Modeling and analysis of critical speed for tail drive shaft of helicopter considering space maneuvering flight

The universal dynamical model of tail drive shaft of helicopter considering maneuvering flight was established. The reasons for maneuvering flight affecting the critical speed of tail drive shaft of helicopter were analyzed. It is pointed out that only a portion of the rotational motion components can affect the critical speed of tail drive shaft, including: pitching angular velocity, yawing angular velocity, rolling angular velocity and angular acceleration. The influence law of the pitching angular velocity, yawing angular velocity and rolling angular velocity on the first three order critical speeds of drive shaft was discussed through a numerical example. The results reveal that the pitching angular velocity reduces the critical speeds of tail drive shaft, but only has a greater impact on the first order critical speed of tail drive shaft in a backward whirl, and the yawing angular velocity has the same influence. The positive rolling angular velocity increases the critical speed of tail drive shaft in a forward whirl, and reduces the critical speed of tail drive shaft in a backward whirl; but in the case of negative roll maneuver, there is a reverse case compared with the positive roll maneuver that the backward rolling angular velocity reduces the critical speeds of tail drive shaft in a forward whirl and increases the critical speeds of shaft in a backward whirl, before the boundary of the rolling angular velocity equals to a special value. The rolling angular velocities corresponding to the boundary of variation curve of the first, second and third critical speeds are respectively 1.86, 27.41 and 124.5rad/s.