Analysis on natural characteristics of four-stage main transmission system in three-engine helicopter

The vibration model of four-stage main transmission system in helicopter was established through lumped mass method. In the model, many factors, including time-varying meshing stiffness and torsional stiffness of gear shaft were considered. The differential equation of the system was solved via Fourier method, and the influence of the torsional stiffness of shafts on the first five orders of the system’s natural frequency was studied. Some theoretical results were summarized as guidelines for further research and design of four-stage deceleration helicopter at last.