Dynamics Analysis Of One Light Helicopter’s Tail Transmission

As an important part of the aircraft, helicopter has a lot of advantages, such as its flexible and convenient, vertical take-off and landing, hovering in the air, etc. So that it gets very wide range of applications in the national economy and national defense construction. Transmission system is one of the three key moving parts of the helicopter, tail transmission is an important subsystem of helicopter transmission system, if the tail drive system has design defects, when it works at a high-speed, strong vibrations will be caused, then the mechanical parts should be damaged, this makes a serious threat to the flight safety of the helicopter. This paper analyzed the dynamics of a light helicopter’s tail transmission, providing the necessary theoretical basis for improving the helicopter dynamic performance and the optimization of the helicopter transmission structure.Firstly this paper used finite element analysis method to analyze the dynamic characteristics of the helicopter tail transmission system based on the elastic vibration theory. PRO/E software was used to establish three-dimensional solid model of the main components of tail transmission system, and the equivalent kinetic models of helicopter tail drive shaft, bearings, gears and tail rotor were established. The finite element model of transmission system was established in the use of APDL parametric modeling language of ANSYS software. The paper analyzed the bending vibration mode of the horizontal axis of the tail drive system, it analyzed the effect of the parameters on the bending mode, such as the number、quality and the stiffness of bearing supporting. The paper the analyzed the impact of torque and thrust of the tail rotor on the modal of transmission system.Finally, the critical speed of horizontal shaft section was obtained through mapping the Campbell diagram. Then, the paper carried out the bending vibration harmonic analysis of tail rotor shaft and the torsional vibration harmonic analysis of the tail transmission, and obtained the frequency-response curves of the unbalanced loads.Through this study, the paper gained the conclusion that the natural frequency of the tail transmission can be changed with the change of the structure and parameters, The natural frequency can be significantly improved by reducing the bearing span and he increasing of bearing stiffness. When bearing’s stiffness is much greater than the bending stiffness of the shaft, it can be considered as a rigid supporting; The reducing of quality can increase the natural frequency of the system, particularly, the increasing of quality at the position at the maximum value of a vibration mode can effectively increase the natural frequency. Under the action of torque and the tail rotor’s thrust, the natural frequency of tail transmission can be decreased in a lesser extent. The working status of light helicopter’s tail drive system is subcritical speed. Under the action of steady unbalanced loads, the tail transmission system generates a corresponding imbalance response, and when the frequency of the excitation loads close to the natural frequency of the system, it reach the peaking value.