Inside the aircraft, the throttle quadrant is a bit different than that used for the Thielert engines, but operation is still single lever—push them up to go faster, pull them back to go slower. Prop RPM and fuel flow are all handled automatically by the FADECs, with the results displayed on the Garmin G1000. Speaking of which, the G1000 obviously has new software to accommodate the Bosch FADECs and the display is, frankly, somewhat busy. There’s no CHT or EGT to monitor, but in place of that, there’s coolant temp, oil temps, fuel flow and, plus gearbox temp. It takes a concentrated look at the engine sidebar to sort everything out.
The NG’s fuel system is the same as the DA42, with 50 gallons in two 25-gallon wing cells, plus two 13-gallon aux tanks in each nacelle behind the engine. Most airplanes are ordered with the aux tanks, since 50 gallons is shy for long-range flying, even with a diesel. Internal pumps move the fuel from the aux tanks into the mains and the system is equipped with auto sensing to keep from accidentally pumping fuel overboard. The G1000 annunciates the aux pumping function.
Feeding the engines are a pair of low-pressure pumps that deliver fuel to the high-pressure common rail pumps. In normal flight, only one of these pumps is running, but both are switched on manually for takeoff. (The Thielert engines didn’t have these pumps.)
For electricals, the NG has a 28-volt alternator on each engine, plus a single ship’s starting battery. The FADECs live in the lower nacelle behind the engine, accessible via a large removable cover. As with the engine in general, they’re equipped with heavy duty mil-spec connectors, not the automotive grade hardware used in the Thielert airplane. A Diamond factory tech in London—who only recently laid eyes on the NG—said the FADECs were more easily accessible than in the previous model. Each FADEC is dual channel—the engine will run on either—and is equipped with a small keep-alive battery that’s independent of the ship’s electrical system. This is the result of a lesson Diamond learned the hard way when a DA42 suffered a dual engine failure after takeoff because the FADECs packed up the engines after the voltage caved due to a low battery.
Flying It
We demo’d the DA42 at Diamond’s London, Ontario plant with production test pilot Bill Scott. He did the flying, while we did the performance checking and note taking. When we flew the DA42 in Austria five years ago, we were impressed with
Diamond’s Austro Diesel
its ease of starting and the smoothness of the engines. The Austros deliver similar impressions. Rather than a flurry of mixture rich, throttle cracked and boost pumps humming, you simply flip on the engine master switch and bump the starter. We tried to count blades, but the engines seemed to start before a full rotation. After a whiff of diesel exhaust, they settle into a vibrationless idle.
Preflight engine checks are push-button automated. On an angled panel to the right of the pilot’s PFD are two momentary buttons labeled ECU Test. Holding them down runs the engine through checks of both channels of each FADEC, including a brief increase in power to check prop and power monitoring functions. When the FADECs swap channels, there’s a noticeable roughness that immediately smooths out. There’s also a toggle switch labeled Voter that allows the pilot to manual select or test each FADEC channel. After that, everything else is conventional. Check the trim and controls and the fuel valves and go.
Performance
Scott said the Austro-powered NG lacks the kick in the pants acceleration of the Lycoming-powered L360 DA42, but we can’t honestly say the difference is that great. On a standard day, the NG needs 2405 feet of runway, while the Lycoming requires 2229. The Austros seem to have plenty of punch.
Climbing out, we saw numbers the POH said we should expect. With power set at 100 percent, the NG climbed on both engines at about 1200 FPM at a Vy of 86 knots. There’s a five-minute limit on 100 percent power, after which 92 percent is available for continuous use. This knocks about 150 FPM off the climb rate. FADEC scheduling allows 100 percent power to about 10,000 feet, after which it decreases linearly to 18,000 feet. To set power, you simply set the levers where you want them; the G1000 shows percent power directly.
In cruise performance, the NG bests the POH a little. At 4000 feet and 75 percent power, we noted 154 knots TAS on 6.6 GPH per side. Full power—92 percent continuous—yielded 167 knots TAS on 8.3 per side. Climbing to 12,000 feet, gave us 165 knots TAS on 6.6 GPH per side. Allowing for a 45-minute reserve, this allows a still-air range of 850 miles. Dialed back to a 55 percent max economy cruise, the NG tools along at 138 knots TAS on 4.7 GPH per side and the range increases to around 1000 miles, with 45 minutes reserve.
Throughout our trials, all of the engine parameters remained comfortably in the green, with the exception of the oil temperature, which rose into the yellow arc. Diamond’s Scott says the London factory hasn’t done enough testing to know if this was a sensor or baffling issue. Coolant temperature were on the high side of green.
Single-engine performance was as the book predicted. At 6000 feet, caging the left engine produced an initial sink rate, followed by a not-too-difficult to achieve 200 FPM climb on the right engine. Shutting one down and bringing it back is simple. Just idle it and flip the engine master off. It auto feathers and stops in about two seconds. To bring an engine back, flip the master on and bump the starter, then advance the throttle when the engine is warmed up. For unfeathering, the Austro has an oil-pressure accumulator.
Ergos, Payload
The NG we flew was lavishly appointed with leather seats and TKS—what Diamond calls the Platinum options. Its empty weight was 3253 pounds for a useful load of 927 pounds. With full fuel, there’s room for 418 pounds of bags and people, meaning it’s a two-person airplane with generous baggage or three people, light
Diamond’s Austro Diesel
The DA42 NG’s FADECs live inside the lower engine cowl. A critical part of maintenance monitoring is downloading recorded data. X’d out displays in G1000 indicate the data writing is complete.
bags and down-fueled to four hours of endurance.
By direct comparison, the Lycoming-powered L360, at 2941 pounds empty, has 172 pounds more of useful load—about one person’s worth. With three people in the L360, there’s room for bags and full fuel and an endurance of about 3 hours at 155 knots, leaned rich of peak. That gives a still-air range of 500 miles, with reserves. It will do better at economy settings but it won’t outrange the NG.
The NG retains Diamond’s signature wide cabin, with excellent visibility and good ventilation. Although we didn’t need it, the NG’s heating system draws from the each engine’s coolant circuit and runs heated air into a central manifold under the cabin floor. The back seat is easily accessible through a top opening hatch over the left wing. And once you’re in it, it’s as comfortable and roomy as any airplane in this class.
Conclusion
In our view, the NG is more about economic performance than flight performance. Although it set no speed records, the Thielert-powered DA42 was adequate to the task as a multi-engine trainer and personal transportation machine with the safety of a second engine.
Where it failed was in promised reliability at a cost of operation its customers could afford. Thielert seems to have vastly underestimated both and when the engine tanked mechanically, the company couldn’t support warranty claims and bankruptcy—from which it has not yet emerged—soon followed. Diamond wasn’t in a position to back up Thielert’s failed warranties.
Against that backdrop, we can’t judge the NG yet. Our initial take is that Austro’s decision to more or less let the engine’s weight run wild will probably impact durability favorably. It’s just a beefier engine and diesels may just need that weight. (One complaint about the SMA diesel—a design that’s essentially gone nowhere—is that it’s too heavy.)
Diesels may also need to command an eye-opening purchase price. The NG certainly does. At $731,850, it’s getting up there with the Barons and the Mirages. We’re not sure if the glamour of a Jet-A burning diesel will overcome that price barrier or not. Diamond’s Peter Maurer told us that schools that purchase new airplanes are less concerned about capital costs than operating costs. If he’s right and if the Austro can deliver good dispatch reliability and eventually a 2400-hour TBO on low operating costs, the NG could succeed where the Thielert-powered airplanes did not.
We’ll re-examine the subject in a couple of years, when Diamond has fielded enough Austros to accumulate some service history.
