# Design and Verification of a Large-Scaled Flapping-Wing Aircraft Named \"Cloud Owl\"
## Materials and Methods
### Wing Design
It is an essential factor in determining how well flapping-wing micro air vehicles  
Figure 4: Schematic of flapping wing reference area. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **K** & **\(p\)** & **Estimated Results** \\ \hline Wing span & 1.237 & 0.368 & 1.3624 m \\ Wing area & 0.164 & 0.667 & 0.1954 m\({}^{2}\) \\ Flapping frequency & 3.991 & \(-\)0.202 & 3.785 Hz \\ Minimum Power Speed & 8.704 & 0.158 & 9.0724 m/s \\ Maximum Range Speed & 11.591 & 0.158 & 12.0816 m/s \\ Flight Power & 45.21 & 0.728 & 54.7249 W \\ Maximum power & 84.388 & 0.734 & 102.14 W \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of aircraft parameters based on scale-rate estimation. perform in the stall, climb, take-off, and landing phases, as well as during hovering. The tangential wing load is an important parameter to characterize the size and flapping range, acceleration and deceleration performance, and residual power of flapping-wing micro air vehicles. The parameter Q thus represents the dual capacity of the flapping-wing vehicle in the lift direction and thrust direction, which can be called an equivalent wing load due to the use of the equivalent wing area. In the results of the scale law calculation, the flapping wingspan and the flapping wing area are small, and the equivalent wing load is large, which is not conducive to improving the flight time, so the flapping wing area should be appropriately increased to reduce the wing load. The initial half of the wingspan is 0.8 m.  
The design procedure goes as follows: the wing area is estimated using the dynamic equation of the cruise state, the flight speed is temporarily set to 8 m/s, and the initial parameters of the wing can be determined. Next, the wing shape and flapping parameters were optimized using the CFD method, and the best flapping parameters were ultimately determined by combining this with wind tunnel testing. The design procedure is displayed in Figure 5.  
The investigation of transient simulations is conducted by resolving the three-dimensional Navier-Sir George Stokes 1 st Bar-one equations and utilizing the computational fluid dynamics program Fluent [18; 19; 20; 21]. Based on an overlapping grid approach, the motion of a flapping wing is reproduced. The backdrop grid and component grid that make up the overlapped grid are appropriate for simulating large-scale motion. The backdrop grid does not move during dynamic movement; instead, the entire component grid moves as a rigid body. By adjusting the function's user-defined coordinate transformation form in order to vary the wing-flapping motion. The mesh around the wing in the deformable zone is updated using the dynamic mesh technique as the wing moves. The calculation's airfoil model mimics the actual flapping wing's airfoil and plane form. The wing is taken to be a rigid body whose only motion is rotation about the \(x\)-axis in order to streamline the model and speed up numerical convergence. Using user-defined functions (UDF), wing trajectories with rotation (i.e., flapping amplitude and frequency) are implemented. The impact of wing morphology parameters can be investigated via CFD calculations and wind tunnel tests. Figure 5: The process of flapping wing design. The base airfoil, Eppler 378, has the geometric characteristics of the cross section of a bird's wing, which is displayed in Figure 6. It has good aerodynamic performance, which is obviously high lift with minimal resistance. The design factors for flapping wings are as follows: wing forms; six or seven wing ribs; polyester or linen film; additional airfoil or not. According to the four design variables, thirteen different flapping wings were created and tested in a wind tunnel. Literature [22] can be consulted to learn more about the method and outcomes of CFD calculations and wind tunnel tests.