The Miles M.52 was a turbojet-powered supersonic research aircraft project designed in the United Kingdom in the mid-1940s. In October 1943, Miles Aircraft was issued with a contract to produce the aircraft in accordance with Air Ministry Specification E.24/43. The programme was highly ambitious for its time, aiming to produce an aircraft capable of a speed of at least during level flight, and involved a very high proportion of cutting-edge aerodynamic research and innovative design work.
Until 1945 all work on the project was undertaken with a high level of secrecy. In February 1946, the programme was terminated by the new Labour government of Clement Attlee, seemingly due to budgetary reasons as well as the disbelief of some ministry officials regarding the practicality of supersonic aircraft. In September 1946 the existence of the M.52 project was revealed to the general public, leading to criticism of the decision and calls for an official explanation of why the project had been terminated. The Ministry of Supply controversially decided to investigate the design with six different configurations of wing and control surfaces, but as a series of unmanned rocket-powered 30 per cent scale models instead of a manned full-scale aircraft. The contract was awarded to Vickers rather than Miles. The models were air-launched from a modified de Havilland Mosquito mother ship.
A model with the M52 configuration of wing and control surfaces achieved Mach 1.38 in controlled transonic and supersonic level flight, a unique achievement at that time and which provided "some validation of the aerodynamics of the M.52 upon which the model was based". Prior to the flight the decision had already been made to terminate the programme. Work on the afterburning version of the Power Jets W.B.2/700 turbojet was also cancelled, and Power Jets was incorporated into the National Gas Turbine Establishment. According to senior figures at Miles, the design and the research gained from the M.52 was shared with the American company Bell Aircraft, and that this was applied to their own Bell X-1, the experimental aircraft which broke the sound barrier.
Development Background Prior to the Second World War, conventional wisdom throughout the majority of the aviation industry was that manned flight at supersonic speeds was next to impossible, mainly due to the apparently insurmountable issue of compressibility.Wood 1975, p. 27. During the 1930s, few researchers and aerospace engineers chose to explore the field of high-speed fluid dynamics; notable pioneers in this area were the German aerospace engineer Adolf Busemann, British physicist Sir Geoffrey Taylor, and British engine designer Sir Stanley Hooker.Wood 1975, pp. 27–28. While Germany gave considerable attention to exploring and implementing Busemann's theories on the swept wing and its role in drag-reduction during high-speed flight, both Britain and the United States largely ignored this research. It was only by 1944 that information about the rocket-propelled Messerschmitt Me 163 and the jet-propelled Me 262, both with swept wings, caused attitudes on its merits begin to change. By then the British Air Ministry had already launched a research programme of its own.Wood 1975, pp. 27–29.
In Autumn 1943, the Air Ministry issued Air Ministry Specification E.24/43 calling for a jet-powered research aircraft capable of flying at over in level flight (over twice the existing speed record) and the ability to climb to in 1.5 minutes.Wood 1970, pp 28-29 The E.24/43 has been described as being "the most far-sighted official requirement ever to be issued by a Government department...a complete venture into the unknown with engine, airframe, and control techniques beyond anything remotely considered before". In fact, the specification had only been intended to produce a British aircraft that could match the supposed performance of an apparently existing German aircraft: the 1,000 mph (supersonic) requirement had resulted from the mistranslation of an intercepted communication which had reported that the maximum speed to have been 1,000 km/h (subsonic). This report is believed to have been referring to either the Messerschmitt Me 163A or the Me 262."UK Space Conference 2008: Test Pilot Discussion." www.space.co.uk. Retrieved: 12 October 2009.
The Miles Aircraft company had its beginnings in the 1920s and had made a name for itself during the 1930s by producing affordable ranges of innovative light aircraft, perhaps the best known amongst these being the Miles Magister and Miles Master trainers, large numbers of both types seeing extensive use by the RAF for pilot training. Although the company's products were relatively low-technology aircraft,Brown 1970. Miles had a good relationship with the Air Ministry and the Royal Aircraft Establishment (RAE), and had submitted several proposals for advanced aircraft in response to ministry specifications. Miles was invited to undertake a top-secret project to meet the requirements of Specification E.24/43.Wood 1975, p. 29. The decision to involve the company has been alleged to have been partially in order to resolve a dispute about a separated contract that allegedly had been mishandled by the Ministry of Aircraft Production; Wood states that the Minister of Aircraft Production Sir Stafford Cripps had been impressed by Miles' designs and development team and thus favoured it to meet the specification.
F. G. Miles of Miles Aircraft was summoned to the Ministry of Aircraft Production to meet Ben Lockspeiser, the director of scientific research, who outlined the difficulties and challenges involved in developing such an aircraft. The project required the highest level of secrecy throughout, Miles being responsible for the development and manufacturing of the airframe while Frank Whittle's Power Jets company developed and produced a suitable engine to equip the aircraft. For this project, Miles would cooperate with and receive assistance from the Royal Aircraft Establishment (RAE) in Farnborough and the National Physical Laboratory. On 8 October 1943, Miles received the formal go-ahead to proceed from Air Marshal Ralph Sorley, and immediately set about establishing appropriate secure facilities for the project.
Early development Faced with limited amounts of existing relevant information from available sources upon which to base the aircraft's design, Miles turned to the field of ballistics instead. He reasoned since bullets could reach supersonic speeds, aerodynamic properties that would enable an aircraft to be capable of becoming supersonic would likely to be present amongst such shapes. In particular, as a result of studying this design data, the aircraft would have both a conical nose and very thin wings complete with sharp leading edges. This contrasted with many early jet aircraft, which had rounded noses, thick wings and hinged elevators, resulting in these aircraft having local regions of supersonic flow (critical Mach number) at relatively low flight Mach numbers; thus they were less suitable for research into high subsonic speeds (in dives) than the earlier Supermarine Spitfire with its thinner wings. In 1943, RAE tests conducted using Spitfires had proved that drag was the main factor that would need to be addressed by high-speed aircraft.Brown 1980, p. 36.
Another critical addition was the use of a power-operated stabilator, also known as the all-moving tail or flying tail, a key to supersonic flight control which contrasted with traditional elevators hinged to tailplanes (horizontal stabilizers). Conventional control surfaces became ineffective at the high subsonic speeds then being achieved by fighters in dives, due to the aerodynamic forces caused by the formation of shockwaves at the hinge and the rearward movement of the centre of pressure, which together could override the control forces that could be applied mechanically by the pilot, hindering recovery from the dive.Beamont, Roland. Testing Early Jets. London: Airlife, 1990. . A major impediment to early transonic flight was control reversal, the phenomenon which caused flight inputs (stick, rudder) to switch direction at high speed; it was the cause of many accidents and near-accidents. An all-flying tail is required for non-delta winged aircraft to pass through the transonic region to supersonic speeds without a loss of control. The M.52 was the first instance of this solution.
An initial version of the aircraft was to be test-flown using Frank Whittle's latest engine, the Power Jets W.2/700. This engine, which was estimated to be capable of providing 2,000 lb of thrust, calculated to be only capable of providing subsonic performance in level flight but when flown in a shallow dive capable of transonic flight. Wood described the engine as being "remarkable as it incorporated ideas far ahead of its time". For the M.52 to achieve supersonic speeds a higher thrust version of the W.2/700 engine would be necessary.
The extra thrust required for a fully supersonic version of the aircraft, would come from more airflow from an augmentor fan drawing air around the engine through a bypass duct and combustion of fuel in the bypass air behind the fan. These changes were estimated to provide an additional 1,620 lb of thrust at 36,000 ft and 500 mph. Much greater thrust gains were believed to be available at speeds in excess of 500 mph.
The M.52's design underwent many changes during development due to the uncertain nature of the task. The overseeing committee was concerned that the biconvex wing would not give sufficient altitude for testing the aircraft in a dive. The thin wing could have been made thicker if required, or a section added to increase the wing span. As the project progressed, an increase in total weight led to concerns that power would be insufficient; thus, the adoption of rocket assistance or extra fuel tanks were considered. Another proposed measure was that the M.52 be adapted to become a parasite aircraft, launching at high altitude from beneath a large bomber serving as a mother ship.Wood 1975, p. 31. The calculated landing speed of (comparable with modern fighters but high for that time) combined with its relatively small undercarriage track was another concern; however, this arrangement was accepted.Brown 1970, p. 272.
Design In order to achieve what was at the time previously unachievable speeds a very high number of advanced features were incorporated into the design of the M.52; many of these were the result of detailed study and acquired knowledge of supersonic aerodynamics. Wood summarises the qualities of the M.52's design as possessing "all the ingredients of a high-performance aircraft of the late fifties and even some of the early sixties".
The fuselage of the M.52 was cylindrical and, like the rest of the aircraft, was constructed of high tensile steel with light alloy covering.Wood 1975, p. 30. The fuselage had a 5 foot diameter with an annular fuel tank around the engine. The engine was positioned with its centre of gravity close to that of the airframe and the wings were attached to the main structure just aft of the engine. The use of a shock cone in the nose was another key design choice; the conical shockwave from the pointed nose produced a lower loss in ram pressure for the engine than a supersonic aircraft pitot intake. A retractable tricycle undercarriage was used. The nose wheel was positioned between the pilot's feet and the main wheels were accommodated within the fuselage, folding out under the wings when deployed.