Static Structural Testing of Composite Wing Structure for Vertical Takeoff and Landing (VTOL) Unmanned Aerial Vehicles

The vertical takeoff and landing unmanned aerial vehicle (VTOL UAV) must ensure robust structural integrity and meet a 130 kg maximum takeoff weight (MTOW) requirement, as it functions as an aerial module within docking-undocking unmanned systems. To satisfy these requirements, the airframe structure of the unmanned aerial vehicle was carefully designed with appropriate load paths to ensure sufficient static margin of safety. The most reliable method to demonstrate the structural integrity of an aircraft design is to conduct static structural tests, adequately reflecting the ground and flight load conditions applied in the design. This paper presents the overall process and results of the static structural testing of the VTOL UAV. This includes the methods for determining and validating test loads, analyzing test results, and evaluating structural integrity. The wing structure, expected to support the highest loads, was chosen as the test specimen. To calculate and validate the test loads, the static structural test FEM (SST FEM) was generated. Based on the detailed design results of the airframe structure, five critical load conditions were chosen as test conditions, and test loads for each condition were defined using the SST FEM. The test loads were calculated to achieve an accuracy within 2% of the maximum VMT loads for the SST FEM, compared to the VMT design loads for the full-scale FEM. Static structural testing was conducted for all test load conditions, including limit load tests for each condition and one ultimate load test for a critical condition. From all test results, it was confirmed that no detrimental permanent deformation and catastrophic failure occurred, ensuring the structural integrity of the design. In addition, the test results measured from strain gauges were compared with the numerical results of the SST FEM to validate the finite element model and analysis methods used in the design process. The findings of this paper can serve as a reference for design criteria and structural integrity validation methods necessary for the development of VTOL UAVs of similar scales.