Drucella Andersen
Headquarters, Washington, D.C.                                          
January 31, 1994
(Phone:  202/358-4701)

Michael Mewhinney
Ames Research Center, Mountain View, Calif.
(Phone:  415/604-9000)


RELEASE:  94-14

NASA TESTS NOISE-REDUCING NOZZLE FOR SUPERSONIC AIRLINERS

     NASA is evaluating an advanced exhaust nozzle concept that 
could reduce noise made by 21st century supersonic jet airliners 
to the level of today's new subsonic jets without affecting 
takeoff performance.

     The wind tunnel tests at NASA's Ames Research Center, 
Mountain View, Calif., uses an experimental nozzle attached to 
the rear of a one-tenth scale model of a jet engine.  The 
subscale engine simulates the exhaust of a future supersonic 
airliner under takeoff conditions.  Jet engine noise comes from a 
plane's exhaust or "plume" of turbulent air in its wake.

     "This future supersonic airliner undoubtedly will have to 
comply with Federal Aviation Administration regulations, so we're 
trying to make it as quiet as future subsonic airliners," said 
Ames Project Manager Paul Soderman. 

     The nozzle is an "ejector suppressor" type designed by GE 
Aircraft Engines, Cincinnati.  It scoops in outside air and mixes 
it with the high-energy jet exhaust.  That lowers the speed of 
the exhaust and consequently, the noise.

     In the tests, engineers use a laser and an infrared video 
system to measure the engine's exhaust flow.  They also employ a 
pair of microphones mounted on 15-foot struts to measure the 
noise.  The struts move back and forth beside the nozzle to 
obtain data.

     "We know how much noise a jet engine makes in our wind 
tunnel," said Soderman, an aeronautical and acoustical engineer.  
"We want to learn how much noise  it makes with an advanced 
suppressor on."
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     "We're also testing the engine's thrust loss caused by using 
the ejector  suppressor, because thrust loss affects a plane's 
takeoff performance," Soderman added.  "If we can keep the loss 
below 5 percent, we will be very pleased."

     The nozzle tests in the 40- by 80-foot test section of Ames' 
National Full-Scale Aerodynamics Complex are the first in a 
scheduled series.  They are all part of NASA's High-Speed 
Research Program, which is conducting research to provide 
technology for an environmentally compatible, economically 
practical next-generation supersonic transport.

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