When the Concorde crashed back in July, it may have spelled the end of service for the 30-year-old supersonic transport. But why isn’t there any replacement ready to step out from the wings?

It’s not for lack of trying. Several countries have attempted to come up with viable solutions, but ultra fast passenger travel has been plagued by difficulties. But that doesn’t mean scientists have given up.

From the time the Wright Brothers took to the skies in 1903, the hope has been to keep flying faster and higher. For a while, technology progressed at such a rapid rate that it looked as if the sky was the limit and that supersonic travel would become the norm. "There’s no doubt about it," says John Sullivan, professor of aeronautics and astronautics at Purdue University, "if you go back to the 60s it was certainly planned that supersonic transport would be very commonplace. It would be the way people fly across the Atlantic, and eventually the Pacific. The airplanes were being developed by all the major air frame companies in the world and it was considered to be the new mode of transportation."

While everyone has heard of the Concorde, it wasn’t the first jet to achieve supersonic status. The European Concorde program began in 1963, but Russia was the first to fly a supersonic transport, or SST. The Tupolev-144 had its maiden flight in 1968, but the "Concordski," as the press later dubbed it, was eventually grounded in the late ’70s after it suffered two fatal crashes, including one at an air show in France in 1973 that killed 13 people.

image: Boeing

The Plane that Never Was Before Congress pulled the plug on the Boeing 2707, which would have been America’s first SST, 26 airlines ordered 122 aircraft. Boeing initially designed a plane with hinged wings that could be extended for slower speeds and swept back when the plane was going faster. But it eventually went with a delta-shaped wing, like the Concorde. The final design also featured a needle-shaped nose that would drop during takeoff and landing for improved pilot visibility. The 2707 was 318 feet long and would have had a cruising speed of Mach 2.7. It was supposed to be able to hold 350 people per flight (much more than the Concorde’s 100). The 91-foot nose section of the mock-up is on display at the Hiller Aviation Museum in San Carlos, California.

Meanwhile, the U.S. tried to get in on the action with its own SST project, but it never got off the ground. Boeing beat out Lockheed and North American Aviation in a competition to develop an SST in 1966. A mock-up of the Boeing 2707 was completed. But in 1971, just as Boeing was about to manufacture the first one, the program got canned because it was considered to be harmful to the environment and too expensive due to rising fuel costs.

That left the Concorde, which has been flying commercially since 1976 and was a symbol of national pride for France and England, who built and operated it. But even before the fatal crash this summer, Concorde may have been doomed. "Concorde is an old airplane," says Sullivan. "It’s no longer state of the art. It’s one of the main reasons why the Concorde will probably never fly again."

The Concorde traveled at Mach 2, or twice the speed of sound. Achieving that kind of speed requires not only the right aerodynamics, but large quantities of fuel (a transatlantic crossing carried one metric ton of fuel for each of its 100 passengers) and more expensive materials that can take the higher temperatures generated at such speed. "It was only after they finished construction of the aircraft that they realized it was going to cost a lot more to build and operate than initially planned," points out Steven Schneider, assistant professor in the school of aeronautics and astronautics at Purdue. "To some extent the supersonic transport is a flying fuel tank," says Dennis Bushnell, Chief Scientist at NASA’s Langley Research Center. "Fifty to 68 percent of its initial weight is fuel, [and you need so much] because of the additional wave drag." Wave drag is the extra resistance a supersonic aircraft faces because of the shockwave it creates.

Russia’s Tupolev 144 image: NASA

In addition to the huge fuel costs associated with faster-than-sound flight, Concorde was also limited to where it could fly at those high speeds—because of the sonic booms generated as it passed the sound barrier, it could only be used to fly over water.

But there was another problem, associated not only with flying so fast but with flying at an altitude of 60,000 feet—five miles above jumbo jets, where you can see the curvature of the earth. At this altitude Concorde began sharing its space with the ozone layer, so engine exhaust could contribute to the growing hole in the ozone layer. More recently, scientists have found that the emission of water vapor at high altitudes could contribute to the greenhouse effect, according to Bushnell.

Even with its drawbacks, supersonic travel is appealing because it reduces travel time so much. So, in the mid 1990s, NASA took another look at supersonic commercial aviation and even chartered one of the remaining Russian SST’s to test new materials and technology. "The basic goals of the High-Speed Civil Transport program were to determine whether or not it would be environmentally and economically feasible to start a developmental program of a civilian supersonic transport," says Bushnell.

Although scientists made headway in addressing the environmental issues, the cost of building and operating SSTs remained too high, according to Bushnell , and the program was dropped.

"I think that the question of the future of the supersonic transports is a question that’s true of a lot of technology," says Sullivan. "For example, space launch is not purely a technological question any more. It’s a question of the cost effectiveness of developing a large new technical system which has a large cost."

A model of the Hyper-X. image: NASA

There is presently some military interest in supersonic cruise machines which would be used for reconnaissance, according to Bushnell. The technology researchers are looking into includes using the injection of liquid water to reduce takeoff noise, very extreme aerodynamics configurations, and materials that weren’t available a few years ago, he says.

While Bushnell says that NASA will periodically revisit the problem of commercial supersonic aviation, its latest high-speed aircraft will leave even Concorde in the dust. The exotic 12-foot long test aircraft known as the X-43 or Hyper-X, is expected to pass supersonic speed, venturing into hypersonic. It may get up to Mach 7, or seven times the speed of sound. It will be air-breathing, meaning that it will use oxygen—in this case from the atmosphere—to burn the fuel it carries on board, which is hydrogen. The first flight is scheduled for next month, according to NASA.

While no one is looking at ideas yet for a commercial version, or even a manned one, it remains a tantalizing glimpse into the future of high speed aviation.

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