Plane & Pilot
Tuesday, October 22, 2013

Fourth Time’s A Charm

In its fourth iteration, Diamond’s DA42-VI is a far better twin

On the latest version of the DA42, Diamond progressively improved Austro thrust and power by extending the composite MT props' diameter and recontouring the blades to more of a semi-scimitar configuration, adding three knots to cruise in the process. The company also redesigned the nacelles and air intakes to improve cooling and thrust, realizing another eight knots.

Out on the wings, the curved TKS anti-ice panels that cover the leading edges were reworked to bond flush with the wings, a major concern since drag is most critical in that area. Diamond claims another 2.5 knots from the flush TKS panels.

At the wing-trailing edge, Diamond added flushed and faired aileron and flap hinge fairings. The DA42-VI also received roughly 240 replacement flush-mounted screws on the wingtips and tail to replace the raised head hardware on the previous NG version. During flight testing of the improvements, Diamond discovered that the boarding assist steps presented slightly less drag if they were reversed, so Diamond simply turned them 180 degrees.
Diesels burn jet fuel, so they cleverly side-step considerations of fuel availability, since jet fuel is becoming readily available worldwide.
The rudder was redesigned to enhance directional stability, and the T-tailed stabilator improved to provide a five-knot reduction in minimum, single-engine control speed, better known as Vmc. That, in turn, allowed a shorter takeoff run.

The overall speed improvement over the previous NG was about 15 knots, but another significant result of all the aerodynamic cleanup was a single-engine service ceiling equal to the airplane's max operating altitude. In other words, for pilots willing to strap on a mask and ascend to 18,000 feet, you could lose an engine at FL180 and continue to cruise on the remaining mill without losing altitude.

Inside the cabin, Diamond made a number of improvements designed to increase comfort for pilots and passengers. To help counter high temperatures, Diamond upholstered the seats with a new type of leather that includes a radiant barrier designed to repel heat. The seats offer recline and lumbar support, as well, and they're enclosed within a cabin that's 50 inches wide. Backseat passengers also enjoy a foot enclosure on the floor that extends slightly forward, below the front seats.

There's a new rooftop-mounted air distribution system that can channel air-conditioning or standard outside cooling air into the cockpit. The baggage compartment benefitted from new hinges and a better door seal that allows the door to close tighter for less drag. Sun visors are an option.

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