# Specific Modeling Issues on an Adaptive Winglet Skeleton
## 1 Introduction
Innovative aerodynamic design: extended laminar flow, 3D riblets, morphing winglet, morphing flap to stay in condition of maximum aerodynamic efficiency during the cruise, development of techniques for load control and alleviation (LCA system based on an innovative wing tip and morphing winglet) [17]. Adaptivity: high lift performance using an innovative leading edge (droop nose) compatible with laminarity requirements and coupled to Morphing Flap  
In line with the main targets of AIRGREEN2, specific morphing concepts have been being under investigation [1]. They will contribute to enhance the performance of the A/C, to optimize the load distribution on the wing structure and to increase the lift generation. Four different concepts have been conceived:  
1. An adaptive leading edge, able to increase its curvature, to generate the so called droop nose effect [18]. The smooth morphed geometry dramatically contributes to the lift generation capability at specific operational conditions (take-off and landing), while the absence of geometric discontinuities in clean configuration cooperates in keeping the laminar flow in cruise. The device is constituted by a compliant internal structure, moved by a spanwise torque actuator. The deformation is then transmitted to the surrounding skin, a carbon fiber laminate. 2. A multifunctional flap, relying upon an adequate number of degrees of freedom (DOFs) to change its curvature, through a finger-like kinematic architecture [19]. The role of the device is to cooperate with the adaptive leading edge to generate additional lift (change of the curvature along the entire chord in fully extracted configuration) and to enhance the aerodynamic efficiency and optimize the load distribution (deflection of the aft tabs in fully retracted configuration). 3. An adaptive wing tip, a 1 DOF aerodynamic movable surface mounted at the tip of the wing [20]. Deflected by an electromechanical actuator, its role is to cooperate with the multifunctional flap in the load control and alleviation operations. 4. An adaptive winglet, mounted alternatively to the just mentioned wing tip and constituted by a fixed structure equipped with independent movable surfaces [21,22]. The scope is to adaptively alter the load distribution along the wing span to increase the aerodynamic performance, from one side, and to alleviate the stress level, from the other side. The novelty of aforementioned devices is different for each of them. Adaptive trailing edges are very popular in literature and different architectures and concepts may be found in bibliography. The main characteristics of the one herein reported, and originally developed by the University of Napoli \"Federico II\", stands in its capability of combining up to three modalities of morphing (classical flap-like modification, tab-like movement, and artificial chord-extension), while keeping low the number of parts and therefore its complexity. The adaptive winglet developed by CIRA is almost an innovation itself, since the previous experiences on that topic mainly concern the introduction of a tab-like system, mainly vibrating at high frequencies in order to try gust effect alleviation strategies (Airbus Innovation Work, 2015), or introducing hinged wing tips for the modification of the configuration in-flight. In this case, the system is instead conceived to perform both static and dynamic functionalities along all the aircraft mission. It should be reminded that this kind of system shows the intrinsic challenge of implementing large weights at the extremity of the wing, therefore modifying intimately the aeroelastic behavior of reference aircraft. The adaptive leading edge is characterized by an internal compliant architecture that cooperates with the external structure in absorbing loads and at the same time drives the deformation, leading to the drooped nose configuration. The device jointly to the multifunctional flap action leads to a significant hyper lift generation, moving upward the lift curve of the wing and increasing the stall angle.