After we completed the post-start checks, we rolled out of the chocks with very little thrust. Indeed, we needed to extend a thrust reverser from time to time to control taxi speed without riding the brakes. Howard pointed out that turning off the engine bleed air and using the APU for the packs causes a drop in engine ground idle rpm, thus reducing idle thrust.
Holding short of Runway 19, Howard ran through the pre-takeoff checklist and checked the flight controls for proper movement on the MFD flight controls page. Taxiing on to the runway, Howard armed the ground spoilers before we advanced the throttles, thereby causing them to pop up. Only by keeping one of the throttles slightly advanced above the idle stop could we make the ground spoilers retract. This functionality is carried over from legacy large-cabin Gulfstreams and seemed somewhat antiquated. We'd prefer to see the system updated with ground speed sensing so that the spoilers would pop up until the aircraft reaches a reasonable initial takeoff roll speed.
With a takeoff weight of about 69,600 lb. and 37,800 lb. of thrust, acceleration was sporty, even by Gulfstream standards. Shortly after rotation, the aircraft left the runway in about 3,000 ft. Control response was crisp and the aircraft was well damped in pitch, no doubt due in large part to the 36.6-ft. span, 439-sq.-ft. horizontal stabilizer that provides considerably more pitch control authority compared to those on the G450 or G550. But the high-level FBW control laws surely played a significant role as well in the G650's well-mannered behavior.
The aircraft also had pleasant artificial roll control feel and good roll response with adequate control yoke centering, but very little on-center breakout force. Engineers with Gulfstream and Rockwell Collins, which supplied the control yokes and rudder pedals, worked together closely to fine tune artificial feel and control response. Quite candidly, your fingertips might tell you this is a $200 million FBW Boeing even though the data plate says it's a Gulfstream.
The aircraft exhibited excellent short-period stability in all three axes, but it's difficult to tell how much was contributed by natural aerodynamics versus high-level FBW control laws. On the way up to initial cruise altitude, we had a couple of intermediate level-offs required by ATC and comparatively sharp turns. Yet, using a 250 KIAS/260 KIAS/Mach 0.85 climb schedule in mostly ISA conditions, the aircraft leveled off at FL 470 in 23 min. At ISA-7C, it cruised at Mach 0.85 or 480 KTAS on 2,400 pph at a weight of 67,500 lb.
Then we pushed up the throttles because high-speed cruise is the G650's forte. The 67,400-lb. aircraft smartly accelerated to Mach 0.90, resulting in 506 KTAS on 3,000 pph in ISA-7C conditions. There is only a 1.5-2.0 dB increase in cabin noise when cruising at Mach 0.90 instead of Mach 0.85 long-range cruise, Gulfstream claims. Horne also noted that the cabin altitude only was 4,300 ft.
We couldn't perform our usual long-period (phugoid) pitch stability check because the FBW system masks the natural, high-Mach aerodynamic stability characteristics of the aircraft. But we did check Mach buffet margins. A wind-up turn indicated the aircraft has robust high-speed buffet margins, albeit at a comparatively light weight. We didn't encounter buffet until about 1.4 g at Mach 0.88 in a 45-deg. turn.
Then we descended to FL 430, using idle thrust and speed brakes. We noticed only mild buffeting and a slight pitch change when the speed brakes were extended. Once level at that flight level, we again pushed up the thrust to check how fast the aircraft would cruise. Horne reported the cabin altitude was 3,380 ft.
As for speed, the G650 did not disappoint. At max cruise thrust, it accelerated to its Mach 0.925 redline at a weight of 67,000 lb. while burning 4,100 pph. Some operators doubtlessly will dash across North America or the North Atlantic at 530 KTAS or faster depending upon OAT. But BCA estimates that maximum range will be cut to 5,000 nm or less at that speed.