A Novel Modeling Strategy for the Dynamical Analysis of Coupled Coaxial Rotors/Auxiliary Propeller/Drive Train System

The coupled coaxial rotors/auxiliary propeller/drive train system of a compound helicopter may exhibit torsional instability. A novel modeling strategy based on the transfer matrix method is developed and used to analyze the coupled torsional system. In contrast to the finite element method, the proposed modeling strategy offers more elegant formulations of the dynamic equations for the rigid-flexible multibody system. The highlight includes the overall transfer equation that can be directly obtained according to the topology figure of the system by introducing a virtual branch element to decouple the tree topology system as a combination of the chain systems. Besides, another virtual connection element is introduced to deal with the state vector dimension mismatch problem, improving the computational efficiency by further reducing the scale of the overall transfer matrix. A new transfer matrix of a rotor blade for lead–lag motion is derived. The influences of different flight conditions on torsional vibration are highlighted. And several suggestions on torsional vibration design are concluded.