Down at 15,000 ft., we flew a series of standard air work maneuvers. Steep turns are easy to fly. The HUD's flight path vector (FPV) and velocity trend vector provide precision guidance cues. Stick force is moderately heavy, but that's appropriate for this class of aircraft. We also flew clean and dirty stalls, at least to the maximum AOA permitted by the FBW control laws.
We used a clean configuration for the first stall. At a weight of 66,800 lb., we trimmed the aircraft for a 156 KIAS Vref speed or 0.67 normalized AOA, reduced thrust and decelerated. “Normalized” means that 1.0 AOA is the maximum lift coefficient adjusted for high-lift configuration and local Mach number because of its influence on buffet and stall. At 15,000 ft., though, the effect of local Mach number on the wing is insignificant.
The pitch limit indicator appeared on the PFD and HUD at 0.75% maximum normalized AOA. During the approach to clean stall, the stall-warning stick shaker fired at 129 KIAS or 0.94 normalized AOA. At 0.97 AOA, the FBW system limited elevator and horizontal stabilizer pitch control authority to prevent untoward handling characteristics. Holding the control wheel full aft, the nose thus gently pitched down and we initiated recovery.
The dirty stall, with gear down and flaps extended to the full 39 deg., was equally non-dramatic. We trimmed for 122 KIAS or 0.67 AOA, commenced a normal glidepath-like descent and then leveled off without adding thrust, thus allowing the aircraft to decelerate. After the stick shaker fired, we continued to pull aft on the yoke until reaching the stops. At 0.98 normalized AOA, the nose gently dropped and we initiated recovery with only a slight loss of altitude.
The two maneuvers quite clearly demonstrated the G650's improvement in high AOA behavior compared to previous generations of large-cabin Gulfstreams. If both stick shaker and stick pusher are ignored in some of the legacy Gulfstream models, positive stick force gradient can be neutralized or even reversed. Stall recovery thus becomes much more challenging and there can be a substantial loss of altitude.
Returning to Savannah, we prepared for a WAAS LPV precision approach to Runway 19. Horne computed Vref at 120 KIAS for a 65,500-lb. landing weight and a non-factored landing distance at 2,873 ft. based upon 13-kt. headwinds. It's apparent that the G650's ref speeds at typical landing weights will be similar to those of the G550, even though it is a heavier airplane with more wing sweep.
We bugged the target airspeed at 125 KIAS and let the auto throttles maintain speed in gusting wind conditions. The G650's big airfoil with low wing loading doesn't provide as smooth a ride in turbulence as the more highly loaded airfoils of competitors' aircraft. But it does enable the aircraft to cruise higher where the air generally is smoother for most of the mission.
The HUD's azimuth and glidepath guidance cues, along with the FPV marker, made it easy to hand-fly the approach. We noted that the airport database used by the HUD needs a little updating. The synthetic runway outline displayed was 2 deg. right of the actual pavement borders. In addition, runway touchdown elevation and glideslope/glidepath data must be manually entered through the standby multifunction controller because the HUD isn't fully integrated with the FMS airport database.
The FBW system transitions from high level control law to direct law for takeoff and landing, so the G650's smooth handling behavior during approach reflects its aerodynamic refinement. At 50 ft., we pulled back the thrust to idle and continued to use the HUD until touchdown. The aircraft appears to float less than the G550, but touchdown behavior was nonetheless very smooth. We deployed the thrust reversers, but kept the throttles at idle, thereby allowing the aircraft to decelerate leisurely. A light touch of the brakes and we turned off at Taxiway B1 after a touchdown roll of about 5,200 ft.