THE PLANE THAT NOBODY KNEW ABOUT (well hardly anybody)

Ron tells us about the plane that never was...

In the second world war the Germans made big strides in the development of liquid fuelled rocket engines. This development manifested itself in the infamous V2 long range missile that was used to bombard London in the latter stages of the war, and in the Messerschmitt 163, a rocket propelled fighter aircraft. The Allies had restricted their use of rockets to the solid fuelled type which they used to good effect, primarily in air to ground missiles. They concentrated their development efforts on improving conventional aircraft, improved electronics in the form of radar and communications and, of course, on new weapons, especially the atomic bomb. When the German rocket propelled devices appeared the Allies were stunned.

After the war, and to everyone's dismay, the 'cold war' soon began and Russia was seen as a threat to our security. It was known that Russia had some very high altitude long range bombers and the need was identified for a high performance interceptor fighter with exceptional performance at high altitude, something like the concept pioneered by Messeschmitt seemed ideal. The rocket engine's thrust increases with increasing altitude whereas the thrust of a conventional jet engine falls off as the density of the air decreases with altitude thus, for example, a jet engine capable of generating 10,000lb of thrust at sea level would produce less than 2000lb at 40,000ft whereas a rocket engine producing 10,000lb at sea level would produce in excess of 11,000lb at 40,000ft. One can see the enormous advantage a rocket powered aircraft would have at that altitude. The disadvantage of the rocket plane is, of course, that it has to carry its own oxidant as well as its fuel and this is bound to impose strict limits on the operational time.

Around 1952 the Ministry of Supply (nowadays Min. of Defence) produced a specification for a mixed power plant interceptor fighter. It was to have a rocket engine with thrust control over a wide range, something that had not been achieved by anybody at that time, and a conventional jet engine. The jet engine would provide the power for normal flying whilst the rocket engine would be limited to operational use. A contract was subsequently awarded to Saunders Roe on the Isle of Wight, better known for their work on flying boats, for a design study. At first glance it seemed an unlikely choice to design a supersonic fighter but when it is remembered that Supermarine, a sea plane company from just across the water, gave us the Spitfire, it may not be so surprising. Contracts for the rocket engine development were given to Armstrong Siddeley, Napier and de Havilland. Saunders Roe's initial design was for an aircraft fitted with the de Havilland rocket engine, the deH Spectre 1A, and an Armstrong Siddeley Viper jet engine. This aircraft was designated the SR53 and orders were placed for two aircraft for assessment. Subsequent studies by Saunders Roe led to the design of an enhanced version of the SR53, designated the SR177. This was to employ the de Havilland Spectre 5 rocket engine and the deHavilland Gyron Junior jet engine, a much more powerful and advanced engine than the Viper. This aircraft was seen as the operational version. During the war a culture of extreme secrecy developed in relation to weapon development and production, and this persisted into the cold war period with the result that this whole project was classified as 'Secret', which meant that any disclosure was a serious punishable offence.

Progress with the design and build of the aircraft was fairly rapid and the development of the rocket engine went well despite many difficulties in exploring a new technology, the requirement for controllability imposing a major obstacle. In 1957 the rocket engine passed its type test and flight testing took place with the engine mounted in the bomb bay of a Canberra. This all went well and the engine was installed in the aircraft. Initial ground testing and later flight testing took place in 1958/9 at the ministry's experimental airfield at Boscombe Down. All the initial testing went well, the performance of the aircraft and the rocket engine exceeded expectations. All the early flight work was conducted using the long runway but, when another need for that runway arose and confidence in the SR53 had been established, the flight testing was switched to the short runway. On the first take off on this runway, when halfway down the runway the test pilot radioed calmly that he was abandoning his take off, closed the throttles of both engines and asked for a tractor to tow him back. Unfortunately he had passed the point where he could do this safely and the aircraft ran off the end of the runway, one wing caught the post supporting a boundary light and the aircraft swung violently and broke up, sadly the full load of rocket fuel then exploded into a giant fireball. The rocket engine was flung clear when the plane hit the post and it was subsequently established that there was no fault with that engine. The reason for the pilot's decision was never established, neither was it understood how he could not have realised that it was a suicidal decision, but his calm manner and request for a tractor would suggest that he fully expected to be able to stop safely; it seemed like an inexplicable and tragic mistake. No other explanation was ever found for the crash.

After the crash, flight testing with the second aircraft was suspended pending an investigation. By this time the threat from high altitude bombers was seen as less cause for concern than that from inter-continental ballistic missiles, furthermore defence against bombers was switching to ground to air missiles and the decision was made not to proceed with the SR177. It was inevitable, but it was disappointing that the SR53 did not get more flying in, its performance at altitude was outstanding and in a different league altogether to conventional aircraft of the day. Very little, if anything, was publicised and the SR53 project disappeared. The photograph here is a very rare shot of SR53, XD145, in flight with its rocket engine running. It can be seen from the photograph how advanced the design was for a time some 50years ago.

Ron Watts