Drivetrain Influence on the Lead-Lag Motion of Helicopter Rotors

Kurzfassung

Simulations of helicopter rotor dynamics typically only model the rotor, and assume that the rotational hub speed is undisturbed (baseline model). The presented simulation study drops this assumption. The structural model is extended by the drivetrain to study its influence on the rotor dynamics (rotor-drivetrain system). Comparisons of the rotor-drivetrain system's mode shapes and eigenfrequencies with those of the baseline model show how the drivetrain modifies the collective lead-lag modes. The effects of the drivetrain inertia and stiffness are identified and distinguished. Aeromechanic simulations of the rotor-drivetrain system reveal considerable changes in the blade passage frequency harmonics of the lead-lag loads compared to the baseline model. Since the modified eigenfrequency of the second collective lead-lag mode is near the blade passage frequency, this mode is responsible for the drivetrain's influence on the lead-lag loads in steady flight. It is investigated whether reduced drivetrain models are suitable for predicting this influence. Finally, it is shown that the inclusion of the drivetrain in the structural model improves the agreement between simulated lead-lag loads and measurements from a wind tunnel test.