Farfield Investigation of No Boom
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
Looking ahead: FaINT will help identify the physical boundaries
of the sonic boom envelopes of future commercial supersonic
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.