Impact of Figures of Merit Selection on Hybrid-Electric Regional Aircraft Design and Performance Analysis

The adoption of hybrid-electric propulsion, allowing us to partially replace fuel with batteries and to reduce aircraft in-flight emissions, represents one of the main investigated solutions to mitigate the aviation climate impact. Despite its environmental potential being appealing for a practical application, two main drawbacks limit the actual implementation of this technology: first, the low gravimetric energy density of the batteries restricts hybrid-electric aircraft payload and range capabilities; second, the production of electricity is currently not entirely based on renewable energy sources, hence a non-direct emissions budget may limit the benefit in terms of overall decarbonization. When designing hybrid-electric aircraft, even projecting its actual entry into service in the next decades, it is necessary to take these limitations into account depending on both the more reliable technological forecasts on the development of electric components and on the estimates of electricity production. A proper analysis of the figure of merits related to the operation of such an aircraft, therefore, becomes crucial in assessing the impact related to its introduction into service. In this context, trade-offs between different performance metrics may be needed to efficiently exploit the environmental benefits of such an advanced concept, while limiting the possible drawbacks coming from its utilisation. This paper provides a performance analysis of hybrid-electric aircraft through an assessment of the relevant figures of merit characterizing its operations. In particular, direct and non-direct emissions, climate impact, ground pollution, operating costs, fuel consumption, weight, and a combination of these figures of merit allow us to define a proper development perimeter in which a possible (future) hybrid-electric aircraft can express its maximum potential towards all the aspects of its utilisation. The trade-off analyses provided in this paper allow us to identify more effective paths for the actual development of hybrid-electric aircraft, highlighting the impact of the selected design variables on the performance metrics, and bringing to light also the possible related limitations.