## 3 Overall Design of Bionic Multi-Section Variable-Sweep Wing UAV
### Determination of Design Parameters of Targeted Morphing UAV  
The high-aspect-ratio wing UAVs in active service are mostly in the range of medium and low subsonic speeds, with poor maneuverability, but good endurance performance [39; 40]. The MQ-9 Reaper has a long range, long endurance, and large releasable payload-carrying capacity. It is the integrated UAV system with the largest amount of equipment and is the most widely used in the world today [41; 42; 43]. Taking MQ-9 as the design reference,  
Figure 2: Lateral/directional augmentation system. The body-axis roll rate is fed back to the ailerons and sweep angle to modify the roll subsidence modal, and yaw rate is fed back to the rudder on the V-tail to modify the Dutch roll mode. the UAV designed in this study adopts a conventional layout. The fuselage structure is slender and approximately cylindrical. The head is hemispherical, with built-in guidance, control equipment, and a mission load. The antenna is placed under the nose. The high-aspect-ratio multi-section variable-sweep wing is located in the middle of the fuselage. The wing can be divided into the following three sections: the weapon, and the inner and outer wings. The weapon section has underwing pylons. The centroid self-trim compensation for the configuration change in the UAV is realized by the reverse coordination deformation of the inner and outer wing sections. The trapezoidal V-tails are located at the rear of the fuselage with a tail fin. The lower fuselage has a retractable front three-point landing gear with external underwing pylons, and the main landing gear on either side of the centroid, as shown in Figure 3.  
Based on the above analysis and referring to the flight conditions of MQ-9, the flight performance parameters of the multi-section variable-sweep wing UAV designed in this study are determined as follows:  
1. Cruising Mach number: Ma = 0.3, maximum Mach number: Ma = 0.6;
2. Cruising altitude: H = 9000 m;
3. In cruise flight, the maximum lift/drag ratio of the wing: \(L/D>20\). A shearing variable-sweep wing is chosen for the targeted morphing UAV. The wing adaptively changes the sweep angle if the flight state needs to be changed. The wing profile at each spanwise position is translated linearly in the flow direction, and the closer to the wingtip, the greater the translation. The wing tip is along the flow direction, and the airfoil on the windward side remains unchanged during the morphing process, which has little influence on the structure of the turbulence field [44, 45]. Owing to the large mass of the weapon section, the change in its sweep angle has a significant influence on the stability of the UAV. Therefore, the sweep angle of the weapon section remains fixed during the wing deformation process. Based on the above considerations, the design parameters related to the multi-section wing, tail, and fuselage of the UAV in this research are determined, as shown in Table 1.  
Figure 3: Schematic diagram of the bionic multi-section variable-sweep wing UAV with a conventional layout. The wing can be divided into the following three sections: weapon wing, inner wing, and outer wing. According to the weight estimation method in the overall design stage [46], the mass and centroid positions of the major components of the targeted morphing UAV studied in this research are listed in Table 2.  
The multi-section variable-sweep wing UAV designed in this research aims to realize the centroid self-trim compensation during the morphing process by using the reverse coordination sweep angle change in the inner and outer sections. To more accurately describe the influence of sweep angle change on the wing structure distribution, and evaluate the influence of the wingspan ratio of the inner and outer sections on flight performance, the multi-section variable-sweep wing structure of the targeted morphing UAV needs to be designed before the aerodynamic calculation and stability analysis.