It was odd that, as I taxied out in the number three prototype of the Diamond D-Jet, the last thing on my mind was that there is only one engine. As with any other business jet you can't see the engines, and the sounds and sensations of one jet engine spinning away are the same as two or three. This thing is a real jet, not half a jet.
The sensations of takeoff were also like those in any of the dozens of other jets I have flown. I wasn't sure how strong initial acceleration and climb would be, but nobody will be disappointed. It was easy to get close to 3,000 fpm initial climb rates even though the day was hot and muggy and Diamond's home airport at London, Ontario, is at nearly 1,000 feet elevation. The slight but steady vibration and hum of the engine you expect in a jet were just right.
The third D-Jet conforms pretty closely to what Diamond expects to be the finished airplane. It is the first to have the new Williams FJ33-5A engine capable of as much as 1,900 pounds of thrust, about 200 pounds more than the version in the first two prototypes. Serial number three has no interior or environmental systems installed, but the aerodynamic shapes are close enough to the final that useful performance and flying-quality data can be collected.
Diamond announced development of the D-Jet in 2006 and had the original proof of concept airplane flying shortly after. Serial number two had a number of aerodynamic changes and conformed quite closely to the expected final, but now number three, with the production engine and redesigned engine-air inlets, provides a useful glimpse at what the production D-Jet can do.
Because the airplane is a prototype and does not have pressurization, Diamond test pilot Howard Judd and I were in full military-style flight suits, helmets, oxygen masks and parachutes. The airplane had been cleared to fly at its maximum cruise airspeed, and preliminary low-speed and stall testing had been done, but we were restricted to the normal flight envelope by the Canadian authorities with a non-essential crewman -- me -- flying the airplane.
There are several locations for the engine on a single-engine jet, each with its own pluses and minuses. Diamond elected to go with a centerline location, feeding air into the engine through inlets in each wing root via a Y-duct. The center engine location puts the thrust line close to the so-called waterline of the airplane, so there is little concern about power changes causing pitch forces. Among the negatives of this engine location are some ram air losses in the duct, a greater chance that foreign debris will be kicked up into the inlets and the need to heat the duct to prevent ice formation.
The Williams engine, like all recently designed jets, is electronically controlled by a full-authority digital engine computer (fadec). And, as expected in real jets, the fadec has dual channels and four independent sources of electrical power plus the ship's battery. The fadec automates starting and also limits engine thrust so the pilot can move the throttle to any position - including full forward - without over-speeding the engine.
About the only time it crossed my mind -- other than when looking at the fuel flow reading - that there was only one jet behind me was when preparing for takeoff. In twin-engine jets you are required to calculate how much runway is necessary to either stop or continue the takeoff with sufficient engine-out climb in case one engine quits at the worst possible moment. In the D-Jet the pre-takeoff calculation is like any other single. Is the runway long enough, and where will I set it down if the engine quits? The D-Jet has such low drag with no propeller and such an efficient design that it can glide for more than 65 miles from its 25,000-foot ceiling, and the test pilots have confirmed that a turn back to the runway for landing is easily accomplished from 1,000 feet agl or higher.
With all the flight test gear installed, two of us with all our gear, and 1,000 pounds of fuel, the D-Jet weighed 5,500 pounds for takeoff. Rotation speed is 85 knots, and the airplane leaves the ground instantly when you apply back pressure instead of rolling along on the mains for some time as most larger jets do. The target airspeed for the 50-foot-high point was 100 knots, which I blew right through because the airplane was accelerating so briskly. The best rate of climb is about 160 knots.
The D-Jet controls feel completely natural and just as I expected. I would categorize the stick force as medium - higher than most piston singles but lighter than the small, conventional business jets. Stability is excellent, and I found the workload to be very low in holding target airspeeds and then maintaining altitude when level. As in other jets with a wide margin between minimum and maximum airspeeds, the D-Jet has a larger pitch trim range than a piston single. That means you get your thumb on the trim switch right after takeoff and run it nose down as the airplane accelerates quickly, and reverse the process when maneuvering for landing. It's entirely normal in any jet, but a pilot new to jets may find it surprising at first.
Toronto Center assigned several altitudes on the way up to 25,000 feet so I didn't get a usable time to climb. However, I did get to capture several altitudes, retrim and stabilize, and each time it was remarkably easy to hit and hold the target. The last step was from 23,000 to 25,000, and the D-Jet went up at 1,300 fpm without slowing close to the best-rate-of-climb airspeed.
As we leveled at FL 250 the true airspeed was right at the 255-knot expected long-range cruise speed, so I pulled power back - a long way - to hold that speed. The fuel flow settled down around 315 pounds per hour (pph), but that even may have been a little too high because the airplane kept accelerating gradually. Diamond calculates the D-Jet can cover around 1,100 miles with full tanks at that airspeed in still air. However, the air is never still, so I think the lower long-range speed will be useful only with a tailwind.
