Drucella Andersen
Headquarters, Washington, D.C.                                                 
May 10, 1993
(Phone: 202/358-4727)

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


RELEASE: 93-81

WORLD'S LARGEST WIND TUNNEL WILL BE WORLD'S QUIETEST


   The world's largest wind tunnel soon will be the world's 
quietest, thanks to a $25 million NASA sound insulation project.

   NASA will design and install an acoustic lining in the 
40-by-80-foot test section of the National Full-scale Aerodynamics 
Complex (NFAC) at NASA's Ames Research Center, Mountain View, 
Calif.  The improved wind tunnel ultimately will help U.S. 
industry design quieter engines for a future high-speed civil 
transport and for new, advanced helicopters.

   "It will provide the United States with a world-class 
capability that will help us greatly during the next generation of 
aeronautical research," said Ames Project Manager John Allmen.  
"After workers install the acoustic lining, echoes will be greatly 
reduced.  Microphones will be able to measure engine and rotor 
sounds much more accurately with fewer sound waves bouncing off 
the walls." 

   Background noise and echoes in the wind tunnel test section 
cause problems for measuring sound during engine tests.  The 
deeper the acoustic liner, the lower the sound frequency engineers 
can measure accurately.

   Construction workers will install a dense acoustic lining in 
the NFAC's 40-by-80-foot test section walls, floor and ceiling.  
The insulation material comes in wedges 42 inches deep and about 4 
feet square to cover that entire area.  The new lining is similar 
to the spun Fiberglas commonly used to insulate houses.



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   Project design will take the next 2 years.  Construction is 
scheduled to begin in the spring of 1995.  During construction, 
the test section will shut down for more than a year. 


   Workers also will modify the wind tunnel's motor generators to 
let engineers send more electric power to the main drive motors.  
"Normally, we rotate the main drive motors at 180 rpm, but now we 
will be able to rotate them at half that speed and cut the noise 
levels by 75 percent, " Allmen said.  "This major reduction in 
background noise will allow us to reach speeds of 100 knots (105 
mph) quietly."

   Allmen noted that the tunnel's net operational costs will not 
rise after the project is complete.  "The modification costs are 
about one-twentieth of the cost of building a new facility, which 
would cost more than $500 million," he said.

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