A supersonic aircraft is an aircraft capable of supersonic flight, that is, flying faster than the speed of sound (Mach 1). Supersonic aircraft were developed in the second half of the twentieth century. Supersonic aircraft have been used for research and military purposes, but only two supersonic aircraft, the Tupolev Tu-144 (first flown on December 31, 1968) and the Concorde (first flown on March 2, 1969), ever entered service for civil use as airliners. Fighter jets are the most common example of supersonic aircraft.
The aerodynamics of supersonic flight is called compressible flow because of the compression associated with the shock waves or "sonic boom" created by any object traveling faster than sound.
Aircraft flying at speeds above Mach 5 are called hypersonic aircraft.
History
The first aircraft to fly supersonic in level flight was the American Bell X-1 experimental plane which was powered by a thrust rocket powered by liquid oxygen and ethyl alcohol. Most supersonic aircraft have been military or experimental aircraft.
Aviation research during World War II led to the creation of the first rocket- and jet-powered aircraft. Several claims of breaking the sound barrier during the war subsequently emerged. However, the first recognized flight exceeding the speed of sound by a manned aircraft in controlled level flight was performed on October 14, 1947 by the experimental Bell X-1 research rocket plane piloted by Chuck Yeager. The first production plane to break the sound barrier was an F-86 Canadair Sabre with the first supersonic woman pilot, Jacqueline Cochran, at the controls. According to David Masters, the DFS 346 prototype captured in Germany by the Soviets, after being released from a B-29 at 32800 ft (10000 m), reached 683 mph (1100 km/h) late in 1951, which would have exceeded Mach 1 at that height. The pilot in these flights was the German Wolfgang Ziese.
On August 21, 1961, a Douglas DC-8-43 (registration N9604Z) exceeded Mach 1 in a controlled dive during a test flight at Edwards Air Force Base. The crew were William Magruder (pilot), Paul Patten (copilot), Joseph Tomich (flight engineer), and Richard H. Edwards (flight test engineer). This was the first supersonic flight by a civilian airliner other than the Concorde or Tu-144.
In the 1960s and 1970s, many design studies for supersonic airliners were done and eventually two types entered service, the Soviet Tupolev Tu-144 (1968) and Anglo-French Concorde (1969). However political, environmental and economic obstacles and one fatal Concorde crash prevented them from being used to their full commercial potential.
Design principles
Supersonic flight brings with it substantial technical challenges, as the aerodynamics of supersonic flight are dramatically different from those of subsonic flight (i.e., flight at speeds slower than that of sound). In particular, aerodynamic drag rises sharply as the aircraft passes the transonic regime, requiring much greater engine power and more streamlined airframes.
Wings
To keep drag low, wingspan must be limited, which also reduces the aerodynamic efficiency when flying slowly. Since a supersonic aircraft must also take off and land at a relatively slow speed, its aerodynamic design must be a compromise between the requirements for both ends of the speed range.
One approach to resolving this compromise is the use of a variable-geometry wing, commonly known as the "swing-wing," which spreads wide for low-speed flight and then sweeps sharply, usually backwards, for supersonic flight. However, swinging affects the longitudinal trim of the aircraft and the swinging mechanism adds weight and cost. Use of a delta wing, such as those used on the Aerospatiale-BAC Concorde generates a vortex which energises the flow on the upper surface of the wing at high speeds and attack angles, delaying flow separation, and giving the aircraft a very high stall angle. It also solves the issue of fluid compressibility at transonic and supersonic speeds. However, it is, of course, inefficient at lower speeds due to the requirement of a high angle of attack, and therefore need the use of flaps.
Heating
Another problem is the heat generated by friction as the air flows over the aircraft. Most subsonic designs use aluminium alloys such as Duralumin, which are cheap and easy to work but lose their strength quickly at high temperatures. This limits maximum speed to around Mach 2.2.