Gulfstream Patent Confirms SSBJ Still Has a Pulse

 - October 3, 2007, 11:54 AM

After a flurry of interest late in the last decade that appeared to lose momentum in the wake of 9/11, there is evidence that progress toward defining a supersonic business jet continues quietly. While asserting that its Mirage and Rafale expertise makes it at ease with the supersonic realm, Dassault has continued to voice concerns about the technical complexity and financial risks of developing a suitable powerplant for an SSBJ, but Rolls-Royce Deutschland, for one, dismisses the technological concerns at least. Sukhoi would have had an SSBJ in service by now if all it took were enthusiasm and confidence. And over the years Gulfstream, teamed at times with both Sukhoi and Lockheed Martin’s Skunk Works, has certainly succeeded in piquing the interest of fractional heavyweight NetJets, the most likely launch customer for such an airplane.

Tempering the enthusiasm for speed has been word that the sort of person who could be expected to get excited about an SSBJ might, in fact, prefer flying long legs in the expansive comforts of a BBJ over sitting for shorter stints in a smaller and almost certainly pricier sprinter.

Some nuggets have surfaced in these intervening years that indicate all is not moribund in the quest for speed. A couple of years ago, this magazine noted that Lockheed Martin in 1999 received a patent for a “Shock Suppression Supersonic Aircraft” with a novel slotted wing design intended to tame the sonic boom.
Northrop Grumman and DARPA (with Gulfstream involvement too) have been testing an F-5 with a reprofiled nose and belly, and the results have been encouraging enough that there is talk of more flight-test research, possibly even involving an aircraft as large as a reshaped B-1B.

Now Gulfstream has obtained a patent for a telescopic nose probe that might also reduce the sonic signature of an SSBJ to the point that it could operate over land without disconcerting the populace below. It is universally agreed that any future atmospheric supersonic civil airplane must be able to operate over land if it is to be economically viable.

A sonic boom from a suitable distance is not an objectionable noise to those of us who like airplanes, but we are in the minority. On a family vacation in Nova Scotia last August, I was in the backwoods workshop of a folk artist, writing a check for a woodcarving, when Concorde’s characteristic double boom reached our sparsely populated spot on the earth’s crust. The SST was headed toward a landing at New York Kennedy Airport a few hundred miles to the southwest, and we had heard the double thunderclap the day before on the beach at the same hour. The woodcarver said he heard the boom-boom most days, and he was at once fascinated finally to discover what caused it and surprised to learn that in a couple of months it would be silenced forever. From the beaches of Nova Scotia, Concorde’s passage high offshore was marked by a muffled but unmistakable pair of dull booms, felt as much as heard, and insignificant enough to make one wonder: why the fuss?

Gulfstream’s telescopic nose probe aims to spread the aircraft’s weight over what the air will perceive as a longer fuselage (thereby reducing boom pressures) and to manipulate how the vehicle greets the air unable to scurry out of its path.
Titled “Supersonic aircraft with spike for controlling and reducing sonic boom,” the patent lists the inventors as Preston Henne (Gulfstream senior v-p for programs, engineering and test), Donald Howe, Robert Wolz and Jimmy Hancock, and the assignee as Gulfstream Aerospace. Gulfstream applied for the patent in March 2002, and it was issued on March 2 this year.

This is not simply a Concorde-style needle nose, as revealed in the abstract:
“An aircraft includes a spike projecting from the leading end of the fuselage and/or rearward from the trailing end of the fuselage. The spike can include a single section
or two or more sections of varying cross-sectional area. Transition regions between sections of varying cross-sectional area are located and shaped to reduce coalescence of shock waves created thereby during supersonic flight.

“The spike can be collapsible and can be retracted into the fuselage. The spike can have a cross-sectional shape wherein the nose thereof lies on a line formed by the intersection of the bottom of the spike with a plane tangent to the bottom of the spike. A spike thus shaped causes an asymmetric pressure distribution during supersonic flight, wherein the ground-directed pressure contour is of lesser magnitude than the pressure contour propagating in other directions.”

What this asymmetrical nose spike aims to do, then, is to manipulate the origins of the pressures that generate the boom so that, to the fullest extent possible, it travels everywhere but down to the mammals below. The Gulfstream patent mentions other patents that make boom-reduction claims for ringed spikes, slotted spikes, blunt noses and shaped forebodies, but, as it notes in closing, “none of them addresses the sonic-boom signature shaping technique” of the Gulfstream device.
Gulfstream has already conducted small-scale wind-tunnel testing and is now working on a half-scale ground structural test article of the spike, according to Wolz, co-inventor and Gulfstream’s director of new product development. If progress with early test articles is satisfactory, a Gulfstream spokesman told AIN, the spike would likely be flight-tested on a subsonic aircraft initially to prove the structural soundness