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February 2018

“The wing makes all the difference”

by Hendrik Thielemann

“Aerodynamically speaking, it’s the best you can get – an amazingly smooth surface, no edges, nothing.” Anyone joining Thomas Imke for a visit to the RUAG assembly hall in Oberpfaffenhofen will plainly see this salesman’s enthusiasm for his product. Imke is talking about the airfoils of the Dornier 228, and there’s probably no better way to sum it up than when he says: “The wing makes all the difference.”

A MacBook among airfoils

Bildgroesse_article-7a “The wing makes all the difference”

One way to describe the wings of the Dornier 228 is as the Mac-Book of airfoils: Just like the housing of the superlative laptop featuring the apple with a bite taken out of it, the Dornier 228 airfoil panels and all their structural reinforcements are milled out of a single large aluminium sheet.

Dornier engineers designed the specialized wings of the Dornier 228 as part of a program funded by the German Federal Ministry of Education and Research. They took an airfoil devised by specialists at NASA in the U.S. and developed it further into a highly capable wing.

An aircraft wing usually consists of many individual components: bent metal sheets are riveted to a framework of spars, ribs and stringers. In contrast: “The Dornier 228 has a total of just six wing panels plus a couple of stringers,” Imke explains. Each of these six panels is manufactured from a single enormous sheet of aluminium. At the start, the sheet is some five centimetres thick. A five-axis milling machine manufactures all the necessary ribs and structural reinforcements out of the sheet. The panels produced in this way are even and straight to start with. However, each panel must be bent, and bending an element complete with structural reinforcements into the desired shape is anything but easy. “The expertise is in the bending process,” says Imke. The stringers have to be compressed using special hydraulic clamps, the oblong mid-panels can be shaped with machines, and the triangular exterior panels are done by hand. As Imke explains, “This gives us exactly the wing profile that we need.”

Investment pays off

This is a time-consuming and costly process, which explains why the Dornier wing design is more expensive than a conventional design. But in the long run, the investment pays off for the aircraft operator, because the airfoil’s excellent aerodynamics help reduce drag and therefore fuel burn. The Dornier 228 consumes roughly one third less fuel than comparable aircraft in its class. It’s not only the wing’s special construction, but also its shape that plays a role, as the Dornier’s triangular wings have an advantage over conventional rectangular wings. And because the wings are tapered, they function much in the same way as winglets, which can be seen at the tips of the wings on most jets today. This tapering reduces the formation of vortex trails that result from the pressure differential between the upper and lower surfaces of the wing. These in turn increase drag, and thus have a negative impact on the aircraft’s performance and fuel efficiency.

Less fuel consumption automatically means greater range, longer flight times and increased payload. What’s more, its outstanding aerodynamics enable the Dornier 228 to take off and land on particularly short runways: even fully laden, a Dornier 228 needs less than 800 metres to take off at sea level. These characteristics make the Dornier a versatile aircraft for special missions, as well as passenger and cargo operations – especially in regions with poor infrastructure.

Aerodynamically solid

The wings of a Dornier 228 not only ensure the necessary performance and optimum controllability but also serve as the aircraft’s fuel tanks: “The largest part of the wing is wet,” Imke explains. This means it is sealed from the inside, so the airfoil interior can be directly filled up with kerosene – without requiring an additional inner lining or rubber bladder, as in helicopters, for example. Here, too, the wing’s special construction offers certain benefits: because it consists of far fewer components and has hardly any joints or rivets, it is much easier to seal the wing and significantly lower the risk of fuel leaks, thus improving the reliability of the aircraft.

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