RESEARCH FOR FLUTTERING WINGS
Kerosene accounts for more than a quarter of the cost of a flight. Lighter, slimmer wings can help to further reduce fuel consumption in aviation.
“The flutter phenomenon leads to material fatigue,” says Sebastian Köberle, research assistant at the Department of Aerospace Systems at TUM. “This can even lead to the wing breaking off.” Although each wing begins to flutter at a certain speed, shorter and thicker surfaces would have a higher structural rigidity and thus stability. “To build wings that are just as stable with a greater span would therefore also add more weight,” says Köberle. And that would mean losing out on the advantages.
First, they built a three-and-a-half-meter-long flight model – a demonstrator – with a large wingspan of seven meters and integrated the systems developed by their European partners, which are mainly sensors. For the initial flights, the demonstrator was equipped with conventional reference wings in order to fly automatically predetermined routes. Experts from the TUM developed manuals and comprehensive checklists for the flight tests.
There are strict safety regulations for operating the autonomous model: The aircraft, which is driven by a powerful mini-turbine, must be visible from the ground at all times so that the researchers can intervene with a remote control in an emergency. All flight maneuvers can therefore only be carried out within a narrow radius of about one kilometer. “After all, the flight demonstrator flies so fast that even the new wings would theoretically have to flutter,” Köberle explains. “At such high speeds we have to be sure that nothing goes wrong.”
“IF THE WING IS BENT BY THE AERODYNAMIC FORCES, IT TWISTS AT THE SAME TIME AND AVOIDS THE WIND PRESSURE, SO TO SPEAK.”
Meanwhile, the demonstrator is already on the starting blocks for the next round of test flights, for which it will have new wings fitted. The developers at TUM call them “super-efficient flutter wings” made of glass fibers. If flutter occurs at high speeds, flaps are extended at the outer edge of the wings to act as dampers. “This built-in active flap control increases the possibility for a significantly lighter design,” reports Gertjan Looye, who works at the DLR Institute of System Dynamics and Control Technology in Oberpfaffenhofen.
The aim of the project is clear. The flight demonstrator will not be the only aircraft to lift off with the two innovative wing types. In the near future, the promising results will also be transferred to the design of large freight and passenger aircraft.
THE FLEXOP PROJECT
FLEXOP partners include the Hungarian Academy of Sciences, Airbus Group Innovation, Airbus Group Limited, aircraft component manufacturer FACC, Integrated Aerospace Sciences Corporation (INASCO), Delft University of Technology, the German Aerospace Center (DLR), the Technical University of Munich, Bristol University and RWTH Aachen University.
Photos: DLR, TU München (Fabian Vogel)