Short Sperrin

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SA.4 Sperrin

Type	Experimental aircraft
Manufacturer	Short Brothers and Harland, Belfast
Maiden 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

The Short SA.4 "Sperrin" (named after the Sperrin Mountains, a range of hills in Northern Ireland) was a British jet bomber design of the early 1950s built by Short Brothers and Harland of Belfast. It first flew in 1951.

1 Design and development
- 1.1 Design
2 Testing
3 Specifications first prototype (VX158)
4 References
5 Related content

[edit] Design and development

In the post-Second World War war period, 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.14/46 ^[1]for an advanced jet bomber that should be the equal of anything that either the Soviet Union or the Americans would have. The exact requirments included a weight of 140,000 lb, the ability to fly to a target 1,739 miles distant at 500 knots from altitudes of 45,000-50,000 ft and be simple enough to maintain at overseas bases. A further stipulation that a "special" in RAF jargon, a nuclear bomb, weighing 10,000 lb and measuring 30 ft (length) and 10 ft (diameter) could be accommodated.

There had already been specification "B.35/46" the previous year 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 kilometers] from a base which may be anywhere in the world."^[2]

The 1947 request anticipated that the fully laden weight would be under 100,000 lb (45.4 tonnes), the bomber have a cruising speed of 500 knots and that the service ceiling would be 50,000 feet (15,200 m). This request would be the foundation of the V-bombers.

However the Air Ministry accepted that the request might prove to be beyond the reach of Britain's aircraft manufacturers and prepared for a fall-back position in the form of an earlier specification B.14/46 which was more conservative in its demands and under this they placed a contract for two flying prototypes and a static-test machine with Shorts.

[edit] Design

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 tricycle undercarriage. 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, navigator, and radio operator, though only the pilot had an ejection seat.

[edit] Testing

By the time the first prototypes were ready, the project was already cancelled, although the Ministry of Supply in 1950 determined that the Sperrin would serve as a research aircraft. The first prototype (VX158) powered by four Rolls-Royce Avon RA.2 engines of 6,000 lbs of thrust, piloted by Tom Brooke-Smith had its maiden flight on 10 August 1951. Work on the two prototypes was continued with the second prototype (XV161) flying on 12 August 1952 with S/L "Wally" Runciman^[3] 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.

First prototype Sperrin with one Gyron Gy1 engine fitted below the Avon on the left wing

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 (66.7 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 lbs 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.^[4] VX158 was flown at the Farnborough Air Show 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".^[5]

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" ^[6].

Among other test work, VX161 (which had a fully operational weapons bay) was involved in trials relating to bomb shapes with concrete mock-ups of the Blue Danube nuclear bomb and the Blue Boar missile. Neither project was continued.

[edit] Specifications first prototype (VX158)

General characteristics

Crew: 5
Length: 102 ft 2 in (31.14 m)
Wingspan: 109 ft (33.2 m)
Height: 28 ft 6 in (8.69 m)
Wing area: 1,897 ft² (176.2 m²)
Empty weight: 72,000 lb (33,000 kg)
Max takeoff weight: 115,000 lb (52,200 kg)
Powerplant: 4× Rolls-Royce Avon turbojet, 6,000 lb (27 kN) each

Performance

Maximum speed: 567 mph (493 knots, 912 km/h)
Range: 3,200 mi (2,800 nm, 5,150 km)
Service ceiling: 45,000 ft (13,700 m)

The Sperrin had four different engine configurations

Four Rolls-Royce Avon RA.2 turbojets of 26.6 kN (6,000 lbf) thrust each (VX158)
Four Rolls-Royce Avon RA.3 turbojets of 28.1 kN (6,500 lbf) thrust each ( (VX161))
Three Rolls-Royce Avon RA. turbojets of 26.6 kN (6,000 lbf) thrust each (two on the starboard wing, one in the upper part of the port engine nacelle) and one de Havilland Gyron Gy1 turbojet of 66.7 kN (15,000 lbf) thrust in the lower part of the port engine nacelle ( (VX158)) (see image above)
Two Rolls-Royce Avon RA.2 turbojets combined with two de Havilland Gyron Gy2 turbojets of 100 kN (20,000 lbf) thrust each ( (VX158))

[edit] References

^ Gunston 1980, p. 341.
^ Wood 1975, p. 130.
^ Sqdn.Ldr. W.J. Runciman, A.F.C, D.F.M
^ Barnes & James 1989, p.429.
^ Barnes & James 1989, p.429.
^ Barnes & James 1989, p.431.

Barnes, C.H. with revisions by James, Derek N. Shorts Aircraft since 1900. London: Putnam, 1989 (revised). ISBN 0-85177-819-4.
Gunston, Bill. "Short's Stop-Gap Bomber." Aeroplane Monthly, Vol. 8, no. 7, July 1980. p. 340-346.
Wood, Derek. Project Cancelled. Indianapolis: The Bobbs-Merrill Company Inc., 1975. ISBN 0-672-52166-0.