In March Gulfstream announced development of a new model, the 650, the first clean sheet Gulfstream business jet since the G-II laid the foundation for the most successful line of large cabin business jets in the 1960s. The 650 is a response to Gulfstream customers who want more cabin space, longer range and more cruise speed, and it will set the standard in each of those categories.
The G650 cabin will be 14 inches wider than the cabin on the G550 and other Gulfstreams, the first cabin cross-section size change since the original Gulfstream I turboprop was designed in the 1950s. And the 650 will have three inches more headroom, so even people 6 feet 5 inches can stand straight and tall in the cabin.
The G650 promises an amazing combination of both speed and range increases over the G550, the current leader in the category. Increased cruise speed also increases drag so flying both faster and farther are usually mutually exclusive. But the all-new G650 wing is so low in drag at high speed that the airplane will have 7,000 nm range while cruising at Mach .85 (488 knots). That is 250 nm more range than the G550 has while cruising at Mach .80 (459 knots), and a full 1,000 more nm than the G550 can fly at Mach .85. Even more impressive is that the G650 can cover 5,000 nm at a high-speed cruise of Mach .90 (516 knots). The only existing airplane that can fly at Mach .90 is the Citation X, and at that speed it has less than half the projected range of the new G650. Top speed (Mmo) for the new G650 will be Mach .925, besting the Citation X by .005 Mach to claim the title as the fastest business jet, and fastest civilian airplane I can think of in any category.
Despite its astonishing performance, the G650 will be very much a business jet able to use all of the airports where business jets operate today. Takeoff runway at maximum weight will be 6,000 feet or less, and landing runway will be 3,000 feet even at maximum landing weight. But perhaps even more importantly, maximum takeoff weight will be under 100,000 pounds at 99,600. Some high-profile airports such as Teterboro, which is located just west of New York City, already have a 100,000-pound weight limit that has been tested and upheld in the courts, and it seems likely that other airports around the world may impose such a restriction to keep out the airline jets that are now configured for personal travel.
Gulfstream formally made an internal G650 program launch in May 2005, but the concept of a new airplane had been under study for several years before that. So, with a clean sheet in hand, a fundamental question is how big should the new cabin be? Gulfstream operators were, in general, satisfied with the cabin comfort of the existing airplanes and didn’t really want an airliner-size cabin. But many do want more cabin width so that it is easier for passengers, or the flight attendant, to pass each other in the aisle. And a few inches more headroom would always be welcomed by taller people.
A circle is the most efficient structural shape for a pressure vessel, and the fuselage on existing Gulfstreams-and most other jets-is a circle. But a circular fuselage is not the most efficient way to gain cabin width while minimizing aerodynamic drag. Since the cabin floor must be located far above the bottom of the circle to maximize usable cabin width, the lower radius of a circular fuselage hangs down in the slipstream, adding drag but nothing to cabin comfort.
The G650 solution is a complex oval-shaped fuselage that actually has four distinct radii. The benefit is that the bottom of the fuselage is flattened so less “wetted” area is exposed to the slipstream to create drag, while the floor can be located lower, near the widest point of the fuselage. Such a shape is structurally complex, but the floor carries loads in tension so the weight penalty is minimized. The new fuselage is so strong, in fact, that the G650 will have the lowest maximum cabin altitude of any jet at 4,850 feet, while the airplane is at its certified ceiling of 51,000 feet. At the typical initial cruise altitude of 41,000 feet the cabin altitude will be only 2,765 feet. Gulfstream cabin altitude has always been below the allowable 8,000 feet, but the G650 sets a new standard that will help reduce passenger fatigue during the 12-hour-plus missions the airplane can fly. And, as with other Gulfstreams, 100 percent fresh air is pumped into the cabin with no recirculation.
The new cabin will expand on another of Gulfstream’s trademarks-the huge oval windows. The new windows will measure 28 inches in width, increasing window size by 16 percent. And the window spacing will be stretched out, creating more room between seats while still placing each passenger next to one of those 16 giant windows.
Gulfstream has also established a new attitude toward cabin system reliability, a demand almost as stringent as for critical safety of flight items such as wing spars. The FAA standard for flight-critical structure and system reliability is 109, which equals one in a billion. Gulfstream’s chief of programs and engineering, Pres Henne, has decreed that essential cabin systems will meet a 107-one in 10 million-reliability standard. What that means is that the toilet will always flush, water will always flow and drain, voice communication from the cabin to the ground will always be available and no single point failure can deprive the cabin of power. The goals will be met in the same way flight-critical standards are, by adding redundancy and isolating system components so individual failures do not cripple an entire system. It is a radical concept, until you consider the G650 can fly nonstop between most any civilized points on the globe, and its passengers must be properly cared for over those vast distances.
The key to achieving G650 speed and range goals is, obviously, the design of the wing. Despite the high speed potential of the wing, Gulfstream did not abandon its core design principles, which are to have very long span-99 feet 7 inches-and enormous wing area-1,283 square feet-without any movable leading edge devices or external flap tracks hanging down. At a glance, the G650 wing looks like a simply larger version of the G550 wing, but there are subtle but crucial differences.
The new wing has more sweep, which at 33 degrees is six more than the G550 wing, and that helps control the transonic shock wave at high-speed cruise. The new wing also has a curved leading edge that, at about one-quarter span, begins a very gradual bend aft that then sweeps gently forward to the tip. This curved leading edge, along with a continuously variable airfoil, helps to control the sonic shock wave that develops over the wing as air accelerates to a speed well beyond Mach 1 to flow over the upper surface.
Gulfstream engineers eschewed the “cranked” wings that are the norm on other fast jets. On a cranked wing the inboard trailing edge goes straight out and usually has an individual flap section, before the outer trailing edge begins to sweep back. The G650 wing has a small radius at the trailing edge root, and then the wing with its internal flap tracks and mechanisms sweeps aft over its span. The new wing has a continuous, gentle dihedral angle instead of the steep angle of most new jet wing root sections that then flatten out for the outer span. And Gulfstream seals the main gear behind tight fitting doors while most jets now leave the main wheel well open to save weight and complexity. Both upper and lower surfaces of the wing are smooth with tightly sealed controls surfaces and internal flap retraction. The G650 fuselage, like all newly designed jets, sits atop a one-piece wing, but the flattened oval bottom of the fuselage makes for a more compact and lower drag intersection. A new wing-to-body fairing is very understated compared to many other jets, but is effective at controlling drag. The tight wing-to-fuselage mate keeps the total cross-section area at that point as small as possible so the fineness ratio is improved. At cruise speeds approaching the speed of sound, the longer a body can be compared to its cross section, the lower the drag, and that is why the fineness ratio is important.
The G650 wing and fuselage will be built from metal, but many elements of the airplane will be made from composites. The horizontal stabilizer and rudder will be all-composite, as will be the winglets, rear pressure bulkhead, engine cowlings, cabin floor structure and many fairings. Composites are used where Gulfstream engineers can demonstrate to themselves a proven, no-risk improvement in weight and performance.
The G650 cockpit will look very much like those in the current G400 and G500 family, with the big flat-screen PlaneView II avionics dominating. The cockpit will be so similar that Gulfstream expects pilots will be able to fly the G650 with the same type rating now issued for the large cabin Gulfstreams that have the PlaneView system. But while the G650 will look and act familiar to Gulfstream pilots, its systems will be very different because the airplane will have three-axis fly-by-wire controls.
In a fly-by-wire control system the pilots’ inputs are sent to a computer that considers all factors and then commands the necessary flight controls to move. Hydraulic muscle will still actually move the control surfaces, but there is no mechanical link between the pilots’ controls and the hydraulic actuators. Fly-by-wire is the norm in newly designed airline jets such as the Airbus family, the Boeing 777 and 787 and the Embraer 170/190 jets, but only one business jet, the Falcon 7X, has fly-by-wire controls so far.
As you would expect, Gulfstream has some very specific attitudes about how a fly-by-wire control system should operate. Most fundamental of those beliefs is that the human pilot should have a continuous way to monitor what the autopilot is doing with the controls or what the guy in the other seat is doing. That means you need control wheels on columns because sidesticks don’t provide visual feedback and actually don’t move much at all as they respond to the pressure applied by the human pilot. And when the autopilot is flying, the sidestick doesn’t give you any clue how the controls are being moved.
So, in the G650 when you grab the yoke and move it, the one on the other side will respond just as it does in a conventional airplane. The same will be true when the autopilot is engaged and moving the controls-the yokes will move in unison. The cockpit controls will be connected to each other to provide this feedback, but movement of the controls will send signals to two flight control computers that each have independent channels for each axis to provide quadruplex redundancy. On top of that will be a backup flight control computer system with “get home” capability that has its own independent hardware and software.
In a fly-by-wire system it is possible to program the airplane’s flying qualities into the computers. For example, an airplane could be unstable-meaning it doesn’t want to return to a trimmed condition-but the computers could make it fly as though it were conventionally stable. Such a characteristic is desirable in a fighter, for example, where maneuverability and stability are opponents. It is also possible to reduce drag in this way because you can lower the balancing force needed from the horizontal tail to keep the airplane on its trimmed speed. But Gulfstream is not going that far with the G650 and the airplane will have natural stability, but the computers will provide “envelope” protection.
Envelope protection means that, for example, no matter how hard a pilot pulls back on the yoke the computers will not pitch the G650 up to the stalling angle of attack. This protection is achieved in conventional airplanes with a stick pusher that slams the controls forward before the airplane can reach an aerodynamic stall, but the fly-by-wire system will be much more sophisticated and transparent. The computers will also protect the airplane from exceeding its high-speed limits, but in between the extremes, the human pilot will be in charge.
The new certification standards are driving virtually all new jets that are large enough to require hydraulically boosted or powered controls to use fly-by-wire. The level of redundancy required is almost impossible to meet with mechanical systems. For example, the G650 will have dual hydraulic actuators, each fed hydraulic pressure from systems that have at least two sources of power, for each control axis. On top of that are backup hydrostatic actuators that use their own internal electric motors to produce the hydraulic power necessary to move the control surface. Even though there are four independent electrical systems-including a backup ram air turbine generator that pops out into the slipstream in an emergency-on the airplane, there are also dedicated batteries to power the flight control computers and hydrostatic actuators. The system exceeds the already stringent certification requirements for fly-by-wire flight control redundancy.
All other systems on the G650 are being redesigned to take advantage of new technology and to simplify operation and maintenance. For example, a solid-state electrical power distribution system for non-flight-critical items such as lights, cabin systems and so on, saves 300 pounds of weight, eliminates 400 circuit breakers and relays, and removes more than three miles of wire. New brake-by-wire systems maximize braking performance under all runway conditions, while also monitoring both brake temperature and tire pressure. And the fuel system allows the G650 to be fueled to its 44,200-pound capacity in 26 minutes, compared to 45 for the G550. As always in large Gulfstreams, all fuel is carried in the wing where, like the G550, heated fuel is returned so that on those 12- to 14-hour flights in below-standard temperatures the fuel continues to flow.
As with all other large-cabin Gulfstreams since the turboprop G-I, the G650 will be powered by Rolls-Royce engines. The BR725 is a new member of the same engine family used on the G550. The new engine is rated at 16,100 pounds thrust for takeoff, up from 15,385 in the G550. Rolls achieved significant weight savings in the BR725, so its thrust-to-weight ratio is 3.1 percent better and fuel efficiency is 3.5 percent superior. Thanks to a higher bypass ratio and newly designed fan, plus many internal refinements, the new engine is 4 dB quieter, which puts it a full 16 dB below the coming Stage 4 airport noise standard, plus emissions and smoke are reduced by as much as 50 percent.
Almost every other aspect of the G650 will be superior to other Gulfstreams and to other business jets. The company has achieved remarkable gains in cabin sound level in acoustic testing, for example. The baggage compartment is 11 percent larger than in the G550 and is accessible by passengers at any altitude in flight, but the new larger external door is lower to the ramp for easier loading. The newly designed main entry door is the biggest in the business jet fleet with more than six feet of door height. And, of course, the infrared enhanced vision and newly certified synthetic vision systems will be standard in the G650.
First flight of the G650 is scheduled for the second half of 2009, with certification by the FAA and Europeans in 2011 and entry into service expected in 2012. The wing design was frozen in 2006, and a preliminary design review was completed last year. Models have been tested successfully in seven wind tunnels, with two more test regimes scheduled to be completed soon for a total of 1,400 hours in wind tunnels. A conforming fuselage barrel has been built and was successfully tested to beyond certification limit loads for bending and pressurization, including pumping it up to 18.37 psi to validate the new window structure.
Gulfstream expects to fly three test airplanes and two production G650s for a total of 1,800 hours of testing to complete certification. A new factory to assemble the G650 was recently completed, and tooling is already moving into the enormous 308,000-square-foot clear span building. All major component and subassembly suppliers are signed up and have begun work. Gulfstream officials refuse to say how large an investment the G650 requires, but since Cessna estimates it will spend $780 million to build the much smaller Citation Columbus, can at least $1 billion be far off the mark?
The G650 is priced in the “upper $50 million range” in 2012 dollars, which is about $10 million more than the G550 costs today. The G550 will continue in production, and Gulfstream sees no reason to believe that demand for it will diminish. Though Gulfstream talked about the coming G650 to many operators around the world in utmost secrecy, it took no orders or deposits before the official announcement in March. Whoever’s deposit check gets there first will be first in line.
It had long been rumored that Gulfstream was working on an all-new model, and most expected it to have a larger cabin, which it does, but the cruise speed and range increases are downright phenomenal. But then, biggest, fastest and longest range is what we have all come to expect from Gulfstream, and the company has not disappointed.