[Objective] Full-model flutter test is crucial for the aeroelastic design and verification of aircraft. One of the key challenges of the test is ensuring that the model's suspension design meets the natural frequency and motion adjustment range requirements. This study proposes a cable suspension system with four cables/three springs for the full-model flutter wind tunnel test under transonic conditions to address the current research gap in verifying suspension systems other than the existing two-cable or three-cable suspension mechanisms. The designed four-cable suspension method is expected to offer distinct advantages for transonic wind tunnel tests, such as suitability for the static unstable aircraft models and their intelligent controls. [Method] The stability and kinematic characteristics of the proposed four-cable suspension system are analyzed and validated through a series of methods. First, the stiffness expression of the mechanism is established based on the differential kinematics and used for deriving the stability criterion in light of the principle of virtual work by considering the system dynamic equations and the aerodynamic model of the aircraft. Subsequently, the eigenvalues of the stiffness and aerodynamic derivatives matrix are determined, and the pose variations of the aircraft model subjected to aerodynamic forces are numerically investigated to demonstrate the suitability of the suspension system for static unstable aircraft models. Additionally, the system impact response and the factors influencing its frequency are studied, proving that the four-cable suspension system meets the natural frequency requirements of the full-model flutter wind tunnel test. Numerical calculations and Adams software simulations are performed to verify that the four-cable suspension system can achieve effective adjustment of the aircraft model pose by controlling the cable length and manipulating the aileron and rudder surfaces. Finally, a simple prototype is built for modal frequency experiments to verify the feasibility of the proposed theoretical method. [Results] The simulation and numerical calculation results demonstrated that the proposed four-cable suspension method was a viable solution for the full-model flutter wind tunnel test under transonic conditions, providing five degrees of freedom to the model. The high-speed incoming flow dynamic response results revealed that the four-cable suspension system exhibited outstanding stability, with the largest magnitude observed in the centroid displacement along the sideslip direction of the aircraft model, which was less than 0.04 m, while the rotational angle amplitudes did not exceed 15.0°. The initial pre-tension force could be adjusted to ensure that the cable continuously remained in tension. Furthermore, the natural frequencies of the mechanism in the three rotation directions were approximately 0.8~1.0 Hz, and the natural frequencies in the sideslip and heave directions were within 3.0 Hz. The study also examined the influence of different traction positions and spring numbers on the natural frequency and revealed that the attitude angle adjustment range of the four-cable suspension system with three springs could meet the requirements of the test through cable length adjustment and rudder surface control. The simple prototype frequency experiment demonstrated that the roll, pitch, and yaw direction modal frequencies were less than 3.0 Hz. [Conclusion] This study demonstrates the feasibility of using the proposed four-cable suspension system for transonic full-model flutter wind tunnel testing through numerical calculations, software simulations, and prototype experiments, providing a approach for the model suspension technology in transonic full-model flutter test. © 2023 Press of Tsinghua University. All rights reserved.
