Short Sperrin

https://en.wikipedia.org/wiki/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 as 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. The two aircraft completed were retired in the late 1950s
and ultimately scrapped sometime thereafter.

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 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 United States Strategic Air Command. In late 1948, the Air
Ministry issued their specification B.35/46 for an advanced jet bomber that
would serve as a successor to the Avro Lincoln, the then-standard heavy aircraft
of RAF Bomber Command, and that it 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.

Design

Many design elements of the Sperrin had more in common with aircraft of the
Second World War than those of the new jet age. The design was relatively
straightforward in most aspects, with the exceptions of the flight controls and
the unusual engine arrangement: The engines were mounted in pairs in nacelles
mid-wing, one engine being stacked above the other, for a total of four engines.
VX-158 had the distinction of being the first aircraft to receive production
Rolls-Royce Avon engines; other engines such improved Avon models and the de
Havilland Gyron would also be installed on the two prototypes for test purposes.
The airframe was built largely of light aluminium alloys, principally the 75ST
alloy; the outer skin of the aircraft had a highly smooth stressed-skin surface
also composed of light alloys, in part due to this, the measured drag was
considerably low.

The Sperrin employed a traditional straight wing, although the wing's fixed
leading edge was slightly swept and featured curved fillets at the junction with
the engine nacelles. The trailing edge had simple flaps inboard of the nacelles
and large ailerons outboard; the outer flaps were to incorporate air brakes, but
this was replaced with split-brakes prior to the first flight. Both the flaps
and air brakes were primarily operated hydraulically, an independent system for
emergency actuation was also present. Up to 6,170 imperial gallons of fuel could
be housed in a total of 22 fuel tanks, 14 of these being contained within the
wings and a further 8 within the fuselage; these tanks were pressurized to
prevent collapse during fast dives and other manoeuvres. The wing was fixed to
the fuselage at a mid-wing position, located between the bomb bay and fuselage
fuel tanks.

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 positions were fitted with opaque nosecones, as the
Sperrins were never used for live bombing. The pilot was the only member of the
crew to have a Martin-Baker-produced ejector seat underneath a jettisonable roof
panel; other crew members were intended to bail out via a door located under the
navigator's console. The other three crew positions were located behind the
pilots, facing rearwards. Unusually, the pilot's flying controls lacked any
direct connection to the aircraft's flight control surfaces, control input was
instead directed into a gearbox to actuate rotatable ball-screw jacks to move
each flight surface via aerodynamic load instead; a corresponding artificial
feel system was also installed. Bill Gunston and Peter Gilchrist describe the
control system as having been simple, light, reliable, and low-friction and
contrast it positively against powered systems of the era.

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

Testing

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.

Specifications (first prototype)

General characteristics
Crew: 5 (pilot, co-pilot, bombardier, navigator and radio operator)
Length: 102 ft 3 in (31.17 m)
Wingspan: 109 ft 0 in (33.22 m)
Height: 28 ft 6 in (8.69 m)
Wing area: 1,896 sq ft (176.1 m2)
Aspect ratio: 6.27:1
Airfoil: AD.7
Empty weight: 72,000 lb (32,659 kg)
Gross weight: 115,000 lb (52,163 kg)
Fuel capacity: 6,200 imp gal (7,400 US gal; 28,000 L)
Powerplant: 4 × Rolls-Royce Avon turbojets, 6,500 lbf (29 kN) thrust each

Performance
Maximum speed: 564 mph (908 km/h, 490 kn) at 15,000 ft (4,600 m)
Cruise speed: 500 mph (800 km/h, 430 kn) 40,000 ft (12,000 m)
Combat range: 3,860 mi (6,210 km, 3,350 nmi)
Service ceiling: 45,000 ft (14,000 m)

Armament

Across the two aircraft, the Sperrin had four different engine configurations:
1.Four Rolls-Royce Avon RA.2 turbojets of 26.6 kN (6,000 lbf) thrust each: VX158
2.Four Rolls-Royce Avon RA.3 turbojets of 29.0 kN (6,500 lbf) thrust each: VX161
3.Three Rolls-Royce Avon RA. turbojets of 26.7 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
4.Two Rolls-Royce Avon RA.2 turbojets combined with two de Havilland Gyron Gy2
turbojets of 89 kN (20,000 lbf) thrust each: VX158





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