Set for success

Aircraft development is not an easy venture. The ongoing challenge to fly higher, faster, farther or more efficiently tests the mettle of any manufacturer from Beechcraft to Boeing.

Taking that extra step to pioneer new technologies can be even more trying as the 787 Dreamliner attests. Yet without the vision and perseverance of this handful of aircraft makers, the industry risks being stalled at the junction as the world moves on.

Diamond’s DA42 is a wonderful case in point. First certified in 2004, this carbon composite light twin-engined aircraft has pushed the boundaries in several areas. Aside from its Garmin G1000 cockpit, the company aimed at making diesel the powerplant of the future when it equipped the original Twin Star with Thielert engines capable of operating using Jet-A or Jet A-1 fuel.

An example of the type subsequently flew non-stop across the Atlantic, sipping about 22lt an hour in the course of the 12-and-a-half-hour flight. That’s 22lt an hour in total. It seemed the world was at its nosewheel.

Alas, like many great ventures, the road became a little rocky. The Thielerts were plagued by a relatively poor service record and ongoing parts replacement, resulting in added cost and a tarnished reputation. Ultimately, Thielert Engines entered into insolvency proceedings in 2008.

Diamond and owners alike had been let down by one aspect of a very promising aircraft but rather than abandoning the project, the company set about seeking a solution, the initial fix being the fitting of Lycoming IO-360 fuel injected engines in place of the diesels.

And while the Lycomings were a familiar friend they lacked the fuel-frugal qualities and wonderful range of their diesel counterparts. The fight was far from over.

Perfect match

Combining a suitable airframe with the ideal engine has been the making of many of history’s most famous aircraft. The mating of the P-51 Mustang with the Rolls Royce Merlin engine is one that comes to mind. In the DA42, Diamond undoubtedly had the airframe but needed a powerplant that would showcase the aircraft’s best qualities — enter the Austro AE300 diesel engine.

The new engine was born when Diamond decided to provide its own aerodiesel engines for the DA42. Austro Engine was established to create a new generation of general aviation powerplants in conjunction with notable partners including MB Tech (Mercedes Benz) and Bosch. This saw a blend of Mercedes automotive design and production expertise and Diamond’s aviation experience to provide the DA42 with the engines it deserved.

The new-look diesel offered 25 per cent more power and even better fuel economy than its predecessor. It boasted an improved gearbox, new engine mountings and a stronger cast-iron crankcase to replace the earlier aluminium unit. The turbocharger, induction system and cooling system were redesigned to ensure the engine’s power was retained as it climbed away from the thicker air at sea level. All the while, those components that possessed an automotive heritage remained unchanged to bring their proven reliability levels.

The AE300 engine won European certification in 2009 and in 2010 the FAA granted certification in the United States. The DA42NG began forging its own new frontiers the same year when it impressed Berlin Air Show visitors by flying its display using algae-derived jet fuel. The ‘Next Generation’ had arrived.

Standing out

The light twin market has seen little change over recent decades. Stalwart trainers the Beech Duchess and Piper Seminole continue to service flying schools relatively unchallenged. And while the Duchess has long ceased to be produced the Seminole continues to be built, with only new avionics and instrument panels offering any significant change — making the DA42 very popular when it first arrived on the scene.

The Twin Star offered not only a stylish new look but the incredible fuel economy of diesel engines, traits highly sought after by flying schools. And with the DA42NG, Diamond continues the ‘fleet philosophy’ that sees the similarity in cockpit layout of all types, offering a smooth transition each time the student pilot moves up the performance chain.

However, the market reached further than flight training organisations as the comfort and style on offer combined with the bonus of twin-engined security attracted touring pilots. Now that the Austron AE300 engine has thrust the DA42NG back into the spotlight, this broad market is set to welcome its arrival yet again.

Externally, there is little apparent change in the look of the DA42NG from its predecessors other than where its diesel engines are housed. From its sleek nose and streamlined cabin to its tapered aft fuselage and swept T-Tail, the aeroplane shares the same clean lines with its predecessor.

The nose section now boasts a useful locker with a 30kg capacity accessible via doors on either side. The high-aspect ratio wing is in keeping with its fine lines.

The NG empennage still consists of a large elevator fitted to its T-tail and a substantial strake beneath the aft fuselage, the strake enhancing longitudinal stability in the face of the tapered fuselage and providing a mounting station for an adequately sized rudder. An electrically powered variable elevator backstop limits elevator up travel above certain engine power settings.

Almost in contrast to its sleek airframe, the DA42NG sits on a sturdy tricycle retractable undercarriage. Featuring trailing arm suspension and substantial oleos, the undercarriage is built to offer flattering landings and sustain the trials of trainee pilots in equal measure.

The landing gear is operated by electrically operated hydraulic valves with a squat switch to prevent inadvertent retraction on the ground. Should the situation be reversed and the landing gear needs to be extended in an emergency, a simple emergency gear extension lever below the instrument panel is pulled, releasing hydraulic pressure and allowing the gear to free-fall.

Having been re-jigged to accommodate the Lycoming engines, the cowlings have transformed once more to encase the heart of the NG — its AE300 diesel engines. To enable adequate airflow through the engines a series of intake and exhaust ducts gives the NG its distinctive cowling.

A grilled duct feeds the intercooler from the side of the cowling while the lower intake performs traditional radiator cooling. More ducts on the side and rear of the cowlings facilitate air being vented overboard. All in all, the futuristic-looking cowlings balance well with the sleek lines of the rest of the airframe and even offer a beefed-up look that suggests these engines mean business.

Let’s consider the performance these engines bring to the table: the four-cylinder AE300s generate a maximum of 168hp a side and offer a true airspeed of 150kt at 60 per cent power. And while the diesels are heavier than their Lycoming siblings, the weight and balance issues that were a factor in the Lycoming-powered version are now a thing of the past.

Similarly, the Austron engines restore the astounding fuel economy and incredible range. With the main wing tanks storing 192lt of Jet-A1 fuel and a power setting of 60 per cent consuming about 39 an hour, we have almost five hours endurance at 150kt without reserves.

However, should you opt to fill the auxiliary tanks in the rear section of the engine nacelles, another 104lt is available for a total of almost 300lt— more than 7.5 hours total endurance and well over 1,000 nautical miles.

On the front of each engine is a three-bladed MT constant-speed, fully feathering propeller. Notably, the propellers are not counter-rotating as found on trainers such as the Duchess, hence the DA42NG does possess a critical engine; in this case the left hand engine. This aspect of asymmetric control simply calls for a little more rudder input should the left engine fail rather than the right.

All aboard

As with all models of the DA42, entry is to the front seats on either side via an overwing walkway. In keeping with its single-engined siblings, the cockpit features a large bubble canopy hinged at its leading edge while the rear row is only accessible on the port side.

Stepping down into the cockpit therre’s an integral handhold on the dashboard to prevent pilots placing undue wear on the coaming. As with all of the Diamond range there are dual control sticks between the legs while the Garmin G1000 dominates the clean instrument panel, complete with autopilot and yaw damper.

The cockpit’s commonality with its Diamond brethren is immediately apparent and if one were to ignore the different throttle quadrant, this cockpit is to all intents and purposes a DA40, from the control column between the legs to the high-pitched canopy and its excellent visibility.

The seat is fixed and the pedals are adjusted to suit the individual, removing the chance of a sliding seat on take-off and maintaining a constant position between seat, control column and throttle quadrant. With its standard seating position quite low and aft, the use of cushions will be prudent for shorter pilots. Otherwise, the dominant sensation is an overwhelming feeling of commonality with the other Diamond aircraft.

The DA42NG’s throttle quadrant is a highlight. Gone are the full set of dual levers for the Lycoming’s variable pitch propellers, mixture controls and throttles, replaced by simple, single power levers, one per engine.

Each engine is controlled by twin electronic engine control units, which monitor the engines and offer the simplicity of full authority digital engine control (FADEC), significantly simplifying engine operation by providing settings for propeller pitch and engine RPM from the sole pilot action of moving the single power lever.

Undoubtedly, this reduces pilot workload and makes aircraft operation simple and attractive to the touring private pilot. For advanced flight schools, particularly those training airline cadets, the presence of FADEC and ‘pseudo thrust levers’ is an early introduction into jet-like thrust management.

Sitting down, strapped in and ready to go, it’s now time to see how the DA42NG takes to the air.

Sheer simplicity

The Hawker Pacific Demonstration pilot for the flight was Alan Begg. As we readied ourselves to get under way, I confess to being particularly interested in the engine operation of the DA42NG.

I had anticipated little difference in the handling characteristics compared with the Lycoming-powered variant as the airframe and aerodynamics seemed very similar. But it was these superb engines that were to grab my attention — and my fascination began immediately I called “Clear prop!”

The ease of operation of the FADEC engines was apparent right away. There was no priming, pushing throttles or waiting to catch the spark with the mixture lever. It was all too easy. The left engine master toggle was selected ‘On’ and then the centrally located key was switched towards that engine to start.

In a heartbeat the engine fired first time and settled into a smooth idle. I then selected the right engine master, turned the spring-loaded key again and the second engine began to hum. In a matter of moments both engines were up and running and being monitored by the ECU.

As Alan and I sat there I was amazed at the speed of the start — no cranking, no guesswork. And once they were idling the noise level was minimal and vibration even less. These were two sweet, very smooth engines that made the cockpit a comfortable place to be and potentially an ideal place for training.

After brakes release, taxiing is simple and minimal inputs are required to guide the aircraft along the taxiway. The long, sleek wings and winglets require an appropriate level of attention when manoeuvring in confined areas such as parking areas and run-up bays. Along the taxiway, the functionality of the cross-feed system is verified before flight by making the appropriate tank selection.

In the run-up bay, there is a small wait for the temperatures to rise on this crisp winter’s day before engine checks can be performed. Then with the park brake set, the two ECU test buttons are pressed and the DA42NG runs itself up to 1,900 rpm and performs its own engine checks.

I sit there feeling rather redundant and hovering over the brake pedals as the aeroplane runs through a series of self-tests and prop checks during its two cycles. I sit on my hands and wait to see if this clever machine detects any faults. It doesn’t, so we complete our pre-flight checks and we’re ready to go.

Lined up on Bankstown’s runway 29 I advance the power levers smoothly and the aircraft moves of with sprightly acceleration. I rotate at 80kt, raise the gear and accelerate towards a 90-kt climb. There are no pitch levers and throttles to retard, just a pair of levers to manage and with the torque set at 90 per cent we climbed away at about 1,300fpm.

As we climbed, cruised and wheeled around the training area west of Sydney, the simple balanced controls of the DA42NG were evident and seemed no different to its Lycoming- powered predecessor.

The Garmin display reminded me of control zone steps while the TCAS highlighted any traffic in my area. Yet it was hard to draw the eyes back inside the cockpit on such a beautiful day. There are no windscreen pillars on this aircraft and the view from the wrap-around windscreen is both spectacular and safety enhancing.

Along with Alan, a series of steep turns were flown without issue although they improved once I realised the rudder trim wasn’t quite centred. At lower speeds, the control inputs remained relatively crisp and continuing to fly the aircraft into the stall at around 69kt was a non-event.

There was a copybook ‘nose drop’ and a slight tendency to drop a wing easily countered by the substantial rudder, which also was very effective in ‘engine-out’ operations. But once again, it was the engines that stole the show.

To shut down an engine you simply select the engine master for that engine to ‘Off’ and make the appropriate flight control inputs to continue flying the aeroplane. The propeller automatically feathers and the ECU’s switch off. It’s that simple.

On one engine, directional control was straightforward and the aircraft could still climb at about 200fpm at 4,000ft with full main tanks and two on board. To restart the engine the process, the procedure is reversed and the engine master switched to ‘On’, ideally between 125-145kt indicated airspeed. The propeller than unfeathers and begins to turn over before the engine returns to life.

Making our way back to Bankstown, the air becomes increasingly turbulent with the passage of the forecast southerly change. Even so, the ride in the DA42NG is very comfortable and the high-aspect ratio wings ride the bumps smoothly. With a crosswind limit of 25kt, the wind at Bankstown is not far off that number so it’s an ideal chance to see the DA42 near its limit.

Decelerating into the circuit on downwind is achieved by reducing power, maintaining level flight and allowing the airspeed to decay to below 133kt, when the first stage of flap can be extended.

It’s a sleek machine but with some anticipation, the Diamond twin is not difficult to slow down. At a pinch, the gear can be lowered at up to 188k, if needed, to slow down the aircraft. It isn’t, so the undercarriage is extended late downwind and the aircraft slows to about 90kt on base.

There is a substantial wind pushing us towards final approach so an early turn sees us roll out on final with a good deal of drift before selecting the final stage of flap and targeting 85kt on approach. Down final only minimal thrust changes are required even in these windy conditions.

At this stage, I disengage the yaw damper via the button on the top of the control stick and fly the aircraft down to the runway, still with a good deal of drift on as we cross the threshold.

Over the centreline, I ease in the rudder and slightly lower that long, thin wing to prevent drift downwind. We touch down on the centreline at around 70kt and easily slow to make one of the earlier taxiways. It’s great when the aircraft makes the job look easy.

Here to stay
Paired with the Austron AE300 diesel engines the DA42NG is a winner. The airframe was always a class act waiting for the right powerplant and now it seems to have found it.

I marvelled at the simplicity of the engine operation throughout the air test, from startup to shutdown. When combined with a total fuel burn an hour of 39lt and a Jet-A1 price advantage of 40 cents a litre over AVGAS, the DA42NG wins with sound economics, simplicity and style.

Hawker Pacific’s Stephen Pembro holds high hopes for the DA42NG to grow beyond the 150 already operating around the world. A number of these are multi-purpose platform models used on specialised tasks such as surveillance. And beyond the NG, Diamond Aircraft is looking to squeeze even more efficiency and speed out of the DA42V1.

The DA42NG is a major step forward in the world of light multi-engined aircraft. Its fuel efficiency and straightforward engine operation provide the outline while its attractive lines, handling and finish complete the picture.

The Twin Star NG once again demonstrates that while the frontiers of technology can take time to forge, with persistence and vision the results can be well worthwhile.

The Diamond DA42NG has arrived — with a throaty twin-diesel roar.