Quieter Aircraft to Take Cues From Birds, NASA Expert Says

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Finding successful noise reduction solutions also requires engineers to consider all the sound sources on an aircraft from takeoff to landing and then tweak several of them at once.

(Explore 3-D models of past and present aircraft with this online feature.)

Huff likens the task to tuning down each instrument in an orchestra to get an overall noise reduction, not asking just the violinist to play more quietly.

In the case of the chevron nozzle, the researchers considered the jet engine itself and what happens to the air when it exits the engine.

"The trick is to do something to the engine to change the flow field downstream of the engine in a way that reduces jet noise," he said.

According to Huff, the chevron nozzle is a winning technology, because it significantly reduces noise while reducing jet performance by less than 0.25 percent.

Once the chevron nozzle concept was proven in the lab, NASA researchers shared their results with the airline industry.

From there, Huff says, several manufacturers funded the development of nozzles for their engines.

"We ended up with a couple of those; those are the real winners," he said. "For each of those, we have a dozen that did impact performance or cost, and they came off the drawing board."

Future Technologies

Scott, the Boeing spokesperson, says that in addition to trying the chevrons, the manufacturing firm is currently working with engine companies to further reduce fan and jet noise.

The company is also exploring ways to reduce noise created as air flows over the airframe, especially around the flaps and landing gear.

Ultimately, Scott said, Boeing aims to keep all "objectionable noise" within "noise compatible" areas around airports.

"Achieving such large noise reduction will require revolutionary changes, new technologies, and a significant expenditure of capital," he said.

Huff said future aircraft will likely look more and more like birds to achieve desired noise levels.

"I see a morphing of the structure, a smart structure approach to different components," he said.

Such systems would be less rigid than today's aircraft.

Already, Huff says, Boeing is working on a "smart" chevron nozzle design that can essentially turn on and off.

That way aircraft noise can be reduced near the ground, but once airborne the nozzle changes position so the airplane can regain any loss in performance.

"That's more the way birds are constructed, and that's a good thing," Huff said.

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