Story ID: 772GulfstreamMEBAA
Gulfstream Continues Supersonic Business Jet Research
By: Chad Trautvetter
Caption: U.S. company recently issued two new patents for technologies that would enable development of a supersonic business jet.
Word Count: 780
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. 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, Ga.-based aircraft manufacturer’s most prominent research in this field is the Quiet Spike, a telescoping nose designed to reduce greatly 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, the “Gulfstream Whisper,” to demonstrate the spike’s effectiveness.

However, the company has noted that the engine inlet is also a major factor in reducing sonic boom noise. A patent issued to Gulfstream on November 1 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 Concorde also employed fuel load shifting, it did so for moving the center of gravity for the supersonic realm and was a manual process, using a series of toggle switches controlled by flight engineer on the flight deck. 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 employs a system with processors and sensors to automatically and instantly adjust fuel loads. This computing and sensor technology is the underlying basis of the patent.

SSBJ Clues

The patents also give some clues about what a Gulfstream supersonic business jet might look like, should the company decide to undertake such an ambitious project. According to information and drawings 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 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 wascreated at the time. Cowart still heads this research at the company.

As Gulfstream and Bombardier Aerospace approach subsonic large-cabin business jets with ranges approaching 8,000 nm—enough to fly halfway around the globe nonstop—speed would seem 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 airline side 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 closely 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 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.

 

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