SSBJ Study Still in the Works

Attention, all show visitors who are still suffering the effects of being confined for 16 to 20 hours in a metal tube -- there may be relief on the distant horizon.

Gulfstream Aerospace and Lockheed Martin's Skunk Works are still engaged in studies of a supersonic business jet. Their SBJ design, revealed in a patent issued late last year, differs from most earlier supersonic transport studies in that it uses aerodynamic technology which suppresses the airplane's sonic boom, allowing it to fly at supersonic speeds overland.

The two companies consider such technology to be essential for a business jet, and it would also expand the market for a supersonic airliner.

The US government has indicated support for the concept, providing some $15 million in the FY2000 budget for "supersonic noise reduction" technology. This is expected to be the first slice of government support for a five-year demonstration project, leading to the flight-testing of a low-boom supersonic cruise prototype as early as 2005. A supersonic business jet could be on the market by 2010.

The SBJ design in the patent is a twin-jet, arrow-winged aircraft with a Gulfstream-size cabin and two distinctive features: an extended nose with a plain conical tip, and an inverted V tail that is integrated into the wing trailing edge. The two companies are not talking about how it works, but the available literature on low-boom designs provides some clues.
A sonic boom is a pressure wave, caused mainly by the lift from the airplane's wing, with steep pressure rises at each end. The peak of the wave rattles doors and windows and the sharp pressure changes cause the double-bang noise.
The jet's conical nose creates a local pressure spike which increases the velocity of sound and stretches out the first pressure rise. The wing (possibly combined with the V-tail) develops its lift along most of the airplane's length, so that the pressure wave is longer and flatter than it would be if the lift was concentrated around the mid-point. The V-tail may also be designed to smooth out the pressure rise at the rear. Result: there is still a pressure wave on the ground, but the high peak and the rapid changes that the groundlings feel and hear are gone.

There are some indications, too, that Lockheed Martin may be planning to use plasma technology in the SBJ. Cutting-edge research (much of it in Russia) has indicated that supersonic drag and boom can be reduced by generating an electrically charged field, or plasma, around the nose of an airplane.

There are still problems to be overcome, even if the low-boom technology can be shown to make the sonic boom almost imperceptible. The airplane needs a durable engine that's quiet on takeoff and efficient in cruise, and does not cost multiple billions of dollars to develop, and engine manufacturers are scratching their heads over how to do that. Development costs for the airplane itself will not be trivial, and will be spread over a few hundred units at most. Lockheed Martin, after a traumatic 1999, may yet decide to drop out of the project because of these and other uncertainties.

Lockheed Martin and Gulfstream, however, are being encouraged by mega-investor Warren Buffett. The Omaha magnate's properties include the large and rapidly growing NetJets fractional-ownership franchise, making him the world's largest customer for business jets, and he apparently sees the SBJ as a logical next step for shared jet ownership.

According to some NASA sources, the Skunks have sketches of a grown-up SBJ with seats for 100 premium-class passengers. A civilized breakfast in Singapore and lunch in London? Having been fortunate enough to enjoy that experience (a Concorde sales tour in 1977) I heartily recommend it.