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Sept. 02--Gulfstream Aerospace Corp.'s ultra-long-range, ultra-large-cabin flagship, the Savannah-built G650, reached Mach 0.995 in flight testing last week, further solidifying its claim as the world's fastest civil aircraft.
The aircraft, one of four G650s currently involved in flight testing, achieved the top speed during flutter testing, which evaluates the aircraft's damping responses following input from an external test device.
Flutter testing is performed at a variety of frequencies, speeds, altitudes, weights and centers of gravity.
To achieve the maximum speed, Gulfstream senior experimental test pilots Tom Horne and Gary Freeman -- along with flight test engineer Bill Osborne -- took test plane 6001 into a dive, pitching the aircraft's nose 16 to 18 degrees below the horizon.
During the dive, flutter exciters introduced a range of vibration frequencies to the wing, tail and flight control surfaces to ensure the aircraft naturally dampened out the oscillations without further action from the pilots.
Even under such extreme circumstances, the G650 performed flawlessly, the crew said.
"The airplane is very predictable," said Horne. "It's very easy to control and to get precise control at those speeds. 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."
During the flutter test missions, a team of multi-disciplinary engineers in Gulfstream's state-of-the-art telemetry center in Savannah monitored the aircraft's behavior and determined the real-time damping characteristics of the aircraft.
"We're doing very well," said Pres Henne, senior vice president of programs, engineering and test. "The demonstrated flutter margins met or exceeded our expectations out to maximum speeds. That's a good sign."
As Gulfstream 6001 continued with flutter testing, Gulfstream 6005 -- the fifth and final aircraft in the G650 flight-test program -- completed initial phase manufacturing and began engine testing.
Each of the five aircraft involved in what will be an estimated 1,800 hours of flight testing has a specific purpose, with 6001 focused on envelope expansion, air-data calibration, flutter, in-flight performance and flight controls.
The 6002 is used to evaluate the aircraft's systems as well as its takeoff and landing performance, while 6003 tests the avionics, in-flight load measurement and ice-protection system.
Gulfstream 6004 will be the first G650 outfitted and tested with a full interior, which is being installed, and 6005 will participate in the reduced vertical separation minimum testing.
The G650 flight-test program officially began Nov. 25 of last year. Through Aug. 25, the four airplanes currently flying in the program have completed more than 170 flights and 575 flight-test hours.
Gulfstream expects to obtain certification for the G650 next year, with deliveries of the $64.5 million aircraft beginning in 2012.
