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Gulfstream Progresses on Supersonic As Work
Advances on Hushing Boom
Gulfstream studies consistently show a strong market for a
supersonic business jet, according to senior vice-president for
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 lbs and cost about
$70-$80 million about twice as much as a Gulfstream V.
The company's current Quiet Supersonic Jet (QSJ) design features
an arrow-shaped wing, body-mounted engines and a T-tail, and could
use the same 6.000-foot runways as today's aircraft. It would
seat eight passengers, cruise at speeds between Mach 1.6 and Mach
2.0, and have a range of at least 4,000 nm. Gulfstream also estimates
that it would be profitable on a scheduled service, with 14 seats,
at today's business-class transatlantic fares.
Without disclosing the numbers of people involved in QSJ, Henne
says that the company has "a respectable preliminary design
project" under way. The company has hired engineers with
relevant experience from Lockheed Martin, NASA and other places,
and has issued consulting contracts to other specialists.
The Defense Advanced Research Projects Agency started its Quiet
Supersonic Platform (QSP) project at the beginning of this year.
Lockheed Martin, Northrop Grumman and Boeing have prepared designs
for a supersonic aircraft which could form the basis for a corporate
jet or a long-range supersonic attack aircraft. Within a few days,
two of those companies will be selected for another year of more
focused work. 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 transport that NASA and Boeing studied in the 1990s),
and cutting airfield noise.
Northrop Grumman and Lockheed Martin have concluded that it may
be possible to meet DARPA's target for the sonic boom by changing
the shape of the aircraft, and without using exotic technologies
such as plasmas. 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 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 eliminate the huge noise suppressor designed for the Boeing/NASA
SST. DARPA has selected GE as its exclusive engine contractor
for QSP. The company is looking at a variable-cycle engine. Compared
with the Boeing/NASA propulsion technology, it is 20 per cent
more efficient in the cruise and weighs one-third less because
of its simpler nozzle.
Rolls-Royce is looking at a fixed-cycle turbofan based on the
core of the Trent 800. It would have a single-stage, high-pressure-ratio
swept fan and a bypass ratio of around 3:1. Simple in design and
relatively inexpensive to develop, it offers almost equal performance
to a variable-cycle engine at speeds up to Mach 2.
"Warren Buffett wants one" is not a conclusive argument
in favor of a supersonic business jet, but it is a good start.
He has indicated he will buy 50 for his NetJets fractional-ownership
program.
By Bill Sweetman
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