The origins of Miles Aircraft Ltd can be found in the mid-1920s, and the company came to the lightplane fore in the 1930s with several competitively priced series of light aircraft. The company became best known for its Magister and Master training aircraft, which were flown in large numbers for RAF pilot training. The company’s light and training aircraft were of the low-technology type, but Miles nonetheless possessed a good relationship with the Air Ministry and the Royal Aircraft Establishment, and did submit several proposals for advanced aircraft in response to official requirements. In resolution of a dispute about a contract which had been mishandled by the Ministry of Aircraft Production, Miles was invited to undertake a top-secret project to Specification E.24/43 for a turbojet-powered research aeroplane with supersonic capability.
Awarded in October 1943, the contract demanded an ‘aeroplane capable of flying over 1,000 mph (1610 km/h) in level flight, over twice the existing speed record, and climb to 36,000 feet (10975 m) in 1.5 minutes’. The specification had been framed to create a British aeroplane offering performance equal to that supposed for a German aeroplane, either the Messerschmitt Me 163 rocket-powered interceptor or Me 262 turbojet-engined fighter, and the supersonic speed of 1,000 mph (1610 km/h) resulted from the mistranslation of an intercepted communication stating that the maximum speed of the German aircraft was 1000 km/h (620 mph), which was subsonic.
Many early turbojet-powered aircraft had round noses, a thick-section wing and hinged elevators, which was a combination giving them critical Mach numbers well below the speed of sound, and were in fact somewhat less suitable for research into high subsonic speeds (although only in the dive) than the Supermarine Spitfire with its thinner wing. It was in fact RAE tests with the Spitfire in 1943 which had shown that that drag was the principal factor requiring a solution in the production of high-speed aircraft.
Many advanced features incorporated into the resulting M.52 design suggested an advanced knowledge of supersonic aerodynamics: in the absence of this type of data for aircraft, Miles had used data already used for the stabilisation of high-speed projectiles. The design therefore had a conical nose and sharp wing leading edges, as it was known that round-nosed projectiles could not be stabilised at supersonic speeds. The thin wing was of biconvex section of the type proposed by a Swiss aerodynamicist, Jakob Ackeret, for low drag. The wing was so thin that it became known as the ‘Gillette’ wing’ after the famous razor. The tips of this wing were clipped to keep them clear of the conical shock wave generated by the nose of the aircraft. The fuselage had a cross-section just large enough to allow the installation of a centrifugal-flow engine of the type on which the British were concentrating in World War II, and the fuel tankage was of the saddle type above the engine.
Another advanced, and indeed critically important, feature was a power-operated stabilator (otherwise all-moving tailplane). As later proved by practical trials, this was a key element of supersonic flight control. Traditional tailplanes, with a fixed surface carrying a hinged elevator or elevators, included a mechanical linkage with the pilot’s control column. Control surfaces of this type became ineffective at the high subsonic speeds then being achieved by diving fighters as a result of the aerodynamic forces caused by the formation of shockwaves at the hinge and the rearward movement of the centre of pressure, which could combine to exceed the control force applied mechanically by the pilot, hindering recovery from the dive if not actually making it impossible. Another major problem in early transonic aircraft was control reversal, the phenomenon in which flight inputs to the moving tail surfaces switch direction at high speed, and the all-flying tail as first adopted for the M.52 is seen as wholly necessary to allow acceleration through transonic speeds without the pilot losing control.
An initial version of the M.52 was to be test flown using Frank Whittle’s latest turbojet engine, the Power Jets W.2/700, which was expected to deliver thrust sufficient to give the M.52 transonic speed in level flight and supersonic speed in a shallow dive. It was also planned to develop a fully supersonic version of the M.52 by incorporating an afterburning version of the engine for greater thrust. In this reheated jetpipe arrangement, fuel was to be burned with the unused oxygen in the exhaust within the jetpipe to avoid overheating the turbine blades, and to supply more air to the afterburner than could move through the fairly small engine, an augmentor fan powered by the engine was to be fitted behind the engine to draw air around the engine and duct it to the afterburner.
The design included another very significant element, namely a shock cone in the otherwise cylindrical nose inlet to slow the incoming air to the subsonic speeds best suited to the engine’s aspiration requirement.
Novel escape system
The M.52 was to be constructed of high-tensile steel covered with light alloy. The pilot’s cramped cockpit was located inside the shock cone, and in an emergency the entire section was to have been separated from the rest of the aeroplane by the detonation of explosive bolts, whereupon air pressure would force the capsule away from the fuselage before the opening of a parachute slowed its descent. The pilot would then have departed the capsule at a lower height to take to his conventional parachute.
The design of the M.52 went though many changes during its development in reflection of the task’s several uncertainties. The overseeing committee was concerned that the biconvex wing would not allow the aeroplane to reach an altitude sufficient for dive testing. The thin wing could have been made thicker if required, or a section could have been added to increase the span. As the design began to mature, its increasing weight prompted concerns that the power would be inadequate, and thought was therefore given to rocket boosting or the addition of larger fuel tankage, as was the possibility of air-launching from a bomber at high altitude.
The calculated landing speed was in the order of 160 mph to 170 mph (255 to 275 km/h) and was considered high for the time, and the track of the main landing gear units was narrow, but these factors were deemed acceptable in a technology prototype.
A Miles M.3B Falcon Six lightplane, which had been used for RAW wing tests, was allocated to the company in 1943, and on this a full-sized wooden model of the M.52’s wing, test instrumentation, and revised landing gear were fitted. The revised aeroplane recorded its maiden flight on 11 August 1944 and, by comparison with the standard Falcon Six with a wing of 12% greater area, the landing speed increased by slightly more than 50% to 61 mph (98 km/h).
For high-speed testing, the all-flying tail was fitted to a Spitfire as this was the fastest aeroplane available, and the test pilot flew this revised fighter during October and November 1944 to a speed of Mach 0.86 in a dive from high altitude.
Cancellation at the critical moment
In 1944 the design work was considered 90% complete, and the company was ordered to proceed to the construction of three M.52 prototypes. Then in February 1946, during the period of financial austerity and research retrenchment following the end of World War II, the new Labour government introduced dramatic budget cuts and the Director of Scientific Research, Sir Ben Lockspeiser, later cancelled the M.52 project. Other factors contributing to the cancellation included doubts about pilot safety, as well as assessment of captured German research data suggesting that a swept wing was desirable at supersonic speeds.
At the time of the project’s cancellation, the first of the three M.52 prototypes was 82% complete, with test flights planned to begin in a few months. The test programme was to have involved trials without an afterburner with the object of attaining Mach 1.07 by the end of 1946.
Miles Aircraft Ltd entered receivership in 1947, and its aircraft assets, including the design data for the M.52, were bought by Handley Page. Cancellation of the project considerably slowed British progress in supersonic design technology.
Only comparatively small sums would have been needed to complete the first M.52, but the government had opted for a different tack and embarked on a new programme of pilotless expendable rocket-propelled missiles. The M.52 design was passed to Dr Barnes Wallis at Vickers-Armstrongs, and engine development took place at the RAE. The result was a radio-controlled 30% scale model of the M.52 design powered by an Armstrong Siddeley Beta rocket engine.
The first launch took place on 8 October 1947 at high altitude from a de Havilland Mosquito, but was unsuccessful inasmuch as the rocket motor exploded shortly after release. Only days later, the Bell X-1 broke the ‘sound barrier’ in the USA. On 10 October 1948, a second rocket-powered model was launched, and reached Mach 1.38 in stable level flight. However, instead of diving into the sea as planned, the model failed to respond to radio commands and was last observed (on radar) heading out into the Atlantic. Following that successful supersonic test flight, further work on this project was cancelled.
Many important design principles incorporated in the M.52 did not reappear until the mid-to late 1950s, with the development of truly supersonic aircraft such as the Fairey Delta 2, and the English Electric P.1 which formed the basis of the Lightning interceptor. Both of these aircraft were developed in initial response to Requirement ER.103 of 1947, which combined the knowledge gained from the M.52, missile research projects and captured German experimental data.
Type: single-seat supersonic research aeroplane
Dimensions: span 27 ft 0 in (8.23 m); length 28 ft 0 in (8.53 m), wing area 108.1 sq ft (10.04 m²)
Weights: loaded 7,710 lb (3497 kg); maximum take-off 8,200 lb (3720 kg)
Powerplant: one Power Jets W.2/700 turbojet engine rated at 4,000 lb st (17.79 kN) with augmentor and afterburner
Performance: maximum speed 1,000 mph (1609 km/h) at 36,000 ft (10975 m); climb to 36,000 ft (10975 m) in 1 minute 30 seconds; service ceiling 50,000 ft (15240 m)