The Short SA.4 Sperrin (named after the Sperrin Mountains, in Northern Ireland) was a British jet bomber design of the early 1950s built by Short Brothers and Harland of Belfast, popularly abbreviated ‘Shorts’. It first flew in 1951. The design was not an intended option for the Valiant bomber as has been suggested; but as a fall-back option in case the more advanced jet designs of the Vulcan and Victor V-bombers were delayed. It was not put into production however because these swept-wing designs were by then proven and available. The Sperrin prototypes were however valuable for research data on large jet aircraft.
Specification B.35/46 for a medium-range bomber that could carry a 10,000 pound [4,500 kg] bomb to a target 1,500 nautical miles [2,780 km] from a base anywhere in the world. The B.14/35 specification required that the fully laden weight would be under 100,000 lb (45 tonnes), the bomber should have a cruising speed of 500 knots (930 km/h) and a service ceiling of 50,000 feet (15,200 m). This request would be the foundation of the UK V-bombers.
However the Air Ministry accepted that the requirement might prove to be difficult to achieve in the time-scale required and prepared for a fall-back position. As early as 17 December 1946 the Air Ministry initiated drafting of an ‘insurance’ specification (B.14/46), first issued 11 August 1947, for a less ambitious conventional type of aircraft, with non-swept wings and some sacrifice in performance, as an insurance against failure to speedily develop the more advanced types that evolved into the Vulcan and Victor. The only significant performance changes specified by B.14/46 were a lower speed of 435 knots (806 km/h) and a lower height over the target of 35,000 ft (11,000 m) to 45,000 ft (14,000 m) so under this requirement they placed a contract for two flying prototypes and a static airframe with Shorts. As a possible production aircraft, the Sperrins were built on production jigs, which dramatically slowed their construction.
The design, known initially as SA.4 and later as the "Sperrin", had more in common with the Second World War designs than the new jet age. It was straight winged, although the leading edge was slightly swept. The engines were mounted in nacelles mid-wing, two engines per wing, with one engine stacked above the other. The airframe was built largely of aluminium alloys with a tricycle undercarriage (nose wheel and two, four-wheel bogies), the nose gear retracting backward and the main gear in the wings towards the fuselage. The SA.4 was designed for a crew of five: pilot, copilot, bombardier ("air bomber"), navigator and radio operator. The prone bombardiers position was a tube extending forward of the cockpit above the radome; the crew compartment being pressurized. The prototypes were fitted with opaque nosecones as they were never used for live bombing. An ejection seat and accompanying hatch was fitted for the pilot alone. The three crew positions behind the pilots faced backward. The crew entrance was below.
The first prototype (serial VX158), powered by four Rolls-Royce Avon RA.2 engines of 6,000 lb thrust and piloted by Tom Brooke-Smith, made its maiden flight on 10 August 1951. By this time, in the light of the latest knowledge, and the fact that the Valiant project was now proceeding well and only six months behind the Sperrin, the judgement of the Air Ministry was that an insurance project was now no longer needed, and a decision was taken to order the Vickers Valiant in larger quantities and the Sperrin project was cancelled.
The Ministry of Supply subsequently determined that the Sperrin would serve as a research aircraft for the V-bomber programme. Work on the two prototypes was continued, with the second prototype (VX161) flying on 12 August 1952 with Sqn Ldr "Wally" Runciman at the controls, accompanied by Flight Test Development Engineer Malcolm Wild. It was fitted with more powerful Avon RA.3s of 6,500 lbf (28.1 kN) thrust.
Both Sperrins were used in a variety of research trials through the 1950s, including engine tests using VX158 as a testbed for the de Havilland Gyron turbojet - a large engine delivering 15,000 lbf (66.7 kN) thrust. The first flight of VX158 with a new engine ‘fit’ took place on 26 June 1956, with Jock Eassie and Chris Beaumont at the controls. During this flight the port outer undercarriage cover fell off. Aircraft #2, VX161 was flown over from Farnborough and its corresponding cover was used to repair VX158. VX161 never flew again and was scrapped at Sydenham in 1957. VX158 was flown at the Farnborough Airshow in 1956 (photo #2) with two Avons and two Gyrons fitted but six months later the Gyron programme was discontinued and VX158 was scrapped at Hatfield in 1958. Among other test work, VX161 (which had a fully operational weapons bay) was involved in trials relating to bomb shapes with mock-ups of the Blue Danube nuclear bomb and the Blue Boar missile.
Specifications first prototype (VX158)
Crew: Five (pilot, co-pilot, bombardier, navigator and radio operator)
Length: 102 ft 3 in (31.14 m) Wingspan: 109 ft (33.2 m) Height: 28 ft 6 in (8.69 m) Empty weight: 72,000 lb (33,000 kg. Max takeoff weight: 115,000 lb (52,200 kg) Engines: 4x— Rolls-Royce Avon turbojet, 6,000 lbf (27 kN) each. Fuel capacity: 6,200 gallons
Maximum speed: 564 mph (490 knots, 912 km/h) at 15,000 ft.
Cruise speed: 435 knots at 40,000 ft. Range: 3,200 mi (2,800 nm, 5,150 km) Ceiling: 45,000 ft (13,700 m) Wing loading: 60.6 lb/sq ft.
Armament: Bombs: 20,000 lb maximum. Across the two aircraft, the Sperrin had four different engine configurations:
Comparable aircraft:
Convair XB-46
English Electric Canberra
Ilyushin Il-28
Martin XB-48
North American B-45
Tupolev Tu-14
With such an historic and interesting aircraft it's a pity no one has produce an injection mould kit. Only one model exists and that is from S&M in 1/144. The model is mostly solid resin and weighs a ton, so the undercarriage needs to be completely rebuilt to take the weight.The wheels are complete rubbish and totally inaccurate so the perfect solution is four wheels from a spare Revell Arado E555 , the hub detail being almost perfect.The nose wheels are resin and also need replacing. Also missing were the three trim tab on the port side of the rudder , easily made up from scrap card. The same kit was issued by 'Anigrand' but they included a complimentary Javelin, Lightning and Harrier for company.
The fuselage cross section is a bit too boxy and needs to be completely filed and sanded to a more rounded cross section.This in turn leads to a major problem in that the vac form canopy is squared off and has to be heated ( gently), and given a coat of Kleer to get it to conform to the new fuselage shape ( thankfully they provide you with two of these !!)..Next problem was that there are NO window shapes on the vac so it's back to the reference pics ( of which I have a rather large collection now!!).
Apart from the rather fetching Farnborough scheme both a/c remained in natural metal for the rest of their development life.
