Aeroacoustic Tests

by Stephen M. Jaeger

March 10, 1998

I have worked on a number of interesting acoustic tests at NASA. These include tests of scale-model jet airplanes, half-span models and jet engines. We use a variety of tools and techniques for measuring aircraft noise. Specially designed speakers and other noise devices enable us to test and calibrate these tools.

Figure 1: A bullet-shaped microphone is used to measure noise in wind tunnels.
	Figure 2: The loud bang of a small yachting cannon can be used to find echoes in a wind tunnel test section.
Figure 3: A speaker box with multiple drivers can produce a variety of sounds in the wind tunnel to test our microphone arrays.
	Figure 4: A microphone array (mounted on the pylon in the back) recorded the noise from a propane-burning jet engine in the 40- by 80-Foot Wind Tunnel.
Figure 5: Microphones (hanging from the ceiling), and a microphone array (left, center) measure the noise from a half-span model of a supersonic jet in the 40- by 80-Foot Wind Tunnel.
	Figure 6: A microphone array (mounted in the foreground) measures the airframe noise of a DC-10 model in the 40- by 80-Foot Wind Tunnel.
Figure 7: The microphone array creates a color map of the DC-10 model, revealing noise sources at the wing flaps and wing slats.
	Figure 8: Our newest microphone array, shown being tested in an anechoic chamber, has 100 microphones and is presently being used in the 7- by 10-Foot Wind tunnel.