Nov. 1, 2012 Sonic booms created by aircraft flying faster than
the speed of sound certainly aren't known for being faint, but
rather for their loud, make-you-jump startle effect for those
who experience them. However, sonic booms have a quieter,
fainter side, too. NASA's Supersonics Project is embarking on
its latest effort to characterize or define that fainter side of
sonic booms as a NASA F/A-18 aircraft takes to the air in a
project called Farfield Investigation of No Boom Threshold, or
FaINT. As the latest in a continuing progression of NASA
supersonics research projects aimed at reducing sonic boom
levels, FaINT is designed to enable engineers to better
understand evanescent waves, an acoustic phenomenon that occurs
at the very edges or just outside of the normal sonic boom
envelope. For an aircraft flying at a supersonic speed of about
Mach 1.2 or less at an altitude above 35,000 feet, the
shockwaves being produced typically do not reach the ground, so
no sonic boom is heard. This is because shockwave