A plane spike to cut sonic boom
Back in 2004, NASA engineers worked with DARPA to reduce the sonic boom intensity in order to develop silent supersonic planes. Now, they're teaming with Gulfstream Aerospace on a project named Quiet Spike to reduce sonic booms. They've put a 24-foot-long lance-like spike weighing 470 pounds on the nose of an F-15B aircraft. And engineers are now testing the modified aircraft. The first flights of a series of about 20 took place in August. If all the tests are successful, Gulfstream could build a supersonic business jet in the future. But read more...
Here are two short paragraphs of this NASA's Dryden Flight Research Center news release.
Gulfstream Aerospace and NASA's Dryden Flight Research Center have teamed in a project called Quiet Spike to investigate the suppression of sonic booms.
The project centers around a retractable, 24-foot-long lance-like spike mounted on the nose of NASA Dryden's F-15B research testbed aircraft. The spike, made of composite materials, creates three small shock waves that travel parallel to each other all the way to the ground, producing less noise than typical shock waves that build up at the front of supersonic jets.
In "Device may cut sonic booms," the LA Daily News bring some more details about this retractable spike.
Made of composite materials and weighing 470 pounds, the spike extends from 14 feet in subsonic flight to 24 feet in supersonic flight.
So here is how this spike looks like. Below is a photo of the NASA's F-15B testbed aircraft with the Gulfstream Quiet Spike sonic boom mitigator [undergoing] ground vibration testing in preparation for test flights. (Credit: Tony Landis, for NASA, May 1, 2006)
And on this second photo, you can see the same NASA's F-15B landing after its first test flight equipped with the Quiet Spike. (Credit: Tony Landis, for NASA, August 10, 2006)
You can find other pictures in various formats in this NASA's photo gallery.
But how such a spike will suppress -- or at least, cut -- sonic boom? Here is Jim Skeen's answer.
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.
With this plane spike, engineers expect to reduce this sonic boom. For more information about the sonic boom physics and the progress made in sonic boom reduction, here is a link to a presentation made by Gulfstream Aerospace Corp. at a Aircraft Noise and Emissions Reduction Symposium held in May 2005 in Monterey, CA, "Small Supersonic Civil Aircraft" (PDF format, 24 pages, 2.96 MB)
So will we see supersonic planes again? As it's not a technological challenge, but an environmental -- and a political -- one, I'm not sure.
Sources: NASA's Dryden Flight Research Center news release, October 4, 2006; Jim Skeen, Daily News of Los Angeles, October 1, 2006; and various websites
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