In order to contribute to achieving noise and emission reduction goals, Fraunhofer and Airbus deal with the development of a morphing leading edge (MLE) as a high lift device for aircraft. Within the European research program “Clean Sky 2”, a morphing leading edge with gapless chord- and camber-increase for high-lift performance was developed. The MLE is able to morph into two different aerofoils—one for cruise and one for take-off/landing, the latter increasing lift and stall angle over the former. The shape flexibility is realised by a carbon fibre reinforced plastic (CFRP) skin optimised for bending and a sliding contact at the bottom. The material is selected in terms of type, thickness, and lay-up including ply-wise fibre orientation based on numerical simulation and material tests. The MLE is driven by an internal electromechanical actuation system. Load introduction into the skin is realised by span-wise stringers, which require specific stiffness and thermal expansion properties for this task. To avoid the penetration of a bird into the front spar of the wing in case of bird strike, a bird strike protection structure is proposed and analysed. In this paper, the designed MLE including aerodynamic properties, composite skin structure, actuation system, and bird strike behaviour is described and analysed.

In the context of ambitious targets for reducing environmental impact in the aviation sector, dictated by international institutions, morphing aircraft are expected to have potential for achieving the required efficiency increases. However, there are still open issues related to the design and implementation of deformable structures. In this paper, we compare three constrained parameterisation strategies for the aerodynamic design of a morphing leading edge, representing a potential substitute for traditional high-lift systems. In order to facilitate the structural design and promote the feasibility of solutions, we solve a multi-objective optimisation problem, including constraints on axial and bending strain introduced by morphing. A parameterisation method, inherently producing constant arc length curves, is employed in three variants, representing different morphing strategies which provide an increasing level of deformability, by allowing the lower edge of the flexible skin to slide and the gap formed with the fixed spar to be closed by a hatch. The results for the optimisation of a baseline airfoil show that the geometric constraints are effectively handled in the optimisation and the solutions are smooth, with a continuous variation along the Pareto frontier. The larger shape modification allowed by more flexible parameterisation variants enables an increase of the maximum lift coefficient up to 8.35%, and efficiency at 70% of stall incidence up to 4.26%.

The present study is concerned with an experimental study into the effect of superimposed creep deformation, varying local fiber orientation distributions, and more complex multiaxial stress states on the fatigue of short fiber reinforced thermoplastics. The cross-interaction of these effects is a relevant feature in all fields of applications of short fiber composites since molding related variations of the local fiber orientation states cannot be avoided for injection molded structures. Long term loading will result in a combined occurrence of fatigue and creep and thus an interaction of the related effects. The study is based on a short glass fiber reinforced polyamide 66 as reference material which is a common material grade in many automotive applications. A basic characterization is performed by means of tensile and DMA experiments. Subsequently, creep and creep fatigue experiments are performed at ambient and elevated temperatures. In order to include the effects of locally varying fiber orientation situations and locally multiaxial loading situations, the coupon experiments are complemented by experiments on breadboard specimens featuring notches, holes, and structural component related external geometries. Superimposed creep deformation might accelerate fatigue failure, however, for notched specimens might also result in an increased fatigue lifetime due to creep-induced stress relief at the notch roots. The results reveal that care has to be taken when transferring the results on idealized coupon specimens to generalized, realistic problems. The results also serve as a development and validation data base for a continuum damage mechanics material model presented in an oncoming contribution.