Will It Fly? : Edwards Is Testing Ground for Supersonic Innovations
For the past few months, NASA pilot Dana Purifoy has been zooming through the skies north of Edwards Air Force Base in an F-16 jet loaded with what amounts to a space-age vacuum cleaner.
As he races along a restricted military flight corridor, the machine cranks to life, sucking air through millions of tiny, laser-drilled holes in a titanium panel covering most of the jet’s left wing.
The experimental system is designed to reduce air turbulence on the wing’s surface, cutting drag and fuel consumption. But after seven test flights, whether it works is still unknown.
The radical new design is part of NASA’s ambitious, $1.9-billion effort to score a string of major engineering breakthroughs that would pave the way for construction of a supersonic airliner that would be faster, cheaper and quieter than the Concorde, a commercial flop.
Flying at 2.4 times the speed of sound and carrying 300 passengers, the titanium-skinned jetliner, called the High Speed Civil Transport, could travel from Los Angeles to Tokyo in just four hours, slicing six hours off the current commercial-carrier timetable.
NASA hails the aircraft as the most important industrial initiative in the nation’s future and hopes it will help the U.S. retain its fragile world dominance in large-aircraft sales.
“It’s a small investment to keep the U.S. in a leadership position in one of the areas where we have a favorable balance of trade,” said Alan Wilhite, deputy manager of NASA’s high-speed research program.
The space agency estimates that up to 1,000 copies of the aircraft could be sold for $200 billion, generating about 140,000 manufacturing jobs in the U.S. NASA has contracted with Boeing and McDonnell Douglas to build the experimental airframe and with General Electric and Pratt & Whitney to build its engines.
*
But for the project to succeed, NASA and its contractors must solve a number of complex technical and environmental problems, and NASA’s Dryden Flight Research Center at Edwards is a proving ground for several developing technologies, including the lower-turbulence wing.
As air passes over a wing in flight, it changes from a smooth flow at the leading edge to a turbulent flow toward the trailing edge. At sustained supersonic speeds, this turbulence creates drag on an aircraft.
To draw roiling air off wing surfaces, NASA and its engineers developed a suction device powered by a cabin-pressurization pump once used in an old Boeing 707 airliner.
The pump, located in the F-16’s ammunition bay, pulls air through 10 million minute holes in a titanium panel, or “glove,” that covers three-quarters of the top of the jet’s left wing.
The system has been undergoing flight-testing since October, with Purifoy flying it from the air base to the Owens Lake area in Inyo County. But NASA officials say it is too early to tell if the device can produce laminar, or smooth, air flow.
“We have not completely analyzed the data,” said Marta Bohn-Meyer, who manages the glove project. “We’ve only got two flights where the suction was operating, and another two flights where we collected a lot of flight data, but we have not gotten all the way through it to say if we had laminar flow or not.”
Engineers encountered an unexpected problem, she said, because the glove is secured to the wing with hooks instead of bolts. The hooks allow the more rigid glove to slide around a bit when the wing bends during flight.
But the resulting gap under the glove produces more air pressure on the wing, making the jet twist to the left and forcing pilot Purifoy to slow down and ease off on tight turns and other high-performance maneuvering.
“The faster you go, the more [the F-16] wants to go sideways,” he said.
The difficulty is particularly acute when Purifoy tries to jockey his plane up beneath a larger air tanker for midair refueling. He must refuel twice per test flight.
“You have to take a little more care so you don’t do hard maneuvering when you refuel,” he said.
*
But even if the anti-turbulence system eventually is perfected, several other major technological obstacles remain.
Engines on supersonic jets are extremely noisy, and the high-speed transport would have to meet noise standards at major airports to be commercially successful. Engineers are trying to develop quieter propulsion systems.
A related problem is that the transport’s engine combustion chambers would operate at 3,600 degrees, hot enough to liquefy steel alloys in present-day engines. NASA hopes to come up with a new chamber using fiber-reinforced ceramic composite liners that could resist the heat.
NASA also is seeking ways to muffle the sonic booms such an aircraft would make. Federal law prohibits sonic booms over land, and some scientists warn that repeated booms may harm marine life when emitted over oceans.
An aircraft’s mass, shape and speed determine the severity of a sonic boom, which is an atmospheric shock wave that trails behind it, like a bow wave trailing a boat. Although reducing the thunderous crack of a boom is possible, it must be done without seriously reducing flight efficiency.
*
The High Speed Civil Transport is a direct descendant of the ill-fated supersonic transport, or SST, that was killed by Congress in 1971 over concerns that nitrogen oxide in its engine emissions was damaging the Earth’s protective ozone layer. Ozone filters out much of the sun’s ultraviolet radiation, which can cause skin cancer, cataracts and crop damage.
NASA and its contractors believe they have conquered that problem with a new engine that burns fuel more completely. And a NASA-financed study estimated that a fleet of supersonic jetliners would erode only 1% of the ozone shield, a loss that NASA believes is acceptable to the public.
But environmentalists warn that because 5% of the ozone layer over North America has already been lost to pollution, even small additional losses are unacceptable and would raise skin-cancer rates.
