Researchers Fight Noise, Pollution to Build New Version of Concorde : Airliner: U.S. designers aiming for a jet that would travel at Mach 2.5, carry 300 passengers and cost slightly more than conventional flights.

With a collection of engine nozzles and a giant stereo speaker, Krishan Ahuja is working to help create a new supersonic jet that will speed from Los Angeles to Tokyo in about four hours--less than half the time of a conventional jet.

The United States hopes to fly the next generation of the Concorde by 2005, but its success depends on whether scientists like Ahuja can decrease the noise and pollution emitted by a jet traveling at 2.5 times the speed of sound.

“We are getting close,” said Ahuja, an aerospace professor at Georgia Tech. “But we still have a lot of work to do.”

Britain and France fly the world’s only supersonic passenger jet. The Concorde carries 100 people at Mach 2--twice the speed of sound--for thousands of dollars a ticket.

The United States spent $800 million trying to beat them to the jet but killed the project in 1971 when Americans objected to its noise, sonic booms and pollution.

Now U.S. researchers are designing a jet that would travel at Mach 2.5, carry 300 passengers and cost only slightly more than conventional flights. Europe and Japan are designing similar models. Experts say the struggling U.S. airplane industry needs to get its craft in flight first.

“Our leadership of this program could be vital,” said Sam Gilkey of General Electric, which is designing supersonic engines. Just 500 supersonic planes, the minimum anticipated demand, would generate as much revenue as the nation’s entire 747 fleet production, he said.

But to fly, the planes must be three times quieter than the Concorde and emit very little of the nitrogen oxides that deplete the ozone layer.

“We hope to have answers to the noise and pollution questions by 1996,” said NASA researcher Kevin Shepherd. “We’re cautiously optimistic.”

That’s where Ahuja comes in. At a Georgia Tech lab north of Atlanta, he is testing volunteers’ reactions to sonic booms that roar from a giant speaker system he built outside a tiny house.

Jets create sonic booms when they crash through air particles at the speed of sound. These deafening shocks also have low-frequency waves that rattle houses.

The shape of the airplane affects what the boom sounds like, but there’s no way to stop the rattle. Ahuja’s test will determine which booms are tolerable and whether they’re more annoying indoors or out.

“If people can’t stand any of the booms or if it bothers people to hear the china rattle, we won’t be able to fly at supersonic speeds over houses,” he said as a boom shook the floorboards.

That wouldn’t kill the jet, said Tom Cole of Boeing Commercial Airplanes Co., which has 100 engineers working on the project.

At Mach 1 at a high altitude, sonic booms aren’t strong enough to reach the ground, he said. Over water, where booms wouldn’t affect people, the jets could rapidly hit Mach 2.5.

All this work is expensive, despite more than $100 million in grants NASA has dispersed. So GE and its archrival, Pratt & Whitney, teamed up to design a cleaner-burning supersonic engine.

As the temperature of burning engine fuel increases, so does nitrogen oxide pollution that harms the ozone layer. The companies are testing two types of combustors that decrease the pollution by lowering the fuel’s temperature, said GE researcher Paul Heberling.

Supersonic planes also produce more airport noise than current planes because their engines are more powerful and turbulent air creates shock waves when it careens through their exhausts.

One way to battle noise is to get the plane off the runway and into high altitudes faster. Georgia Tech engineer Bob Englar is working on building wings that would lift the plane more quickly.

Ahuja is testing other methods in flight simulators and echo chambers at the Georgia lab. He has found that changing the shape of the engine exhaust nozzle deflects noise and that shrouding nozzles or sticking metal tabs inside them eases noisy turbulence.

“The plane will never be silent,” he said. “It just depends on what the public will accept to get better international travel.”

“It will be just a much better aircraft than the Concorde, and the U.S. needs to get the jump into that market,” added Georgia Tech aerospace lab director Robert Cassanova. “It has tremendous economic potential.”

Building a Better Jet

How the supersonic passenger jet would compare with a 747:

Supersonic Jet

* Speed: Mach 2.5, or about 1,850 m.p.h.

* Travel time: Los Angeles to Tokyo, 4 hours 20 minutes; Los Angeles to Australia, 7 hours.

* Cruising Altitude: 65,000 feet.

* Construction Cost: $250 million.

* Ticket price: 10% to 15% higher than conventional overseas flights in 2005, the year the United States hopes to fly its supersonic jet.

747 Jet

* Speed: 600 m.p.h.

* Travel time: Los Angeles to Tokyo, 10 hours; Los Angeles to Australia, 14 hours.

* Cruising Altitude: 35,000 to 40,000 feet.

* Construction Cost: $125 million.

* Ticket price: Varies, but a typical sale price for Los Angeles to Tokyo is about $1,300 round trip.

Source: Associated Press