Gulfstream is Quietly Chasing the SBJ As Are Big-Name Engine Developers

Gulfstream has carried out two serious in-house studies of the supersonic business jet (SBJ) market and commissioned a third, according to senior VP programs Pres Henne.

"We can easily identify a market for 200-300 aircraft," says Henne, based on company estimates that the aircraft would weigh about 125,000 pounds and cost about $70-$80 million--about twice as much as a Gulfstream V.

Gulfstream is staffing an internal project called Quiet Supersonic Jet (QSJ). Without disclosing the numbers of people involved, Henne says that the company has "a respectable preliminary design project" under way.

Gulfstream has hired some engineers with relevant experience and has issued consulting contracts to other specialists, and the QSJ team is growing.

The Defense Advanced Research Projects Agency--which lists the Internet and stealth on its resume--started its Quiet Supersonic Platform (QSP) project at the beginning of this year. Lockheed Martin, Northrop Grumman and Boeing are working on designs for a supersonic aircraft that could form the basis for a corporate jet or a long-range supersonic attack aircraft. If the project continues, an X-plane could fly as early as 2006, and technology would be ready for a full-scale development program to start in 2008.

Already, QSP is producing encouraging results in two critical areas: reducing the sonic boom, so that the SBJ can cruise at supersonic speeds overland (unlike Concorde or the 300-passenger supersonic that NASA and Boeing studied in the 1990s), and cutting airfield noise.

Northrop Grumman has concluded that it may be possible to suppress the sonic boom by changing the shape of the aircraft. The idea is not to eliminate the pressure wave ("Ye canna change the laws of physics, Jim") but to change the normal "N-wave" profile of the boom to a smooth hump, removing the rapid pressure rises at the nose and tail of the aircraft.

In early August, DARPA awarded Northrop Grumman a contract to demonstrate this technology in flight in August 2002. The company will modify an F-5E with a longer nose and other changes, and plans to fly nine sorties and 18 tests at speeds up to Mach 1.5. An unmodified F-5E will fly on the same path immediately before or after the test aircraft. The goal of the test is to show that the difference between the boom signatures is the same as the designers' computational fluid dynamics (CFD) codes have predicted.

On the engine side, GE and Rolls-Royce are exploring solutions that avoid the use of a complex noise suppressor. GE, says program manager Harvey Maclin, is looking at a variable-cycle engine. The engine takes off and lands at its highest bypass ratio, meeting Stage 4 noise rules without a complex suppressor, goes to a near-pure-jet cycle for transonic acceleration and cruises at an intermediate bypass setting. Compared with the fixed-cycle low-bypass engine technology in HSR, it is 20% more efficient in the cruise and weighs one-third less because of its simpler nozzle.

Rolls-Royce, according to Gulfstream's Henne, is looking at a fixed-cycle turbofan based on the core of the Trent 800-a concept that dates back to Gulfstream-Sukhoi studies in the early 1990s. Pratt & Whitney is believed to be looking at concepts based on the F119 engine of the F-22 Raptor.

"Warren Buffett wants one" is not a conclusive argument in favor of a supersonic business jet, but it is a good start. The owner of Executive Jet, Inc. and its NetJets fractional-ownership program helped bring Lockheed Martin and Gulfstream together for their first joint SBJ investigations in 1998. A small team at Executive Jet continues to monitor the SBJ scene and provide the user's perspective, and Buffett's company has indicated that it would buy at least 50 SBJs as soon as such an aircraft became available.

-Bill Sweetman