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.