Flight test: the Diamond DA42 NG

The vertical-speed indicator tells me the aircraft is climbing at 700ft per minute as I coax it over a hurdle of fluffy clouds.

This would be a reasonable rate of ascent for most light aircraft, but this Austrian-made Diamond Twin Star is doing something much more impressive: it is climbing on just one engine.

This aircraft, like many others, has two engines – mainly for safety reasons. However, many twins do not perform well when one engine has gone quiet, and some older aircraft are unable to climb at all. In that context, the 700ft-per-minute ascent of this “new generation” Diamond is the equivalent of rocketing into the sky.

Heading towards the ridge at Stokenchurch in Buckinghamshire, I can admire the shadows of the same clouds I am dodging – rather than worry about crashing into the rising ground, as I would in many twins with one engine out.

When I first tested the new Diamond DA42 Twin Star about five years ago it seemed almost too good to be true. A sleek carbon-fibre airframe was equipped with fuel-sipping engines to cut petrol costs, and the motors were controlled by sophisticated electronics to make the pilot’s life easier. It won swift support from pilots seeking safety without breaking the bank, and training organisations keen to replace traditional twins, which guzzle aviation gasoline.

Sadly, the package was not as promising as it first seemed. Rumours surfaced of engine problems and then, in 2008, Thielert, the maker of the DA42’s diesel engines, went bust. Owners started to grow nervous about overhauls, warranty claims and resale values.

But all was not lost. Christian Dries, chief executive of Diamond Aircraft, had already been developing his own Austro engine, which was certified last year. So the production lines could start rolling again.

Diamond claims the Austro is a hefty 46 per cent less thirsty than its gasoline rivals. Even better, it runs on diesel or jet fuel, which is almost half the price of aviation gas. With optional auxiliary tanks the Twin Star has a fuel capacity of 76 US gallons, or 287 litres – quite a saving every time you refuel.

In the cockpit of the Twin Star, the range map shows that from our vantage point above sun-dappled Home Counties fields we could reach the Czech Republic without stopping. The soft slithering of air past the canopy, and the tireless droning of the engines, convince me that the aircraft would be happy to show off its stamina.

So fuel-frugal is this aircraft that Diamond has developed an unmanned observation version that can stay aloft for more hours than mortal pilots could bear. Even the manned surveillance variant, with its loitering speed of 90 knots, has carried out 13-hour missions.

As Henrik Burkal, Diamond UK’s managing director and my co-pilot for the day, points out, a twin-turbine helicopter performing the same sort of observation role will burn a DA42 NG’s full load of jet fuel in less than an hour.

I wouldn’t want to spend 13 hours in it, but the passenger version’s spacious cockpit is more like that of a car than the cramped space in most light aircraft. But there are some flashy features you won’t see on the motorway. The Garmin G1000 avionics system, already fearsomely competent half a decade ago, now features synthetic vision – an accurate three-dimensional picture of what the world looks like outside the cockpit.

The NG’s autopilot has a system with sophisticated capabilities more usually seen on much bigger aircraft. Changing altitude and direction, or following an airport’s restricted-visibility instrument approach procedure, are but a knob-twiddle away. If I want to fly using all these systems, the Twin Star does so with serene efficiency. And if I want to fly by hand, the Diamond will obediently follow my instructions with the sort of smooth and undramatic handling that passengers as well as pilots appreciate.

The airframe has proved reliable and durable, with about 600 built and sold. Even the composite construction, which permits the aircraft’s startling swoopy style, has been easier to repair than some mechanics had feared.

The new engines, though, are still an unknown quantity. Aviation regulators want each motor overhauled after 1,000 hours of flying – and some engine accessories checked or changed at mere 300-hour intervals. But as experience increases, the time between overhauls is expected to lengthen to 2,000 hours or more.

In the world of piston-engined aircraft, the DA42 NG’s new engines bring the ease of operation that flyers should have been growing accustomed to for years – but with some very welcome extra power. The Thielerts did not fulfil their promise. If the Austro motors do, we’re back on track to the future.

The details

Better than ever: Diamond’s DA42 Twin Star reborn

How much?

In standard specification, €522,750 plus taxes

How powerful?

Two Austro AE 300 turbocharged two-litre diesels, with 168bhp and single-lever control of engine and propellers

How fast?

At 14,000ft, max cruise 184 knots (212 mph) true air speed; at 75 per cent power 174kts; at 60 per cent power 152kts

How thirsty?

At 75 per cent power 13.6 US gallons per hour total; at 60 per cent 10.3 galls/hr

How far?

Range with auxiliary tanks at 75 per cent power 950 nautical miles; at 60 per cent power 1,180nm

Also consider

A cheaper but thirsty and maintenance-fund-gobbling secondhand twin from Piper or Beechcraft

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