## 6 Results and Discussion  
As described in the previous sections, aerodynamic analysis and optimization were conducted on the VSMTW for the UAS-S4 under different flight conditions [50]. Thus, their results were then integrated into the optimization problem. This optimization problem considered the parameters that characterized a structure's overall performance. All these parameters were considered as either optimization objectives or constraints. Skin thickness and other wing components are known as sizing and topology variables, respectively. Sizing optimization (SO) of the wing skin for both segments was performed by adding the design constraints to the structural stiffness. A very small number of optimization iterations were used to converge rapidly towards the optimal solution by obtaining a highly efficient skin thickness, as shown in Figure 13.  
An initial wing skin thickness was chosen to be 2 mm for both wing segments. The FEM evaluations of a fixed and a moving wing skin are shown in Figure 15. This optimization relies on an FEM static analysis under extreme flight conditions, and it creates stress and deformation. The maximum stress value of the wing two segments skin was restricted to 200 MPa for the highest efficiency in order to withstand the aerodynamic loading acting on its  
Figure 14: Sizing optimization (SO) results for (**A**) fixed wing and (**B**) moving wing. Figure 13: Convergence graph of the objective function for (**A**) fixed wing skin and (**B**) moving wing skin. Figure 15: FEM results for fixed and moving wing segments: (**A**) fixed wing, and (**B**) moving wing, obtained using the sizing optimization problem. This component simulation-based TO approach guides detailed structural design and provides an alternative way to reduce wing spars' structural weight. Furthermore, Table 5 shows that the proposed component simulation-based TO approach can be an efficient, as well as logical design technique for the continuum design of wing components with high efficacy and reliability. The same procedures applied to the wing spars were chosen for the wing ribs as well. An optimization approach based on the Finite Element Model (FEM) was implemented for each rib, depending on its calculated loading. The material density of each element was defined as a design variable. Two analysis responses expressed in terms of structural compliance and volume fraction were identified, in which the volume fraction was classified as a constraint, and the compliance was defined as an objective function. The typical setup of the TO led to compliance minimization by using the volume fraction parameter as a constraint; the converged solution was obtained using an iterative process, as illustrated in Figure 20.  
Figure 21 depicts the material density obtained by TO for the wing ribs (for simplicity, Figure 21 shows ribs 1 and 2 for the fixed wing, and ribs 1 and 6 for the moving wing). The FE models based on the TO process for the selected ribs shown in Figures 22 and 23 demonstrate that an important weight reduction was obtained without affecting the components stiffnesses. Table 6 displays the VSMTW rib TO results obtained using their various starting values based on the aerodynamic loading distribution. The comparison of the weight values of ribs before and after optimization reveals that their weights were substantially reduced following the calculated loads acting on the rib. The maximum stresses and displacements of all ribs were very small; thus, the optimized ribs satisfied the strength and stiffness requirements. The seventh rib of both the fixed and moving wings models were excluded from the optimization process, as these wings must be solid without hollows.