In a joint effort by the Technical University of Munich (TUM) and the German Aerospace Centre (DLR), researchers have successfully developed new technologies for lighter aircraft wings that are still extremely stable. These innovative wings could soon make flying both greener and more cost-efficient. Known as aeroelastic wings, they have made their successful first flight at the airfield in Oberpfaffenhofen.
Wings with a wider wingspan and less weight also have less air resistance and better energy efficiency. Optimised lift behaviour could save fuel and thus reduce both emissions and costs. The limiting factor for building wings like these is the aerodynamic phenomenon known as ‘flutter’. Aerodynamic drag and wind gusts result in continuously increasing wing vibration, similar to a flag in the wind.
"Flutter leads to material fatigue and can even go as far as ripping off the wing," explained Sebastian Köberle, research associate at the TUM Professorship for Aircraft Design. Although every wing begins to flutter at a certain speed, shorter and thicker wings have higher structural rigidity and thus higher stability. Making wings that have a wider wing-span and are still exactly as stable and add much more weight.
In the European project FLEXOP (Flutter-Free FLight Envelope eXpansion for ecOnomical Performance improvement) scientists from six countries are working on new technologies which can bring flutter under control and at the same time make it possible to build lighter wings.
The TUM researchers are responsible for the conceptual design and execution of the test flights. The tests are to demonstrate the actual behaviour of the two innovative wing designs developed in the project: The aeroelastic wing and the flutter wing.
At the TUM scientists first built a 3.5 metre long, 7 metre wide flight demonstrator in which they integrated the systems provided by the European partners. Using reference wings configured especially for this purpose, the researchers then worked to make the flight demonstrator automatically fly a predefined test flight path. They figured out the optimum settings and developed manuals and checklists for the test flights. "The flight demonstrator is supposed to fly so fast with the new wings that they would theoretically have to flutter," said Köberle. "When flying at such high speeds we have to be absolutely sure that nothing goes wrong.
Successful first flight of the aeroelastic wing
The wing, which took off for the first time at the Oberpfaffenhofen airfield, is the aeroelastic optimised wing developed by the DLR in collaboration with Delft University of Technology and is made of carbon fibre. A special alignment of the fibres when making the wing let the researchers influence its flexural and torsional behaviour. "If the wing is bent by the force of the air, it turns at the same time, avoiding the force of the wind," noted Wolf-Reiner Krüger from the DLR Institute of Aeroelasticity in Götting.
The second super-efficient wing developed in the project is referred to as the ‘flutter wing’, designed by TUM and made of fibreglass. When flutter occurs, the outermost flaps are deployed, functioning as dampers. "The integrated active flap controls developed at DLR significantly increase the possibilities for a much lighter design," said Gertjan Looye from the DLR Institute of System Dynamics and Control in Oberpfaffenhofen. Looye is responsible for coordinating the DLR portion of the project.
A second flight control system is being developed by the Computer and Automation Research Institute of the Hungarian Academy of Sciences (MTA SZTAKI). The project director Bálint Vanek of MTA SZTAKI added: "A wing like this could make it possible to transport 20 per cent more freight or use seven per cent less fuel." Since the technology involved is very complex, the tests on this wing will not be conducted until a later point in time.
Read about NASA’s collaboration with MIT to revolutionise wing design here.