NASA news November 21:
FLIGHT TESTS CONFIRM NEW
HELP QUIET THE SKIES
According to recent flight tests involving NASA and corporate
industry, new technologies can help silence jet aircraft, both in the
passenger cabin and on the ground. The three-week flight test
program, called the Quiet Technology Demonstrator 2, confirmed the
effectiveness of a number of significant airplane noise reduction
The tests were a cooperative effort between NASA's Langley Research
Center in Hampton, Va.; The Boeing Company, Seattle; Goodrich
Corporation, Charlotte, N.C.; and GE
Transportation Aircraft Engines,
Cincinnati. All Nippon Airways, Tokyo, Japan provided one of its new
777 airplanes for the test.
"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. "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."
Chevrons are scalloped or serrated edges that can be seen on some
newer plane engines already in use. Flight test results also
indicated the improved chevron that included asymmetrical scallops
around the engine can do even better than previous state-of-the-art
chevron designs in reducing community and cabin noise.
During flight tests at a remote Boeing facility in Glasgow, Mont.,
technicians fitted the plane with eight different noise reduction
combinations between the landing gear and the engine inlet and
exhaust combinations on the right wing. The production engine
remained on the left wing.
The new fan and engine core chevron exhaust configurations achieved as
much as a two decibel improvement in community 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. The
team had outfitted the cabin with advanced microphone systems to
study the noise inside the plane.
Another technology development that proved successful was the
"seamless" sound-absorbing liner, which is designed to keep sound
waves from bouncing off the seams between treated areas in the engine
inlet. The new inlet liner, built by Goodrich, reduced the fan tones
heard in front of the aircraft by up to 15 decibels, so that they
became almost inaudible. The design of the inlet liner was based on
tests conducted at NASA Langley and industry acoustics facilities.
The NASA/industry team also tested a concept to help reduce noise on
landing. Goodrich designed and built a toboggan-shaped cover, or
fairing, for the 777's main landing gear that was designed to
streamline the gear to make it less noisy. Researchers are still
studying the flight test results to determine what impact the fairing
had on reducing noise.
Earlier laboratory tests showed the cover may help reduce main landing
gear noise as much as four decibels. NASA and Goodrich tested the
concept in a wind tunnel at Virginia Polytechnic Institute and State
University in Blacksburg on a 26-percent scale model of the 777
landing gear. NASA research indicates when air is rushing past the
landing gear as aircraft are coming in on approach, the noise from
the aircraft structure, which includes the landing gear, is almost as
loud as the noise coming from the engines.
The flight test was the culmination of an intense NASA and industry
research effort into noise reduction concepts. Researchers are using
the results of that research combined with the data from the advanced
set of acoustic flight test instrumentation to improve the
understanding of and prediction methods for aircraft noise. That
could lead to future developments to make airplanes quieter.
Aircraft noise reduction research is part of the Fundamental
Aeronautics Program in NASA's Aeronautics Research Mission
Directorate. The program's goal is to advance breakthrough aerospace
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