Just as the Concorde heads toward the scrapheap comes a wakeup call
from across the Atlantic: supersonic flight over populated areas may
not be idle fancy.
During a highly successful demonstration over the Californian desert,
a modified F-5E supersonic jet fighter provided proof that
a change in an aircraft's shape mitigates the intensity of its sonic
Sporting a modified nosecone
"This technology could eventually enable unrestricted supersonic
flight over land," says Charles Boccadoro, programme manager with
Northrop Grumman, which modified and flew the jet under a $7m
US government-backed research program.
For the test, Northrop modified the fuselage and nose of an F-5E
fighter jet, giving it a slight pelican-beak appearance.
of preparation, the modified plane, as well as a regular F-5E, left the
firm's Palmdale, California plant on 27 August and flew to Edwards Air
Force Base, located in the Mojave Desert.
The planes then sped down
the same supersonic corridor flown by Chuck Yeager 56 years ago when,
for the first time, an aeroplane flew faster than the speed of sound.
"We were all blown away by the clarity of what we measured," says
Peter Coen, with Nasa's Langley Research Center in Virginia, a
partner in the programme.
Chasing and listening
Sensors on the ground and aboard other aircraft showed the modified
jet produced a sonic boom with one-third less intensity than the
"There was no change in performance," added Northrop's Jim Hart.
"They were both flying at full-throttle - about Mach 1.36."
A quieter boom
All aircraft flying through the atmosphere create pressure waves,
similar to the waves created by the bow of a boat as it moves over
When airplanes travel faster than sound waves, which move at
about 1,200 km/h (750 mph) at sea level, the pressure waves merge to form shock waves,
which are heard as sonic booms when they hit the ground.
showed that designing aircraft to a particular shape will keep
pressure waves from merging, reducing the intensity of the sonic boom.
Discussions to continue the Shaped Sonic Boom Demonstration programme
are under way, said a representative with the Defense Advanced
Research Projects Agency (Darpa), which manages the programme as part of its
Quiet Supersonic Platform (QSP) initiative.
QSP's aim is to identify and
develop technologies that could allow military and business aircraft
to operate with reduced sonic booms.
Darpa's goal is to cut sonic
boom noise by 75%.