This investigation presents a model-based degradation study of a Hybrid Electric Propulsive System in parallel configuration for Urban Air Mobility. Literature studies on hybrid-electric aircraft are mainly devoted to the sizing and the management of hybrid systems and the energy flows are usually analyzed with a steady-state model applied to each flight phase while the role of hybridization in supporting the engine during transients has been only hinted at. In fact, the faster response of the electric drive can be used to stabilize the rotor shaft so that the dynamic response of a hybrid electric powertrain is quite different from a conventional configuration. To this scope, a complete model of the power system including the coaxial rotors, the mechanical connection, the turboshaft engine, the electric motors, and the battery is used in the present investigation. The inputs of the model are the pilot commands and the speed components of the rotorcraft. The model is used to highlight the degradation of the dynamic response as a consequence of component deterioration, with different degradation criteria, both on the thermal and the electric path. The results obtained in this work revealed how the torque contribution of the electric machine not only reduces fuel consumption and improves the dynamic response of the powertrain as already known in literature but also reduces the effect of engine deterioration on the performance of the power system. The outcome of the investigation is a dataset useful to train machine learning algorithms for the diagnostics and prediction of the state of health, especially considering the lack of experimental data in this field.

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