With its
extendable nose, a NASA
research jet may resemble some sort of high-flying Pinocchio, but this
supersonic aircraft tells no lies.
The F-15B
research jet's elongated nose - dubbed the Quiet Spike - is part of an
experiment by Gulfstream Aerospace Corp. and NASA's Dryden Flight Research
Center (DFRC) to determine ways to hush the sonic booms from aircraft flying
faster than the speed of sound.
"We're
really focused on more of the civilian applications," said researcher Michael
Toberman, NASA's DFRC project manager for the Quiet Spike experiment at Edwards
Air Force Base in California, in an interview. "It's really just fundamental
research into fully understanding sonic booms and how to mitigate them so that
we can one day fly over the United States without having any concerns."
Current
Federal Aviation Administration (FAA) regulations prohibit commercial
supersonic flights over land and restrict military flights to special corridors
to limit the effects of humans and the environment below.
Military
aircraft the world over have been flying at supersonic speeds since U.S. test pilot broke the sound barrier aboard the rocket-powered X-1 aircraft in 1947. It
was the Russian
Tu-144 and the joint British-French
Concorde supersonic planes that carried commercial passengers around the
globe at twice the speed of sound, or Mach 2.
The
Concorde, which carried
passengers through 2003, was limited to subsonic speeds while flying over
land.
"We believe
we can reduce the sound made, for example, by the Concorde to the tune of
10,000 times," Gulfstream spokesperson Robert Baugniet told SPACE.com.
'Spiking'
sonic booms
Sonic booms
result from shockwaves that build up around supersonic aircraft as they
approach Mach 1, or about 760 miles per hour (1,223 kilometers per hour)
at sea level.
"In
standard [supersonic] aircraft, there's usually two booms because the
shockwaves coalesce into two large shocks," Toberman said.
The
Savannah, Georgia-based Gulfstream developed and patented the Quiet Spike
technology to determine how best to control or suppress the intensity of
aircraft sonic booms for potential supersonic commercial aircraft over land.
Three
conical fairings along the length of the Quiet Spike are designed to produce
three parallel shocks that head Earthward independently - rather than folding
into a two large shocks - where their effects are muted, compared to the
average sonic booms.
"You'll
still have the booms," Toberman said. "They'll just be really small and they
won't make much of an impact."
NASA has
conducted past research to suppress sonic booms, including test flights in 2003
and 2004 to show that aircraft
shaping can reduce the intensity of sonic booms.
"I think
this is really building up a lot of interest in the industry into this sort of
technology," Toberman said. "I'm hoping that it'll feed into a larger research
[project] so that we can develop a full vehicle that will actually have a low
signature...a low boom."
One long
nose
The current
F-15B tests are aimed at determining the structural integrity of grafting a
telescoping spike to the nose of a supersonic aircraft.
"You're
putting this large structure protruding out from the front of the aircraft and
it could have some destabilizing effects," Toberman said. "We want to make sure
that the stability and control is acceptable for the pilot."
Built of a
carbon composite structure over an aluminum frame, Gulfstream's Quiet Spike
measures a total length of about 24 feet (seven meters) when fully extended.
The spike consists of three primary segments - a four-foot (1.2-meter) tip that
tucks into a six-foot (1.8-meter) section which slides into a 14-foot (4.2-meter)
trunk protruding from NASA's F-15B aircraft.
The entire
spike can be fully extended with electric motors in 21 seconds, though the
deployment can be controlled during that process as well, Toberman said.
To date,
test pilots have flown six subsonic flights with the Quiet Spike-equipped
F-15B, reaching speeds of Mach 0.8, or about 608 miles per hour (978 kilometers
per hour).
Over the
next two weeks, project managers plan to push the Quiet Spike up to speeds of
about Mach 1.8, or about 1,370 miles per hour (2,205 kilometers per hour), but
don't expect any supersonic silence from their F-15B aircraft.
"That's
really because the actual aircraft itself is rather noisy," Toberman said,
adding that the research F-15B has not undergone modifications to quiet its
inlets.
Instead,
NASA test pilots will fly a second F-15 aircraft alongside the test vehicle to
measure the structural integrity of the Quiet Spike at supersonic speeds.
Subsonic
tests have proven favorable according to test pilots, Toberman added.
"Actually,
the pilot's comments have all been very benign," he said of the subsonic Quiet
Spike tests. "He doesn't even know it's on there for the most part."
advertisement
