Gulfstream G150
It would be unfair to say that Gulfstream people have a swagger, but they do exude confidence. And why not. Gulfstreams are the world leader in large cabin, extremely long-range business jets, and with the new midsize G150 in service, they are now setting new performance and comfort standards in that category, too. I had flown the G150 in 2005 shortly before it was certified, and its performance and flying qualities are impressive. But with the airplane now in service it was time for a look at what it could do in the real world of business flying. So the Gulfstream people invited me to fly along on a couple of record runs. Gulfstream holds dozens, maybe hundreds, of performance records so there was nothing unusual about the plan - except it called for a coast-to-coast westbound flight in the dead of winter. What midsize jet maker decides to show off its airplane under the worst possible conditions? Only the one who is confident in what it can deliver. This past winter has been unusual with extreme cold and storminess on the West Coast, and way above average temperatures in the East. In between have been some of the consistently strongest winds aloft in memory, along with air temperatures that are well above the international standard atmosphere (ISA). Blame it on El Niño, I guess, but the conditions are as difficult as possible for long-range westbound flights. The G150 has the range to easily make it from New York to California, or the West Coast to Hawaii, against 85 percent probability headwinds with the air temperature aloft near ISA. A couple of its competitors can also make the trip nonstop under the same conditions, though at a significantly slower cruise speed. But the weather in mid-January promised to be anything but standard. Winds in the jet flight levels were topping 150 knots in the middle of the country, and all the forecasts called for way above standard air temperatures at cruise. An excellent test, in other words. The Universal Weather flight planning service calculated that staying north of the more direct route from Westchester County Airport, near New York City, to Long Beach would avoid the strongest of the headwinds, even though it would add distance. The flight plan route would be about 2,250 nm and, with the G150 operating at max cruise power the whole way, the trip would take about six hours. With five passengers and two crew, the G150 could carry 10,000 pounds of fuel and be just under its 26,100 pound maximum certified takeoff weight. The completed G150s are actually coming in below the target basic operating weight of 15,100 pounds, which is very rare in a new airplane program. This particular airplane weighed 14,929 pounds with two pilots and cabin stores, including two big rafts required for oceanic trips. Take out the rafts for domestic flying and you can add another passenger. It had snowed lightly at Westchester County but the runway was clear when we taxied. With temperatures near freezing we needed only 4,851 feet of runway for a balanced field despite our maximum weight. But on the taxi out, New York Center changed our clearance to a more southerly route that would put us in stronger headwinds. It took nearly 30 minutes to sort out the clearance, and fuel was going out the tailpipes the whole time, nearly 200 pounds of it. The G150 didn't need that fuel if the flight plan predictions were close, but it would have been nice to have it in the tanks. One of the many changes that Gulfstream and its partner Israel Aircraft Industries (IAI) made while transforming the much smaller G100 - née Astra - into the G150 was to add more powerful balance tabs to the elevator. Rotation forces on the controls of the G100 were very high, actually at or near the certification limit. The new tabs cut those forces in the G150 in half and make takeoff a very pleasant and positive maneuver for pilots. The G150 doesn't climb as spectacularly as some of the very big wing airplanes like the Citation Sovereign, but it does okay. Including a five-minute level off, the G150 was at its initial cruise altitude of 38,000 feet in 25 minutes, despite air temperatures starting to soar way above standard at 26,000 feet and higher. Air temperature is crucial to jet airplane performance because engines burn air and fuel by the pound, and when the temperature is warmer each unit of air is less dense. The wing also loses efficiency when air density drops, so there is greater drag to lift the airplane. The combination of less thrust and lift really takes a big bite out of a jet's cruise performance. Temperatures aloft are counterintuitive, with it being coldest over the equator and warmer as you near the poles. In the winter the warm air aloft typically sinks toward the equator, but this past winter that phenomenon was even more pronounced with temperatures over the lower 48 states as warm as you expect on a far north Atlantic crossing. A few degrees above standard doesn't matter too much, but when the air gets to 10º and 15º C above ISA, performance falls off drastically. So, what did we find at FL 380? Winds at 80-plus knots on the nose and air temperature 13º C above standard. Despite such adverse conditions the G150 posted a true airspeed of 443 knots, about Mach .75, with a fuel flow of 1,370 pounds per hour. The Collins flight management system (FMS) calculated a specific range through the air of .3216 nm per pound of fuel burned. That is amazingly efficient for an airplane of this size traveling at more than 500 mph. As the fuel burned off, our true airspeed climbed to 455 knots over Michigan; the wind was still blowing 72 knots and the temperature was plus 12º C. The cruise speed was 12 knots faster than the Gulfstream flight manual predicted for the conditions, though the fuel flow was 40 to 60 pounds lower. Better to deliver more than the book promises than to be wishing for more range down the road.
The G150 has four 10-by-12-inch Collins Pro Line 21 displays while other midsized jets have the smaller 8-by-10-inch flat panels. The difference is dramatic. The entire instrument panel is covered with bright, crisp displays, and you can use Gulfstream's unique cursor control device (CCD) to select what you see on them. The CCD is a pistol grip-style handle that has a trigger for the enter functions, a thumb wheel to scroll through ranges and menus, and buttons under your thumb to move the cursor from one display to the other. Nothing as complex as the CCD and PlaneView avionics system can be truly said to be intuitive, but it doesn't take long to learn to use the CCD. And the design of the handle allows a comfortable and sure grip under any bumpy conditions. The TFE731 engines on the G150 have digital electronic engine computers (DEEC) that behave exactly like full-authority digital engine controls (fadec), except that the DEECs have a mechanical backup while fadec uses multiple electronic channels. The bottom line for pilots is that with DEEC, just as with fadec, you move the levers to a preset spot for takeoff, climb and max cruise, and the electronics take care of setting the power to suit atmospheric conditions. The G150 power levers have flat spots that help you find the power settings by feel, but the PlaneView displays also show you by posting the letters "CLB" when climb power is selected and "CRZ" for maximum cruise. We let the G150 accelerate in CLB, but never moved the power below maximum CRZ thrust for the entire flight until descending into southern California. The G150 cockpit is very comfortable and roomy, just about the best for the traditional midsize jets. The crew seats are specifically designed for the airplane and are a monumental improvement over the seats in the G100 and Astra. And the visibility is excellent with large swept windshields and big single pane windows beside each pilot. But the real reason for the G150 to exist is not cockpit size but cabin comfort. The G150 cabin is one foot wider than the G100 and has 25 percent more volume. However, Gulfstream preserved the nearly flat sides of the cabin, so the G150 has a full foot more room than the competition when measured at the passenger's seated head position. The competitors have circular cabin cross sections, so they also have less room for your feet. The G150 we flew was fitted with a seven-seat cabin that included a club four in the rear, a single forward facing seat on the right and a two-place divan on the left. Divans are very popular with passengers but are difficult to certify in new airplanes because the side facing passenger must pass the same head impact safety criteria used for seats facing fore and aft. The passenger restraint system is key to certifying a divan, and Gulfstream passed the test. With five full-size adults - some of us a little more than full size - in the cabin, there was plenty of room to stretch out, and the 5-foot-9-inch cabin height made it easy to move around. The aisle is 16 inches wide, another contributor to comfort. Gulfstream also designed new cabin chairs with arm rests that fold into the seat back instead of dropping straight down. The new arm rests make it easier to get in and out of the seat, and more comfortable to slouch, something we all do on long flights. The lavatory is in the rear of the cabin and is plenty big enough and private enough for comfortable use. One of the many operational convenience changes Gulfstream made to the G150 was to move the lav service port to the leading edge of the right wing and use international standard fittings. On the previous model the lav service port was near the trailing edge of the wing right next to the single-point fuel connection, so you couldn't service the lav and take on fuel at the same time. At two hours and 10 minutes into the trip we climbed to FL 400 where the temperature was still 8º C above standard and the headwind 73 knots. At three hours true airspeed was up to 458 knots true, about Mach .79, the temperature was plus 7º C, the headwind 75 knots and we had 5,450 pounds of fuel in the tanks, very close to the flight plan despite the nearly 200 extra pounds burned waiting on the ground. The G150 carries fuel in the wings, of course, but the wing is quite thin so a lot of fuel is in the fuselage. With a system of standpipes, fuel is burned from the aft fuselage tank, then the center tank and then the last of the aft tank until finally wing fuel is left. The entire process requires no crew input, and the CG moves very little and always stays well within limits no matter the fuel load. At four hours we were up to FL 430 and were leaving the warmest air and headwinds behind. We could have stayed at that level, but FL 450 beckoned and there we found temperature near standard and headwinds down to 36 knots. Fuel flow dropped to under 1,200 pounds per hour though cruise Mach stayed at .78. Five hours and 20 minutes into the flight we started the descent for Long Beach and landed five hours and 53 minutes after takeoff. There was 1,900 pounds of fuel in the tanks, way above necessary reserve despite the 200 pounds we burned on the ground back at White Plains. The FMS computed that we had flown 2,223 miles over the ground, but 2,542 nm through the air. Average true airspeed was 432 knots, average headwind 54 knots and, most difficult of all, the average air temperature was 10º C above standard. The flight goes into the National Aeronautic Association books as a city pair speed record, but it is really a marathon test for a midsize business jet. On some day with more typical winds and temperatures another midsize jet may make the trip faster, but on this day it's doubtful that any other midsize could have made the trip with the same payload without stopping, and certainly none could come close to the speed.
| The airplane flown for this report was among the first delivered. Options installed included a dual Collins file server system that allows a redundant source of electronic approach chart display, so no paper charts are required. Also installed was an XM Weather receiver to download weather information. All data here is from the airplane flight manuals and reflects standard day conditions unless otherwise noted. |
The fact is the G150 is better than even Gulfstream expected. The company targeted a standard day maximum weight takeoff runway requirement of 5,830 feet, but the finished airplane can do it in 5,000 feet. Same for landing where the promise was a runway requirement of 3,450 feet, but Gulfstream delivered 2,880 feet. And the range goal was 2,700 nm in still air, but the actual airplane can do 2,950 nm, all with NBAA IFR reserves, of course. The G150 beat all of its goals thanks to obsessive attention to seemingly small details. One of the biggest drag reductions, and thus range extenders, was the design of the engine-mounting pylon. The pylon has three distinct shape changes from front to rear, oddly twisting up at the end. It is not intuitive, but it works, and its contribution can be measured. Another improvement was at the wing to winglet juncture where flow visualization testing revealed a dead spot where air was actually moving forward. A series of small triangular vortex generators solved the problem. Airflow visualization testing also revealed that air was leaking from under the wing to the top. New seals of all gaps solved that problem. The careful shaping of the nose and cockpit also cut drag dramatically, but so does use of thicker metal in some areas to remove ripples. Over five or six hours of flying, small drag improvements add up, and Gulfstream is the master of dealing with drag details. For the return trip we decided to set a record from Aspen back to Westchester County. Aspen, with its 7,800-foot elevation and 7,000-foot runway, is one of the most challenging in the country. For a midsize jet to haul five passengers out of Aspen all the way back to the East Coast, particularly at maximum cruise speed, is remarkable. It was cold in Aspen in January, of course, so that mitigated the impact of the high airport elevation somewhat. However, with our five passengers and 7,100 pounds of fuel we could have made the trip even if it was 70º F at Aspen. If you want to slow down to long-range cruise you could make the trip leaving on an 86º F day at Aspen, so our winter trip wasn't a sidestep on temperature. Plus, winter is what Aspen is all about. With a takeoff weight of 23,000 pounds we needed only 5,820 feet of Aspen's runway. If an engine had quit, our second segment climb gradient with the engine out would have been 6.7 percent. The engines kept running, as usual, and we climbed directly to 41,000 feet where air temperature was still 8º C above standard, holding cruise Mach back to about .79 for a true airspeed of 455 knots. At least the wind, though not as strong, was on the tail and we covered the 1,584 nm from Aspen to Westchester County in three hours and eight minutes using 4,590 pounds of fuel. Average ground speed was 503 knots and air temperatures stayed above standard for the entire trip. The G150 is a very complete and capable airplane with a standard auxiliary power unit (APU) that warms and cools the cabin on the ground, and which can be started in the air up to 20,000 feet and run up to 35,000 feet to supply a third source of electrical generating power. The airplane has no stick shaker or pusher because when you approach a stall the wing leading edge slats deploy automatically, and the airplane stalls straight ahead under full control like a light airplane. The ailerons have hydraulic boost with manual reversion, but other flight controls are manual. Ground spoilers deploy automatically on touchdown and the yaw damper automatically turns itself off. The airplane systems are a combination of automation to minimize pilot workload, but also are mechanically basic and robust to increase reliability. The G150 is designed to airline maintenance standards that use testing and analysis to predict wear instead of only flying hours or calendar time. Already the "A" inspection interval has been increased from 250 to 500 hours. Gulfstream expects the A inspection to take less than two days to complete and no other routine maintenance is required until the annual check. And, Gulfstream's network of maintenance facilities is global and frequently named the best in all of corporate aviation. I am pretty sure that Gulfstream won't build a jet smaller than the midsize G150, but the company has only one standard of quality and performance and it has brought the G150 to that level. Even though it is the smallest Gulfstream, the G150 delivers at the highest level in cabin comfort and performance, even when the winds and temperatures conspire against you. Gulfstream customers don't deal well with excuses, and with the G150, there won't be any.
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