Gulfstream's innovative approach, which enabled the G650 to retain the dual 3,000-psi hydraulic circuit design, involves using remotely located, DC-powered packs in hybrid flight control actuators. Seven of the 16 flight control actuators can function either as conventional electrohydraulic actuators or as DC electrically powered actuators in the event of the loss of normal left or right hydraulic pressure. Gulfstream calls these components electric backup hydrostatic actuators, EBHAs for short. The EBHAs can power the ailerons, elevators and rudder, along with the outboard spoilers, thereby providing the redundancy, but not the weight or complexity, of a third hydraulic system.
There's EASA type certification pre–cedence for the dual hydraulic, electric power pack backup design approach. Airbus uses a similar architecture on its A380 super-jumbo and A400M military airlifter, but the electrohydraulic actuators work full-time instead of just being backups.
Aboard the G650, both left and right 3,000-psi hydraulic systems are powered by engine-driven pumps most of the time. The left side does most of the heavy lifting, including powering part of the flight controls, as well as the landing gear, flaps, nosewheel steering and inboard brakes, plus on-side thrust reverser. If the left engine-driven pump is inoperative, a DC auxiliary pump or a right-to-left power transfer unit also can power the left side. The right hydraulic system powers part of the flight controls, along with the outboard brakes and on-side thrust reverser.
The main landing gear employs a trailing link design for smooth touchdowns. The brake-by-wire system has both brake temperature and tire pressure monitoring through the EICAS. However, there is no auto-brake function. The nose gear has a digital steer-by-wire with up to 7 deg. of authority through the rudder pedals and up to 80 deg. of authority with the tiller, depending upon groundspeed. If the tiller sensor fails, nosewheel steering authority through the rudders increases to 16 deg. Notably, the nosewheel steering links do not have to be disconnected for towing.
Bleed air is used for wing leading edge and engine cowl anti-ice protection, cabin pressurization and air-conditioning, along with main engine starting and for sucking ambient air through the total air temperature probe. The APU, an external cart or the cross-side engine can supply air for starting a main engine. The APU supplies more bleed air than both engines at idle thrust, so it's advisable to turn off the bleed air from the main engines and use the APU to supply the twin air-cycle machine packs during ground operations in warm weather. In addition, engine ground idle rpm is reduced with the bleeds off, thus there's less residual thrust and reduced need to use the brakes while taxiing.
The interior has three-zone temperature control, with one thermostat in the cockpit and two at opposite ends of the passenger cabin. Chilled air also is used to cool the forward electrical equipment racks. Maximum pressurization is 10.69 psid, so typical cabin altitudes range from 3,000 ft. at FL 410 to 4,850 ft. at FL 510.
The G650 has a fully MSG-3 maintenance friendly design with 600-hr. basic inspection intervals.
Upgraded Passenger Comfort
The G650's passenger cabin is 14-in. wider, 3-in. higher and substantially longer than that of the G550. Finished dimensions are 8.2 ft. wide, 6.3 ft. tall and 42.9 ft. overall length from cockpit divider to the baggage compartment bulkhead. The floor is a full 15-in. wider than the G550's, making it the widest among purpose-built business aircraft. The aircraft's new four radii cross-section was inspired by the non-circular design of G150, one that maximizes head, shoulder and elbow room for the available cross-section. The G650 has 28% more total cabin volume and 30% more floor area, along with 3 in. more legroom in each seating area than the G550. Gulfstream's signature wide oval windows are 16% larger and 3.4-in. higher for better viewing. The 16 cabin windows are by far the largest of any business jet. Yet, the linear weight of the fuselage pressure vessel is essentially the same as that of the G550. That's impressive structural efficiency, considering the aircraft has the highest pressurization of any current production ultra-long-range aircraft.
The G650 has the first electrically controlled and latched door in an FAR Part 25 aircraft. It's 6.3 ft. high by 3.0 ft. wide with an air-stair design having illuminated treads, sturdy left and right hand rails and an offset hinge that increases headroom when entering the vestibule. There is no manual door handle, other than a maintenance door release buried behind the cover. Electric locking and unlocking, along with electric actuation, enables the flight attendant or the flight crew to open or shut the door from their crew stations.