Miles M.52 - Design and Development

Design and Development

The British Miles Aircraft company had its beginnings in the mid 1920s, making its name in the 1930s with affordable ranges of innovative light aircraft. They became best known perhaps for the Miles Magister and Miles Master trainers, large numbers of which were used by the RAF for fighter pilot training. Although the company's products were relatively low-technology trainers and light aircraft, and did not include any jets, 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. In order to resolve a dispute about a contract mishandled by the Ministry of Aircraft Production, the company was invited to undertake a top-secret project to Air Ministry Specification E.24/43 for a jet-powered research plane to reach supersonic speeds. The contract, awarded in October 1943, called for an "aeroplane capable of flying over 1,000 mph (1,600 km/h) in level flight, over twice the existing speed record, and climb to 36,000 feet (11,000 m) in 1.5 minutes." The specification was intended only to match the supposed performance of a German aircraft: the 1,000 mph (supersonic) requirement resulted from the mistranslation of an intercepted communication stating that the maximum speed was 1,000 km/h (subsonic). This report dealt with the Me 163A and/or the Me 262.

Many early jet aircraft had round noses, thick wings and hinged elevators, giving them critical Mach numbers well below the speed of sound, and were less suitable for research into high subsonic speeds (in dives) than the Spitfire with its thinner wings. RAE tests with the Spitfire in 1943 had proved that drag was the main factor to be addressed in high speed aircraft.

A huge number of advanced features were incorporated into the resulting M.52 design, many of which hint at a detailed knowledge of supersonic aerodynamics. With no other sources of such information Miles had turned to design data for stabilising projectiles. In particular, the design featured a conical nose and sharp wing leading edges, as it was known that round-nosed projectiles could not be stabilised at supersonic speeds. The design used very thin wings of biconvex section proposed by Jakob Ackeret for low drag. These wings were so thin that they were known to test pilots as 'Gillette' wings, named after the famous razor. The wing tips were "clipped" to keep them clear of the conical shock wave generated by the nose of the aircraft. The fuselage had the minimum cross-section allowable around the centrifugal engine with fuel tanks in a saddle over the top.

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 hinged tailplanes (horizontal stabilizers) connected mechanically to the pilots control column. 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. 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 considered to be a minimum condition of enabling aircraft to break the transonic barrier safely, without losing pilot control. The Miles was the first instance of this solution, and has since been universally applied.

An initial version of the aircraft was to be test flown using Frank Whittle's latest engine, the Power Jets W.2/700, calculated to give transonic performance, except in a shallow dive where it would go supersonic. Meanwhile it was planned to develop a fully supersonic version of the aircraft by incorporating a reheat jetpipe - also known as an afterburner. Extra fuel was to be burned in the tailpipe to avoid overheating the turbine blades, making use of unused oxygen in the exhaust. 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 in ducts.

Finally the design included another critical element, the use of a shock cone in the nose to slow the incoming air to the subsonic speeds needed by the engine.

The fuselage of the M.52 was cylindrical and, like the rest of the aircraft, was constructed of high tensile steel with alloy covering.

The pilot would have sat in a small cockpit inside the shock cone in the nose of the aircraft, and in an emergency the entire area would be separated from the aircraft using explosive bolts. Air pressure would force the capsule off the fuselage and a parachute would slow its descent. The pilot would then exit the capsule at a lower height and parachute to safety.

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 and rocket assistance or extra fuel tanks were considered, as was high altitude air-launching from a bomber.

The calculated landing speed of 160 mph to 170 mph (comparable with modern fighters but very high for that time) combined with the small undercarriage track was a concern, but had to be accepted.