Airport Noi. se
Remarkable advances have been made in propulsion since jet engines were introduced. Over the past 25 years there has been about a 204 reduction in the amount of fuel required to produce a unit of thrust (261 Because much of this gain has come from higher bypass ratios, take-off noise levels have fallen in some cases below those required by current noise regulations. Current SST engine concepts, without augmented suppression systems, are probably 15-20 decibels (equivalent perceived noise decibels) above these standards. Further noise suppression adds weight and reduces thrust. Low lift-to-drag ratios at takeoff demand considerable thrust, and this, in turn, leads to larger exhaust velocities and more noise At the moment there are sound ideas, but no tried techniques, on how to accomplish this noise reduction with acceptable weight increases. Unlike the some boom, however, we arc not up against a fundamental momentum balance A breakthrough is possible. Given that subsonic transport noise levels continue to fall, and the near certainty that conventional supersonic transports will operate only from selected coastal cities, current noise regulations need to be examined to see what airport noise levels might be acceptable from a small fleet of supersonic aircraft.