Hybrid-electric propulsion for commercial aircraft is currently a key industry interest.
While there are multifarious publications on its design and performance estimation, mod-
els 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 pro-
pulsion degradation is a multidisciplinary task that combines methods of sizing and de-
sign as well as operational factors for conventional and electric subsystems. The imple-
mentation 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 deg-
radation 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 signif-
icant 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 den-
sities, 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.