FOR six years, aeronautical engineers have been designing the next generation of supersonic jetliners. They envision an aircraft powered by ceramic engines with ozone-safe exhaust, piloted from a cockpit with no front windows, and with fares cheap enough to appeal to the pennywise.
What they envision, however, has up to now been a gleam on a computer screen or a model in a wind tunnel. Because the United States has no large supersonic commercial aircraft, engineers have had little real-life information on how such craft operate now, let alone on how far they need to go to meet their goals. This June, however, a modified Russian TU-144 supersonic transport will begin test flights that will help researchers fill in these gaps.
Crammed with high-tech equipment and laced with sensors, the 15-year-old plane is expected to yield data on everything from cabin and cockpit noise to the searing conditions inside the plane's powerful engines.
The flight tests are part of a $4.8 billion technology demonstration program funded by American and British aerospace companies, as well as the National Aeronautics and Space Administration. By 2002, the US partners hope to know enough about the necessary technologies to allow aircraft builders to decide whether to begin building a fleet of supersonic airliners, according to NASA and aerospace officials.
Early efforts to develop a US supersonic airliner ended in a flame-out in the 1970s, largely over concerns that the high-altitude planes were uneconomical and would damage the earth's ozone layer. Meanwhile, Britain and France teamed up to build the Concorde, and the Russians built the TU-144.
Since then, economic growth along the Pacific Rim, a grueling 14-hour flight time to cross the Pacific in conventional jets, as well as advances in new materials, computers, and sensors, have combined to brighten the prospects for a high-speed transport.
Even so, experts say, researchers will be pushing the technological envelope. To meet the economic test, a new supersonic transport must carry between 250 and 300 passengers more than 5,000 miles. Ticket prices must be no more than 20 percent higher than today's subsonic fares. And the craft would have to be as reliable as today's airliners and comparably quiet. By contrast, the Concorde carries about 100 passengers and has a range of about 3,000 miles. At upwards of $3,000 for a one-way ticket (vs. about $1,000 aboard a 747), the Concorde is platinum-priced. And it is so noisy that the Federal Aviation Administration has to waive its airport noise restrictions at the few US airports the Concorde serves.
Moreover, engine emissions from a new supersonic airliner would have to be extremely clean. "That is an absolute going in," says Craig Martin, a spokesman for Boeing Company, the lead contractor in the US research project.
Engine designers say they are finding ways to burn fuel while reducing oxides of nitrogen, a byproduct of combustion, to acceptable levels. Drastically cutting these emissions is vital because such oxides speed chemical reactions that destroy stratospheric ozone.
The very size, payload, and projected range of the new plane mean that the engines also will have to endure higher temperatures for longer periods than any engine flying today, says Dick Hines, the manager of Pratt and Whitney's supersonic transport propulsion program. "These engines might be the first to use composite materials, such as ceramic composites in the combustion chamber," he says.
A new plane also will get something of a nose job. To generate enough lift, the Concorde and TU-144 must take off and land at a steep angle. Yet the streamlined noses are too long to allow pilots to see where they are going during these phases of flight. To ensure visibility, the nose is hinged and droops on command. The crew raises the nose for supersonic flight. This approach, however, adds several thousand pounds to the plane's weight.
To counter this, designers have proposed a fixed nose with no front windows. Pilots would use high-resolution digital displays that combine video, infrared, and radar data to "see" what's ahead of them. In January, NASA tested a prototype system mounted in the main cabin of a modified 737. For pilots used to flying in the nose of a plane, "the physiological cues are different in the center of the plane," says Bob Yackovetsky, a NASA test manager in Hampton, Va. Yet that didn't seem to affect the test pilots' performance.