G650 the Best Flying Gulfstream Yet

Design harmony becomes poetry in motion
g650, aviation, technology, avionics
Written By J. Mac McClellan

You’ve been hearing it a lot lately—the Gulfstream G650 was designed to have the fastest cruise speed, longest range, largest cabin, latest technology, quietest cabin, and so on. I suppose we could shorten all of the superlatives that end in “est” and just say the G650 is the “best.” True enough, but one subject we haven’t touched upon is what the G650 is like to fly. Every pilot wonders and this lucky pilot got to find out.

For those sitting in the cabin who often traverse continents or the globe, the G650’s attributes are immediate and impressive. But what’s it like for the crew in the front office who fly the G650? Having just done so, I would say that, along with the engineering and design that allows the G650 to be intuitive to fly for any pilot with large-cabin business jet experience, the G650 is a pilot’s delight, an aircraft that makes crews confident and passengers comfortable, productive and content in their travel.

Gulfstream engineers began to shape the initial design of the G650 nearly 10 years ago, a significant decision they faced was how the large and extremely fast aircraft should handle. Every aircraft design team must consider the flying qualities pilots will experience, but this time everything was different. The G650 would incorporate fly-by-wire controls, so the ability to tailor the control feel and response of the new aircraft was almost unconstrained.

To experience how the G650 feels in flight I was privileged to fly with Gulfstream experimental test pilot extraordinaire Tom Horne, whose specialty is flight control systems and handling qualities. During the aircraft’s development, Horne helped define the initial handling quality requirements with Gulfstream’s teams of engineers and test pilots.

OWNERS, PILOTS DRIVE DESIGN

As we would before launching on any flight, Horne and I started with a walk-around—but not just any walk-around. It was an unmatched learning opportunity to make the preflight inspection of the G650 with one of the experimental pilots who has lived with the aircraft since its inception. These pilots know every little detail about the aircraft, including why the design choices were made that resulted in the amazing G650.

For example, the main cabin door on the G650 is an all-new design and—for Gulfstream—the first to be electrically controlled. The press of a button sends the door and its airstair up or down and latches it. The pilot even has a button at his/her seat to open the door without leaving the cockpit.

The main landing gear on the G650 is shorter than other large-cabin Gulfstream aircraft, which is a subtle difference but one resulting from a design choice to keep the baggage compartment hatch closer to the ground to make loading and unloading easier. Additionally, the owners and pilots who advised Gulfstream on G650 design details asked for the baggage door to be made wider—large enough to swallow a main gear wheel since many operators carry a spare when traveling to remote destinations.

Horne also pointed out that the G650 fuselage cross section is not a circle because the tube is flattened on the bottom. That shape makes the cabin wider at the floor and midpoint of the cabin sidewalls. To contain the high pressurization of the cabin, which reduces the effects of jet lag on long flights, Gulfstream uses machined fuselage frames that are very strong, along with massive floor beams and a carbon fiber floor surface.

The cockpit of the G650 is very familiar to pilots who fly other large-cabin Gulfstreams equipped with the PlaneView avionics suite. There are a few differences in switches, and system architecture is not exactly the same, but operation of the avionics and navigation systems, including the head-up display enhanced vision system that Gulfstream pioneered, is the same. But with its nearly 100-foot wingspan, and elegant 33 degrees of wing sweep, the G650 cockpit incorporates a different side window shape so pilots can still see the wing tip while sitting in the driver’s seat.

As Horne and I began to taxi toward the runway I noticed that the G650 brakes are uncommonly smooth. It is very difficult to create a brake system that is powerful enough to stop an aircraft the size of the G650 in just a few thousand feet on landing and not grab and jerk when gently applied at low taxi speeds. But that just isn’t a problem in the G650 because its brake system, like the flight controls, operates through electronic commands. Passengers will enjoy a lurch-free ride on taxi and G650 pilots won’t need to worry about bringing the aircraft to a smooth stop.

Before takeoff in a conventional aircraft pilots “stir” the controls by moving the control wheel and rudder pedals to be sure the ailerons, elevator and rudder respond correctly and freely. I wondered if a pilot would do the same with the fly-by-wire control system in the G650. Yes, is the answer. The flight control diagnostic display on PlaneView showed the control surfaces move in response to my control inputs just as they do on other Gulfstreams.

SMOOTH TAKEOFF, FAST CLIMB

On takeoff pilots select a pitch command on the attitude display as a reference for the optimum takeoff nose-up angle, and I did exactly that for my first takeoff in the G650. Horne told me there would be a very linear response when I pulled back on the controls to rotate the nose up for liftoff—meaning the G650 would respond smoothly and in predictable proportion to the amount I moved the control. And he was right.

On that very first takeoff the G650 response exactly matched my instinctive control inputs without any compensation by me, or any need to “learn” the aircraft. Test pilots use the Cooper-Harper rating scale, which ranges from one to 10, to rank the flying qualities of an aircraft. On this scale one is best, not 10. You want a one because that suggests the pilot doesn’t need to compensate for any unexpected or unwanted response by the aircraft. The G650 is as close to a one as any of the countless aircraft I have flown. The G650 simply has no equal.

The speed advantage of the G650 over other business jets begins shortly after takeoff because it flies so fast in the climb. As soon as we were clear of the low altitude air traffic control speed limits I let the G650 accelerate to 300 knots, at least 50 knots faster than other business jets fly in the climb. I held that airspeed until transitioning to Mach 0.85 above 30,000 feet and continued the climb to 45,000 feet at that speed. Think of that. The G650 flies faster in climb than most business jets can achieve in cruise. And the climb rate is exceptional. We were level at 45,000 feet 20 minutes after takeoff.

All who have flown it agree–the G650 is the best flying Gulfstream yet.

CONCISE CONTROLS, LONG RANGE

At all airspeeds the G650 control response was perfect. Small movements of the controls immediately initiate appropriate response from the aircraft. There is no “dead band” as in many other jets where you must move the controls substantially before the aircraft responds.

The control forces in the G650 are lighter than in many large business jets, and the force remains the same at any airspeed, while in conventional aircraft the forces increase with airspeed or can change with flaps extended. It takes one pound of force on the G650 controls to move the airspeed up or down five knots from the trimmed airspeed. And the fly-by-wire system has damping logic so if the G650 is bumped around by turbulence or pilot input it settles back down immediately into stable flight.

The slowest effective cruise speed for the G650 is Mach 0.85, which is about 488 knots true airspeed. If you fly slower the aircraft is actually less fuel efficient, but other jets must slow to Mach 0.80 (459 knots) or even less for maximum range.

Typical cruise speed for the G650 is Mach 0.90 (516 knots) and nonstop range at that speed is 6,000 nautical miles/11,112 kilometers, compared to the maximum range of 7,000 nm/12,964 km at Mach 0.85. And I found the G650 easily accelerated to its maximum Mach operating speed of Mach 0.925 in level flight at 45,000 feet.

Sound levels in the G650 cockpit are the lowest of any jet I have flown, and the quiet is even more impressive in the cabin. Most cabin noise is caused by the air rushing past the fuselage, but the G650 is so quiet I couldn’t tell any difference in the super low sound level when flying at Mach 0.85 or 0.90 or 0.92. The incredibly low noise level is primarily the result of Gulfstream being the only business jet maker with a hemi-anechoic acoustics laboratory. These experts, and their specialized laboratory, were involved in all steps of the design and flight testing to locate and minimize noise sources.

Another new and impressive feature of the G650 is its very low cabin pressure altitude. At 41,000 feet the cabin air pressure is the same as you would experience on the ground at 3,000 feet, which is about the elevation of western Kansas. When we were flying at 45,000 feet the cabin altitude was only 3,705 feet, which as a matter of perspective is about half as high as in other jets.

FLY-BY-WIRE CONTROL

Flying the G650 at very high altitudes—something almost always left to the autopilot—was a very low pilot workload task thanks to the precision of the fly-by-wire system. On descent, under Horne’s direction, I allowed the airspeed to approach the maximum limits and the fly-by-wire system gently nosed the aircraft back up to slow down while the airspeed display turned red and a chime warned of the speed limit. If a pilot sleeps through those alerts the G650 still won’t exceed its speed limit.

At a lower altitude I intentionally pulled back on the control column without adding power and watched as the airspeed slowed. As in other jets a stick shaker vibrated the controls, providing warning as I approached stalling speed, but unlike other jets, the G650 didn’t push the stick forward or stall. The aircraft flew straight ahead giving me warnings, along with the more than 50 pounds of pull it took to hold the controls back, waiting for me to wake up and add power. Another safety benefit of the fly-by-wire system.

The control system in the G650 also reduces the pilot workload significantly while maneuvering for landing. There is no need to change the trim when flaps and landing gear are selected. The control forces are light and precise at all airspeeds. And the G650 flies its final approach in a nearly perfect touchdown attitude so there is very little for the pilot to do except keep the aircraft aligned with the runway centerline. My first touchdown was one I would have been pleased with even after 1,000 G650 landings, another testament to how well the control system design functions.

Passengers know, or soon will, that the G650 can make trips no other business jet can in terms of speed, cabin comfort and quiet, and nonstop range. And pilots are finding out that it is a nearly perfect aircraft to fly. All who have flown it agree—the G650 is the best flying Gulfstream yet. I don’t think there can be a higher compliment.

Rolls-Royce and Gulfstream: The power behind the throne for 55 years

Ever since the Gulfstream I first flew 55 years ago, large-cabin Gulfstream aircraft have been powered by Rolls-Royce engines. Collectively, the Rolls-Royce and Gulfstream combination has reigned supreme as the king of the large-cabin class by being the most popular (and prolific) engine and airframe marriage in business aviation history.

As you would expect, Rolls-Royce jet engines enjoy a well-deserved reputation for power and durability, two major reasons they have long been selected by Gulfstream for large-cabin models. The new BR725 engines on the G650 continue that tradition by working for 10,000 hours before the first major maintenance is scheduled.

But the BR725 turbofan engines also are setting new standards for fuel-efficiency, low noise and low emissions. The engines on the G650 exceed all international requirements for noise and emissions, including proposed stricter standards that may be adopted in coming years.

The G650 is the first aircraft to use the BR725 engines. The engines are rated at 16,900 pounds of thrust each, and their performance is part of the reason the G650 can fly nonstop for 6,000 nautical miles/11,112 kilometers at Mach .90 which far exceeds the design goal of 5,000 nm/9,260 km at that speed. No other business jet can cruise so far so fast.

The BR725 uses technology Rolls-Royce developed for its very large Trent series of transport engines. The internal improvements make the BR725 4 percent more fuel-efficient than the previous engine in the 700 family. The fuel-efficiency gain primarily results from improved aerodynamics within the engine where more efficient compressor and turbine blades process more air at higher pressures and temperatures.

Rolls-Royce also created a new combustion section for the BR725 that burns fuel more completely so NOx emissions are reduced by 21 percent.

The new BR725 is also a good airport neighbor because it produces as much as one-third less noise during takeoff and approach for landing. The quieter engine also is a key element in the amazingly quiet G650 cabin environment.

Rolls-Royce and Gulfstream teamed up to package the BR725 in a very compact and efficient nacelle. The BR725 fan located in the front of the engine is 2 inches larger in diameter than the previous engine in the series but the G650 overall nacelle diameter is unchanged. A larger fan increases power and efficiency, but a smaller nacelle reduces drag at cruise speed. It’s a win-win combination for the G650 and, pardon the pun, it makes the newest Rolls-Royce engine our biggest fan.



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