Gulfstream Aerospace on Friday evening said its G650 S/N 6001 skirted the speed of sound on August 12, reaching Mach 0.995 during flutter testing as part of the 1,800-hour flight-test program for the wide-cabin, long-range business jet. For the initial series of flutter tests, the aircraft achieved clearance out to both its design dive speed (Vd) and design Mach dive speed (Md) at altitudes ranging from 10,000 feet up to the aircraft’s ceiling of 51,000 feet.
To achieve the maximum speed of Mach 0.995, Gulfstream test pilots Tom Horne and Gary Freeman put T1 (for test aircraft 1) 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. The G650 performed “flawlessly,” Gulfstream said.
“The airplane is predictable,” said Horne, senior experimental test pilot. “It’s easy to control and to get precise control at those speeds. The airplane response has matched the expectations of our engineers, and we’ve easily been able to fly the test conditions and march through the test plan.” During the flutter test missions, a team of engineers at Gulfstream’s telemetry center in Savannah monitored the aircraft’s behavior and determined in real time the damping characteristics of the aircraft. The vibration frequencies exerted on the aircraft ranged from 2 Hertz (twice per second) to a much faster 58 Hertz.
“We’re doing well,” said Gulfstream senior vice president of programs, engineering and test Pres Henne. “The demonstrated flutter margins met or exceeded our expectations out to maximum speeds. That’s a good sign.”
As S/N 6001 continued with flutter testing, S/N 6005–the fifth and final aircraft in the G650 flight-test program–completed initial phase manufacturing and began engine testing.
The test aircraft all have specific purposes: S/N 6001 is focused on envelope expansion, air data calibration, flutter, in-flight performance and flight controls; S/N 6002 is used to evaluate the aircraft’s systems, as well as its takeoff and landing performance; S/N 6003 is testing the avionics, in-flight load measurement and ice protection system; S/N 6004 will be the first G650 outfitted and tested with a full interior, which is currently being installed; and S/N 6005 will participate in RVSM testing.
As of late last week, the four flying test G650s had completed more than 170 flights and 575 flight-test hours. Gulfstream said it will meet its goal for FAA and EASA certification of the wide-cabin jet next year, followed by entry into service in 2012.