investigation of resonance phenomenon occurrences probability in the composite rotor blades of a helicopter

In this paper, vibrational analysis of a composite rotor blade of a Helicopter, which is required by industrial application, is carried out using Lumped Masses method to investigate probability of occurrences of resonance phenomenon. First of all, out of plane and in-plane equations of motion of rotor blade were obtained, and vibration equations of blade and boundary condition at center of rotation and root blade with and without hinges were derived. Effect of different parameter on blade natural frequency was investigated. To obtain mode shapes of blade, the Myklestad method was used, and using computer code in Matlab software and after its validation, the spoke diagram of blade vibration was represented. The results show the resonance phenomenon will not occurs at first and second modes of vibration of helicopter working condition. As the rotor speed increases, the frequencies in the out-of-plane direction increase faster than the in-plane frequencies. Also increase of rotating velocity (rpm) leads to increase of centrifugal force, thus it increases the related force for evaluation of stiffness distribution along blade. Furthermore, the maximum variation of displacement is transmitted to blade tip and the same behavior for increase of stiffness distribution appeared.