GRAHAM WARWICK / WASHINGTON DC
Northrop Grumman's F-5 shaped sonic boom demonstrator (SSBD) has proved for the first time in flight that the shockwave signature of a supersonic aircraft can be reduced by airframe shaping.
In back-to-back tests of the SSBD and an unmodified Northrop F-5E at Edwards AFB, California, the aircraft generated a "flat-top" sonic boom with a much lower initial overpressure than the traditional "N-wave" signature.
Observers reported the SSBD produced a "muffled rumble" compared with the "sharp crack" of the unmodified F-5, says Northrop Grumman Quiet Supersonic Platform programme manager Charles Boccadoro. Both aircraft were flown at Mach 1.37 and 32,000ft (9,760m) over a line of ground sensors, the unmodified US Navy F-5E following 45s behind the SSBD, which is an F-5 fitted with a nose glove to shape the aircraft's shockwave pattern.
The test results were an exact match with predictions, Boccadoro says, and were the first proof that a modified flat-top shockwave signature would persist to the ground.
Northrop Grumman and NASA are now discussing a flight-test programme to look at the effects of aircraft manoeuvres and atmosphere changes on shaped sonic booms.