The technology wrapped up into the G650 is head and shoulders above anything Gulfstream ever embraced in developing its previous jets. The deeper one delves, the more one appreciates the design details.
Structure, Aerodynamics and Systems
Gulfstream's customers dictated the terms of the G650's design. Overwhelmingly, they favored a go-slow approach toward embracing new technologies, especially composite airframe construction. Accordingly, the G650's primary airframe structure, including the fuselage pressure vessel and wings, is made of high-strength aluminum alloys, augmented with steel, stainless steel and titanium, similar to previous Gulfstream aircraft. However, more composites are used in the G650 than in earlier Gulfstreams, including the horizontal stabilizer, elevators and rudder, plus floorboards, rear pressure bulkhead, engine nacelles, winglets and various fairings, among other secondary structures.
Fuselage frames are evenly spaced at 17.5-in. intervals, wider than that on previous Gulfstreams. The design change makes room for longer-spaced cabin windows. That also increases legroom in the seating groups because seat placement is based upon window spacing. The windows also are larger, visually complementing the larger fuselage cross-section.
Structural efficiency also is improved. While the aircraft has a larger fuselage cross-section than the G550, it has about the same weight per linear foot, plus it has considerably higher pressurization. But green aircraft empty weight goes up by more than 5,000 lb. because of the new aircraft's 3.3-ft.-longer fuselage, larger wing, engines and empennage, among other factors.
Aerodynamically, the G650 leaps ahead of previous Gulfstream large-body jets. The nose has been completely recontoured to reduce shock-wave drag. The windshields and side windows are much larger than on legacy large-cabin Gulfstreams, greatly improving outward visibility.
As with its previous large-cabin models, Gulfstream elected not to fit the G650 with leading edge slats because its engineers believed the additional weight and complexity did not offset the improvement in high angle-of-attack (AOA) lift. Instead they fitted the aircraft with a 1,283-sq.-ft. wing that results in the lowest wing loading of any ultra-long-range business aircraft. This results in acceptably low takeoff and landing speeds.
The wing also has 33 deg. of sweep at quarter chord to reduce Mach-induced drag. Large, outwardly canted, highly swept, blended radius winglets will help reduce wingtip vortices, an important design feature considering the wing's modest 7.73:1 aspect ratio. The airfoil thus is optimized for Mach 0.855 cruise, which is Mach 0.055 higher than the G550's airfoil. It also generates 8% more peak lift at cruise speed. The G650 is the first large-cabin Gulfstream to have an area ruled aft fuselage to reduce high-speed interference drag between the engine nacelles and fuselage. That's a drag cheating technique long used by Bombardier and Dassault on their large-cabin aircraft to lower the local Mach number in that section of the airframe.
The result is an aircraft that can cruise 7,000 nm at Mach 0.85+ and 6,000 nm at Mach 0.90. It also consumes less fuel while cruising at Mach 0.85 or better than any other large-cabin aircraft in current production. It can fly nonstop from San Diego to Sydney, Chicago to Cape Town or even Hamburg to Hawaii at long-range cruise. The G650 is the first purpose-built business jet that can fly from New York to Tokyo, Seoul or Beijing in well above ISA conditions, even with less than optimum routing and ATC climb clearances.
Most G550 systems are carried over but have been updated to improve redundancy, simplicity and reliability. The electrical system, for instance, has many more backups because of the aircraft's digital fly-by-wire (FBW) control system and electrically powered backup flight control hydraulic system.