## 1 Introduction
Between 2011 and 2015, several morphing structures were developed, manufactured, and tested within the European project \"Smart Intelligent Aircraft Structures (SARISTU)\". These included a morphing trailing edge [13], a morphing winglet [14, 15], and a morphing leading edge [16, 17]. The MLE developed within this framework follows the concept of an enhanced adaptive droop nose with a glass-fibre reinforced composite skin. The demonstrators were tested in the wind tunnel as well as subjected to bird impact loading to demonstrate the aerodynamic effectiveness and safety of the design. Besides the aerodynamic and structural design, the SARISTU project team also developed shape sensing systems based on Fiber Bragg Grating sensors [18], which have also been used by [PERSON] and [PERSON] [19] as well as [PERSON] [20]. Additionally, load monitoring systems employing optical fibres and strain gauges have been developed within SARISTU [21]. These technologies help to verify that the MLE is operating within the operational window. TU Delft has also been working on the development of a morphing leading edge within the \"Green Regional Aircraft\" platform of the European Project \"Clean Sky\". The approach followed by TU Delft foresees a deformable aluminium skin, which is actuated by a Linak LA23 series linear actuator [22]. It was demonstrated that the system is capable of reaching the target shapes with sufficient accuracy. [PERSON] et al. [23] developed a glass fibre reinforced plastics (GFRP) skin MLE, which is actuated by one harmonic drive rotational actuator per kinematic rib. Whilst the system showed to work satisfactorily, the authors commented that one of the big future challenges would be to reduce the structural mass of the system. An alternative approach to classical actuation systems is the use of shape memory alloys (SMA) for actuation, as successfully demonstrated by [PERSON] [24]. Fraunhofer has also investigated efficient aviation structures within the \"Green Regional Aircraft\" platform of the European Project \"Clean Sky\". In this context, Fraunhofer LBF developed, manufactured, and tested a 1:1 scale smart morphing leading edge demonstrator. It was realised as a full-scale morphing leading edge of 3 m span for ground demonstration. The setup was also validated in a climate wind tunnel under icing conditions. Besides, the electromechanical morphing actuation system and additional technologies were integrated in the demonstrator like optical fibre Bragg grating sensors, for shape reconstruction and strain measurement as well as an ice protection system based on carbon nanotubes. Figure 1 shows the leading-edge demonstrator in the climate wind tunnel [25]. Improvement of aerodynamic properties without deterioration of acoustic properties can be achieved with adaptive and gapless high-lift devices. However, this kind of device is not established in series production aircrafts, because of the complex requirements regarding this sort of technology. They must have enough stiffness to carry the aerodynamic loads as well as the flexibility to reach the different desired aerofoils for the wing [26]. Of course, the leading edge (LE) design in these cases has to avoid a gap in the connection with the wing. [PERSON] et al. [27] have demonstrated that the development of a morphing leading edge with relevance for the aeronautical industry is a very complex and thus challenging task covering several, sometimes rivalling, disciplines, and design objectives. Some of the main aspects to be considered during the development of a morphing leading edge are summarized below:  
* Aerodynamic performance;
* deformation capability of the skin material;
* structural integrity including fatigue and impact loading;
* actuation concept;
* low structural weight;
* mounting concept. Whilst there have been many efforts to address individual aspects of a morphing leading-edge design, only a few works have addressed the full picture. In these cases, the skins were either made from aluminium [5; 23] or GFRP [17; 27].