The Saunders-Roe SR.53 was a British prototype interceptor aircraft of mixed jet and rocket propulsion developed for the Royal Air Force (RAF) by Saunders-Roe in the early 1950s. As envisaged, the SR.53 would have been used as an interceptor aircraft, using its rocket propulsion to rapidly climb and approach incoming hostile bombers at high speeds; following its attack run, the aircraft would then return to its base using jet propulsion.

Although the SR.53 proved to have promising performance during test flights, the requirement for such an aircraft had been overtaken by rapid advances in surface-to-air missile technology, leading to reconsideration of the aircraft's purpose. In July 1960, the development programme was formally cancelled, by which time a total of 56 test flights had been performed.

Design and development

Background

The Second World War had demonstrated the importance of strategic bombing to modern warfare, and as the emerging Cold War developed, the development of new and more effective air defences against large waves of hostile bomber aircraft armed with nuclear weapons became a priority for many nations. During the war, Nazi Germany had extensively developed its own rocket-powered aircraft to augment its interception capabilities, in the final two years of the war, it had been able to deploy aircraft such as the Messerschmitt Me 163 and Bachem Ba 349 which, via rocket propulsion, had been capable of unparalleled rates-of-climb, enabling them to (at least in theory) rapidly sortie to intercept enemy bombers before they reached their targets. As the performance of these aircraft had become increasingly well known to the Allies, RAF experts were eager to explore and understand the underlying technology.

In the aftermath of the war, German rocket technology was studied extensively by various members of the former Allied nations. Britain had quickly opted to commence a programme to develop liquid-propellant rockets with the aim of boosting aircraft during the take-off phase, known within the RAF as rocket-assisted take-off gear (RATOG), and during the climb-to-altitude phase of flight. Accordingly, a capable defence interceptor that could form part of the nation's measures to counter this threat would need to be capable of similar speeds and an exceptionally high rate of climb in order to reach high altitude bombers in time.

The development of the Sprite and the Snarler had led to the possibility of a more powerful rocket engine being developed as the planned powerplant for a viable "point defence" interceptor. The requirements of O.R. 301 were considered onerous, including a ramp launch and landing on a skid, and with the compliance of the companies which had approached to tender, the amended Specification F124T allowed for a mixed powerplant configuration along with the adoption of a conventional undercarriage.

Submissions and selection

Saunders-Roe had not been one of the companies who received the Specification; this is likely due to the Ministry of Supply not considering them to be relevant, as the firm had typically been involved in the production of flying boats.

By the end of April 1951, Saunders-Roe submitted their detailed proposal. Saunders-Roe had originally proposed to develop their own rocket motor to power the SR.53, having not been initially pleased with the performance of either the Spectre nor the Screamer; however, it was recognised that this would take substantial development work. The changes of the defined specification mainly revolved around armament changes, adopting the Blue Jay infrared-guided air-to-air missile, which replaced the originally-envisaged retractable battery of rockets. During the first four months of 1953, Saunders-Roe had to perform a structural redesign of the SR.53's fuselage, wing, and undercarriage due to a determination by the Royal Aircraft Establishment (RAE) that the wing required a greater anhedral angle than had originally been designed for.

Issues and proposals

Saunders-Roe, recognising that it would need to outdo the competing Avro 720 if the SR.53 was to be likely to survive, upon having been issued with the contract to build the three prototypes, set a schedule that called for a first flight to be conducted in July 1954, along with a projected service introduction date of 1957. However, Wood observes that this was far too ambitious as it did not leave time to address the complexity of the aircraft, nor did it accommodate room for delays in the supply of the separately-produced Spectre engine. Accordingly, the maiden flight of the SR.53 began to fall further and further behind schedule. In January 1954, the Ministry reduced its order from three SR.53 prototypes to two, which were constructed side by side at Saunders-Roe's Cowes facility.

By September 1953, the programme to develop these aircraft came under scrutiny due to a need to implement cost cuts; as a result, the contract for the Avro 720 was eventually cancelled. One of the reasons for preferring the SR.53 was although the aircraft was developmentally behind, its use of hydrogen peroxide as an oxidiser was viewed as less problematic than the Avro 720's use of liquid oxygen, which posed a fire hazard. However, the validity of this reason is undermined somewhat by the fact that Avro had been proposing to switch to using HTP and the Spectre, the same engine that was used by the SR.53. Another factor that had influenced the cancellation was the hesitancy of the RAF to back either project, the service had apparently wanted to wait until after flight evaluations had been conducted before it was to make any determination on its preference. It was sized to be able to carry a useful airborne radar, which Brennan had deemed to be essential for interception at the high altitudes at which the new fighter was meant to operate. The new, larger aircraft was also to be developed into separate versions for maritime use by the Royal Navy and for West Germany as well as for the RAF. Saunders-Roe worked on both the SR.53 and SR.177, the latter being worked on by a newly formed High Speed Development Section.

Operational history

thumb|right|Drawing of the first SR.53

In October 1951, Saunders-Roe obtained facilities at RAF Hurn, Dorset, to support the site's use as a base for test flights of the SR.53. This measure had been necessitated by a lack of suitable airfields on the Isle of Wight, where the company was based and typically conducted development from. To this end, the firm constructed a HTP storage facility at the Hurn site; specialised radio aids were also installed and initially tested using a specially-modified Gloster Meteor which had been lent by the Ministry of Supply. This setup would ultimately remain unused as flying trials were centered at RAF Boscombe Down instead. On 16 January 1957, the first installed ground run of its Spectre engine was performed; on 16 April 1957, this was followed by the first installed ground run of its Viper engine. On 9 May 1957, XD145 conducted the type's first ground taxiing trial.

While testing at RAE Boscombe Down, XD151 crashed on 5 June 1958 during an aborted takeoff on its 12th flight. Running off the runway, the aircraft struck a concrete approach light, exploding on impact and killing its pilot, Squadron Leader Booth.

Operators

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  • Ministry of Supply

Specifications

See also

References

Notes

Bibliography

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  • Rocket interceptors and S177
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  • Unreal Aircraft