Will V-wing passenger aircraft be successful

Slim wingsResearchers are testing new wing geometry for aircraft

Sebastian Köberle works at the Chair of Aviation Systems at the Technical University of Munich. And when he's on the airfield in Oberschleißheim north of Munich, he's also an operator. He gives the pilot instructions on how to control the small, unmanned aircraft from the ground.

"A test flight like this lasts between 18 and 25 minutes and it is always the fastest 25 minutes of the day. And the longest too. Because everyone is in the situation and sees to it that the test goes well, that one always feels afterwards surprised that 20 minutes have passed even though you have only just started. "

The airplane looks like a glider pilot, but is operated with a motor: "So we have a wingspan of 7 meters and a length of around three and a half meters. So you can already see from the proportions that it is a special airplane for a special application. "

Before the test flights in Oberpfaffenhofen: Christian Rößler next to the flight demonstrator in front of the ground control station. (Fabian Vogl / TUM)

The purpose of these test flights: The scientists want to design slim aircraft wings. Because such a higher aspect ratio, the technical term, reduces the air resistance at the wing tip and thus ensures more efficient lift.

Slimmer wings could save five to ten percent kerosene

For this reason, gliders have particularly long, slender wings with an aspect ratio of over 20. The latest passenger aircraft, on the other hand, only have an aspect ratio of about 10. This value could be increased to 13 to 14, the scientists suspect.

According to calculations, this could save between five and ten percent kerosene in typical traffic machines. When you consider that a flight from Europe to New York consumes over 100,000 liters of fuel, then it becomes clear what the dimensions are.

The flight demonstrator takes off. (F. Vogl / TUM)

The big problem with such slim wings with a high aspect ratio: They tend to flutter more, explains Sebastian Köberle: "So basically every wing starts to flutter at some point if you fly fast enough. That is why nowadays care is taken to ensure that the wings are stable are built so that during normal operation one does not penetrate into the speed range where flutter could occur. "

Flutter. What sounds harmless is actually a disaster. Because the wings are set in vibrations that can swing up. This promotes premature material fatigue and can even cause the wing to break.

High aspect ratios tend to flutter

An international team of scientists from six countries is therefore working to drive out the flapping of the wings. In the EU-funded FLEXOP project, they are pursuing two approaches: a passive and an active technology. With the passive technology, developed at the University of Delft, the innovation lies in the construction of the wing. Coupling effects in the material should influence the bending and torsion behavior of the wing in such a way that it does not even flutter. Andreas Hermanutz, also an employee at the Chair of Aviation Systems, explains it like this.

"Let's assume we have a plate and would press on it, then it would simply bend. But we have manipulated the plate in such a way that when we press on it, it also begins to twist, to twist."

In such a way that the air has less surface to attack and dangerous vibrations cannot arise in the first place. The active technology, on the other hand, relies on actively dampening the flapping of the sash, with control flaps on the trailing edge of the sash. Andreas Hermanutz:

"The active technologies are everything where a regulator somehow controls something, that is, moves flaps. We can of course cover even more states, that is, make the aircraft even more efficient. But this has the disadvantage that if the regulator fails, flutter occurs immediately and the wing would break off. "

Active damping should prevent dangerous vibrations

The flight tests with the actively damped flutter wing are still pending. Computer simulations have shown that it should start fluttering at a speed of 53 meters per second, i.e. at 190 kilometers per hour. Then the control technology has to prove that it can stop these oscillations. If you don't succeed and the wing breaks, the scientists have to deploy the parachute on board and hope to at least save the rest of the aircraft.

Sebastian Köberle usually doesn't have time to look at the sky on the airfield: "I can't see the plane. Because I have to report speeds right up to the end. Until someone pats me on the shoulder and says:" It's okay, we are landed."