November 1, 2006
Steven W. Ells
You might expect the first new light twin in more than two decades to look a little different — and the Diamond DA42 doesn't disappoint. In fact, the DA42's looks are such a departure from the norm for light twins that it's difficult to get close to one at the big airshows — the only thing that's more popular is Starbucks.
After logging 14 hours in the left seat of serial number 42 on a cross-country flight from California to Oshkosh last summer, it is clear that Christian Dries, chief executive officer of Diamond Aircraft, and his design and production team have sculpted a twenty-first-century twin-engine flying sports sedan — if a three-door airplane can be called a "sedan."
The DA42 is a four-passenger twin-engine airplane with a maximum takeoff weight of 3,935 pounds. Empty weight averages around 2,750 pounds. The fuselage is of semimonocoque construction and the airplane's smooth lines result from extensive use of fiberglass and carbon-fiber materials and production technology. The wings feature two-spar fail-safe technology. Fuel is stored in aluminum tanks in the wings. Standard fuel capacity is 52 gallons with 50 usable. Extended-range tanks are an option and are installed in the aft part of each engine nacelle. Fuel capacity with the extended-range tanks is 79 gallons with 76 usable.
The DA42 is an electric airplane. The retractable-landing-gear system is actuated hydraulically by an electric motor driving a hydraulic pump. The landing-gear sequencing valves are electrically controlled, as are the wastegates for the engine turbocharger systems. The two-position flaps also are electrically actuated.
There are three batteries. The main battery is a 24-volt 10-amp-hour size. Electrical power is provided by two 24-volt 60-amp alternators — one on each engine. There also is a 24-volt 1.3-amp-hour alternator-excitation battery to provide alternator start-up (excitation) voltage if the main battery is discharged below the required excitation threshold. The third battery is a stand-alone emergency battery that powers the electric artificial horizon and an instrument floodlight for one and a half hours.
Front-seat comfort is so good that after nearly eight hours of cross-country flight from Paso Robles, California, to Wichita's Colonel James Jabara Airport, I was able to jump back in N240TS and successfully fly an hour-and-a-half formation flight so that Mike Fizer, AOPA Pilot senior photographer, could shoot his masterful in-flight photos of the DA42. Formation flight in the DA42 is a breeze simply because the Thielert Centurion 1.7 engines are very responsive, and the visibility from the front seats is impressive.
The DA42 has a center stick control — which is unusual in a new airplane — but it's easy to get accustomed to. It's more of a hassle to figure out how to negotiate the stick while settling into the pilot's seat than it is to use it to control the airplane.
I overshot the turn to final on my first landing because I hesitated to crank in enough aileron, but the second pattern was square and in line with the final approach course. Since the nose slopes down quickly, the visual reference while landing seems too low. This led to a tendency to flatten out the descent to the runway while flying the final approach to landing. The turn-to-final was made at 80 knots. Landings are not so much a matter of flaring as they are of merely arresting the sink rate by leveling the airplane above the runway and slowly pulling off power. The DA42 proved to be an easy airplane to fly.
There is a second, and unexpected, reason for the lack of fatigue at the end of that long flying day. The engine-prop combination is very smooth. Diamond installed engine vibration isolators (often called "mounts") that are many times softer and more flexible than is typical. It's a little disconcerting to see the prop and spinner move about relative to the cowling while transiting rough air in flight, but the soft mounts sure work well at keeping engine-prop vibrations out of the cabin.
The DA42 is powered by two 1.7-liter (103.1-cubic-inch displacement) Jet A- fueled, four-cylinder compression-ignition (diesel) engines that each produce 135 horsepower. Has there ever been another economically successful light twin with so little power? Never! The closest is general aviation's very first light twin — Piper's Apache, which was introduced in 1953 with two 150-horsepower Lycoming engines.
And what about that fuel capacity? Even the Apache carried 74 gallons. A capacity of 50 gallons seems much too small to be a practical fuel load for any twin-engine airplane. What's the catch?
The catch — actually it's the trump card — in this puzzle is the capability of the two engines. Derived from aluminum-block liquid-cooled Mercedes-Benz automobile diesels, these engines have been converted to aircraft use and certified in Europe under Joint Aviation Requirements (JAR) 23 and in the United States under FAR 33 by Thielert AG. Thielert has a state-of-the-art machining and manufacturing facility in Germany. Thielert's Centurion 1.7-liter engines are turbocharged so that 100-percent power is available up above 10,000 feet msl.
During the in-flight photo shoot, we shut down and feathered the left engine at 10,000 feet msl, and in spite of the fact that the air temperature was 5 degrees Celsius (10 degrees C above standard) there was no problem maintaining level flight. These engines can safely be flown at 85-percent power — which is certainly not recommended by conventional engine manufacturers — all day long. And they just sip Jet A.
Would you believe that the DA42 burned less fuel on the 3.8-hour leg from Paso Robles to Show Low, Arizona, than my personal Piper PA-24 Comanche with a four-cylinder 180-horsepower Lycoming engine? The sleek retractable-gear Comanche with its constant-speed propeller is no slouch when it comes to economical air traveling, but the DA42 used less fuel than the Comanche (which uses 100LL avgas), and the Jet A the Twin Star burned cost 50 cents less per gallon.
The reason for this uncommon economy? The 18-to-1 compression ratio of the engine. Compression-ignition (diesel cycle) engines are much more thermally efficient than gasoline-fueled engines. Specific fuel consumption numbers reveal that the Centurion 1.7 engine has a specific fuel consumption number of 0.36 pounds of fuel per horsepower per hour. The average small-bore Lycoming, such as the O-360 or even the higher-compression IO-360, can get its specific fuel consumption numbers down to only around 0.45 pounds of fuel per horsepower per hour at 65-percent power and leaned to the manufacturer's economy cruise settings.
But here's the kicker. The Thielert Centurion engines are managed by full authority digital engine control (FADEC) systems that are so advanced that all the pilot has to do is select the percent of power desired — with a single engine-control lever — and forget forever the tasks of juggling fuel mixtures, propeller rpm, manifold pressures, and cowl flap openings. There aren't even exhaust gas temperatures or cylinder head temperatures displayed on the Garmin G1000 flight instrument and navigation system.
Thielert's FADEC is the first general aviation engine control system that successfully controls the propeller rpm, fuel mixture, and the engine power setting through a single lever. This ease of operation is especially important during high-workload conditions such as a missed approach during instrument meteorological conditions.
The FADEC also completely eliminates hot-start problems. DA42 owners will never have to perform the shenanigans often required when trying to start a heat-soaked fuel-injected engine after a quick fuel stop.
There is a two-minute cool-down before engine shutdown, but that's common with turbocharger-equipped aircraft engines. A couple of other advantages not yet mentioned: Every Centurion engine — a 350-horsepower version is being installed in selected airframes and a 230-horsepower version is moving through certification — has a propeller-reduction-gearbox between the engine and the propeller. This slows the propeller rpm for more efficiency and less propeller-generated noise. A torsional vibration dampener and clutch assembly prevent engine damage in the event of a prop strike by disconnecting the link between the engine and the propeller. Time between overhauls is a thing of the past. Thielert engines are rated in time between replacement (TBR), which is presently 1,000 hours, projected to be 2,400 hours. When TBR arrives, the engine is replaced with a new Thielert engine. Costs for a replacement engine are reported to be around $20,000.
In addition to the low vibration, comfortable and quiet cabin, the do-all and see-all Garmin G1000 integrated avionics system, and the efficient and easy-to-manage powerplants, the DA42 can be certified for flight into known icing by installing a TKS deicing system — a $57,200 factory option. The TKS system consists of a fluid reservoir, fluid pumps, ice-recognition lights, a set of titanium leading-edge cuffs installed on the airfoils, and fluid delivery systems for both propellers. The cuffs are micro-drilled with thousands of tiny holes. When the system is activated, extremely low-freezing-point fluid is pumped to the props and the cuffs. The system provides both deicing and anti-icing. TKS systems are very reliable and efficient. The only drawback is the weight — 94 pounds when the fluid reservoir is full — and the necessity of storing, or finding an FBO that stocks the fluid.
Other options include Garmin's GDL 69A satellite datalink receiver ($7,100), extended-range fuel tanks ($6,850), and a built-in oxygen system ($17,552). The airplane I flew was fitted with what Diamond calls its Platinum Edition Option Package, which sells for $22,419 and includes interior refinements such as premium leather seats, premium carpet, and various appearance touch-ups inside and outside the airplane.
Totaling up the numbers and weights reveals that a well-equipped DA42 (with TKS and all the options stated in the preceding paragraph) will still have a useful load of 1,053 pounds at a list price of $589,778. Filling the fuel tanks (mains and auxiliary) with Jet A (6.9 pounds per gallon vs. 6 pounds per gallon for avgas) will reduce the useful load by 524 pounds, leaving a full-fuel useful load of 528 pounds. N240TS, the airplane flown for this report, was not equipped with TKS, datalink, extended-range fuel tanks, or installed oxygen, so its useful load was 1,169 pounds. Our two-person flight crew and baggage weighed 460 pounds. Full fuel accounted for another 342 pounds, leaving us 367 pounds below maximum takeoff weight.
Put another way, if those same crewmembers had piled into the more-equipped DA42 with their baggage and filled the extended-range tanks, that airplane would have been just 59 pounds less than its maximum takeoff weight.
Although the DA42 is a very capable all-weather airplane that features a pair of refined fuel-sipping, turbocharged, Jet A-fueled aircraft engines, the airplane is not particularly fast. Because of the conservative size of the standard fuel tanks, and our desire to stop only once for fuel before landing in Wichita for the night, we chose economical low power settings compared with what the engine is capable of. Three hours into the leg at a density altitude of 11,295 feet and 70-percent power, the true airspeed was 148 knots. Each engine was burning 5.2 gallons per hour and the propellers were turning a very quiet 2,070 rpm. An hour earlier at a density altitude of 13,256 feet and 80-percent power, 155 KTAS was recorded, with a fuel burn of 5.8 gallons per hour per engine. Prop rpm at that power was 2,150.
Pilot's-operating-handbook performance charts for 70-percent power predict speeds of 152 KTAS, and 80 percent is predicted to result in true airspeeds of 156 knots. High-speed cruise power settings of 85-percent power can be maintained up to 11,500 feet, where performance charts predict true airspeeds of 160 knots and fuel-consumption figures of 6.6 gallons per hour per engine.
Like that of most light twins the DA42's performance is very serviceable — when both engines are healthy. For instance, on a standard day, at sea level and maximum takeoff weight (MTOW), after a ground run of 1,350 feet, a DA42 will climb at 1,150 feet per minute when the airspeed is nailed at 79 KIAS. We settled into a comfortable 800-foot-per-minute cruise climb at 104 KIAS on our initial climbout. Measured cockpit noise (dBA scale) in cruise at 11,500 feet msl was 88 between the front seats. This is about 4 dB less than most single-engine airplanes.
If an engine is lost just after landing-gear retraction on takeoff, the DA42 under the same standard day, sea level, MTOW conditions as above should be able to climb at 170 feet a minute after the propeller is feathered and the indicated airspeed is held at 82 knots.
According to the performance charts, a positive rate of climb can be maintained up to approximately 6,000 feet msl. If the engine is lost at 14,000 feet, the remaining engine will slow the descent rate of the same airplane under the same conditions to 100 feet per minute. The knowledge that the second turbocharged engine — an engine built for extended high-power operations — is there ready to pick up the slack is bound to calm the "what ifs" when flying over large bodies of water or rugged terrain.
The FADEC controls the engine power by measuring camshaft and crankshaft rpm, fuel-injection rail fuel pressure, manifold pressure, manifold air temperature, ambient air temperature, propeller governor oil pressure, power lever position, and aircraft bus voltage. These data are crunched in dual engine control units (ECUs) and then signals are sent to the propeller governor pressure valve, the fuel rail-pressure regulation valve, the fuel-injection nozzles, and the turbocharger wastegate. During starts the ECUs also activate glow plugs to preheat the engine for more efficient starts.
All the pilot has to do is move the power levers to the percent of power desired — displayed digitally on the Garmin G1000 primary flight displays and multifunction displays — and forget it. Climbs and descents will not change the power setting.
When the power setting is changed the ECUs automatically manage the propeller rpm. This fully automatic system rarely permits the annoying "wow-wow" sound, caused when the propellers on twin-engine airplanes are out of synch, to last more than a few seconds.
Each engine is equipped with an ECU A and an ECU B. Either one is capable of complete engine control. Since these boxes test and monitor every engine parameter in a matter of seconds, there's no conventional engine runup before takeoff. With the engines at idle, the pilot presses and holds down two black buttons. In about 10 seconds the ECU automatic tests are completed. Then the pilot manually switches from ECU A to ECU B on each engine and back. If there are no indications of any abnormalities, the runup is complete.
Noise-conscious airport neighbors and slightly nervous backseat passengers never have to endure the traditional mag-check exercise. Push a couple of buttons, flick a couple of switches, and the engine has been completely checked out. It's a very civilized engine diagnostic and management system.
Since the DA42 fuselage is closely patterned after the Diamond single-engine DA40, stowing baggage takes some forethought. There is a door on each side of the nose for storage but this space is limited to 66 pounds and it's pretty small. The main baggage area is behind the passenger seats. After the seats are folded forward and the bags are lifted over the door sill — there's a single door on the pilot's side for backseat and baggage-area access — baggage can be stowed.
The weight limit in the main cabin baggage area is 100 pounds, and a smaller area located immediately aft called the "baggage extension" is limited to 60 pounds. However, if the baggage pieces take up room in both sections, the limit is 100 pounds. These numbers are reasonable, but the space is limited since it's located where the fuselage cross section tapers down to the boomlike section forward of the empennage. Soft-sided baggage may be the only answer when all four seats are occupied. Perhaps Diamond or an entrepreneurial soul will design a set of fitted luggage to fully take advantage of the airplane's limited baggage space.
Another drawback is the DA42's 44-foot-plus wingspan. This is too big to fit through the 40-foot-wide doors of most general aviation-size hangars.
The DA42 Twin Star is a revolutionary airplane that has arrived on the market at the right time. Fuel costs are up and the DA42's diesel engines are very fuel efficient. The future of leaded avgas is uncertain; the DA42 burns Jet A, which is plentiful around the world. The two engines are kindergarten-simple to start, test, and manage. The landing gear can be extended at speeds up to 194 knots for quick letdowns, liquid-cooled engines eliminate the possibility of shock-cooling the cylinders, and the airplane is equipped with a super-capable suite of Garmin's finest avionics.
In addition, the weather datalink, the proven flight-into-known-icing TKS system, and the turbocharged engines that provide the power to quickly climb through icing layers are valuable tools for dealing with en route weather.
The DA42 is comfortable, smooth, and competent. And it's just jazzy looking enough to stop business-jet-bound boardroom members in their tracks. Diamond has built more than 160 DA42 airframes, and just more than 20 have been delivered to customers in the United States. According to Jeff Owen, Diamond's director of North American sales, the delivery window for a DA42 order today is 12 to 18 months. Support includes factory transition training using Diamond-manufactured Level 5 wraparound visual-flight-training devices. Visit the company's Web site and let officials know you're interested. You're sure to get excited about the future of general aviation after flying one of Diamond's revolutionary DA42s.
E-mail the author at firstname.lastname@example.org .
Links to additional information about Diamond Aircraft may be found on AOPA Online .
For more information, contact Diamond Aircraft Industries GmbH, Wiener-Neustadt, Austria; www.diamondair.com .
The DA42 flown for this article had a max gross weight of 3,757 pounds. Diamond has applied for a gross-weight increase to 3,935 pounds. The figures in this table — with the exception of the "as tested" entries — are from the POH of a 3,935-pound DA42. All specifications are based on manufacturer's calculations. All performance figures are based on standard day, standard atmosphere, sea level, gross weight conditions unless otherwise noted.
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