Hybrid-electric propulsion for commercial aircraft is currently a key industry interest. While there are multifarious publications on its design and performance estimation, models for its maintenance, repair and overhaul (MRO) are virtually inexistent–even though direct maintenance costs (DMC) account for a substantial proportion of direct operating costs in commercial aviation. Modelling the fundamentals of hybrid-electric aircraft propulsion degradation is a multidisciplinary task that combines methods of sizing and design as well as operational factors for conventional and electric subsystems. The implementation of these operational factors is crucial for profound modelling of maintenance scenarios as MRO is highly influenced by operator-individual utilisation.
The present paper proposes a methodology for modelling hybrid-electric propulsion degradation with the example of an Airbus A320 aircraft. A parameter study on the degree of hybridisation for a parallel hybrid-electric engine based on the V2500 shows a significant influence on the operating range of MRO-relevant parameters. Initial estimations suggest that gas turbine-related DMC might be substantially decreased, yet they may be counterbalanced by DMC of additional components in hybrid-electric systems. An initial design illustrates the influence of high power densities, realised through high current densities, on thermal aging in electric machines for aircraft applications, necessitating some balancing between power density and machine service life. Thermo-mechanical stresses are considered as driving mechanisms in power electronic systems degradation and thus form a basis of the corresponding lifetime model introduced herein.