Monday, July 5, 2004

'Mute' button for jets explored

By Carrie Spencer
The Associated Press

COLUMBUS - The latest, most advanced jet engines have seemingly simple zigzags cut around the metal exhaust nozzle to control noise.

A mechanical engineer who helped in the years of research leading to that idea is trying to replace it with an aircraft mute button.

Ohio State University professor Mohammad Samimy and associate professor Igor Adamovich have shown that they can change the patterns of exhaust turbulence - one of the main causes of aircraft noise - with high-voltage electric current.

Unlike the metal cutouts, the current can be switched off when the noise reduction isn't needed, saving fuel, said Samimy and Joseph Grady, project manager for engine noise reduction at NASA Glenn Research Center.

"When you're up six miles in the air, you don't care how much noise you're making," Grady said.

Airports spend tens of millions of dollars buying and soundproofing nearby homes because of noise. It also keeps airlines from scheduling night flights that might lead to lower fares. Meanwhile, residential areas are creeping closer to military bases, which then deal with more noise complaints.

Commercial aircraft today are four times quieter than they were in the 1970s, and Cleveland-based NASA Glenn is sponsoring several studies with a goal of halving the noise heard around airports by 2008 and cutting it in half again by 2020.

Samimy's research, supported by $100,000 from NASA, is one of four or five ideas being considered for the longer-term goal, Grady said.

The next step is taking it from lab simulation to testing on a scale model engine and then the real thing. Samimy said he's not comfortable guessing at how much the device would reduce noise.

"It looks encouraging and it passed the first hurdle," Grady said.

Cincinnati-based GE Aircraft Engines uses the new zigzag nozzles, which encourage outside air to mix with the exhaust and reduce the roaring noise from blobs of air slamming against each other at high pressures and temperatures. They're an important part of meeting the 2008 goal, Grady said.

But the technique reduces thrust, burning more fuel for the whole flight. If Samimy's concept works, the engines could be quieted only during takeoff and landing.

"What we'd like to do is what I guess professor Samimy is doing, which is turn the effect on at will and off at will," said Mike Benzakein, general manager of advanced engineering at GEAE.

GE is also exploring "smart" metals that can change shape with temperature and a University of Cincinnati study on shooting small jets of air into the exhaust, Benzakein said.

"Five years from now we'll probably have to pick a concept," he said.

Industry experts said Samimy's idea could be 10 to 15 years from appearing in airports, if it makes it at all. Samimy is hoping for four to five years.


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