The Short Sperrin - before the "V Bombers"
In the postwar period, Great Britain built not one but three long-range jet bombers -- the "Valiant", "Victor", and "Vulcan" -- as the backbone of that nation's nuclear deterrence force. The first of these "V-bombers" was the Vickers Valiant , which served through most of the 1950s and into the early 1960s. What is often forgotten is that these three British jet bombers were preceded by the Short Sperrin. The "V bomber" designs were highly advanced leading edge designs, so the Short Sperrin was comissioned as a simpler interim aircraft. This document provides a history and description of the Short Sperrin.
Short Sperrin - the "Insurance" bomber
The British Royal Air Force's (RAF) Bomber Command left World War 2 with a policy of using heavy four-piston-engined bombers for massed raids, and remained committed to this policy in the immediate postwar period, adopting the Avro Lincoln, an improved version of the WW2 Lancaster, as their standard bomber.
The development of jet aircraft and nuclear weapons soon made this policy obsolete. The future appeared to belong to jet bombers that could fly by themselves at high altitude and speed, without defensive armament, to perform a nuclear strike on a target. To be sure, even at the time there were those who could see that at some time in the future, guided missiles would make such aircraft vulnerable, but development of such missiles was proving difficult, and fast and high-flying bombers were likely to serve for years before there was a need for something better.
In any case, massed bombers were unnecessary if a single bomber could destroy an entire city or military installation with a nuclear weapon. It would have to be a large bomber, since the first generation of nuclear weapons were big and heavy. Such a large and advanced bomber would be expensive on a unit basis, but thanks to the awesome power of the "nuke", the aircraft wouldn't need to be built in large quantities. Britain had been economically bled dry by World War 2 and the potential cost savings were attractive.
The arrival of the Cold War also emphasized to British military planners the need to modernize British forces. Furthermore, Britain's up-and-down relationship with the USA, particularly in the immediate postwar years when American isolationism staged a short-lived comeback, led the British to feel they needed their own strategic nuclear strike force.
After considering various specifications for such an advanced jet bomber in late 1946, in January 1947 the British Air Ministry issued an request for an advanced jet bomber that would be at least the equal of anything the US or the USSR had. The request went to most of England's major aircraft manufacturers.
The request followed the guidelines of the earlier specification "B.35/46", which proposed a "medium-range bomber landplane, capable of carrying one 10,000 pound [4,535 kilogram] bomb to a target 1,500 nautical miles [2,775 kilometers] from a base which may be anywhere in the world." The request also indicated that the fully loaded weight not exceed 45,350 kilograms (100,000 pounds), though this would be adjusted upward in practice; that the bomber have a cruise speed of 925 KPH (500 knots); and that it have a service ceiling of 15,240 meters (50,000 feet).
Since the requirements for B.35/46 were stiff, the Air Ministry also issued "B.14/46", a requirement for a more conservative jet bomber that would provide "insurance" in case the advanced B.35/46 effort ran into trouble. In August 1947, a contract was awarded to Shorts Brothers for the "SA.4" four-engine jet bomber, with the contract specifying construction of two flying prototypes and a static-test machine.
The Shorts SA,4 was, as intended, a conservative design, basically a jet-powered version of a World War II style bomber with conventional tail assembly and straight wings, though the wings did have leading-edge sweep. The only particularly unusual feature was that the four Rolls-Royce Avon engines were fitted in nacelles mounted in the midwing, with two engines in each nacelle mounted in a top-and-bottom fashion.
The "Sperrin", as it was called, was to have a crew of five, including pilot, copilot, bombardier, navigator, and radio operator, in pressurized accommodations. Only the pilot had an ejection seat. The Sperrin had no defensive armament. It was to carry radios, navigation avionics, and bombing radar, and space was set aside for defensive avionics.
The Short Sperrin did have one important design feature which was carried over to all three "V" bombers. Saunders Roe developed a pressurised crew capsule for the five crew. Pressurised to a maximum differential of 9lb/sq. inch (1.6kg /sq. cm), it carried two pilots in a side by side arrangement, behind which the Radio Operator, Navigator and Air Bomber sat.
The Sperrin was of conventional monocoque construction and built largely of aircraft aluminum alloys. It featured tricycle undercarriage, with twin-wheel nose gear retracting backward and four-wheel main gear, arranged as 2-by-2 bogies, retracting from the wings towards the fuselage. A dual-parachute brake chute system was also fitted.
|SHORT SA.4 SPERRIN:|
|wingspan||33.2 meters||109 feet|
|wing area||176.2 sq_meters||1,897 sq_feet|
|length||31.14 meters||102 feet 2 inches|
|height||8.69 meters||28 feet 6 inches|
|empty weight||32,660 kilograms||72,000 pounds|
|MTO weight||52,165 kilograms||115,000 pounds|
|max speed||912 KPH||567 MPH / 492 KT|
|service ceiling||13,715 meters||45,000 feet|
|range||5,150 kilometers||3,200 MI / 2,780 NMI|
The first prototype performed its initial flight on 10 August 1951, with Shorts chief test pilot Tom Brooke-Smith at the controls. It was fitted with Avon RA.2 turbojets with 26.6 kN (2,720 kgp / 6,000 lbf) thrust each. In March 1950, well before the initial flight, the Air Ministry had decided that the Sperrin wouldn't be put into production, but work on the two prototypes was allowed to continue.
The second prototype performed its first flight on 12 August 1952. It was fitted with Avon RA.3 turbojets with 28.1 kN (2,950 kgp / 6,500 lbf) thrust each. The two Sperrin prototypes were used in a variety of trials through the 1950s, including:
- Engine tests for the big de Havilland Gyron turbojet, with 66.7 kN (6,800 kgp / 15,000 lbf) thrust, with the nacelles modified to accommodate a Gyron in the lower half and an Avon in the upper half.
- The "Blue Danube" atomic bomb,
- The "Blue Boar" TV-guided missile, which did not see service.
Both Sperrin prototypes were scrapped in the late 1950s. Shorts also proposed a design based on the SA.4 for the more advanced B.35/46 specification, the "SB.1", featuring a fuselage like that of the SA.4 but with a "tailless" configuration, using the company's "aero-isoclinic" scheme. The outer sections of the wings were pivoted, allowing them to maintain the same incidence even as the wing flexed. The pivoted wingtips acted as both elevators, rotating together to control pitch, and ailerons, rotating in reverse direction to control roll. The SB.1 featured the engine arrangement of the SA.4, with twin Avons in nacelles arranged top and bottom of the wing, but with a fifth Avon added in the rear of the fuselage, with an intake on top.
The SB.1 was too daring for the Air Ministry, though the aero-isoclinic wing was tested on a small demonstrator, the "SB.4 Sherpa", in the early 1950s, with surprisingly good results. However, the aero-isoclinic configuration didn't really seem to have any major advantages over other, more conventional configurations; the line of investigation proved to be a dead end. The Sherpa name would be recycled later for the Shorts 330 / C-23 light twin-engine light transport.
Short Sperrin - the end
The Sperrin was never anything more than a footnote to Britain's strategic bomber development effort. Other work would achieve much more significant and impressive results.
Handley-Page and Avro came up with very advanced designs for the bomber competition, which would become the Victor and the Vulcan respectively, and the Air Staff decided to award contracts to both companies, again as a form of insurance.
While Vickers-Armstrong's submission was originally rejected as too conservative, Vickers' chief designer George Edwards energetically lobbied the Air Ministry and made changes to meet their concerns. Edwards managed to sell the Vickers design to the Air Ministry on the basis that it would be available much sooner than the competition, going so far as to promise delivery of a prototype in 1951 and production aircraft in 1953. The Vickers bomber would be useful as a "stopgap" until the more advanced bombers were available. Apparently the Air Ministry didn't think there could be too much insurance.