Effect of engine torque fluctuations under different flight conditions on the torsional vibration response of helicopter power input chain

Under varying flight conditions, helicopter turboshaft engines generate pronounced torque fluctuations that can intensify torsional vibration in the power input chain, accelerating fatigue damage of critical transmission components and threatening flight safety. A lumped-parameter coupled dynamic model of the power turbine and power input chain is developed with time-varying torque excitation. Measured torque signals from three representative flight conditions – hover, high-altitude climb and descent maneuver, and aggressive vertical maneuvers – are applied as inputs to compare torsional responses. Results show that the torque variation rate dominates vibration intensity, as rapid changes promote transient energy accumulation and inertia mismatch within the transmission system. Aggressive vertical maneuvers produce the highest variation rate and the largest torsional response; the torsional angle at the strut-type overrunning clutch is about 10.3 % higher than that in the high-altitude climb and descent maneuver and 280.0 % higher than in hover. These findings clarify the mechanism by which realistic engine torque fluctuations affect torsional vibration and provide theoretical support for the dynamic design and reliability evaluation of helicopter transmission systems.