Volume 11, Number 3 • Fall 2003 • Aerospace Technology Development

Scientists Test Wake Sounds

Tests in Denver will help scientists determine if sound can be used to detect, track and predict
hazards from aircraft wake turbulence.

NASA’s safety mission goal is to “enable safer, more secure, efficient and environmentally friendly air transportation systems.” NASA’s role in carrying out this goal is to “understand the challenges and develop the long-term, cutting-edge and leap-ahead technological solutions” (NASA 2003 Strategic Plan; 14–15).

In keeping with this mission goal, researchers, including a few from NASA Langley Research Center (LaRC) in Hampton, VA, spent more than three weeks collecting acoustic data at Denver International Airport. They used precisely calibrated microphone arrays to measure sound generated by airplane wake vortices. Two laser radars (lidars) recorded the actual position, track and vortex strength, so scientists and engineers could look for subtle characteristics within the wake acoustic signal.

“The purpose of the test is to acquire the best data ever collected on the wake acoustic phenomena,” said Wayne Bryant, LaRC Wake Vortex Projects Manager. “We hope to establish whether an acoustic-based wake vortex sensor is operationally feasible for the airport environment. One of the key items we will be looking for is a relationship between the recorded acoustic signal and the hazard the wake represents. Estimates of this hazard level will be provided by the lidar systems in our test,” he said.

Aircraft produce wake vortices when they fly, much like two small horizontal tornadoes trailing behind the wing tips. Larger, heavier aircraft produce stronger wakes. Small aircraft following larger ones can encounter a wake vortex, if they are too close. This turbulence can be severe enough to cause a plane to crash.

Wake vortex detectors, such as lidar or possibly a wake acoustic sensor, are envisioned as important parts of a wake vortex avoidance system. Such a system may be able to give pilots advance warning of the location and nature of hazardous wake turbulence.
The technology also could increase runway capacity, because air traffic controllers would have a better idea of where wakes are and how they decay. Controllers could use that information to efficiently separate aircraft.

The Denver test also provided an opportunity to evaluate recent modifications to a laser-based wake acoustic sensor being developed by Flight Safety Technologies and Lockheed-Martin. The Sensors for Characterizing Ring-eddy Atmospheric Turbulence Emanating Sound (SOCRATES) projects low-power laser beams across open space onto a reflector device, which reflects the beams back to a receiver. Developers say the system then measures the changes in the laser beams, which reveal the existence of sound.

Participants in the wake acoustics test included NASA; the Department of Transportation; Volpe National Transportation Systems Center; OptiNav/Microstar/Titan; Coherent Technologies, Inc.; MIT Lincoln Laboratories; United Airlines; Florida Atlantic University; Flight Safety Technologies; Lockheed-Martin; and the German Aerospace Research Center. *

For more information, contact Michael Braukus, Office of Public Affairs, NASA Headquarters, 202/358-1979. Please mention you read about it in Innovation.

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