To start, two engine-driven 40 KVA constant-speed generators and a 40 KVA APU generator supply 115/200 VAC, three-phase, 400 Hz current mainly for motors, heaters and battery chargers. A 15 KVA ram air turbine has been fitted to the aircraft to provide a fourth source of emergency AC power.
Most of the 115 VAC is converted to 28 VDC by five transformer rectifier boxes for use by other equipment. The two battery chargers also can function as transformer rectifiers under certain conditions. Two 28 VDC, 53 AH nicad main batteries supply power for APU starting, operating the auxiliary hydraulic pump, and left and right essential buses if no other DC power is available. There are two 24 VDC, 9 AH nicad emergency batteries, plus uninterruptible power supply and backup flight control hydraulic power pack emergency batteries. Notably, Gulfstream initially announced that the G650 would use lithium-ion batteries, but the development team abandoned that plan in late 2011 when the candidate batteries failed to meet performance requirements. Nicads add about 150 lb. to empty aircraft weight, compared with lithium-ion batteries.
There are comparatively few mechanical circuit breakers in the overhead panel and in the left and right electrical equipment racks just aft of the cockpit. Most AC and DC circuits are controlled by electronic circuit breakers hosted by the secondary power distribution system (SPDS), accessible by means of the MCDUs in the center console. The SPDS eliminates 3 mi. of wiring, 400 mechanical circuit breakers and 300 lb. of system weight.
All interior and exterior lights are LEDs, with the exception of the high intensity discharge (HID) xenon landing lights. Gulfstream developed a proprietary landing light pulsing system for the HID bulbs that makes the aircraft easier to spot by other aircraft and birds.
All fuel is carried in the left and right wet wing tanks. A heated fuel recirculation system prevents fuel gelling during long, high-altitude missions. DC-powered main and alternate pumps in each wing provide positive fuel pressure to the engine-driven pumps. The single-point pressure refueling system has a refuel quantity preselect feature that may be controlled by either the standby multifunction controller in the glareshield or external ground service control panel near the right wing leading edge. Improved fuel distribution and balancing slashes refueling time to 26 min., a 19-min. improvement compared with the G550's upload time. The aircraft also may be refueled by means of overwing gravity ports, but doing so reduces total refuel quantity by 550 lb.
Gulfstream engineered a five-channel FBW flight control system for the G650 having left- and right-side, dual-channel flight control computers, plus a backup flight control unit, for the aircraft. FBW saves 100 lb. of weight and makes it much easier to rig flight control surfaces, and offers more redundancy than a conventional hydromechanical flight control system. FBW also eliminates control cables, pulleys and linkages in the aft equipment bay, greatly improving preflight access to other systems. The G650 thus becomes the first Gulfstream to have fully powered flight controls rather than boosted controls.
Electrical power sources include the two main generators, the APU and the RAT, along with two main, two emergency, single UPS and single backup flight control batteries. With five control channels and 10 power sources, there's actually a great deal more redundancy in the flight control system than with traditional hydromechanical control links.
Conventional control yokes and rudder pedals in the cockpit, supplied by Rockwell Collins, have five signal transducers that send commands to the four flight control computer (FCC) channels and the backup flight control unit (BFCU) built by Thales Canada. Any one of the five channels can command movement of all flight control actuators. The two FCCs or BFCU, in turn, send command information out to remote electronic units, furnished by Parker Aerospace, that command the movements of each flight control actuator.
Each FCC has one active and monitoring channel. It's as though two airplanes were flying in tight formation with one pilot flying and one pilot monitoring aboard each airplane. Thus these four pilots in the two airplanes and all four channels in the two FCCs are different, but they all have to agree on a course of action. The BFCU, though, “flies” solo. It's only there in case the other two FCCs are completely unavailable.