page_title: Sound barrier
section_title: Breaking the sound barrier
hierarchical_section_title: Sound barrier / History / Breaking the sound barrier
caption_attribution_description: English: The Miles M52 - Built in 1943,designed to fly at 1000 miles per hour by Miles Aircraft to meet the perceived threat of a Nazi warplane. The project was cancelled by the British Government 3 months before it was due to fly, after they had given the designs to the United States of America. Many of the innovations in the design (such as fully moving tail control surfaces) appeared in the Bell x-1 and subsequent US experimental craft.
context_page_description: The sound barrier or sonic barrier is the sudden increase in aerodynamic drag and other undesirable effects experienced by an aircraft or other object when it approaches the speed of sound. When aircraft first approached the speed of sound, these effects were seen as constituting a barrier making faster speeds very difficult or impossible. The term sound barrier is still sometimes used today to refer to aircraft reaching supersonic flight. Breaking this sound barrier produces a Sonic Boom.
  In dry air at 20 °C, the speed of sound is 343 metres per second. The term came into use during World War II when pilots of high-speed fighter aircraft experienced the effects of compressibility, a number of adverse aerodynamic effects that deterred further acceleration, seemingly impeding flight at speeds close to the speed of sound. These difficulties represented a barrier to flying at faster speeds. In 1947 it was demonstrated that safe flight at the speed of sound was achievable in purpose-designed aircraft thereby breaking the barrier. By the 1950s, new designs of fighter aircraft routinely reached the speed of sound, and faster.
context_section_description: In 1942, the United Kingdom's Ministry of Aviation began a top-secret project with Miles Aircraft to develop the world's first aircraft capable of breaking the sound barrier. The project resulted in the development of the prototype Miles M.52 turbojet powered aircraft, which was designed to reach 1,000 mph (417 m/s; 1,600 km/h) (over twice the existing speed record) in level flight, and to climb to an altitude of 36,000 ft (11 km) in 1 minute 30 sec.
  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. 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. 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 M.52 was the first instance of this solution, and has since been universally applied.
  Initially, the aircraft was to use Frank Whittle's latest engine, the Power Jets W.2/700, which would only reach supersonic speed in a shallow dive. To develop a fully supersonic version of the aircraft, an innovation incorporated was 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. 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.
  Although the project was eventually cancelled, the research was used to construct an unmanned missile that went on to achieve a speed of Mach 1.38 in a successful, controlled transonic and supersonic level test flight; this was a unique achievement at that time which validated the aerodynamics of the M.52.
  Meanwhile, test pilots achieved high velocities in the tailless, swept-wing de Havilland DH 108. One of them was Geoffrey de Havilland, Jr. who was killed on 27 September 1946 when his DH 108 broke up at about Mach 0.9.  John Derry has been called "Britain's first supersonic pilot" because of a dive he made in a DH 108 on 6 September 1948.
caption: The prototype Miles M.52 turbojet powered aircraft, designed to achieve supersonic level flight.
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