## 1 Introduction
The aerodynamic analysis of the aircraft shows that the symmetrical sweep angle change can significantly reduce the turning radius, and the asymmetric sweep angle change can enhance the ability to resist crosswind. The dynamics equations have been established, and the coupling relationship between longitudinal and lateral/directional during the asymmetric change in sweep angle has been studied. The influence of transient variables on the mission performance has been analyzed [29; 30; 31]. [PERSON] and [PERSON] et al. [32; 33] have studied the aerodynamic performance of a UAV imitating a seagull wing. [PERSON] et al. [34] have used the unsteady vortex lattice method to establish a numerical calculation model for nonlinear and unsteady aerodynamic forces in the morphing process of a seagull wing. [PERSON] et al. [35] have proposed a numerical method for calculating the dynamic loads and energy requirements of morphing wings during the morphing process, based on the vortex lattice method. At different deformation rates, angles of attack, and Mach numbers, [PERSON], [PERSON] et al. [36] have used a numerical simulation method to analyze the unsteady aerodynamic characteristics of the UAV in the process of symmetrical sweep angle change in the outer wing section. In summary, the current research on multi-section morphing wings mainly focuses on bird-sized wings with lightweight film materials and small wingspans, so the movement of the centroid and aerodynamic center, caused by configuration changes, is not prominent. There is a lack of research on the practical application of the multi-section variable-sweep wing in the high-aspect-ratio heavy-duty UAV. In addition, the relevant studies are all focused on a UAV with a specific wingspan of the inner and outer sections. There are also few studies data on the use of reverse coordinated deformation of the inner and outer sections to achieve centroid stability during the morphing process. The influence of configuration changes on the aerodynamic characteristics and stability of heavy-duty UAVs has not been fully clarified, and there is a lack of systematic research on the coordinate trim compensation mechanism of multi-section morphing wings with a high aspect ratio. Under this morphing mode, the wingspan ratio of the inner and outer wing sections of the UAV will affect the design variables that determine the aircraft performance, such as the wingspan, aspect ratio, wing area, and sweep angle. In response to the above problems, a design scheme of a bionic multi-section variable-sweep wing UAV that utilizes the reverse coordinated sweep angle change in the inner and outer wing sections is proposed, which improves the aerodynamic performance and realizes the centroid self-trim compensation. Based on the layout characteristics of this type of aircraft, a reasonable design of the wingspan ratio of the inner and outer wing sections is explored, to reduce the impact of aerodynamic center movement and the change in the moment of inertia, and to balance the contradiction among aerodynamic performance improvement, stability, and maneuverability of the morphing aircraft. Based on the morphing principle of the centroid self-trim compensation, this study analyzes the influence of multiple factors on the aerodynamic characteristics and stability of multi-section variable-sweep wing UAVs. Based on the analysis results, this study proposes a reasonable wingspan ratio of the inner and outer sections and provides a reference for the practical application of the multi-section variable-sweep wing in a high-aspect-ratio heavy-duty UAV. This paper is organized as follows. Section 2 presents the main theories and stability augmentation systems applied in this study. In Section 3, a bionic multi-section design scheme for a variable-sweep wing UAV is proposed. Based on the distribution characteristics of the wing structure, pre-selected models of UAVs with different wingspan ratios of the inner and outer sections are constructed.