Supersonic speed would allow travelers to cut significantly their travel time. However, because of the resulting sonic booms, the Federal Aviation Administration (FAA) and similar associations restrict supersonic travel to transoceanic only. Gulfstream Aerospace Corp. (Savannah, GA) partnered with NASA Dryden in a commercial investigation of the Quiet Spike, a sonic-boom suppression system. Leslie Molzahn was part of Dryden’s investigative team
NASA Tech Briefs: What is the Quiet Spike, and how does it work?
Leslie Molzahn: The Quiet Spike is a commercial investigation, a structural proof-of-concept experiment that Gulfstream Aerospace Corp. put together to investigate the feasibility of this type of object. We partnered together, Gulfstream and NASA Dryden. The Quiet Spike is designed to mitigate supersonic booms, and was mounted onto one of NASA Dryden’s F15-Bs. It extends approximately 14' in front of the F15-B testbed’s nosecone when it is in the retracted position, and it is a telescoping, composite tube mechanism that will extend and partition strong shockwaves into a series of weaker shockwaves at supersonic speeds.
When extended, the Quiet Spike is an additional 10' long, for a total 24' length. The spike is a series of nested tubes, with the largest diameter tube being 16" and the smallest diameter being 4". When it's retracted, the 16" tube is all that is visible. In the extended configuration, a 10" tube and a 4" tube are also exposed. The concept is to initiate a series of less intense sonic boom shock waves as the flow transitions past the Quiet Spike sections, instead of having one strong shock wave. This technique could mitigate the adverse effects of a strong sonic boom shock wave.
NTB: Why was it developed?
Molzahn: Right now, supersonic flight over land isn’t feasible. It isn’t allowed. When it flew, the Concord went supersonic over the ocean only. There could be a huge commercial application if the sonic boom can be mitigated to have less impact on people and resources on the ground. One could potentially get the FAA to lift their restrictions and be able to fly supersonic over, say, the continental US. I personally think it would be incredible to go from Los Angeles to New York in the matter of a couple of hours, instead of the time it takes now.
The sonic boom is a phenomenon that occurs when a vehicle goes the speed of sound, about 769.5 mph, and it is a large pressure differential. When that pressure differential hits the ground, that is what you hear. These are strong shockwaves, very loud, and what the Quiet Spike does is make the one shockwave into a series of smaller shockwaves to help mitigate the pressure differential into a weaker shock. A lot of different companies are looking into ways of mitigating sonic booms. In the, past at NASA Dryden, this F15-B was involved with probing near field shockwaves off of another aircraft that did a flight test program just a few years ago that was an F5-shaped sonic boom investigation. This was done with Northrop-Grumman. What that test did was, it had a different forward fuselage shape to mitigate the pressure wave that comes from the sonic boom. Current technologies trying to minimize the shockwave hitting the ground involve only flying technique. There are techniques of different air speeds, altitudes, and maneuvers where the shockwave won’t hit the ground.