircraft did not emerge, a pair of flying prototypes were instead used to gather research data on large jet aircraft and to support the development of other technologies, such as several models of jet engines. The two aircraft completed were retired in the late 1950s and ultimately scrapped sometime thereafter.
context_section_description: Many design elements of the Sperrin had more in common with aircraft of the Second World War than those of the new jet age. The design was relatively straightforward in most aspects, with the exceptions of the flight controls and the unusual engine arrangement: The four engines were mounted in pairs in nacelles mid-wing, one engine being stacked above the other. VX-158 had the distinction of being the first aircraft to receive production Rolls-Royce Avon engines; other engines such as improved Avon models and the de Havilland Gyron would also be installed on the two prototypes for test purposes. The airframe was built largely of light aluminium alloys, principally 75ST; the light-alloy stressed-skin had a very smooth surface which contributed to the low drag of the aircraft.
  The Sperrin employed a traditional straight wing, although the fixed leading edge was slightly swept and featured curved fillets at the junction with the engine nacelles. The trailing edge had simple flaps inboard of the nacelles and large ailerons outboard; the outer flaps were to incorporate air brakes, but were replaced with split-brakes prior to the first flight. Both the flaps and air brakes were operated hydraulically, with an independent system for emergency actuation. Up to 6,170 imperial gallons of fuel could be housed in a total of 22 fuel tanks, 14 of these in the wings and 8 in the fuselage; the tanks were pressurized to prevent collapse during fast dives and other manoeuvres. The wing was located in a mid position on the fuselage between the bomb bay and fuselage fuel tanks.
  The fuselage of the Sperrin consisted of separate nose, centre, and tail sections, which were constructed as single units; the upper area of the forward fuselage contained the pressurized drum for the crew, while the lower part of the forward fuselage, which initially contained concrete ballast, was intended to house the H2S Mk.9 airborne radar behind a fibreglass radome. There was a flat window for visual aiming. The centre fuselage had four heavy transverse beams, with fixings for the mainplanes.  Neither armament nor countermeasures were installed in either of the prototypes; according to Bill Gunston and Peter Gilchrist, the required bombload of 20,000 lb (9,100 kg) would have been easily achievable and could have been increased. Separate bomb bay and camera doors were fitted to suit either aerial reconnaissance or bombing missions.
  The Sperrin was equipped with a tricycle undercarriage (a twin-wheel nosewheel and a pair of four-wheel bogies). The nose gear retracted backwards and the main gear into the wings towards the fuselage. A safety circuit prevented retraction of the landing gear until a sufficient air speed had been reached. The nose-wheel was steerable which was unusual for a British aircraft, the Sperrin being one of the first British aircraft to be fitted with one; the landing gear was operated by a Messier hydraulic system. A 24/28-volt DC electrical system was supplied by two generators; both generators and a compressor for cabin pressure were driven from two accessory gearboxes that were housed within the wings.
  The SA.4 was designed for a crew of five: pilot, copilot, bomb-aimer, navigator and air signaller (later called air electronics officer). The prone bomb aimer's position was a tube extending forward of the cockpit above the radome. It was fitted with an opaque nosecone, as the Sperrin was never used for visual bomb aiming. The pilots were the only crew members to have Martin-Baker ejector seats and these were positioned beneath a jettisonable roof panel; other crew members had to bail out through a door under the navigator's console from their rear-facing positions located behind the pilots. Unusual for an aircraft of this size, the flying controls were manually operated using servo tabs, a feature also used on the Bristol Britannia; artificial feel was also incorporated. Bill Gunston and Peter Gilchrist describe the control system as having been simple, light, reliable, and low-friction and contrast it positively against powered systems of
caption: Short Sperrin in flight, 1956
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