Coast-to-Coast On the Worst Possible Day

Gulfstream G150

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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.