Rolling out of the chocks, we found the nosewheel steering and new brake-by-wire system to be smooth and precise. We reflected on how far brake-by-wire systems have progressed since the original GIV's primitive system of the mid-1980s.
Once cleared for takeoff on Runway 13R, we advanced the throttles midway and engaged the auto-throttle system. Rpm advanced to 90.6% N1, providing nearly 7,600 lb. of thrust on each engine. With a weight-to-thrust ratio of 2.11 to 1, acceleration was spirited.
Rotation force was moderate and roll force was well harmonized with pitch force. The ailerons and elevator have virtually no perceptible on-center stiction, making the aircraft quite enjoyable to hand-fly. In addition, thrust change causes very little pitch change. Some pilots may not want to relinquish control to the autopilot. But the auto-throttle system is so smooth and precise that there's little reason not to use it.
After takeoff, the pneumatic system automatically switched from APU bleed air to engine bleed air. At that point, we secured the APU.
Following a 250 KIAS/Mach 0.75 speed schedule, the aircraft climbed to FL 450 in 21 min., including a 3 min. ATC delay. That's impressive as the OATs were mostly ISA+15C to 17C until we climbed above FL 300. At FL 450, though, OAT cooled off to ISA-5C. Fuel burn for the climb was about 1,000 lb.
We checked cruise performance at Mach 0.80 normal cruise and Mach 0.84 high-speed cruise at FL 450 at ISA-5C to -6C temperatures. At a weight of 30,800 lb., fuel burn was 1,510 pph at normal cruise and 1,810 pph at high-speed cruise. Gulfstream's AFM indicates the aircraft's long-range cruise speed at this weight is Mach 0.79 and fuel flow should be about 1,400 pph. At Mach 0.84, the book predicts 1,778 pph at that weight and OAT.
We also checked buffet boundaries. The aircraft was buffet free up to 40-deg. angle of bank, corresponding to 1.3 g. At MTOW, the aircraft has 1.2 g of buffet margin from Mach 0.75 to 0.80 at FL 450. Buffet margin drops sharply above normal cruise speed.
We descended to 16,000 ft. for airwork southeast of Abilene, Texas, using idle thrust and the variable position speed brakes for drag. The air brakes produce very mild pitch-up when fully extended and just slight airframe rumble that's unlikely to disturb passengers.
Once level at low altitude, we flew a couple of steep turns. It's easy to maintain altitude using the PFD's flight path marker and airspeed trend vector. Pitch force is moderately heavy, thereby preventing over-control. Roll response, with the help of the FBW roll spoilers, is crisp, but roll effort is moderate, again preventing over-control. Dickerson commented that pilots aren't allowed to use the flight path marker on check rides.
Dickerson next demonstrated the aircraft's low-speed protection system. If the aircraft is slowed to 72% of the angle of attack (AOA) at which the stall warning stick pusher fires, the auto-throttle system automatically engages and power is advanced to prevent the stall. Up to maximum available thrust, the auto-throttle system will not allow angle of attack to exceed 78% of stick pusher AOA.