NASA and three corporations have completed flight tests designed to help quiet jet aircraft noise, both in the passenger cabin and on the ground.

The program was a cooperative effort by NASA, The Boeing Company, the Goodrich Corp., and GE Transportation Aircraft Engines. Japan’s All Nippon Airways provided a 777 airplane for the tests.

The team was pleased to see that concepts we had developed with computer simulations and in wind tunnels worked on a real airplane, said Charlotte Whitfield, NASA’s Quiet Aircraft Technology manager of airframe system noise reduction.

During the three weeks of tests the plane was fitted with various noise reduction combinations, including landing gear and engine inlet-exhaust combinations.

Some new exhaust configurations achieved as much as a two-decibel improvement in noise. In addition, the low frequency rumble heard in the aft cabin by passengers at cruise altitude was reduced by as much as four to six decibels.

Another technology development that proved successful was a seamless sound-absorbing engine liner built by Goodrich, NASA said. It reduced the fan tones heard in front of the aircraft by up to 15 decibels, so they became nearly inaudible.

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