Monday, August 1, 2005
The Force behind the Diamond DA42 Austrian invasion
Power up for takeoff, and you’re looking at a startling 76 inches of manifold pressure. (Not to worry, diesels run much hotter than pistons and are designed for such big numbers.) Takeoff power generates a ridiculously low 8.1 gph per engine, your first hint of the efficiency that’s possible with diesels.
The TAE turbo-diesel’s critical altitude is a fairly low 5,500 feet, above which power begins to bleed off. This is primarily a function of the need to keep the engines cool. Max operating altitude is listed as 18,000 feet. Remember, that’s a max operating altitude, dictated more by systems limitations rather than performance, not a service ceiling.
Hold the 83-knot Vyse after rotation and cleanup, and you’ll see initial climb rates around 1,500 fpm, not that dissimilar from other light-light twins. Few thinking pilots climb at Vy, and pushing over to 100 to 110 knots still generates 1,000 fpm. Just as with the single-engine Star, the Twin Star’s single-piece canopy allows excellent visibility, with only the airspace directly above the pilot blocked off to allow for a semblance of shade.
Level in cruise, the Twin Star enjoys excellent economy. Eighty-five percent cruise burns only 6.3 gph per engine and currently generates about 165 to 170 knots. (Engineering numbers suggested a speed of 183 knots, and Diamond is still tweaking toward that goal.) That’s better than 13 nmpg—in a twin. Consider that the next most efficient production twin, Piper’s Twin Comanche, delivers only about 165 knots on 17 gph, roughly 10 nmpg.
The Twin Star is not simply an alternative to current light twin trainers. Diamond also views the airplane as a viable alternative to high-performance singles. Airplanes operated in instrument conditions, at night and over inhospitable terrain should have powerplant redundancy. Add known icing protection, and it becomes the safest choice for a serious cross-country airplane.
For Twin Stars used in multi-engine training, the airplane has been designed with extremely docile single-engine characteristics. Vmc (single-engine minimum control speed) has been set at 68 knots with either surviving engine generating full power, and Diamond claims a sea-level, single-engine climb of 500 fpm at a Vyse of 83 knots.
Page 3 of 5