A supersonic transport (SST) or a supersonic airliner is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound in terms of air speed. To date, the only SSTs to see regular service have been Concorde and the Tupolev Tu-144, although the Boom Technology Overture SST may succeed in starting service around 2029, which would make it the third operational SST. The last passenger flight of the Tu-144 was in June 1978 and it was last flown in 1999 by NASA. Concorde's last commercial flight was in October 2003, with a November 26, 2003, ferry flight being its last flight. Following the termination of flying by Concorde, there have been no SSTs in commercial service. However, several companies have proposed supersonic business jet designs. Small SSTs have less environmental impact and design capability improves with continuing research which is aimed at producing an acceptable aircraft. Supersonic airliners have been the objects of numerous ongoing design studies such as those of Boom Technology. Drawbacks and design challenges are excessive noise generation (at takeoff and due to sonic booms during flight), high development costs, expensive construction materials, high fuel consumption, extremely high emissions, and an increased cost per seat over subsonic airliners. However, despite these challenges, Concorde was claimed to have operated profitably.
History
Planning Throughout the 1950s an SST looked possible from a technical standpoint, but it was not clear if it could be made economically viable. Because of differences in lift generation, aircraft operating at supersonic speeds have approximately one-half the lift-to-drag ratio of subsonic aircraft. This implies that for any given required amount of lift, the aircraft will have to supply about twice the thrust, leading to considerably greater fuel use. This effect is pronounced at speeds close to the speed of sound, as the aircraft is using twice the thrust to travel at about the same speed. The relative effect is reduced as the aircraft accelerates to higher speeds. Offsetting this increase in fuel use was the potential to greatly increase sortie rates of the aircraft, at least on medium and long-range flights where the aircraft spends a considerable amount of time in cruise. SST designs flying at least three times as fast as existing subsonic transports were possible, and would thus be able to replace as many as three planes in service, and thereby lower costs in terms of manpower and maintenance.
Serious work on SST designs started in the mid-1950s, when the first generation of supersonic fighter aircraft were entering service. In Britain and France, government-subsidised SST programs quickly settled on the delta wing in most studies, including the Sud Aviation Super-Caravelle and Bristol Type 223, although Armstrong-Whitworth proposed a more radical design, the Mach 1.2 M-Wing. Avro Canada proposed several designs to TWA that included Mach 1.6 double-ogee wing and Mach 1.2 delta-wing with separate tail and four under-wing engine configurations. Avro's team moved to the UK where its design formed the basis of Hawker Siddeley's designs. By the early 1960s, the designs had progressed to the point where the go-ahead for production was given, but costs were so high that the Bristol Aeroplane Company and Sud Aviation eventually merged their efforts in 1962 to produce Concorde. In the early 1960s, various executives of US aerospace companies were telling the US public and Congress that there were no technical reasons an SST could not be produced. In April 1960, Burt C Monesmith, a vice president with Lockheed, stated to various magazines that an SST constructed of steel weighing 250,000 pounds (110,000 kg) could be developed for $160 million and in production lots of 200 or more sold for around $9 million. But it was the Anglo-French development of the Concorde that set off panic in the US industry, where it was thought that Concorde would soon replace all other long range designs, especially after Pan Am took out purchase options on the Concorde. Congress was soon funding an SST design effort, selecting the existing Lockheed L-2000 and Boeing 2707 designs, to produce an even more advanced, larger, faster and longer ranged design. The Boeing 2707 design was eventually selected for continued work, with design goals of ferrying around 300 passengers and having a cruising speed near to Mach 3. The Soviet Union set out to produce its own design, the Tu-144, which the western press nicknamed the "Concordski".
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