Diamond in the smooth

DA-42 Twin Star

I caught up with an old friend and a new friend at COPA’s recent Annual General Meeting in Moncton, New Brunswick. Gary Gaudreau, the Customer Support Manager of Diamond Aircraft is based in London, Ontario where he was able to secure a Diamond Twin Star demonstrator for a brief stopover at Moncton en route to a U.S. delivery/destination. My new found friend is the DA42 Twin Star.

Gary and I had worked together in the days when we peddled Cessna products in the 1970’s and as a kind gesture he offered me the opportunity to fly the new diesel twin.

To ballast the aircraft to maximum gross weight – and for his excellent input, I talked our Quebec executive member Frank Hofmann into monitoring our flight from the back seat. The conversation went; "You wanna?" The answer; "You bet!"

With lots of fuel, some baggage and 615 pounds of "us" we nudged the maximum gross of 3,935 pounds for take off. Another nice round number thanks to European certification.

The nose baggage compartment has doors on both sides and is capable of storing two golf bags while the aft compartment is quite large and can accommodate objects seven feet long.

No question the Twin Star garners lots of interest on the ramp and in the air. It takes forever to climb aboard – not because of walk around complexity – that’s easy. It’s all the lookiloos and their questions that cause the delays!

The Twin Star stands tall on its extremely strong trailing link landing gear which can be extended right up to Vne thereby creating drag for rapid descents. Moreover, it extends automatically if hydraulic pressure is lost.

The electrical system is 24 VDC with two, 60 amp alternators. The engines produce 135 hp at 2,300 rpm and burn Jet A or diesel. One caution, at temperatures below +5C, take offs are not permitted when diesel or mixed fuel is used. This is likely due to the thickening properties of the diesel fuel. However, the use of commonly available Jet A (kerosene) should preclude this issue for cold country operators.

Gary showed us the engine oil check access and dipstick and the colour of the oil confirmed the engines were indeed diesels. There was even an access door to check the gearbox lubricant level. Gearbox equipped engines allow the engines to turn at high rpm to maximize power to weight output while also allowing propellers to turn at more efficient rpms adding considerable efficiency.

Mind you, in this twin, you don’t worry about engine parameters such as turbo boost, manifold pressure, mixture or pitch control, engine rpm and calculating percentage power. Why? Essentially, each engine has one control – a throttle – and one power instrument that simply reads percentage output.

All of the power parameters are controlled by an engine control unit thereby simplifying flying tasks while providing protection from pilot produced problems.

Normally you won’t find these advanced engine monitoring and control systems in your airframe unless you invest a million or more. During the Moncton COPA convention, Cirrus had their new turbocharged single parked on the same ramp as the Twin Star. It’s interesting that the big single and light twin are priced similarly and trade off on performance specifications over most of the performance band. However, the DA42 goes one step further by offering increased safety in the event of engine failure – at no extra cost!

Mounting the Twin Star requires a step up onto the wing and over the sill – a feat easily achieved by most passenger/pilots. The back seats are roomy and contoured to provide good support for lengthy flights – something the DA42 excels at.

Not so long ago the twin made a non-stop flight from Gander across the Atlantic to Portugal – on 72 gallons!

The baggage area, accessible from a large baggage door provides considerable space for the four occupants. Like most four place aircraft, the DA42 can’t legally carry four full sized adults, full fuel and baggage (See sample loading further in text). However, the Twin Star doesn’t require a great deal of fuel for medium range trips of 500 miles and is fully capable of operating off short strips with a full load of passengers on these segments.

Frank was initially an anti-Diamond passenger because he would need to have elective surgery to shorten his legs – or perhaps head – so his seated six foot three inch frame would more readily fit in the cockpit/cabin. Mind you, once the offer of a ride evolved, he was prepared to hunker down somewhat to come along to sample the glorious standard equipment Garmin 1000 avionics. (Diamond insiders advise the aircraft will be available with a larger cockpit boasting more headroom shortly).

One option purchasers might want to opt for is "known icing" as these aircraft so equipped utilize TKS weeping fluid to protect wings, windshield and tail.

My chariot was an American dealer’s demo machine weighing in at 2,871.4 pounds empty. A sample loading with full main tanks (50 U.S. gallons), 368 pounds of pudgy in the front seats and 177 pounds in the back with the maximum baggage of 100 pounds puts the aircraft at gross and near the middle of the longitudinal C of G.

Having the nose compartment allows considerable leeway with balance. Our flight was conducted at gross but with different loading as none of us fits the standard passenger weight. The C of G limits are a generous 94.5 to 98.0 inches and the manoeuvring limit loads of the aircraft are +3.8 and -1.52 G.

The harness is comfortable and the pilot position adapts to pilots of varying leg lengths with adjustable rudder pedals. The canopy can be latched partially open on hot days for additional ventilation while taxiing. I like the position of the fuel on/off/cross feed controls as they are readily visible by the throttles and take up very little room on the pedestal and safety latched to avoid inadvertent shut off.

Pre-start checks are easy and the engines start immediately after the glow plug igniters warm up – on a warm day, the engines start without them. Testing all of the automatic engine parameters is easily accomplished as the engine control units complete their own self test functions.

Gary releases the brakes and asks me to assume control in the COPA crowded confines. No problem. The nose wheel steering is linked with the rudder inputs and when combined with differential brakes provides excellent guidance and easily allows the 44 foot wingspan to dance nimbly around the ramp avoiding the fly-in aircraft.

The run up is equally easy – because pushing a button commands the engine to do its own cycling checks. Carb ice and the mixture control are non issues – they don’t exist. One learns to love diesels quickly.

Gary gives me the nod for the back track on Moncton’s 29 and recites the various velocities for rotation, single engine safety speed and climb from the display. The Twin Star continues to make it look like I have flown before and the light trim forces and good response make it easy to take off.

When the inevitable simulated engine failure occurs, one only has to flip a switch and the affected engine shuts itself down and feathers the prop – in a split second! That is an amazing capability and huge safety enhancement for pilots under conditions of heavy workload.

This twin is very quiet in part because the turbocharged engines create their own muffling and the composite structure provides natural absorption of vibration and noise. Visibility is very good to the sides and forward with the engine nacelles and wings obscuring the visibility somewhat in those directions.

Cockpit temperatures are well modulated thanks to excellent ventilation. When the single engine Diamond Star was introduced, Diamond owner Christian Dries and I both flew it at Sun ‘n Fun and we separately concluded the Star needed more ventilation in hot climates. Diamond listened, greatly increasing airflow and in combination with the overhead cockpit sun shield, cooler heads prevail.

Due to mutual scheduling time constraints (I had a turbo 182 Cessna to evaluate) and Gary had to fly to the NE States, my initial Twin Star flight is short. We only climb to 4,000 feet and set up for cruise at 150 knots on 12.6 gph of jet fuel (50 litres per hour). For reasons I do not understand, the aircraft has a maximum certified operating altitude of 18,000 feet. As with any turbocharged aircraft, the higher one flies, the greater the true airspeed – although this effect is reduced after reaching the altititude at which the turbo can no longer provide full cruise power settings.

For normally aspirated aircraft, this occurs in the 6500-8500 foot altitude range. The POH indicates this aircraft can provide 75 per cent power to approximately 15,000 feet. (For turbocharged engines it can vary widely between, say, 12000 and 40,000 feet.)

The single engine cruise at 4,000 feet and 10 degrees C produces an indicated 105 knots at 75 per cent power. Incidentally, trim and control pressures on sudden engine failure are not significant and although the DA42 is a twin, it handles like a medium weight single and could easily be flown by virtually any man or woman. This is more of an issue than many might realize as many women have had to nix purchase of a heavy single because they found the round-out for landing and general control forces too heavy for their musculature/leverage.

While I didn’t fling the DA42 around like a helicopter on fire suppression operations, the control forces and response showed the machine was not only capable as an IFR platform, but also a highly manoeuvrable personal or business steed that would handle itself well around small urban or personal airports. Part of this conclusion is based on the very low landing configuration stall speed of 56 knots which gives the aircraft tremendous short field agility.

Of course the single engine safety speed is always a factor when pilots consider the need to have "balanced field length" capability least an engine fails at an "inopportune" time.

Although I haven’t flown a twin in some time (If you don’t count twin turbine helicopters), I found little workload to flying circuits with the DA42. Being able to lower the gear at any speed while darting in from the upper airwork is very handy and allows the pilot to keep the speed up in busy terminal areas till final approach.

Similarly, the first notch of flap can be extended at 137 knots and there is a desirable, light nose down pitch moment associated with same. Ditto for the second notch of landing flap at 111 KIAS and the nose rotates a little more nose down to keep the approach speed on the notch.

Round out forces are reasonably light and the trailing link undercarriage (often used on carrier based aircraft) makes virtually any landing a good one. Whether it is a greaser or a carrier deck landing, the gear absorbs the vertical speed and produces no bounce.

Twins can be a challenge after an engine failure immediately after take off as they experience loss of control from the asymmetric thrust from one engine overpowering the aircraft’s rudder capability when the other engine takes a time out.

The critical speed is called Vmc (Velocity minimum control) and for the Twin Star this is 68 knots. This is an amazing aerodynamic accomplishment as typical Vmc for twins is in the 80-90 knot range. What this means is the DA42 fully controllable to within 12 knots of its stalling speed and this is a huge safety margin relative to competitors – not that I can think of one that could compete with the Twin Star.

Truth to tell, I wish this freedom machine had been available years ago when my life would have justified owning such a machine. Mind you, the last time I made a statement like that the astute marketing folks at Diamond sold me an Xtreme motorglider. I realize this report is skimpy on details and hope to provide a more detailed report after a lengthy cross country evaluation of the aircraft in the future.

The following specifications are provided by the factory. The author has not provided a comparison with other aircraft as no new twin comes to mind that meets the criteria in the price range. For more information, visit their website at: www.diamondair.com.

AIRCRAFT TYPE Diamond DA42 Twin Star

ENGINES Thielert T.A.E. Centurion 2.0

HORSEPOWER 270

PROPELLERS MT 3 blade fully feathering

LENGTH 28 feet 1 inch

HEIGHT 8 feet 2 inches

WING SPAN 44 feet

MAX WEIGHT 3,935 pounds

USEFULL LOAD 1,174 pounds

FUEL CAPACITY STD 52 U.S. gal

FUEL CAPACITY EXT 79 U.S. gal

FUEL TYPE Jet A, Diesel

T/O ROLL 1,200+ feet

MAX ALTITUDE 18,000 feet

S/E CEILING 10,000 feet

S/E BROC 82 KIAS

S/E VMC 68 KIAS

CRUISE 80% PWR 172 knots @ 12.5 gph

CRUISE 60% PWR 150 knots @ 8.8 gph

STALL CLEAN 62 knots

STALL LDG CONFIG 56 knots

LANDING GEAR EXT 194 knots

MAX CROSSWIND 20 knots

MAX RANGE (Aux Fuel) 917-1129 NM plus reserves