NASA Tests Technologies to Silence Jet Aircraft

December 20, 2005

The U.S. National Aeronautical Space Administration (NASA) and the corporate sector performed flight tests on new technologies that quiet jet aircraft during a three-week flight test program dubbed the Quiet Technology Demonstrator 2. The tests demonstrated several noise-reduction concepts designed to quell cabin and community noises, NASA said.

"Using microphone arrays and other measurement devices we were able to determine that the new engine nozzle chevron designs that take into account the air flow and acoustic differences that occur when the engine is installed on the aircraft can significantly reduce community noise,” said Charlotte Whitfield, NASA's Quiet Aircraft Technology manager of airframe system noise reduction.

The tests, which were performed in a Boeing 777 provided by All Nippon Airways, showed that chevrons with asymmetrical scallops around the engine offer better noise reduction characteristics. During the test, the aircraft was fitted with eight different noise-reduction combinations between the landing gear and the engine inlet and exhaust combinations on the right wing.

Results of new fan and engine core chevron exhaust configurations showed community noise was reduced by a decibel or two and low-frequency noise in the aft cabin was reduced by as much as six decibels at cruise altitude.

The "seamless" sound-absorbing liner, which keeps sound waves from bouncing off the seams between treated areas in the engine inlet, decreased fan tones in front of the aircraft by as much as 15 decibels.

A third tested concept was a toboggan-shaped cover, or fairing, for the 777's main landing gear that was believed to reduce landing noise, although additional tests are needed, NASA said. Previously conducted laboratory tests performed in a wind tunnel at Virginia Polytechnic Institute and State University in Blacksburg on a 26% scale model of the 777 landing gear showed the fairing may decrease landing noise as much as four decibels.

Test participants included NASA's Langley Research Center, Boeing Co., Goodrich Corp., and GE Transportation Aircraft Engines.

Source: National Aeronautical Space Administration (NASA).