Gulfstream's new way to travel fast, far and in quiet comfort is vetted
Gulfstream is turning up the heat in the large-cabin business aircraft competition with its new G650 flagship, the largest, fastest, farthest-ranging—and at $64.5-million per copy—most expensive executive jet in the company's history. The aircraft cruises at nearly 30 kt. faster than the current generation of large-cabin business jets and its 7,000-nm range exceeds that of the G550, the previous distance leader, by 250 nm.
Moreover, the G650's cross-section is wider and taller than that of any rival, save for converted jetliners, its cabin is touted as 5-6 dB quieter than that of hush-quiet G550, and its pressurization system delivers a less-than-5,000-ft. cabin altitude at flight level (FL) 510—all welcome attributes on intercontinental missions that can exceed 14 hr. aloft.
The aircraft features several new systems including Gulfstream's first three-axis digital flight control system and a more redundant electrical system with a new power distribution architecture.
Gulfstream customers dictated the terms of the all-new G650's design, overwhelmingly favoring time-proven aluminum versus new-technology composites for the primary airframe. However, composites are used in the horizontal stabilizer, elevators and rudder, plus floorboards, rear pressure bulkhead, engine nacelles and winglets. Fuselage frames are evenly spaced at 17.5-in. intervals, wider than that on previous Gulfstreams, which makes room for longer-spaced, and larger cabin windows. That also increases legroom in the cabin because seat placement is based on window spacing.
As with all large-cabin Gulfstreams, the G650 is powered by twinturbofans. The 16,900-lb.-thrust BR725 is a growth version of the 15,385-lb.-thrust BR710 that powers the G550. And as with previous models, Gulfstream eschewed leading edge slats.
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. The large, outwardly canted, highly swept winglets 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. 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.
The result is an aircraft that can cruise for 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 than any rival in production. It is the first purpose-built business jet that can fly from New York to Tokyo, Seoul or Beijing in well above ISA (international standard atmosphere) conditions.
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) controls.
Two engine-driven 40 kilovolt ampere (KVA) constant-speed generators and a 40 KVA auxiliary power unit (APU) generator supply 115/200 VAC, three-phase, 400-hz current mainly for motors, heaters and battery chargers. A 15 KVA ram air turbine provides a fourth source of emergency AC power.
Two 28 VDC, 53 AH nickel–cadmium (Ni-Cad) main batteries supply power for APU starting, and two 24 VDC, 9 AH Ni-Cad emergency batteries, plus backup flight control hydraulic power pack emergency batteries.
Gulfstream engineered a five-channel FBW flight control system for the G650, which saves 100 lb., eases rigging of flight control surfaces, offers more redundancy than a conventional hydro-mechanical system, and eliminates control cables, pulleys and linkages.
Direct law is used for takeoff and landing. Up and away, the primary high-level pitch control law is Nz, or vertical acceleration, command with “U” speed stability, meaning the pilot has to trim pitch for speed changes.
While most aircraft with fully powered flight controls need three separate hydraulic systems for required redundancy, Gulfstream instead uses remotely located, DC-powered pumps in hybrid flight control actuators in lieu of the third system. G650 thus retained the dual 3,000-psi hydraulic circuit design of its predecessors.
The main landing gear is a trailing link design for smooth touchdowns. The aircraft has a brake-by-wire system, but no auto-brake function.
Bleed air is used for wing leading edge and engine cowl anti-ice protection, cabin pressurization and air-conditioning, along with main engine starting.
Maximum pressurization is 10.69 psid, so typical cabin altitudes range from 3,000 ft. at FL 410 up to the maximum 4,850 ft. at FL 510.
In the cockpit, four 14.1-in., landscape-configuration LCD screens dominate G650's second-generation PlaneView instrument panel. The glareshield-mounted flight guidance panel has improved functionality, including LED illumination and annunciator buttons
Standard equipment includes's second-generation synthetic vision. HGS-6250 head-up display (HUD) and Kollsman enhanced vision camera, three flight management systems, 3D Doppler weather radar, four SmartProbe air data sensors and auto throttles, among other features.
The flight guidance system also has an automatic emergency descent mode.
The aircraft has a fully MSG 3 maintenance friendly design with 600-hr. basic inspection intervals.
Once outfitted, the G650's passenger cabin 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 15 in. wider than the G550's, making it the widest among purpose-built business aircraft. Gulfstream's signature wide oval windows, eight per side, are 16% larger and 3.4 in. higher than those of previous models.
The electrically controlled and latched main door, a first for a Part 25 aircraft, is 6.3 ft. high by 3.0 ft. wide with an air-stair design that sported illuminated treads and hand rails on both sides.
The layout of the aircraft we flew for this report featured a forward crew area with crew rest compartment, galley and lavatory, three seating areas in the main cabin, an aft lavatory and an internally accessible, 195-cu.-ft., 2,500-lb.-capacity baggage compartment.
The cabin is one of the quietest in the sky, thanks to input from acoustical engineers at Electric Boat, like Gulfstream, asubsidiary. Its architecture assures that no single failure can cause loss of essential systems, including fresh and waste water, air-to-ground communications, lighting, or cabin power and control.
The aircraft has both Iridium and Inmarsat SatCom systems, and its audio-visual system components run the gamut, accessed by dual USB input ports and dual 26-in. LCD monitors.
We recently strapped into the left seat of S/N 6013 for an evaluation flight. Jake Howard, G650 project chief test pilot, was in the right seat and Tom Horne, senior experimental test pilot, rode on the jump seat and recorded data for our test points.
The aircraft's empty weight was 54,372 lb., giving it a potential 1,428-lb. full-fuel payload. Thus, this aircraft can carry seven passengers with full fuel. Each additional passenger, however, only costs about 35 nm of range.
Fuel on board our flight was 15,600 lb., about 35% of maximum. Horne computed the ramp weight at 70,022 lb., or about 70% of maximum. With a field elevation of 50 ft. and outside air temperature at 25C, our computed takeoff speeds were 108 KIAS for V1, 109 KIAS for rotation and 126 for the V2 one engine inoperative takeoff safety speed. TOFL (takeoff fueled length) was 3,400 ft.
Engine start procedure involved switching on the boost pumps, turning on the start master and pressing a start button. Next, open the fuel cock and the Fadec (full authority digital engine control) handles the rest.
With a takeoff weight of about 69,600 lb. and 37,800 lb. of thrust, acceleration was sporty, even by Gulfstream standards. The aircraft left the runway in about 3,000 ft. Control response was crisp and the aircraft was well damped in pitch, no doubt due in large part to the 36.6-ft. span, 439-sq.-ft. horizontal stabilizer. But the high-level FBW control laws surely played a significant role as well in G650's well-mannered behavior.
The aircraft also had pleasant artificial roll control feel and good roll response with adequate control yoke centering, but very little on-center break-out force. Engineers with Gulfstream and Rockwell Collins, which supplied the control yokes and rudder pedals, worked together closely to fine-tune artificial feel and control response.
On the way up to initial cruise altitude, we had a couple of intermediate level-offs required by air traffic control (ATC) and comparatively sharp turns. Yet, using a 250 KIAS/260 KIAS/Mach 0.85 climb schedule in mostly ISA conditions, the aircraft leveled off at FL 470 in 23 min. At ISA-7C, it cruised at Mach 0.85 or 480 KTAS on 2,400 pph at a weight of 67,500 lb.
Then we pushed up the throttles because high-speed cruise is G650's forte. The 67,400-lb. aircraft smartly accelerated to Mach 0.90, resulting in 506 KTAS on 3,000 pph in ISA-7C conditions. Horne noted that the cabin altitude was 4,300 ft.
We checked Mach buffet margins with a wind-up turn, which indicated the aircraft has robust margins, albeit at a comparatively light weight. We didn't encounter buffet until about 1.4g at Mach 0.88 in a 45-deg. turn.
Descending to 15,000 ft. for airwork, we used idle thrust and air brakes. We noticed only mild buffeting and a slight pitch change when the air brakes were extended.
Once level at 15,000 ft., we flew a series of standard air work maneuvers. We especially wanted to evaluate stall behavior because G650 is the first large-cabin Gulstream that does not need a stick pusher to hasten stall recovery. We first attempted a stall in the clean configuration at a weight of 66,800 lb.; we trimmed the aircraft for a 156 KIAS Vref speed or 0.67 normalized AOA (angle of attack), 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.
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 fully aft, the nose 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, began 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.
Returning to Savannah, we prepared for a WAAS LPV (wide area augmentation system with vertical guidance approach procedures) 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.
We bugged the target airspeed at 125 KIAS and let the auto-throttles maintain speed in gusting wind conditions.
The HUD's azimuth and glidepath guidance cues, along with the FPV marker, made it easy to hand fly the approach.
The FBW system transitions from high-level control law to direct law for takeoff and landing, so G650's smooth handling behavior during final approach reflects its aerodynamic refinement. At 50 ft., we pulled back the thrust to idle and continued to use the HUD until touchdown. We deployed the thrust reversers, lightly touched the brakes and turned on to a taxiway after a touchdown roll of about 5,200 ft.
Earlier we flew one engine inoperative (OEI) takeoff and landing in the G650 simulator at FlightSafety International's Savannah training center. Rudder pedal forces on the OEI takeoff were moderate and the aircraft was easy to control. For landing, though, we could not use the auto -throttle because the system only works if both engines are operating. Managing the asymmetric thrust, however, was not difficult.
Conclusions? G650 is the nicest flying large-cabin Gulfstream yet built. The FBW functionality is all but transparent unless probing the extremes of the flight envelope. Pilots might not know it's a FBW aircraft without being told. PlaneView II, the HUD and EVS, among advanced cockpit features provide unsurpassed situational awareness. The cabin environment, including increased volume, window size and pressurization, along with the redundancy and reliability of the cabin management system, make it Gulfstream's most commodious and functional business aircraft yet.
Being able to cruise at Mach 0.80 may have been the benchmark in the 20th century, but it seems slow by 21st-century standards. Even long-haul airliners now can cruise at Mach 0.85.indeed routinely quotes Mach 0.82-0.85 as the normal cruise speed for its current production Global series business jets.
The G650 now raises the standard with its Mach 0.90 high-speed cruise and 6,000 nm range. Slow it to Mach 0.85 and go another 1,000 nm. Among purpose-built business jets, G650 has the best fuel efficiency while cruising at Mach 0.85.
So, Gulfstream's new flagship has a healthy lead in the ultra-long-range business aircraft class. But Bombardier's Global 7000, promising 7,300-nm range at Mach 0.85, is due to arrive in 2016 and its 7,900-nm Global 8000 enters service just one year later. Longer term,could challenge G650 with a growth version of its pending SMS.
But the G650 is here and it's delivering on its promises. The competition has still to prove their claims. And Gulfstream already is studying its next generation of top-line business aircraft because it believes that's the way to stay in front.
Tap on the icon in the digital edition of AW&ST for a video of Fred George flying the G650, and watch his full video pilot report at http://ow.ly/jaDTl
|Wing Loading||77.6/58.2 lb./sq. ft.|
|Power Loading||2.95 lb./lbf.|
|Length||99.8 ft./30.4 meters|
|Height||25.7 ft./7.8 meters|
|Span||99.6 ft./30.4 meters|
|Length||53.6 ft./16.3 meters|
|Height||6.4 ft./2.0 meters|
|Width (maximum)||8.5 ft./2.6 meters|
|Width (floor)||6.3 ft./1.9 meters|
|Output/Flat Rating OAT°C||16,900 lb. each ISA+15C|
|Max Ramp||100,000 lb./45,360 kg|
|Max Takeoff||99,600 lb./45,178 kg|
|Max Landing||83,500 lb./37,875 kg|
|Zero Fuel||60,500 lb./27,443 kg|
|BOW||54,000 lb./24,494 kg|
|Max Payload||6,500 lb./2,948 kg|
|Useful Load||46,000 lb./20,865 kg|
|Executive Payload||1,800 lb./816 kg|
|Max Fuel||44,200 lb./20,049 kg|
|Payload with Max Fuel||1,800 lb./816 kg|
|Fuel with Max Payload||39,500 lb./17,917 kg|
|Fuel with Executive Payload||44,200 lb./20,049 kg|
|Certificated||51,000 ft./15,545 meters|
|All-Engine Service||42,700 ft./13,015 meters|
|Engine-Out Service||25,000 ft./7,620 meters|
|Sea Level Cabin||31,900 ft./9,723 meters|