The PFCCs combine pilot control inputs from the REUs with inputs from various sensors, such as AOA, speed, configuration and vertical acceleration, among others, to calculate the appropriate flight control actuator commands based upon higher level Normal control laws. The PFCCs send back the Normal Law control response to the triple REUs that then command the movement of the flight control actuators.
Parker also furnishes most of the FBW software, along with the flight control surface actuators and other hardware, used aboard the aircraft.
Embraer's high-level Normal Law functions include both soft- and hard-limit protection. Within the normal flight envelope, there are +30-deg. /-15-deg. soft pitch and 33-deg. roll limits, along with 1.1 Vs minimum speed and Vmo limits, that can be overridden by maintaining lateral or longitudinal sidestick pressure. Beyond these soft limits, there are hard vertical acceleration, sideslip, maximum AOA and high-speed limits that cannot be overridden. There are no hard pitch or roll angle limits.
Embraer engineers believe the hard maximum AOA limits enable the designers to take advantage of lower takeoff and landing V speeds to improve airport performance. For users, this translates into a payload increase of up to 900 lb. when operating off of short runways, Embraer officials assert. AOA limit also enables flight crews to extract maximum performance from the aircraft during wind-shear escape or controlled flight into terrain (CFIT) avoidance maneuvers.
Engineers in Savannah took a different FBW design approach than other business jet manufacturers, assuring that the G650 has high redundancy with the minimum number of components. Two dual-channel primary flight control computers (FCCs) are supplied by Thales. The FCCs host the high-level control laws. Each has two computing and two monitoring cards, eliminating the need for stand-alone monitoring computers.
Similar to Embraer's layout for the Legacy 450/500, the G650's dual primary flight control computers provide four dissimilar flight control command channels, any one of which can control all flight control surface actuators.
Unlike Dassault's and Embraer's FBW designs, Gulfstream elected to fit the aircraft with individual remote electronics units boxes, or ACEs, integrally mounted with each of the flight control surface actuators. The 16 hybrid REU/electrohydraulic system actuators (EHSAs) are also made by Parker.
The basic FBW design meets the 10-9 probability of failure required for certification, but Gulfstream wanted an additional level of redundancy to provide 10-10 probability of failure. So, the G650 has a fully autonomous, three-axis backup flight control system (BFCS) computer made by Thales that complements the dual primary flight control computers. It sends its commands to one of two REUs that signal the movement of the flight control surface actuators on the left and right ailerons, left and right outboard spoilers, left and right elevators and the rudder.
The G650 only has two hydraulic systems, rather than the three required for most FBW flight control systems. To meet the triplex power requirement, Gulfstream and Parker Aerospace teamed to create the aviation industry's first dual-mode flight control actuators.