# Experimental Validation and Evaluation of a Coupled Twist-Camber Morphing Wing Concept
## 2 Morphing Wing Concept  
### Design Methodology  
The starting point for the implementation of the concept is the generation of a 2D airfoil morphing capability within two specified target airfoil shapes with different camber. The concept uses an open trailing edge (TE) airfoil in order to allow actuation by reduction in the distance between the upper and lower surfaces TEs. For the purpose of accomplishing camber morphing, an aero-structural optimization procedure was devised that minimized the airfoil section weight while constraining the maximum and averaged deviations from the actuated target shape with and without loading, using finite element models (FEM). The design variables describe the thickness distribution along the airfoil length that is to provide the best approximation to the target shape when actuated. Figure 1 depicts the optimization results. Further details on the 2D camber airfoil design procedure can be found in [25].  
The previous methodology was further expanded to include effects of tapper in the wing platform and non-uniform actuation along the span, therefore, allowing a wider range of attainable configurations and introducing the coupling between camber and twist as another factor in the design. This time, the 2D optimization procedure was used to determine the thickness distribution for morphing wing sections with different chords and those results were used to obtain the thickness distribution of the wing skin for a particular planform shape. A second optimization step was introduced to determine the optimum wing planform shape and the actuation along the span that maximizes performance by including both the lift to drag ratio (L/D) and wing mass in the objective function.  
The wing twist was correlated to the actuation distribution by means of a surrogate model that was updated as FEM results are available during the optimization procedure. Figure 2 presents the data flow during the coupled twist-camber morphing wing design procedure and Figure 3 depicts the FEM and the stress and deformation results for that design. Further details about the 3D coupled camber-twist morphing wing design process can be found in [26].  
Figure 4 depicts the twist-camber coupling. At the top of Figure 4, the tip airfoil was unactuated while the root section was actuated and its camber is increased. As a result, the tip of the airfoil twists down by a visible amount. At the bottom of Figure 4, the root was unactuated while the tip was actuated. The outcome was an increase in the camber of the tip airfoil while the twist was left virtually unaltered. In the middle of Figure 4, the tip  
Figure 1: Optimization results (reproduced from [25]). (**a**) Thickness distribution; (**b**) aerodynamic loading; (**c**) unactuated unloaded; (**d**) unactuated loaded; (**e**) actuated unloaded; (**f**) actuated loaded.  
airfoil is shown when the wing was completely unactuated as a reference for the other two tip airfoil positions.  
Figure 3: Planform detail of the FEM (up); actuation stress intensity in design conditions (down left) and detail of the tip airfoil twist compared to the unactuated position (down right) (reproduced from [26]).  
Figure 2: Data flow for calculations during the actuation distribution optimization procedure. Data generation for objective function and constraints calculation (up); surrogate twist and FEM twist results comparison and surrogate model update procedure (down) (reproduced from [26]).  
The concept offers significant geometrical changes and, therefore, the potential to control the lift distribution that could be used for objectives as roll control capability, drag reduction, and load alleviation.  
Several challenges must be overcome before the successful exploitation of the concept is realized. Proper manufacturing, structural soundness, mass reduction, actuation energy minimization, and morphing strategy determination are some of those challenges which are addressed next.