Image to right: During the three-week Quiet Technology Demonstrator 2
flight test program in November 2005, the NASA/industry research team
tested a specially-adapted GE engine mounted on a Boeing 777. The
improved engine nozzle chevron design used asymmetrical scallops around
the engine to better reduce community and cabin noise. Image credit: The
Boeing Company/Bob Ferguson
During a three-week flight test program called Quiet Technology
Demonstrator 2, the effectiveness of a number of significant aircraft
noise reduction concepts was confirmed. These were the final flight
tests in an intense NASA/industry research effort into noise reduction
concepts first developed through computer simulations and NASA wind
tunnels.
Technicians fitted a Boeing 777 with eight different noise reduction
combinations between the landing gear and the engine inlet, and exhaust
combinations on the right wing. Engine modifications included new engine
nozzle chevron designs that take into account the air flow and acoustic
differences that occur after an engine has been installed on the
aircraft. Chevrons are scalloped or serrated edges that can be seen on
some newer plane engines already in use.
Flight test results indicate 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.
Analysis of research results conducted to date confirms that the new fan
and engine core chevron exhaust configurations achieved as much as a two
decibel improvement in community noise. Low frequency rumble heard in
the aft cabin by passengers at cruise altitude was reduced by as much as
four to six decibels.
Other technologies monitored during the tests included a "seamless"
sound-absorbing liner designed to keep sound waves from bouncing off
seams between treated areas in the engine inlet, and a toboggan-shaped
cover to streamline the landing gear and make it less noisy.
Quiet Technology Demonstrator 2 Team
NASA Langley Research Center, The Boeing Company, Goodrich Corporation,
GE Transportation Aircraft Engines, All Nippon Airways
