Range equation for hybrid-electric aircraft with constant power split

There has been a surge in research related to hybrid-/ electric propulsion (HEP) over the past decade, since this technology has the potential to reduce the energy consumption and in-flight emissions of commercial aircraft and, therefore, to bring the aviation sector closer to the sustainability targets established by the European Commission [1] and NASA [2]. Previous studies have shown that hybrid-electric [3,4] and fully-electric [5] general-aviation aircraft can lead to a reduction in both emissions and operating costs for short ranges, when compared with fuel-based alternatives. However, due to the enormous energy and power requirements of large passenger aircraft, fully battery-based propulsion is not a viable option to substantially reduce the climate impact of the aviation sector as a whole [6], unless the mission range is significantly reduced, or unrealistically high battery energy densities are assumed [7]. For this reason, hybrid architectures (especially parallel [8–10] and turboelectric [11–14] ones) are often investigated as a potential solution for large passenger aircraft.