Farfield Investigation of No Boom Threshold (FaINT)

Farfield Investigation of No Boom

Threshold (FaINT)

The FaINT research project is seeking to characterize evanescent waves, an acoustic phenomenon occurring at the very edges of the normal sonic boom envelope and sounding similar to distant thunder. Certain atmospheric conditions and wave refractions create the 'shadow

side' of a sonic boom, where evanescent waves are generated. The waves quickly fade and disappear, similar to how boat wakes on water decrease with distance. During recent FaINT experiments, researchers collected data during a series of low-supersonic, high-altitude flights via a 1-mile stretch of microphones along the ground, microphones placed more than 2,000 feet above ground, and a microphone on a motorglider at altitudes around 10,000 feet. Characterizing the effects of louder and quieter sonic booms will help provide data necessary for engineers to design future low-boom supersonic aircraft.

Work to date: FaINT provided an extensive database that will be mined for a better understanding of shadow-side sonic booms for years to come. Currently NASA researchers are analyzing data with a focus on defining the acoustic lateral boom cutoff, which is the lateral distance beyond which evanescent waves are no longer distinguishable.

Looking ahead: FaINT will help identify the physical boundaries of the sonic boom envelopes of future commercial supersonic aircraft.

Benefits

 Advances sonic boom research: The

FaINT program is producing valuable data to help characterize evanescent waves and expand knowledge of sonic boom propagation effects.

 Reduces noise pollution: FaINT data allow for accurate knowledge of sonic boom sound levels.

Supersonic Flight Research

Supersonic flight over land is currently severely restricted because sonic booms created by shock waves disturb people on the ground and can damage private property. Since the maximum loudness of a sonic boom is not specifically defined by the current Federal Aviation Administration (FAA) regulation, innovators at NASA have been researching ways to identify a loudness level that is acceptable to both the FAA and the public and to reduce the noise created by supersonic aircraft. Using cutting-edge testing that builds on previous supersonic research, NASA is exploring low-boom aircraft designs and other strategies that show promise for reducing sonic boom levels.

A variety of factors, from the shape and position of aircraft components to the propulsion system's characteristics, determine the make-up of a supersonic aircraft's sonic boom.