The helicopter is an essential and unique means of transport nowadays and needs to hover in space for considerable amount of time. During hovering flight, the rotor blades continuously bend and twist causing an increased vibration level that affects the structural integrity of the rotor blade leading to ultimate blade failure. In order to predict the safe allowable vibration level of the helicopter rotor blade, it is important to properly estimate and monitor the vibration frequencies. Therefore, the mathematical model of a realistic helicopter rotor blade composed of composite material, is developed to estimate the characteristics of free and forced bending-torsion coupled vibration. The cross-sectional properties of the blade are calculated at first and are then included in the governing equations to solve the mathematical model. The natural frequencies and mode shapes of the composite helicopter rotor blade are evaluated for both the nonrotating and rotating cases. The time-varying bending and torsional deflections at the helicopter rotor blade tip are estimated with suitable initial conditions. The validation of the model is carried out by comparing the analytical frequencies with those obtained by the finite element model.

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