A Study on Quantities Driving Maintenance, Repair, and Overhaul for Hybrid-Electric Aeroengines

Hybrid-electric propulsion for commercial aircraft is currently a key industry interest. Consequently, publications on its design and performance estimation are manifold. However, models addressing characteristics of maintenance, repair, and overhaul (MRO) are virtually unavailable—even though direct maintenance costs (DMC) represent a significant part of direct operating costs (DOC) in commercial aviation. Detailed analysis of hybrid-electric aircraft propulsion degradation and maintenance scenarios must integrate both methods of sizing and design as well as operational factors for conventional and electric subsystems, as operator-specific utilization strongly influences MRO. Accordingly, a holistic engine analysis model is currently being developed using the example of an Airbus A320 aircraft, taking into account flight mission, engine performance, degradation, and MRO. This paper presents an implementation of hybridization into the gas turbine thermodynamic cycle calculation for parallel hybrid-electric (PHE) engine architectures with 2 and 5 MW electric motors, and the approach necessary for resizing hybridized gas turbine components. Turbomachinery loading throughout representative short-haul missions is analyzed for conventional and hybrid-electric configurations based on the V2500 high-bypass turbofan engine, whereby unknown or uncertain boundary conditions are considered in a probabilistic sensitivity study. As a result, MRO-driving quantities such as engine performance parameters, atmospheric conditions, and ingested aerosols can be compared. The findings suggest that DMC related to the gas turbine may be considerably lowered through hybridization, as it allows for reduced peak temperatures and more uniform gas turbine operation. However, these gains are at least partially offset by additional components' DMC. For electrical machines, bearings and the stator winding insulation are life-limiting, where the latter becomes increasingly dominant for higher power densities associated with high current densities and copper losses. Thermo-mechanical stresses are considered as driving mechanisms in power electronic systems degradation. Consequently, powerful lightweight machines must be balanced against tolerable thermal and electrical loads to achieve suitable service life.