Gulfstream Aerospace continues to pursue technologies that would enable development of a supersonic business jet (SSBJ), logging two new U.S. patents for such technologies in the past several months alone. Asked about these latest patent awards, a company spokeswoman told AIN, “Gulfstream has a small team committed to researching sonic-boom mitigation. We also continue to work to remove the ban on flying supersonically over land.”
The Savannah, Georgia-based aircraft manufacturer’s most prominent research in this field is its Quiet Spike, a telescoping nose meant to greatly reduce or even eliminate the sonic boom. It has previously tested the Quiet Spike on a NASA F-15 and has even built an acoustic simulator to demonstrate the spike’s effectiveness, which it dubs the “Gulfstream Whisper.”
The company, however, has noted that the engine inlet is also a major factor in reducing sonic boom noise. Thus, a patent issued on November 1 to Gulfstream (Stand A13, A14) is for an “isentropic compression inlet for supersonic aircraft [which shapes] the compression surface of the inlet to defocus the resulting shocklets away from the cowl lip.” This improves inlet drag characteristics and interference drag characteristics, according to the patent.
The company has also developed a way to use fuel loading to mitigate the sonic boom. In a patent issued on September 20, Gulfstream engineers outline a computerized fuel redistribution “to adjust an amount of fuel stored within a wing to minimize a twist in the wing caused by the deviation.” Such redistribution will reduce the magnitude of the sonic boom caused by the deviation, the patent notes.
While the Concorde also employed fuel load shifting, it did so for moving the center of gravity in the supersonic realm and was a highly manual process, using a series of toggle switches controlled by an on-board flight engineer. The Gulfstream application is different—not just because it will be used to twist the wings to minimize the sonic boom, but also because it is employing a computerized system with processors and sensors to automatically and instantly adjust fuel loads. It is primarily this computing and sensor technology that is the underlying basis of the patent.
The patents also give some clues to what a Gulfstream supersonic business jet might look like, should the company actually decide to go ahead with such an ambitious project. According to information and drawings included in these patents, the design would likely employ a swing wing, like that used for the F-111 (built by Gulfstream parent company General Dynamics in the 1960s), and be powered by two engines. Configuration drawings also show a T-tail and the telescoping Quiet Spike, in addition to isentropic compression engine inlets and the fuel-load shifting system. In addition, the patents suggest a top speed of Mach 1.9 for a would-be Gulfstream SSBJ.
Gulfstream has flirted on and off with the idea of an SSBJ since 1989, though it appears to have become more serious about such an aircraft in 2008, when it tapped Robert Cowart as director of supersonic technology development, a position that was newly created at the time. Cowart still heads this research at the aircraft manufacturer.
And as Gulfstream and rival Bombardier Aerospace approach subsonic large-cabin business jets with ranges nearing 8,000 nm—enough to fly halfway around the globe nonstop—speed appears to be the next frontier. In fact, an aviation consultancy specializing in this issue published a study last year that concluded that an SSBJ now makes economic sense.
“We’ve done the study in two ways—on the air transportation side with the airlines, and with the corporate aviation side,” said InterFlight Global CEO Oscar Garcia. “On the airline side, the price premium cannot exceed 30 percent. On the corporate side, the price premium can reach up to 70 percent. The corporate and special-mission government side is much less price sensitive.”
He also thinks that the time is ripe for the U.S. Congress to revisit the national ban on supersonic flight over land. “Congress is looking at this issue again, maybe more than ever before. It is starting to look at the fact that we need speed, we need the ability for rapid reaction,” Garcia noted.
“It’s mostly for the military, but it is permeating into the civilian realm,” he added. “With good research results from Gulfstream and NASA, if that sonic boom gets reduced to a certain level, I wouldn't be surprised if the ban is lifted.” That could happen as early as 2020, Garcia believes.
He envisions an SSBJ as just the first step in developing a pathway to regular suborbital transportation, perhaps as early as 2035. “Propulsion remains the main challenge,” Garcia concluded.