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A vibration load computing method for a coaxial rigid rotor was developed and applied to analyzing its vibration load in rotor interference. The structural dynamics model based on the medium-size deformation beam theory and the double-rotor aerodynamics model that contains unsteady free wake were jointly used to develop the coaxial rigid rotor's vibration load computing method. The wind tunnel test data of the XH-59A helicopter was used to validate this computing method. The vibration load of a rotor hub was analyzed in detail. The results show that the 3 Ω  harmonic wave amplitude of the vertical force  F   z   of the rotor hub and that of its pitch moment  M   y   decrease in high pitch angle, but the 3 Ω  harmonic wave amplitude of the roll moment  M   x   of the rotor hub obviously increases. The vibration load of the rotor hub increases with the decrease of the range of the coaxial rigid rotor; the roll moment and pitch moment of the rotor hub are sensitive to phase angle. The results also show that the increase of the  3Ω  harmonic wave amplitude of the roll moment  M   x   is greater than the decrease of that of the roll moment  M   y   at the phase angle of 30° and that the level of vibration load of the rotor hub is minimum at the phase angle of 0° in forward flight.

Vibration loads analysis of coaxial rigid rotor in rotor interaction