## 7 Conclusions  
In this study, a multi-section variable-sweep wing unmanned aerial vehicle (UAV) design scheme is proposed, which realizes the centroid self-trim compensation through the reverse cooperative sweep angle change in the inner and outer wing sections. While improving the aerodynamic performance, stability, and maneuvering, reducing the influence of the movement of the centroid and aerodynamic center and the change in the moment of inertia of the high-aspect-ratio morphing UAV. Based on the overall design results, and considering the centroid movement caused by the wing structure deformation, the performance evaluation of the targeted bionic morphing UAV under different working conditions is carried out from the following two aspects: aerodynamic characteristics analysis, and stability analysis and augmentation adjustment. The influences of the Mach number, angle of attack, sweep angle, and wingspan ratio of the inner and outer sections are discussed in detail.  
Based on the results of the calculation and analysis, the following main conclusions can be drawn:  
1. The influence of sweep angle change on the longitudinal static stability margin of the high-aspect-ratio UAV can be greatly improved by the coordinate deformation mode of a multi-section variable-sweep wing. Reducing the mass of components near the centroid, for example, with an increase in fuel consumption, the static stability margin of the multi-section variable-sweep wing UAV designed in this research is gradually increased.  
The analysis results show that when the sweep angle of the outer section, corresponding to the configuration, is in the range of 0\({}^{\circ}\)-10\({}^{\circ}\), the aerodynamic force of the UAV changes a little. Among them, the slope difference of the lift line, corresponding to Model3 and Model5, is small. The lift/drag ratios, corresponding to Model4 and Model5, at different angles of attack have a small difference.
3. The longitudinal pitch trimming results of different configurations of the pre-selected models, under steady and flat flight conditions, show that properly increasing the wingspan proportion of the inner section can reduce the trim resistance of tail and engine thrust, and, at the same time, increase the range and duration.
4. The configuration change has little effect on the long-period modal and roll damping under a given working condition. Under the adjustment of the stability augmentation system, the configuration with a smaller sweep angle of the outer section (\(\Lambda_{\text{out}}=0\)-10\({}^{\circ}\)) has better longitudinal stability. Increasing the sweep angle of the outer section, corresponding to the configuration, can improve the lateral/directional stability of the UAV. Considering the influence of the wingspan ratio of the inner and outer sections on the efficiency of the control surface, the pre-selected model of Model3 to Model4 has better dynamic stability characteristics. The damping ratio and oscillation frequency are all in the optimal or suboptimal state, and the range of the value change is small.  
Based on the analysis results of the aerodynamic characteristics, dynamic stability, and augmentation adjustment of the pre-selected models under the centroid self-trim compensation morphing mode, Model3 has better longitudinal stability and Model4 has better lateral/directional stability. The corresponding wingspan ratio of the inner and outer sections ranges from 1.41 to 1.78.  
All the authors conceived the idea and developed the method. [PERSON] contributed to the formulation of methodology and original draft. [PERSON] contributed to the data curation and supervision. [PERSON] and [PERSON] contributed to the editing. All authors have read and agreed to the published version of the manuscript.  
This study was supported by Research Funds for Interdisciplinary Subject of Northwestern Polytechnical University (NWPU). No. 19 SH0304017.  
Not applicable.  
The authors declare no conflict of interest.