DEVICE MAY CUT SONIC BOOMS GULFSTREAM LOOKS TO REDUCE NOISE CAUSED BY SUPERSONIC JETS IN FUTURE.

Byline: JIM SKEEN Staff Writer

EDWARDS AIR FORCE BASE -- Business jet maker Gulfstream wants to know if it's possible to break the wave caused by breaking the sound barrier -- thus reducing the sonic boom created by fast-moving jets.

Working with NASA, Gulfstream is testing out a device it dubs ``Quiet Spike,'' a telescoping pole that would mount on a jet's nose with hopes of reshaping and quieting the pressure wave that causes sonic booms.

``Our research is based on reducing sonic booms to the point where regulators, environmentalists, and consumers can say, I can cope with that,'' said Gulfstream spokesman Robert Baugniet. ``The current testing is to validate the structural integrity of the spike -- can it be deployed, extended or retracted. There's no measurement of sound.''

If testing is successful, Gulfstream will look for an aircraft on which to install the Quiet Spike to test its effect at reducing sonic booms. If that testing is successful, then Gulfstream could look at the financial prospects of building a supersonic business jet, Baugniet said.

``We are moving extremely slowly and deliberately,'' Baugniet said. ``The first step is basic sonic boom research.''

Gulfstream and NASA Dryden Flight Research Center at Edwards Air Force Base are testing the Quiet Spike on NASA's F-15B test aircraft, a converted Air Force fighter jet.

Made of composite materials and weighing 470 pounds, the spike extends from 14 feet in subsonic flight to 24 feet in supersonic flight.

The spike will hopefully change what happens in the air. As a supersonic aircraft speeds along, it pushes aside air molecules with great force and forms a shock wave, much like a boat creates a bow wave.

The shock wave forms a cone of pressurized air molecules which move outward and rearward in all directions and extends to the ground. As the cone spreads across the landscape along the flight path, it creates a continuous sonic boom along the full width of the cone's base.

The sharp release of pressure, after the buildup by the shock wave, is heard as the sonic boom.

The bigger and heavier the aircraft, the more air it displaces. That means that the boom from a passenger-carrying business jet would be greater than the boom from a fighter jet, which are just about the only airplanes that fly at supersonic speeds today.

Gulfstream is hoping the Quiet Spike will alter the pressure wave into smooth and more rounded pressure waves.

``As the shock wave comes, it breaks it up into small shock-lets,'' said Michael Toberman, Dryden's program manager for Quiet Spike testing.

Researchers hope the change in the wave shape will result in sound that is quieter than the sonic boom of the supersonic Concorde jetliner -- now retired -- by a factor of 10,000, according to Gulfstream.

The test effort is in the early stages of about an 18 to 20 flight program. Early flights have looked very good, Toberman said.

``This is a preliminary study to see whether this works,'' Toberman said. ``We'll report the results and see how much interest there is in continuing this effort. Once we can show this works, it gives us leverage for follow-on research.''

james.skeen(at)dailynews

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Photo: (ran in AV edition) Gulfstream's Quiet Spike is mounted on NASA's F-15B aircraft to test how well it reduces sonic booms.

NASA