Graham Warwick/SAVANNAH
FLIGHT TESTING of the Gulfstream V, long-range business jet, is exceeding expectations, despite a shortage of BMW Rolls-Royce BR710 engines. The manufacturer admits that flying has been slowed by a lack of spare engines, caused by development problems and flight-test incidents.
Gulfstream has accumulated some 210h flying on two aircraft. A third GV is due to join the flight test programme in May and will be the first to be powered by "entry-into-service" engines incorporating several design changes. These include a redesigned fan, combustor and high-pressure turbine.
The wide-chord fan has been redesigned following failure in a medium-birdstrike test, and the turbine has been reconfigured to reduce specific fuel-consumption (Flight International, 14-20 February, P12). The combustor has been redesigned to eliminate a combustion instability which causes a loud "rumble" at idle, says Ed Flinn, head of GV customer engineering.
Gulfstream says that one flight-test BR710 had to be removed for inspection after a landing light, mounted in the wing leading-edge forward of the engine, exploded in flight and was ingested. In another incident, a fan rub dislodged an "ice-tray" tip seal, which was ingested by the engine.
These incidents aside, the company is enthusiastic about the results of flight testing so far. Stall speeds are lower than expected, says test pilot Randy Gaston. Approach speeds are 6-10kt (11-18km/h) slower than estimated. This will yield improved field performance. Handling qualities are better than predicted, he says, with "light, crisp" control, "excellent" buffet margins at high altitude and "exceptional" responsiveness on the approach. "To say the GV lands lightly and softly, is an understatement," says Gaston. Approach speed with 2,700kg fuel remaining, is under 100kt, and the nose-wheel touches down at 80kt, he says. Thrust-reversers are "...easy to use and vibration-free".
Gulfstream says that cruise-performance tests, confirm that the GV's 12,000km range target will be met, although the company admits, that the aircraft and its power plant are overweight. Weight-reduction efforts are under way, and drag improvements incorporated into the third GV have yet to be factored in, says Flinn. These include reprofiling of the fuselage above the cockpit and reshaping of the engine pylon.
A "right-wing-heavy" roll-trim imbalance affecting only the first GV has been traced to a manufacturing problem at wing-supplier Northrop Grumman, which resulted in slight differences in twist and camber between the left- and right-wing halves.
Source: Flight International
