## 3 Overall Design of Bionic Multi-Section Variable-Sweep Wing UAV
### Influence Analysis of Static Stability  
Static stability is mainly related to the aerodynamic layout of an aircraft. After the overall parameters are determined, some factors related to dynamic stability are still unclear. Therefore, the static stability is initially used to measure the stability of the aircraft. If the sweep angles of the inner and outer sections change synchronously, the multi-section variable-sweep wing is transformed into a traditional single-section variable-sweep wing. Table 5 lists the longitudinal static stability margins of the single-section wing UAV under different sweep angles. This research also considers the situation in which the wing installation position moves 0.1 m backwards, which can simulate the initial state of the single-section wing with different sweep angles, to a certain extent. As shown in Table 5, the change in the sweep angle of the traditional single-section wing has a significant influence on the longitudinal static stability margin of the high-aspect-ratio wing aircraft. In the absence of other measures, it is not suitable for this type of aircraft to cause a large change in the sweep angle. However, this problem can be solved by the centroid self-trim compensation of a multi-section variable-sweep wing. According to the coordinated sweep angle change in the inner and outer sections of the pre-selected models, under the morphing mode of the centroid self-trim compensation, the variation in the longitudinal static stability margin of the UAV with the sweep angle change in the outer section corresponding to the configuration can be obtained, as shown in Figure 7. As can be observed from Figure 7, when the wingspan of the inner section is relatively small, the variation in \(\Lambda_{\text{in}}\), caused by the change in \(\Lambda_{\text{out}}\), is relatively large. In the coordinate sweep angle change process of the wing sections, the aerodynamic center moves forward gradually, which causes the static stability margin of the aircraft to decrease with the increase in \(\Lambda_{\text{out}}\). As the proportion of the wingspan of the inner section of the pre-selected models increases, the variation in \(\Lambda_{\text{in}}\), caused by \(\Lambda_{\text{out}}\), decreases, and the forward movement of the aerodynamic center gradually decreases, so the decreasing speed of the static stability margin gradually decreases. With a further increase in the wingspan proportion of the inner section, the backward movement of the aerodynamic center, caused by the increase in \(\Lambda_{\text{out}}\), is greater than the forward movement of the aerodynamic center, caused by the decrease in \(\Lambda_{\text{in}}\). The longitudinal static stability margin decreases with the increase in \(\Lambda_{\text{out}}\), and the change rate of the static stability margin shows a gradually increasing trend with the increase in \(\Lambda_{\text{out}}\). In addition, it can be observed that when the UAV does not have releasable payload, the mass of the wing is reduced and the centroid moves forward. Therefore, the longitudinal static stability margin under this condition is greater than that when the UAV has a releasable payload. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sweep** & **Weapon** & **No Weapon** & **Releasable-** & **Without** \\
**Angle/\({}^{\circ}\)** & **Mounted** & **Mounted** & **Payload + Wing** & **Releasable-Payload +** \\
20 & \(-\)5.43\% & \(-\)7.96\% & \(-\)0.13\% & \(-\)2.97\% \\
5 & \(-\)14.50\% & \(-\)16.43\% & \(-\)9.20\% & \(-\)11.44\% \\
10 & \(-\)23.51\% & \(-\)24.86\% & \(-\)18.22\% & \(-\)19.87\% \\
15 & \(-\)32.41\% & \(-\)33.18\% & \(-\)27.11\% & \(-\)28.19\% \\
20 & \(-\)41.12\% & \(-\)41.35\% & \(-\)35.83\% & \(-\)36.36\% \\
25 & \(-\)49.61\% & \(-\)49.31\% & \(-\)44.31\% & \(-\)44.33\% \\
30 & \(-\)57.80\% & \(-\)57.03\% & \(-\)52.51\% & \(-\)52.04\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The value of longitudinal static stability margin at different sweep angles of a single-section wing UAV.