Short Sperrin
Encyclopedia
The Short SA.4 Sperrin (named after the Sperrin Mountains, a range of hills in Northern Ireland
Northern Ireland
Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...
) was a British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
jet bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
design of the early 1950s built by Short Brothers and Harland
Short Brothers
Short Brothers plc is a British aerospace company, usually referred to simply as Shorts, that is now based in Belfast, Northern Ireland. Founded in 1908, Shorts was the first company in the world to make production aircraft and was a manufacturer of flying boats during the 1920s, 1930s, and 1940s...
of Belfast
Belfast
Belfast is the capital of and largest city in Northern Ireland. By population, it is the 14th biggest city in the United Kingdom and second biggest on the island of Ireland . It is the seat of the devolved government and legislative Northern Ireland Assembly...
, popularly abbreviated "Shorts". It first flew in 1951. The design had always been a fall-back option in case the more advanced jet designs of the V-bombers were delayed, and it was not put into production because these swept-wing designs (such as the Vickers Valiant
Vickers Valiant
The Vickers-Armstrongs Valiant was a British four-jet bomber, once part of the Royal Air Force's V bomber nuclear force in the 1950s and 1960s...
) were by then available. The Sperrin prototypes were however valuable for research data on large jet aircraft.
Design and development
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 kilometers] 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 140000 lb (63,502.9 kg). The B.35/46 specification required that the fully laden weight would be under 100,000 lb (45 tonneTonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s), the bomber have a cruising speed of 500 knots (979.9 km/h) and that the service ceiling would be 50,000 ft (15,200 m). This request would be the foundation of the V-bombers.
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
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
Strategic Air Command
Strategic Air Command
The Strategic Air Command was both a Major Command of the United States Air Force and a "specified command" of the United States Department of Defense. SAC was the operational establishment in charge of America's land-based strategic bomber aircraft and land-based intercontinental ballistic...
. In late 1948, the Air Ministry
Air Ministry
The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...
issued their specification B.35/46 for an advanced jet bomber that should be the equal of anything that either the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
or the Americans would have. The exact requirements included that the fully laden weight would be under 100,000 lb (45 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s), the ability to fly to a target 1500 nautical miles (2,778 km) distant at 500 knots (979.9 km/h) with a service ceiling of 50,000 feet (15,200 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 10000 lb (4,535.9 kg) and measuring 30 ft (length) and 10 ft (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
Avro Vulcan
The Avro Vulcan, sometimes referred to as the Hawker Siddeley Vulcan, was a jet-powered delta wing strategic bomber, operated by the Royal Air Force from 1956 until 1984. Aircraft manufacturer A V Roe & Co designed the Vulcan in response to Specification B.35/46. Of the three V bombers produced,...
and Handley Page Victor
Handley Page Victor
The Handley Page Victor was a British jet bomber aircraft produced by the Handley Page Aircraft Company during the Cold War. It was the third and final of the V-bombers that provided Britain's nuclear deterrent. The other two V-bombers were the Avro Vulcan and the Vickers Valiant. Some aircraft...
., as this was to be a less ambitious conventional type of aircraft, with unswept wings and some sacrifice in performance. The only significant performance differences between B.14/46 and the more advance B.35/46 were a lower speed of 435 knots (852.5 km/h) and a lower height over the target of 35000 ft (10,668 m) to 45000 ft (13,716 m).
Under this requirement, the Air Ministry placed a contract for two flying prototypes and a static airframe with Shorts. The design, known initially as SA.4 and later, as the "Sperrin", had more in common with the Second World War
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
designs than the new jet age. It was straight winged, although the leading edge was slightly swept. The engines were mounted in nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
s mid-wing, two engines per wing, with one engine stacked above the other. The airframe was built largely of aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
alloys with a tricycle undercarriage (nosewheel 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 bombardier's position was a tube extending forward of the cockpit above the radome; the crew compartment being pressurized. These were fitted with opaque nosecones, as the Sperrins 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 with the crew entrance below.
As a possible production aircraft, the Sperrins were built on production jigs, which slowed their construction.
Testing
The first prototype (serial VX158), powered by four Rolls-Royce AvonRolls-Royce Avon
|-See also:-Bibliography:* Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:**** a 1955 Flight article on the development of the Avon...
RA.2 engines of 6000 lbf (26.7 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
Vickers Valiant
The Vickers-Armstrongs Valiant was a British four-jet bomber, once part of the Royal Air Force's V bomber nuclear force in the 1950s and 1960s...
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 (28.1 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
De Havilland Gyron
|-See also:-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:** - A 1957 Flight magazine article on the Gyron...
turbojet - a large engine delivering 15,000 lbf (66.7 kN) thrust. The Gyron Gy1 replaced the lower Avon in the port nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
(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 20000 lbf (89 kN) thrust, were fitted, one in each engine nacelle below the original Avon RA.2s.
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
Blue Danube (nuclear weapon)
Blue Danube was the first operational British nuclear weapon. It also went by a variety of other names, including Smallboy, the Mk.1 Atom Bomb, Special Bomb and OR.1001, a reference to the Operational Requirement it was built to fill...
nuclear bomb and the Blue Boar missile.
Specifications first prototype
- Four Rolls-Royce Avon RA.2Rolls-Royce Avon|-See also:-Bibliography:* Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:**** a 1955 Flight article on the development of the Avon...
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 GyronDe Havilland Gyron|-See also:-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:** - A 1957 Flight magazine article on the Gyron...
Gy1 turbojet of 66.7 kN (15,000 lbf) thrust in the lower part of the port engine nacelle: VX158 - Two Rolls-Royce Avon RA.2 turbojets combined with two de Havilland Gyron Gy2 turbojets of 100 kN (20,000 lbf) thrust each: VX158