How do new aircraft designs come about

Circular economy in aircraft construction

When it comes to making air traffic more environmentally friendly, the first thought is often about emissions. Quieter and more efficient engines that are powered by alternative fuels from bio-kerosene to hydrogen, or even electrically. These are great avenues for lower carbon aviation. - But they are not the only ones: As part of the EU project “SUSTAINair”, researchers from the German Aerospace Center (DLR) are already focusing on sustainability and energy efficiency when manufacturing the aircraft.

As heavy as necessary, as strong as possible

Everything is interrelated in an airplane. Purely mechanically, but also metaphorically. It is important to combine the lightest possible materials as permanently as possible. In classic aircraft construction, segments made of aluminum are connected with metal rivets. This method is durable, but does not contribute negligibly to the high overall weight of the aircraft.

New aircraft designs and concepts rely on lightweight composite materials, above all fiber-reinforced plastics. These fiber composite materials are not only lighter, they also have very good material properties in terms of flexibility. The use of recycled materials is also conceivable here.

The safe and permanent connection of different materials, especially plastics and metals in an aircraft, is a particular challenge. The finished aircraft will later carry passengers safely for decades, and is always exposed to vibrations and other mechanical loads as well as extreme temperature differences.

The scientists at the DLR Institute for Materials Research in Cologne are therefore developing and testing combinations of different joining techniques. The surface of metallic components (titanium and aluminum alloys) is roughened by laser at the nano level in such a way that an optimal adhesive bond with fiber-reinforced plastics is achieved. In addition, macrostructures are created with the help of additive manufacturing processes (3D printing), which ensure an additional mechanical connection between the two materials. This can be, for example, small pins on metal plates, which represent a double safeguard of the connection point.

By continuing research into the strength of such joining techniques, safety margins can be defined more precisely in the future, which can contribute to further weight reduction.

Laser and titanium

Another manufacturing technology that is rapidly growing in importance for the aerospace industry is "Laser Powder Bed Fusion (LPBF)", better known as 3D laser printing of metallic components. It is an additive process in which metallic alloys are applied in powder form in a flat bed and then laser-welded in layers with pinpoint accuracy. This enables complex components, such as the compressor blades of aircraft turbines, to be built with geometries that were previously difficult to impossible to produce. Another advantage is that this technology also enables the economical production of individual parts or small series, as often occurs in the aerospace industry. Conventional manufacturing processes, such as milling a component from a metal block, lead to a high proportion of waste that is difficult or impossible to recycle.

The titanium powder from 3D printing, which is often used for highly stressed structures, can basically be reprocessed and reused. During processing, however, attention must be paid to the uniformity of the granular structure and the embrittlement of the titanium due to oxidation must be avoided.

The key to avoiding oxidation of the powdery material lies in the moisture and gas tightness of the workroom in the laser printer. According to current specifications, titanium powder used for aerospace applications must be completely new. “Our goal is to achieve good mechanical properties even in components that have been made from recycled powder in order to enable powder recycling. With costs of around 300 euros per kilogram and considering the production costs, this would be a big step from an economic and ecological point of view, ”says Dr. Miriam Löbbecke, Department of Metallic and Hybrid Materials at the DLR Institute for Materials Research.

SUSTAINair

SUSTAINair is part of the EU program "Horizon 2020". It aims to identify and develop solutions to increase the resource efficiency of aircraft in the sense of a circular economy approach. At the same time, waste and material costs should be reduced over the entire life cycle of the aircraft. SUSTAINair started in 2021 and has a budget of five million euros over a period of three and a half years. The consortium consists of eleven European research and industry partners.