Scientists Listen In On Sounds Of Aircraft Wake Signatures

Researchers, including some from NASA's Langley Research Center (LaRC) in Hampton, Va., will spend more than three weeks collecting acoustic data at Denver International Airport. They will be using precisely calibrated microphone arrays to measure sound generated by airplane wake vortices. Two laser radars (lidars) will record the actual position, track, and vortex strength, so scientists and engineers can 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. 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 could also increase runway capacity, because air traffic controllers would have a better idea where wakes are and how they decay. Controllers could use that information to efficiently separate aircraft.

The Denver test will also provide 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 include 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 information about NASA and aerospace on the Internet, visit: http://www.nasa.gov