# Design and Control of an Ultra-Low-Cost Logistic Delivery Fixed-Wing UAV
## 2 Overall UAV Design
### Wing Design
#### 2.4.3 Analysis of Wing Aerodynamics  
The aerodynamic analysis of the wing can enhance aircraft performance [47]. Initially, this study conducts a preliminary mesh division of the wing model, considering practical engineering applications, and adopts tetrahedral meshing. By ensuring reasonable computational accuracy, this study reduces the number of meshes, ultimately setting the mesh size to approximately 15 mm. The results are displayed in Figure 5.  
Upon completing the preprocessing, this study proceeds to a solution using Fluent, deciding to position the wing within a flow field having an inlet and outlet area of 0.3083 square meters for computations. Taking into account the designated cruising speed of the flight platform and the typical wind speeds in the flight test area, the inlet airspeed is set at 19 m/s. When Fluent is used for iteration, the convergence curve gradually flattens out and approaches the steady state after 100 iterations. Meanwhile, to save computing resources, 100 is selected as the number of iterations. Although convergence to 0.001 was not achieved, it is close to the steady state and can be ignored. The computational outcomes are illustrated in Figure 6. The black area represents the core part of the wing, an internal structure or high-density mesh area for more accurate calculations and analysis. The blue area represents the meshing of the wing surface, which is a tetrahedral mesh. This part of the mesh is relatively sparse and is mainly used for large-scale hydrodynamic calculations to ensure the accuracy of the calculation while reducing the number of meshes. Figure 5: NACA 4412 airfoil establishes the meshing of the wing model. As illustrated in the figure, with the increasing continuity of the iteration numbers, the velocity in various directions and other parameters tend to stabilize. This study also establishes how the wing's lift, lift coefficient, drag, and drag coefficient change as the number of iterations increases. As depicted in Figure 7, the top left shows the wing's lift curve, the top right displays the wing's lift coefficient curve, the bottom left illustrates the wing's drag curve, and the bottom right presents the wing's drag coefficient curve. Based on the computational results, it can be concluded that the wing generates relatively high lift and incurs low drag at the planned cruising speed. This indicates that the initially chosen airfoil and determined parameters, such as the chord length, wingspan, and taper ratio, are well suited to the requirements of our flight. Figure 6: Flow field analysis of NACA 4412 airfoil to establish a wing model. Figure 7: NACA 4412 airfoil model, wing model, lift and lift coefficient, and drag and drag coefficient curves. After completing the iteration calculations, this study proceeds with post-processing of the wing's flow field simulation, as shown in Figure 8. This process also yields several noteworthy analytical results, as discussed below. The figure illustrates the static pressure distribution on the wing surface (top left and top right for the upper/lower surfaces). The pressure on the upper and lower surfaces of the wing is relatively low and evenly distributed. This analysis suggests that during the manufacturing of the leading edge, attention should be paid to enhance its stiffness, and the rational distribution of wing ribs in terms of quantity and material should be considered. Additionally, applying carbon patches near the wingtips may prevent bending at the wing edges. The bottom-left and bottom-right images show the local and overall pressure distributions, respectively. From these images, it is determined that the actual aerodynamic pressure effects in the external flow field are essentially consistent with the static pressure analysis results. As shown in Figure 9, the wing achieves its maximum lift-to-drag ratio at an angle of attack of 2\({}^{\circ}\), with CL/Cd = 17.38. The lift generated at this point is substantial, fully satisfying the requirements for the stable flight of the platform.