MANUFACTURER(S): Short Brothers and Harland - UK
OPERATORS: United Kingdom (cancelled)
POWER: 4 x Rolls-Royce "Avon" turbojet engines developing 6,500lb of thrust each.
Detailing the development and operational history of the Short SA.4 Sperrin Experimental Jet-Powered Bomber Project.
Entry last updated on 5/7/2019.
Authored by Staff Writer. Content ©www.MilitaryFactory.com.
The Royal Air Force's "V-Bomber" force was a trio of capable, high-level jet-powered bombers that supplied the British with a much-needed strategic nuclear strike capability. This allowed the nation a more mobile response to the oncoming Soviet threat and also lessened reliance on the United States in the event of Total War across Europe during the Cold War period (1947-1991). The force was made up of the class Avro Vulcan, Handley Page Victor, and Vickers Valiant and the aircraft continued in their original nuclear deterrent role into 1982 - the group ending their days as converted aerial tankers for a new generation of tactically-minded nuclear-capable aircraft.
Before this trio was realized, however, design plans were being forged for such bombers back in the closing phases of World War 2 (1939-1945) as turbojet technology moved to the forefront. Specification B.14/46 was written up in the immediate post-war world for such an aircraft and this need evolved to become Specification B.35/46.
To this point, the RAF was relying on the war time Avro Lincoln for the strategic long-range bomber role but this prop-driven platform had roots in the war years and saw introduction in 1945 - the final year of the conflict. It became clear that such a mount would soon become outmoded in the jet age so jet-centric bomber programs were now the focal point for the service (Lincolns were flown up until 1963 with the RAF and into 1967 with Argentina).
Against this backdrop, the foundation of the V-Bomber force was being laid. The requirement called for a technologically-advanced jet-powered platform capable of hauling conventional or nuclear loads a considerable distance at high-altitude. Specifics called for an aircraft cutting through the air at near-600mph speeds reaching an altitude near 50,000 feet out to a range of 1,700 miles.
Because of the complexity involved in bringing such a large aircraft to fruition, it was deemed prudent to draw up plans for an interim jet-powered bomber design in the event the new generation of bomber could not be had in time. B.14/36 was reworked for this specific requirement and centered itself around a largely conventional aircraft shape with straight wings, a traditional tailplane arrangement, internal bomb load, and wing-mounted engine nacelles - the simpler the better for speed was of the utmost importance for the program; Initial Operational Capability (IOC) was targeted (rather optimistically) for 1953. It was further decided that the maximum speed requirement be reduced to a more achievable 500mph.
Aircraft-maker Short Brothers beat out three other submissions from British aero-industry and the Air Ministry contracted for two flyable prototypes and a static test bed to see the program through. For the company, the project was filed under "SA.4" and only later (1954) became known as the "Sperrin" (as in the Sperrin Mountains of Northern Island).
The aircraft that Short Brothers drew up was given a relatively slender fuselage with slab sides and rounded dorsal and ventral surfaces. The cockpit was featured in a stepped arrangement aft of the short, rounded nose cone assembly. The nose would eventually house the H2S Mk.9 airborne radar fit as well as the bombardier's prone position. The fuselage tapered as it ran towards the tail unit, the unit encompassing a single vertical fin and the horizontal planes were low-mounted along the fuselage sides. The horizontal planes were canted upwards to give the tail a unique design look. The internal bomb bay ran a partial length of the ventral section and parallel hinged doors were used for access. For ground-running, the aircraft relied on a modern wheeled and retractable tricycle arrangement with the nose leg being twin-wheeled and the main legs each sporting two twin-wheeled bogies. Aluminum alloy was used extensively throughout the aircraft's construction.
The mainplanes, containing pertinent control surfaces, were set near midships and were heavily swept along the leading edges with the trailing edges only slightly tapering. It is worth noting that Short Brothers engineers championed the idea of a wholly swept-wing design to compete with bombers of the era but this desire was overruled by authorities looking for a failsafe bomber. The tips of each member were clipped and each wing was given a paired housing for two of the four total turbojet engines in play. In a rather unique-yet-awkward fashion, the engines were stacked one-over-the-other in the arrangement with the nacelles extending beyond the leading and trailing edges.
Internally, the crew numbered five and included two pilots, a bombardier, flight navigator and radioman. The bombardier took up a position in the nose (laying prone) while the remaining three crewmen sat behind the pilot and facing the rear. Interestingly, only the pilot was given an ejection seat, the rest of the crew intended to bail out via parachute in the World War 2 fashion.
The first prototype (designated "VX158") had a running length of 102.2 feet, a wingspan of 109 feet, and a height of 28.5 feet. Empty weight reached 72,000lb and this was against a gross weight of rating of 115,000lb. Power was from 4 x Rolls-Royce "Avon" turbojet engines. Performance included a maximum speed of 565 miles-per-hour, a cruising speed of 500 miles-per-hour, a service ceiling up to 45,000 feet, and a range out to 3,860 miles.
All proposed armament was to be held in an internal bomb bay, this to consist of a formidable collection of conventional drop bombs or a single "Blue Danube" nuclear air-dropped bomb - a war load of at least 20,000lb was estimated (though never fitted in testing).
Prototype VX158 originally appeared with RR Avon RA.2 series turbojets of 6,000lb output power and achieved its first-flight on August 10th, 1951. However, because sound progress on the project that would begat the Vickers Valliant was being had, the Sperrin project was officially cancelled by authorities - though it was allowed to continue in an experimental sense. This additional work then led to a second prototype, "VX161", being added to the program. The VX161 made it to the air for the first time on August 12th, 1952 and differed in being powered by RR Avon RA.3 turbojets of 6,500lb thrust each.
VX158 was eventually given a single de Havilland "Gyron" turbojet for testing and this unit was fitted in place of the original, lower portside Avon engine in the existing nacelle - though the increased size of the engine now forced an increase in the size of this particular nacelle as a result. In this guise, the bomber project went into the air for the first time on July 7th, 1955 and the experimental configuration continued testing the arrangement into the early part of the following year. Later in 1956, the aircraft took on a pair of de Havilland "Gyron" Gy2 series engines for additional flight-testing work - these units rated at an impressive 20,000lb of thrust each and paired with the existing Avon turbojet units per nacelle (the Gyron engines were given the lower position in each nacelle). A first-flight in this revised configuration then followed on June 26th, 1956.
Meanwhile, prototype VX161 continued along its own development timeline and was flown over the public during Farnborough 1956. It survived into 1957 by which point it was dismantled and officially scrapped. Prototype VX158 continued to test its various experimental engine configurations into 1958 before it, too, was given up for good.
Meanwhile, the V-bombers went on to have useful service lives for the RAF and took on more conventional roles beyond nuclear deterrence before the end (despite the fact that all three were accepted to fulfill the same over-battlefield role to begin with). This left the Sperrin as nothing more than a footnote in the V-bomber program.
Our Data Modules allow for quick visual reference when comparing a single entry against contemporary designs. Areas covered include general ratings, speed assessments, and relative ranges based on distances between major cities.
This entry's maximum listed speed (565mph).
Graph average of 562.5 miles-per-hour.
Graph showcases the Short XV158's operational range (on internal fuel) when compared to distances between major cities.
Useful in showcasing the era cross-over of particular aircraft/aerospace designs.
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