Short Sperrin

The Short SA.4 Sperrin (named after the Sperrin Mountains) 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 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.


Short Sperrin
Class Aircraft
Type Bomber
Manufacturer Short Brothers
Origin United Kingdom - UK (Great Britain)
Country Name Origin Year
United Kingdom - UK (Great Britain) 1951
Country Name Operational Year Retirement Year
United Kingdom - UK (Great Britain) 1951 1958 View
ManufacturerName Production From Production To Quantity
Short Brothers 2 View

The Air Ministry issued a specification on 11 August 1947 B.14/46 for a "medium-range bomber landplane" that could carry a "10,000 pound [4,500 kilogram] bomb to a target 1,500 nautical miles [2,780 kilometres] from a base which may be anywhere in the world", with the stipulation it should be simple enough to maintain at overseas bases. The exact requirements also included a weight of 140,000 lb (64 t). The B.35/46 specification required that the fully laden weight would be under 100,000 lb (45 t), the bomber have a cruising speed of 500 knots (580 mph; 930 km/h) and that the service ceiling would be 50,000 ft (15,000 m). This request would become the foundation of the Royal Air Force's V bombers, Britain's airborne nuclear deterrent.

At the same time, the British authorities felt there was a need for an independent strategic bombing capability—in other words that they should not be reliant upon the American Strategic Air Command. In late 1948, the Air Ministry issued their specification B.35/46 for an advanced jet bomber that should be the equal of anything that either the Soviet Union or the Americans would have. The exact requirements included that the fully laden weight would be under 100,000 lb (45.36 t), the ability to fly to a target 1,500 nautical miles (1,700 mi; 2,800 km) distant at 500 knots (580 mph; 930 km/h) with a service ceiling of 50,000 ft (15,000 m) and again that it should be simple enough to maintain at overseas bases. A further stipulation that a nuclear bomb (a "special" in RAF jargon), weighing 10,000 lb (4,500 kg) and measuring 30 ft (9.1 m) in length and 10 ft (3.0 m) in diameter, could be accommodated. This request would be the foundation of the 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 by re-drafting B.14/46 as an "insurance" specification against failure to speedily develop the more advanced types that evolved into the Vickers Valiant, Avro Vulcan and Handley Page Victor, as this was to be a less ambitious conventional type of aircraft, with un-swept wings and some sacrifice in performance. The only significant performance differences between B.14/46 and the more advanced B.35/46 were a lower speed of 435 knots (806 km/h) and a lower height over the target of 35,000 to 45,000 ft (11,000 to 14,000 m). According to aviation authors Bill Gunston and Peter Gilchrist, the specification's ignorance of a swept wing was odd for the era, and had been made in order to allow the perspective bomber to be delivered more quickly.

A total of four firms submitted tenders to meet the B.14/46 specification, Shorts' submission was selected as it had been judged to be superior. The selection of Shorts was "astonishing" according to Bill Gunston and Peter Gilchrist, and noted that their submission, while being a sound design, had apparently been subject to luck. Under this requirement, the Air Ministry placed a contract for two flying prototypes and a static airframe with Shorts. The design was known initially by the company designations of SA.4 and SA.4; the aircraft would later receive the name "Sperrin".

As the Sperrin was considered to be a possible production aircraft early on, a decision was taken for the two prototypes to be constructed upon production jigs; this served to slow their construction. Bill Gunston and Peter Gilchrist commented that, if a subsequent production order had been issued, an initial operational squadron could have been equipped by late 1953.

The first prototype (serial VX158), powered by four Rolls-Royce Avon RA.2 engines of 6,000 lbf (27 kN) of thrust and piloted by Tom Brooke-Smith, had 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 instead of the Sperrin and the Sperrin project was cancelled, although the Ministry of Supply determined that the Sperrin would serve as a research aircraft. 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 (29 kN) thrust.

The two 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 (67 kN) thrust. The Gyron Gy1 replaced the lower Avon in the port nacelle (see image). For the first flight with this engine configuration on 7 July 1955. VX158 was piloted by Jock Eassie and Chris Beaumont. Testing with this asymmetric engine configuration continued until March 1956, when the single Gyron Gy1 was removed and two Gyron Gy2 engines, each providing 20,000 lbf (89 kN) thrust, were fitted, one in each engine nacelle below the original Avon RA.2s.

The first flight of VX158 with the new engine configuration took place on 26 June 1956, again with "Jock" Eassie and Chris Beaumont at the controls. During this flight the port outer undercarriage cover fell off; 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 with two Avons and two Gyrons fitted but six months later the Gyron programme was discontinued and VX158 was scrapped at Hatfield in 1958.

A photograph of VX158 with both Gyrons fitted can be seen in C.H. Barnes' and D.N. James' definitive work, "Shorts Aircraft since 1900".

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 television-guided glider bomb.

Role Experimental aircraft
Manufacturer Short Brothers and Harland, Belfast
First flight First prototype: 10 August 1951
Second prototype: 12 August 1952
Retired First prototype: 1958
Second prototype: 1957
Primary user Royal Air Force (intended)
Number built 2


General characteristics

  • Crew: Five (pilot, co-pilot, bombardier, navigator and radio operator)
  • Length: 102 ft 3 in (31.16 m)
  • Wingspan: 109 ft (33.2 m)
  • Height: 28 ft 6 in (8.68 m)
  • Wing area: 1,896 ft² (176.1 m²)
  • Airfoil: A.D.7
  • Empty weight: 72,000 lb (32,659 kg)
  • Max. takeoff weight: 115,000 lb (52,164 kg)
  • Powerplant: 4 × Rolls-Royce Avon turbojet, 6,500 lbf (29.0 kN) each
  • Fuel capacity: 6,200 gallons

Performance

  • Maximum speed: 564 mph (490 knots, 907 km/h) at 15,000 ft (4,600 m)
  • Cruise speed: 500 mph (435 knots, 805 km/h) at 40,000 ft (12,200 m)
  • Range: 3,860 mi (3,350 nm, 6,211 km)
  • Service ceiling: 45,000 ft (13,716 m)

Armament

  • Bombs: 20,000 lb maximum

End notes