ENGINEERING advances and demand for more global travel are reviving interest in a supersonic airliner in the United States. Efforts are quietly moving forward in government and industry to see if a plane can be built that would fly faster and carry more passengers than the Anglo-French Concorde.
It would also have to be cleaner burning and sound like something less than a rock band when taking off. Concern about cost, noise, and damage to the ozone layer killed the first US attempt to build a supersonic transport (SST) in 1971, in a rancorous debate in Congress. Those issues still exist.
While scientists believe these problems may now be surmountable, they note that a second-generation SST couldn't be developed until after 2000 - and won't be until the environmental issues are resolved.
``We do have the capability to build a supersonic transport today,'' says Bob Welge, a supersonic specialist at McDonnell Douglas Corporation. ``But the key is to make it economically attractive and environmentally acceptable.''
By the turn of the century, there is expected to be more airline travel between the United States and Pacific Rim countries than between the US and Europe. This does not mean flights across the Atlantic are going to tail off - only that ones across the Pacific are going to pick up dramatically.
This is one reason why engineers are back at their drafting tables sketching pictures of planes with snipe noses that can fly two to three times the speed of sound. In the future, business people and others flying between Los Angeles and Tokyo, which is where many American travelers will be going, won't want to spend too much time in the air, coddling another memo from the boss. Time is important. Also, the Concorde can't make it across the Pacific nonstop. A new-generation SST presumably could.
Studies done by McDonnell Douglas, Boeing Company, and others suggest the market may support a fleet of several hundred supersonic aircraft in the early 21st century, provided the pollution and other problems can be overcome.
``The demand for a speedy airplane is there,'' says Tom Cole of Boeing.
There is one other reason for enduring interest in a US supersonic plane: competition. An environmentally acceptable SST could revolutionize air travel. US companies want to be in on any major advance in aviation, whether alone or as part of an international consortium. The British and French are stepping up their study of a successor to Concorde. The Japanese and Soviets are interested in supersonic aircraft also.
``It may be that to maintain American leadership in aeronautics, we will have to step up to this next plateau in aviation,'' says Howard Wesoky, program manager for high-speed transport research with the National Aeronautics and Space Administration (NASA).
The Concorde is currently the only supersonic airliner in service. Built by British Aerospace and the French company Aerospatiale, the 100-seat plane with the drooping nose and birdlike profile operates on transatlantic routes. Thirteen of the 16 planes originally built are still in service. Small size and lack of range, though, have hampered the commercial success of the aircraft.
In May, Boeing and McDonnell Douglas agreed to team up with Deutsche Airbus of West Germany, as well as British Aerospace and Aerospatiale, to conduct a joint study of the feasibility of a new SST. The British and French are also working on studies on their own, as are McDonnell Douglas and Boeing.
NASA, meanwhile, is in the midst of a six-year, $284-million look at the problems of engine emissions, airport noise, and sonic booms connected with the aircraft. In a change from past practices, the agency is tackling the environmental issues first.
As if to punctuate this point, NASA has formed a special advisory committee to look at ozone depletion. It includes members from industry and government as well as from environmental groups.
The ozone problem will be one of the toughest. Because of the temperatures and stress experienced at high speeds, supersonic aircraft operate in the stratosphere, where the air is thin. This is also where nitrogen oxide emissions from the planes can cause severe damage to the Earth's protective ozone layer, which could lead to global warming.
Recent studies by Harold Johnston, a chemistry professor at the University of California, Berkeley, and two other researchers show that a fleet of 500 supersonic airliners using today's technology would deplete the ozone layer by 15 to 20 percent - far more than the damage predicted from chloroflourocarbons.
``There is a big hurdle they have to jump over - and it's not certain at this point they are going to make it,'' says Dr. Johnston, who sits on the ozone advisory panel.
Engineers are trying to fashion new engine combustors to deal with the problem. Mr. Wesoky of NASA says early tests are encouraging - ``we are getting emission indexes in the range we feel will be necessary'' - although the work in the laboratory is a long way from being ready for the airport.
To cope with sonic boom, researchers are studying new wing designs and nose configurations that would muffle the sound.
Reducing general aircraft noise during landing and takeoff may be a tougher challenge. One idea is to increase lift so the planes leave the airport sooner. Another is to build an engine that would act like a subsonic plane at takeoff and then shift to supersonic speeds. The difficulty is getting an engine to perform efficiently at both levels.
While airframe makers here and in Europe are looking at slightly different designs, there are a few constants. Most envision planes that will fly from twice the speed of sound, the same as Concorde, to 3.2 times the speed of sound.
They are expected to be bigger - carrying 250 to 300 passengers - have greater range, and offer seats for something less than platinum prices. Seats on the Concorde go for several thousand dollars each, relegating them mainly to the Fortunate 500. Manufacturers think new SSTs would have to approach the prices of conventional airliners.
Development costs for a new fleet of supersonic airliners would be high: Estimates run from $10 billion to $15 billion. This may put a new SST out of reach of any one company, requiring instead a consortium. How the banking is ultimately worked out, though, must wait while the engineers attempt their wizardry.
``Solutions to the environmental problems may be difficult, but are not necessarily out of reach,'' Malcolm MacKinnon, manager of high-speed transport design and development at Boeing, recently wrote. ``In the research done so far no show-stoppers have been encountered.''