## 4 Strain Measurement and Calculation of Wings
### Finite Element Modelling  
The 3D shell cells of the wing model were discretized using Finite Element Analysis (FEA) software HyperMesh (Ansys 19.0) [7]. Unnecessary edges and lines were removed, and the model was geometrically processed into a common nodal model. The mesh used in this study consisted of S4R elements, which are four-node surface thin shell elements aimed at reducing integration and eliminating circular controls. The mesh size was 10, resulting in a total of 83,990 elements. The wing material chosen was LY12, and based on ground calibration tests, the wing components were firmly connected to the fuselage structure. The boundary conditions for virtual ground calibration testing were applied at the nodes where the wing connects to the fuselage in the finite element model. These boundary conditions were restricted to six degrees of freedom. The boundary conditions for virtual ground calibration testing were applied to all nodes connected to the wing and fuselage junction, and constrained to have six degrees of freedom, representing a fully fixed support.  
The FEM of the wing is depicted in Figure 5.  
(a) Schematic diagram of the wing finite element method (FEM): This diagram illustrates the structural analysis of the wing using the finite element method, which is a computational tool for predicting the behavior of the wing under various loading conditions. The engine loads were not directly simulated, because the engine layout of this type of Unmanned Aerial Vehicle (UAV) is within the fuselage. However, the loads were correlated with strains by extracting corresponding loads from the FE model provided by the research institute.  
(b) Arrangement of the Bending Moment Bridge: Based on the structural characteristics of the wing, the upper and lower flanges of the wing beam primarily bore the bending moments generated by the wing. Consequently, the bending moment strain gauge bridges were positioned on the upper and lower flanges of the wing beam at the section where measurements are taken. Strain gauge bridges numbered 1 and 4 were placed along the  
Figure 4: The flow chart of proposed sequence important point-based method.  
lengthwise direction of the flanges, while strain gauge bridges numbered 2 and 3 were oriented perpendicular to bridges 1 and 4, respectively.  
(c) Arrangement of the Shear Bridge: The webs and skins of the wing beam and rib primarily withstand the shear forces produced by the wing. Therefore, the shear strain gauge bridges were positioned on the neutral axis or a location close to the neutral axis of the webs and skins of the wing beam and rib. A shear full bridge, composed of four strain gauges arranged at 90-degree intervals to each other, was used to measure the shear forces. This arrangement ensures that the relative bending moment load was minimized, and it was the direction where the maximum shear stress could be most accurately measured by the strain gauges.  
(d) Arrangement of the torque bridge: The wing box of the aircraft wing is mainly subjected to the torque generated by the wing. Hence, the torque strain gauge bridges were positioned at the center of the skin of the wing box section where measurements were conducted. A torque full bridge, consisting of four strain gauges arranged at 90-degree intervals, was utilized to measure the torque. This configuration allowed for the accurate detection of the torque effects on the wing structure.