## 4 Aerodynamic Analysis of UAV Based on the Centroid Self-Trim Deformation
### Multivariable Influence Analysis on Aerodynamic Characteristics of UAV  
According to the flight conditions of the multi-section variable-sweep wing UAV, the aerodynamic characteristics of the four pre-selected models are analyzed within the following range of angle of attack: AOA = 0\(\text{--}\)10\({}^{\circ}\), and the following Mach number: Ma = 0.3\(\text{--}\)0.6. Figure 8 shows the variation in the lift coefficient \(C_{L}\) and drag coefficient \(C_{D}\) of Model2 at different Mach numbers, with the sweep angle change in the outer section \(\Lambda\)out under the coordinate morphing mode when AOA = 0\({}^{\circ}\). The variations in the lift and drag coefficients at other angles of attack are similar to this condition. The following conclusions are drawn:  
Figure 7: The variation in the longitudinal static stability margin of the multi-section variable-sweep UAV with the sweep angle of the outer section based on the centroid self-trim compensation. (**a**) Releasable payload, (**b**) without releasable payload. As the \(\Lambda\)out corresponding to the configuration increases, \(C_{L}\) and \(C_{D}\) both show the law of change that first increases slightly and then gradually decreases. When the sweep angle of the outer section varies in the range of 0-10\({}^{\circ}\), the aerodynamic changes generated by the inner and outer wing sections in the coordinated deformation mode are similar. The total aerodynamic force of the wing changes slightly. 2. For a given wing configuration, \(C_{D}\) first decreases and then increases with an increase in the flight speed. During the coordinate deformation process, the minimum drag coefficient \(C_{D\min}\) of the UAV corresponds to the configuration \(\Lambda_{\text{in}}=0^{\circ}\) and \(\Lambda_{\text{out}}=30^{\circ}\). Figure 9 shows the variation in the lift line slope \(C_{L\alpha}\) of the pre-selected models, with the sweep angle of the outer section \(\Lambda_{\text{out}}\) corresponding to the configuration when the angle of attack is AOA = 0\({}^{\circ}\) and the Mach number is Ma = 0.3. Similar laws can be obtained for other angles of attack and Mach numbers. The following conclusions are drawn:  
1. With an increase in the wingspan proportion of the inner section, the slope of the lift line gradually increases. The slope of the lift line of Model2 is significantly smaller than that of the other three models. When the sweep angle of the outer section, corresponding to the configuration, changes within the range of 0-10\({}^{\circ}\), the numerical difference in the slope of the lift line of Model3-Model5 is small;
2. When the wingspan proportion of the inner section is small, the slope of the lift line increases first and then decreases with an increase in the \(\Lambda_{\text{out}}\) corresponding to the configuration. This shows that when \(\Lambda_{\text{out}}\) is small, the lift decrease caused by the increase in \(\Lambda_{\text{out}}\) is smaller than the lift increase caused by the decrease in \(\Lambda_{\text{in}}\). Overall, the total lift shows a slightly increasing trend. When \(\Lambda_{\text{out}}\) is large, the lift loss caused by the sweep angle change in the outer section is not sufficient to be compensated by the lift generated by the sweep angle change in the inner section, so that the slope of the lift line decreases;
3. For a model with a large wingspan proportion of the inner section, the change in \(\Lambda_{\text{in}}\), caused by the change in \(\Lambda_{\text{out}}\), is relatively small. The lift decrease in the outer wing section is greater than the increase in the inner wing section. The slope of the lift line decreases monotonically, and the decrease in speed gradually increases. Figure 8: Aerodynamic coefficient changes with the configuration of Model2 at different Mach numbers with the sweep angle change in outer section under the coordinate morphing mode when AOA = 0\({}^{\circ}\). (**a**) Lift coefficient, (**b**) drag coefficient.