Gulfstream says its first prototype G650 business jet has successfully passed high-speed flutter testing, a key hurdle in meeting the planned certification of the 7,000nm (13,000km) range, fly-by-wire, Rolls-Royce BR725-powered twinjet next year.
Flutter testing uses exciters to input disturbances ranging in frequency from 2Hz to 58Hz to the wings, tail and flight-control surfaces with the aircraft flying at various altitudes, speeds, weights and centre-of-gravity conditions. Aircraft are designed so that the components naturally dampen out the oscillations without actions by the pilots.
In the most recent flutter tests, which are ongoing, Gulfstream test pilots pitched S/N 6001's nose down to as much as 18° below the horizon to reach a speed of Mach 0.995 with the exciters activated. "The demonstrated flutter margins met or exceeded our expectations out to maximum speeds," says Pre Henne, Gulfstream's senior vice-president of programmes, engineering and test. "That's a good sign." The G650 is set to be the world's fastest production business jet, with a maximum cruise speed of M0.925.
Senior experimental test pilot Thomas Horne says aircraft control was predictable. "It's easy to control and to get precise control at those speeds," says Horne. "The airplane response has matched the expectations of our engineers, and we've been able to easily fly the test conditions and march through the test plan."
As of late August, Gulfstream had four of the eventual five flight-test aircraft flying, accumulating 575h of the 1,800h of flight testing scheduled for the certification programme. S/N 6001 is dedicated to envelope expansion, air data calibration, flutter, in-flight performance and flight controls, while S/N 6002 is being used to evaluate the aircraft's systems as well as take-off and landing performance.
S/N 6003 is being used for avionics tests, in-flight load measurement and ice protection systems operations. S/N 6004, a cabin test aircraft, has joined the fleet but is being outfitted with a full interior. S/N 6005, which has completed initial phase manufacturing and begun engine testing, will be used for reduced vertical separation minimum (RVSM) testing upon completion.
Gulfstream also reports that it has developed a web-based system to reduce the time required to attain a US Federal Aviation Administration letter of authorisation needed to fly business jets at RVSM altitudes - above 29,000ft (8.850m).
The company says the capability is only used internally for Gulfstream aircraft, but may later be made available to customers. Gulfstream says electronic process can reduce the authorisation time from two weeks to "just a few days".