During the flight of the aircraft, the air flow around the high-lift device and the control surface and the fixed part of the wing will suddenly transition. Aerodynamic studies have shown that this transition is the cause of some noise. Researchers from the German Aerospace Center (DLR), Invent and the Technical University of Munich are collaborating on the FlexMat project, hoping to reduce the noise generated in the area by designing a flexible transition skin between the wing and the moving surface .
The flexible skin design between the fixed part of the wing and the moving control surface or high-lift device must be able to withstand extreme aerodynamic loads, but the stiffness must not be too large, otherwise the system that drives the moving parts needs to apply extra force.
Martin Radestock of the Institute of Composite Structures and Adaptive Systems at DLR said: "The continuous transition between the flap system and the main airfoil will be a huge advantage for the future laminar wing, which allows air to bypass without Turbulence will be generated to ensure laminar stability."
The FlexMat project carried out research based on the design of the laminar wing of the A320 aircraft. Research focused on the outer area of the wing. The slats that were originally installed on the leading edge are now replaced by the variable shape leading edge (ie, drooping flaps) that the DLR Institute has been developing since 2007, adding a transitional mask made of rubber and fiberglass composite materials skin.
The skin is composed of ethylene propylene diene monomer rubber (EPDM) and glass fiber reinforced composite materials. Flexible rubber forms the basis of the skin, and the researchers inserted glass fiber composite strips at different intervals on its inner and outer surfaces. The deformation properties of the transitional skin can be adjusted by changing the position of the glass fiber composite slat. The researchers worked hard to keep the local deformation to a minimum, so that the glass fiber composite and rubber would not separate.
DLR tested the transitional skin demonstration piece with a span of 1 meter. "The test results show that the wing skin under test is very wear-resistant and can be deformed to a large extent. In the event of extreme deformation, the only thing that needs to be paid attention to is the painting, which should be ensured that it will not break."
Radestock said, “The results have proven that it is feasible to use flexible skin on the leading edge of the wing. In order to check the extent to which noise and drag can actually be reduced using this technique, and to determine the maximum load limit of the skin, further work will be required test."