Progress in the development of electrical storage and conversion technology progressively attains focus in aerospace motive power research. Novel propulsion system concepts based on hybrid or even entirely electrical energy sources are seriously considered for aircraft design. To this point, unified figures of merit are required in order to allow for consistent comparative investigations of existing combustion engines and future electrically-based propulsion systems. Firstly, this paper identifies the shortcomings of conventional performance metrics used for non-thermal electrical conversion processes and then approaches exergy-based loss methods as means of metrics extensions. Subsequently, energy source-independent figures of merit based on exergy analysis are derived and embedded into the well-known performance definitions. Finally, the unified metrics are demonstrated through application to a conventional turbofan, a parallel-hybrid turbofan, a novel integrated-hybrid turbofan concept and an entirely electrical fan concept.

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