|
A supersonic transport (SST) is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound. To date, the only SSTs to see regular service have been Concorde and the Tupolev Tu-144. The last passenger flight for 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 airborne operation. Following the permanent cessation of flying by Concorde, there are no remaining SSTs in commercial service. Supersonic airliners have been the objects of numerous recent and ongoing design studies. Drawbacks and design challenges are excessive noise generation (at takeoff and due to sonic booms during flight), high development costs, expensive construction materials, great weight, and an increased cost per seat over subsonic airliners. Despite these challenges, Concorde was operated profitably in a niche market for over 27 years.〔(【引用サイトリンク】title=Retirement FAQ )〕 ==History== Throughout the 1950s an SST looked possible from a technical standpoint, but it was not clear if it could be made economically viable. Lift is generated using different means at supersonic speeds, and these methods are considerably less efficient than subsonic methods, with approximately one-half the lift-to-drag ratio. 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-subsidized SST programs quickly settled on the delta wing in most studies, including the Sud Aviation Super-Caravelle and Bristol 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.〔Whitcomb, Randall. ''Cold War Tech War: The Politics of America's Air Defense'', pp. 226–9. Burlington: Apogee Books, 2008.〕 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 could be developed for $160 million and in production lots of 200 or more sold for around $9 million.〔("Here's A Peek At Tomorrow's Huge Planes." ) ''Popular Mechanics'', April 1960, p. 86.〕 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." The SST was seen as particularly offensive due to its sonic boom and the potential for its engine exhaust to damage the ozone layer. Both problems impacted the thinking of lawmakers, and eventually Congress dropped funding for the US SST program in 1971, and all overland commercial supersonic flight was banned. Presidential adviser Russell Train warned that a fleet of 500 SSTs flying at 65,000 ft. for a period of years could raise stratospheric water content by as much as 50% to 100%. According to Train, this could lead to greater ground-level heat and hamper the formation of ozone. Later, an additional threat to the ozone was found in the exhaust's nitrogen oxides, a threat that was, in 1974, seemingly validated by MIT.〔("Environment: Pre-Mortem on the SST" ), ''Time'', September 9, 1974〕 More recent analysis in 1995 by David W. Fahey, an atmospheric scientist at the National Oceanic and Atmospheric Administration, and others, found that the drop in ozone would be no more than 1 to 2% if a fleet of 500 supersonic aircraft was operated.〔.〕〔http://stason.org/TULARC/science-engineering/ozone-depletion-intro/24-Will-commercial-supersonic-aircraft-damage-the-ozone-laye.html〕 Fahey expressed that this would not be a fatal obstacle for an advanced SST development - while "a big caution flag...() should not be a showstopper for advanced SST development.".〔.〕 Nevertheless, in the mid-1970s, Concorde was now ready for service. The US political outcry was so high that New York banned the plane. This destroyed the aircraft's economic prospects — it had been built with the London–New York route in mind. The plane was allowed into Washington, D.C., and the service was so popular that New Yorkers were soon complaining because they did not have it. It was not long before Concorde was flying into JFK. Along with shifting political considerations, the flying public continued to show interest in high-speed ocean crossings. This started additional design studies in the US, under the name "AST" (Advanced Supersonic Transport). Lockheed's SCV was a new design for this category, while Boeing continued studies with the 2707 as a baseline. By this time, the economics of past SST concepts no longer made sense. When first designed, the SSTs were envisioned to compete with long-range aircraft seating 80 to 100 passengers such as the Boeing 707, but with newer aircraft such as the Boeing 747 carrying four times that, the speed and fuel advantages of the SST concept were washed away by sheer size. Another problem was that the wide range of speeds over which an SST operates makes it difficult to improve engines. While subsonic engines had made great strides in increased efficiency through the 1960s with the introduction of the turbofan engine with ever-increasing bypass ratios, the fan concept is difficult to use at supersonic speeds where the "proper" bypass is about 0.45,〔.〕 as opposed to 2.0 or higher for subsonic designs. For both of these reasons the SST designs were doomed by higher operational costs, and the AST programs vanished by the early 1980s. Concorde only sold to British Airways and Air France, with subsidized purchases that were to return 80% of the profits to the government. In practice for almost all of the length of the arrangement, there was no profit to be shared. After Concorde was privatised, cost reduction measures (notably the closing of the metallurgical wing testing site which had done enough temperature cycles to validate the aircraft through to 2010) and ticket price raises led to substantial profits. Since Concorde stopped flying, it has been revealed that over the life of Concorde, the plane did prove profitable, at least to British Airways. Concorde operating costs over nearly 28 years of operation were approximately £1 billion, with revenues of £1.75 billion. The last regular passenger flights landed at London Heathrow Airport on Friday, October 24, 2003, just past 4 p.m.: Flight 002 from New York, a second flight from Edinburgh, Scotland, and the third which had taken off from Heathrow on a loop flight over the Bay of Biscay. By the end of the 20th century, projects like the Tupolev Tu-244, Tupolev Tu-344, SAI Quiet Supersonic Transport, Sukhoi-Gulfstream S-21, High Speed Civil Transport, etc. had not been realised. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Supersonic transport」の詳細全文を読む スポンサード リンク
|