## 9 Conclusions  
The morphing leading edge is an appropriate solution for increasing maximum lift and stall angle of an aircraft. In contrast to classical high lift devices like Krueger flaps, the MLE avoids adding sources of turbulence on the upper wing surface. Additionally, it avoids gaps, which are typically sources of noise radiation. Because of high aerodynamic pressure loads on the leading edge, a structure is required, which is both stiff and deformable. These conflicting requirements are addressed by a CFRP composite structure with a ply stacking sequence optimised for bending, local stiffness variation by tailoring of the composite (Section 3), and a pre-stressed sliding contact (Section 6) at the bottom of the wing. Additionally, using an intermediate baseline shape as initial geometry reduces the required strainability of the material. Cyclic material tests and numerical analysis show that the proposed skin structure is able to withstand the occurring strains for a full service life of an aircraft. The proposed stringer design and positioning combine a high stringer stiffness in the spanwise direction with a minimised impact on deformation of the skin in the peripheral direction. Furthermore, the material composition of the stringers reduces thermal stresses, as explained in Section 3.2. The designed actuation system for the MLE fits completely inside the leading-edge, leaving space for other systems and components like cables und tubes, which are typically located in that region of a wing. The required actuation forces allow for an electromechanical actuation of the MLE system. Together with the proposed mounting concept, which does not require any ingress from difficult to access areas behind or at the sides of the leading edge, the MLE system is designed for minimizing the impact on the aircraft design in order to allow integration in future versions of existing aircraft types. As bird strike is an important issue for the leading edges of any aircraft wing, a protection solution against bird strike has been developed. Numerical simulations show its ability to stop birds from hitting the front spar of the wing. Beyond the design progress presented in this paper, further work on design and qualification of the MLE system needs to be done, before such a system can be used in commercial flight operations. This includes lightweight optimization of the system, exhaustive analysis of functional and structural safety aspects, prototype testing, and certification. Furthermore, a feasible ice-protection system has to be integrated into the skin structure. A possible solution for such a system in a morphing CFRP structure is described in [6]. Further improvement of aerodynamic performance for morphing systems may be achieved using an integrated aerodynamic optimisation approach, which considers material limitations like the one reported in [43] together with structural optimisation algorithms, e.g., [44]. Figure 32: Bird strike simulation. **Left**: Impact configuration; **right**: Interaction of bird with internal structure. **Author Contributions:** Following the individual contribution of the authors is provided: Conceptualization, C.C.A., V.L., and D.L. Methodology, V.L., D.L., and J.-D.W. Formal analysis, S.A. and M.M. Investigation, C.C.A. and V.L. Writing--original draft preparation, C.C.A. V.L., D.L., S.A., M.M., J.-D.W., and J.D. Writing--review and editing, C.C.A., V.L., D.L., and M.M. Visualization, C.C.A. and V.L. Supervision, C.C.A. Project administration, C.C.A. and M.M. All authors have read and agreed to the published version of the manuscript. This research was funded by the EC in the frame of JTI Clean Sky 2, grant number CS2-AIR-GAM-2016-2017 and CS2-AIR-GAM-2018-2019. Not applicable. **Data Availability Statement:** Restrictions apply to the availability of these data. Data was partly obtained from Airbus Defence & Space and are available from the authors with the permission of Airbus Defence & Space.