At first glance, the Diamond DA50 RG might not seem to add much to the ranks of high-performance piston-powered single-engine airplanes. It isn’t especially fast, doesn’t carry a huge load, and it is expensive, with a price tag well over $1 million. Diamond Aircraft, however, isn’t about ordinary, and its airplanes have all carved a niche in the general aviation marketplace.
The DA50 RG is no exception, especially because it carries on Diamond’s penchant for putting jet-A-burning diesel engines into light airplanes.
What makes the DA50 RG stand out are some unique attributes, but for me, it starts when I walk up to the airplane and see just how large it is. In the world of metal single-engine airplanes, only turboprops look larger than the DA50 RG; this is a robust, serious airplane, and it looks professional. Of course, all aircraft require a professional approach, but the DA50 RG practically screams: “Hey, we’re not fooling around here.”
Composite construction is supposed to allow designers to create strong airplanes at lighter weights. In every case where composites are used for major structures, they’ve always looked to me to be far less flimsy than the thin aluminum skins that enfold a monocoque structure. The DA50 RG’s composite airframe is almost intimidating in its appearance of strength and stability. The fit and finish are outstanding and make me feel like Diamond has this method of manufacturing down to a science. Of course, with a list price of $1,150,000, one would expect a high level of fit and finish.
Diesel Power
No lightweight airplane, the DA50 RG’s 4,407-pound maximum takeoff weight (mtow) begs for a healthy amount of horsepower, and for this application, Diamond turned to Continental Motors for the first certified application of its Centurion 3.0 CD-300 diesel engine. What would have been a finicky avgas-burning piston engine running at high power settings is instead an electronically controlled, twin-turbocharged, 182 cu-in displacement diesel engine that barely seems to be working hard, even at full power.
It’s easy to see the difference. On takeoff, a 300-plus-horsepower turbocharged piston engine that displaces almost three times more than the CD-300 will burn about 36 gph and make lots of noise doing so to deliver maximum power. The CD-300 on takeoff burns fewer than 20 gph.
Potential buyers of the DA50 RG inevitably will compare it to other million-dollar-plus piston singles, which include the new Cirrus SR22 G7 (the turbocharged version is the most expensive) and the Beechcraft G36. Both the DA50 RG and G36 lack the Cirrus whole-airplane parachute system, and that may be a dealbreaker for some buyers.
An important number for this class of aircraft is the payload that can be carried with a full fuel load. The DA50 RG is a relatively heavy airplane. The G36 tops out at 3,805 pounds, while the Cirrus SR22T mtow is 3,600 pounds. The SR22T’s payload with maximum fuel is nearly 700 pounds, not as much as the 769 pounds that the G36 can carry. The DA50 RG’s higher mtow gives it the advantage here, and it has a maximum fuel payload of 884 pounds, which provides more flexibility for filling its five seats. It’s not just the mtow difference that helps the DA50 RG carry more but the amount of fuel each airplane needs to carry; the diesel engine’s lower fuel consumption means the DA50 RG can meet performance targets with less fuel, just 49 gallons usable, although jet fuel weighs more than avgas.
Range of the three airplanes is as follows: DA50 RG, 820 nm; SR22T, 1,021 nm; and G36 920 nm.
The G36 is the only one of the three that has a large enough cabin for six individual seats, and its rear cabin is configured as a double-club layout, with a generous door opening into the rear cabin. The SR22 can also seat five, although its cabin isn’t as wide as the DA50 RG’s, at 49 inches versus 50.8 inches. It’s a little easier to get into the back seat of the DA50 RG with a third door aft of the pilot’s door on the left side. The doors hinge upwards so getting in and out isn’t awkward.
These modern airplanes are a big step up from what used to be rather utilitarian interiors decades ago, and that probably helps push their prices up. But that’s what today’s buyers have come to expect, comfortable furnishings akin to luxury cars, not cheesy plastic and seat fabrics that aren’t designed to last.
Stick Flying
Inside, the DA50 RG instantly signals that this is an airplane designed to delight pilots; instead of a yoke for controls, it has a stick. Nothing new here for experienced Diamond pilots, but it is a pleasure to see a manufacturer that understands pilots. However, when flying from the traditional left seat, keep in mind that the pilot flies with the left hand on the stick and the right hand on the throttle. This may be slightly discombobulating for a pilot used to flying a stick with the right hand and throttle with the left hand, but it took no time to get comfortable with this setup. The right stick can be removed, and that is an optional feature ($8,425).
The panel is utilitarian, filled with Garmin G1000 NXi displays, Mid-Continent’s MD302 Standby Attitude Module, and just a handful of switches including a blue level button for the GFC 700 autopilot. The NXi displays have all the normal Garmin buttons for those who prefer that interface, but Diamond engineers added an optional GCU 476 keypad in an unusual place, mounted upside down in the center console. When stowed, the keypad fits flush to make a nice armrest, then flipping it over pulls out the keypad and FMS controls in a place that comes easily to hand. The keypad must be stowed during takeoff and landing and during emergencies. One feature some pilots might not like is the alphanumeric keyboard. It’s a hardware keyboard, so there is no way to switch to a QWERTY keyboard, and that ought to be an option for those whose brains are wired to typewriter keyboards. The keypad FMS option costs $27,250.
Just forward of the center armrest is the single power control; unlike the avgas piston engines in the SR22 and G36, the DA50 RG’s Continental CD-300 diesel engine has a fully automatic digital engine control (fadec), something that has been long overdue in general aviation airplanes and that makes flying so much simpler.
The seats are fixed in place but the rudder pedals are electrically adjustable. This must be done on the ground, however, and isn’t permitted in the air. Like the SR22, the center seat in the back row isn’t designed for a full-size adult. But with two adults, the rear offers plenty of comfortable space.
Seats and upholstery elements are finished with real leather, and modern composite inlays accentuate the interior trim. All seats have USB power outlets and both standard dual headset jacks and powered Lemo headset adapters. The rear seats can be folded down to create more baggage space, plus there are storage compartments under the baggage area floor.
Some other optional features on the DA50 RG are an oxygen system with outlets for each seat (31 pounds and $42,200), TKS weeping wing de-icing (55 pounds and $117,800), and electric-powered air-conditioning (53 pounds and $57,350).
Flying the DA50 RG
Once settled into the front left seat and with the rudder pedals adjusted, I felt immediately comfortable. Sam Linton, national sales director for Diamond distributor Lifestyle Aviation, was the demo pilot for the DA50 RG tour around the U.S., and our flight at Oregon’s Portland International Airport (PDX) was one of his final stops.
It was an unusually gusty day in Portland with a low layer of scattered clouds. Starting the CD-300 engine is simple: just push the start button. No monkeying with mixture and throttle controls as on an avgas engine, no matter the outside temperature. The engine settled into a smooth rumble, and Linton said to run it at 1100 rpm while it warmed up.
We completed the runup on the Atlantic Aviation ramp so as not to clog up the taxiways. Engine checks require pushing the fadec test button and verifying proper operation of each ECU then pushing the Force B button to test a single system as a backup and making sure the engine operates the same.
The DA50 RG has a free-castering nosewheel, a simpler design than a steerable nosewheel. Turns with the brakes are easy but it is necessary to get some forward speed before turning. The DA50 RG has a large rudder, Linton said, and on straightaways and shallow turns, the rudder is strong enough to steer without using the brakes.
The fuel selector mounted on the center console behind the trim wheel is set to the normal position, which draws fuel from the left fuel tank. The right tank’s fuel is transferred to the left during normal operation, and the maximum difference is 9 gallons. Fuel transfer rate is 60 gph, and it automatically stops if the pilot forgets to turn off the transfer switch. Although, it will switch on as the left tank’s quantity drops. The selector also can be switched to the right tank if necessary. Total fuel capacity is 51.5 gallons, with 49 usable.
The electrical system is essential for running the ECUs and various systems, and there are two belt-driven 70-amp alternators. In normal operation, alternator 1 runs most systems while alternator 2 runs the air-conditioning system. Each alternator has its own backup lead-acid batteries to provide field current if the main battery should fail. The 24-volt, 13.6 amp-hour, lead-acid main battery is the backup if both alternators fail. The Mid-Continent MD302, which has its own backup battery, provides standby instrumentation.
With just one power lever to operate the engine, the engine indication system provides power information as a percentage of load. The liquid-cooled CD-300 is a four-stroke diesel with twin turbochargers and intercoolers. The three-blade MT Propeller’s rpm is reduced via a gearbox with a 1.67 gear reduction ratio. Dual fadec ECUs control fuel injection, engine rpm, and propeller pitch.
For the pilot, engine gauges include the percentage of load, prop rpm, oil temperature, oil and fuel pressure, and volts and amps. For pilots new to diesel flying, there are also indicators for coolant and gearbox temperature and fuel temperature. “Jet-A has a tendency of gelling at high altitude,” Linton explained. “But we don’t have that issue because we have a high-pressure fuel system that basically superheats the fuel.”
Elevator trim is set for takeoff according to a mark on the manual trim wheel. Linton suggested trimming aft a little as we had no weight in back. Rudder trim is accomplished with a switch on the throttle quadrant; electric rudder trim is new for the DA50 RG. The DA42 and DA62 have manual rudder trim using a knob.
After checking the front doors and the rear door were closed, we tested the landing gear and stall warning system and then opened the cowl flaps for takeoff.
I taxied to PDX’s Runway 10R, and using Garmin’s SafeTaxi depiction on the G1000 NXi MFD helped with orientation on the airport. Before takeoff, Linton explained that I should take 3 seconds to advance the power. The flight manual cautions pilots to advance power slowly, to avoid over-speeding and excessively rapid rpm changes of the wood-cored MT propeller.
Lining up with the runway, we checked that the fuel pump and lights were on and cowl flaps open with the flight director set for takeoff at 6 degrees pitch up. I advanced the power while counting to three then as we accelerated—which didn’t feel much different than an avgas-powered high-performance single—rotated below 70 knots and climbed out at the 79-knot Vy speed. Once the gear and flaps were up, climb speed went up to 94 knots.
The engine is limited to 100 percent power for 5 minutes, and during the climb, we were burning just 17 gph. After a few minutes, I pulled the power back to 90 percent as I steered around some of the scattered clouds and flew to the north then leveled off at 3,500 feet. Linton told me that using pitch trim helps when flying the DA50 RG, and he was right. I like using manual trim and appreciate that it’s available in addition to the electric trim switch on the stick.
Flying with my left hand on the stick proved to feel natural, and I didn’t experience any hunting for the stick with my right hand.
Once level at 3,500 feet, we closed the cowl flaps and kept the power at 90 percent, with fuel burn at 15.3 gph. True airspeed settled at 156 knots. Linton said that at the optimum altitudes of 8,000 to 12,000 feet, true airspeed would be 170 to 175 ktas while developing less power.
The flight manual shows that cruise performance in ISA conditions at 12,000 feet delivers 172 ktas at 86 percent power (14.7 gph). The same speed is available at 14,000 feet but with 82 percent power and 14.3 gph. Speeds remain in that range or slightly below through 16,000 feet then start dropping to 158 ktas and 60 percent power (11 gph) as the airplane nears its maximum operating altitude of 20,000 feet.
For comparison, a Cirrus SR22T, which has fixed landing gear, at 12,000 feet can fly at 187 ktas burning 18.3 gph at 85 percent power. At about the same fuel burn as the DA50 RG at that altitude, the SR22T would be running at 65 percent power and 167 ktas.
Linton pulled the power back and demonstrated how the Diamond just loafs along with power set at 50-60 percent. “What I love about this airplane is it totally depends on how much power I want to put to it,” he said. “She’ll maintain altitude way down here in the 50s. That’s 10 gph at 60 percent power. It just hangs out here no big deal, super smooth, super calm.”
Hands-off Turns
I played a bit, maneuvering around and getting the feel for the controls. The DA50 RG is well-harmonized, and pitch and bank work smoothly together to give the pilot precise control. Linton had me set up a steep turn, dial in some trim, and then let go of the controls. It stayed perfectly solid in the turn. “One of the fun things about the DA50 is it’s a very maneuverable platform with the pushrod [aileron and elevator controls],” he said.
Turning away from some clouds, I pulled back the power for some slow flight, and we put the gear down and selected takeoff flaps. Flying between 75 and 80 knots, control was still solid, and full aileron deflection didn’t cause any upset. “If you’re tired, not paying attention, or you get slow, this airplane’s not going to magically bite you some way. It’s just very well balanced,” said Linton. We did some more turns, then retracted the flaps and landing gear and climbed to 4,500 feet for a power-off stall demonstration.
After some clearing turns and with the landing gear and flaps down again, I pitched the nose up past the stall warning horn and held the stick all the way back. The airplane just descended, wings level, with no tendency for the nose to drop. “It’s not going to surprise you and drop a wing,” he said. “It’s very relaxed.” Once I let the stick move forward and added power, the stall was quickly over with.
Before we returned to the airport, he pulled back the power to below 20 percent, and because the landing gear was retracted, we heard an audible beeping, saw a “check gear” CAS message, and then heard a vocal alert saying “check gear.”
Linton briefly demonstrated an accelerated descent, although we didn’t have much altitude to lose on the way back to PDX. “Everything is all fadec controlled, and we’re not worried about temperatures,” he said.
The landing gear, he explained, “is basically a gigantic speed brake.” With the gear down and full flaps, he had me point the nose down fairly steeply, which allowed us to descend without picking up much speed. “We’re barely at 100 knots. It’s just a very relaxed descent.”
Linton loaded a visual approach into the Garmin avionics to help ensure alignment with the correct runway, in this case, PDX’s 10L. We were instructed by the Portland Tower controller to keep our speed up for a Phenom jet on base leg, which was easy, not only by adding power and flying faster but then slowing quickly as we neared the runway. “The cool thing about this airplane is we can slow this down like crazy,” he said. Vref ranges from 73 to 77 knots, depending on weight, but we kept it a little high because of the gusty conditions.
The winds were 90 degrees across the runway and gusting from 12 to 23 knots, so Linton helped me with the landing. The DA50 RG took it in stride and settled smoothly on the trailing link landing gear. “For a gusty crosswind she didn’t do too bad,” he said.
Diamond recommends keeping the engine at ground idle for two minutes to cool down the turbochargers, which was pretty much the time it took to taxi from the runway to the Atlantic Aviation ramp. Shutting down the engine is as simple as turning off the engine master switch, then when the engine ceases running, turning off the electric master switch.
A New Market?
Will the DA50 RG make inroads on the most popular modern single-engine piston airplane, the Cirrus SR22? It’s too early to tell, but one factor could make a difference: the DA50 RG’s diesel engine. Cessna’s high-performance avgas-powered TTX could have been a serious contender against the SR22, but it lacked a parachute.
What could make the DA50 RG stand out is if its diesel engine proves to be more reliable than high-performance and non-fadec piston engines, which do have the occasional engine failure. A more reliable engine could eliminate some—not all—of the reasons why a pilot might elect to pull the parachute handle. And the widespread availability of jet fuel compared with the confusion surrounding the switch to a high-octane unleaded avgas and the lack of advanced engine controls on avgas engines could make the DA50 RG a much more attractive option.
The diesel engine has another advantage as well: complaints on pilot forums by SR22 pilots about how difficult their avgas engines are to start in hot weather continue. But the DA50 RG’s electronically controlled engine doesn’t have that problem.