Abstract: Main resonance amplitude of a shaft is concerned with the strength calculation. Based on bending motion equation of a tilting fiber composite helicopter drive shaft with two supports obtained under non-inertia movement coordinate system by theorem of the motion of center of mass and the method of Galerkin, an approximate steady-state solution of the main resonance is obtained by method of multiple scales. The maxi-mum amplitude, amplitude jump characteristic and so on are analyzed. Conclusions of that the motion stability of a fiber composite drive shaft is better and the main resonance amplitude is smaller than that of a drive shaft of steel or aluminum are produced. It is presented that the amplitude jump of a shaft is decreased or removed, and the motion stability is obtained by increasing damping. In condition of increasing damping in the place of larger deflection of a shaft, the amplitude of main resonance can be decreased, effect of the damping is fully brought into play and weight of the shaft is optimized.

Key words: Main resonance, Amplitude, Composite drive shaft, Frequency, Helicopter