Parametric Analysis for Hybrid–Electric Regional Aircraft Conceptual Design and Development

Abstract

This paper proposes a conceptual analysis of the limitations related to the development (and integration) of hybrid–electric propulsion on regional transport aircraft, with the aim to identify a feasibility space for this innovative aircraft concept. Hybrid–electric aircraft have attracted the interest of aeronautical research as these have the potential to reduce fuel consumption and, thus, the related greenhouse gas emissions. Nevertheless, considering the development of such an aircraft configuration while keeping the constraints deriving from technological and/or operating aspects loose could lead to the analysis of concepts that are unlikely to be realised. In this paper, specifically to outline the boundaries constraining the actual development of such aircraft, the influence on overall aircraft design and performance of the main technological, operating, and design factors characterising the development of such a configuration is analysed and discussed at a conceptual level. Specifically, the current achievable gravimetric battery energy density (BED) is identified as the main limiting factor for the development of regional hybrid–electric aircraft, and a sensitivity analysis shows the correlation of this important technological parameter with aircraft performance in terms of both fuel consumption and energy efficiency. In this context, minimum technological development thresholds are therefore identified to enable the effective development of this type of aircraft; namely, a minimum of BED = 500 Wh/kg at battery pack level is identified as necessary to provide tangible benefits. From an operating point of view, flight distance is the most limiting design requirement, and a proper assessment of the design range is necessary if a hybrid–electric aircraft is to be designed to achieve lower emissions than the state of the art; flight ranges equal to or lower than 600 nm are to be considered for this type of aircraft. As a bridging of both of the previous constraints, a change in the design paradigm with respect to established practices for state-of-the-art aircraft is necessary. More specifically, penalisations in maximum take-off weight and overall aircraft energy efficiency may be necessary if the aim is to reduce direct in-flight consumption by means of integration of hybrid–electric powertrains.

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

“…The performance of the electric machines is taken from the review proposed in [28]; namely, a specific power of 13 kW/kg and an efficiency of 0.96 are selected for the electric motors and a specific power of 19 kW/kg and an efficiency of 0.98 are selected for the inverter, whereas for cables, a specific power of 352 kWm/kg and an efficiency of 0.99 are selected. The gravimetric energy density of the battery, which is a key performance metric affecting the whole design of a hybrid-electric aircraft [59,60], is selected equal to 500 Wh/kg [28,61,62]. These performance forecasts refer to a predicted scenario for the 2035.…”

“…In the considered cases, for routes up to 400 nm, the total increase in powertrain efficiency reduces the energy demand of the mission, which instead becomes larger than the full-thermal aircraft Finally, a comment on the energy efficiency of hybrid-electric aircraft is proposed. As described in [28,59,69], the use of electrical power to meet part of the required power for the flight introduces two different contributions that impact the mission energy demand. On the one hand, electrical power systems are much more efficient than thermal ones, and a higher electrical power supply allows for less powertrain losses and consequently for a reduction in the energy required to fly, while the increase in weight due to the presence of batteries makes the flight more energy-demanding.…”

Preliminary Performance Analysis of Medium-Range Liquid Hydrogen-Powered Box-Wing Aircraft

“…Specifically, electrical energy (stored in batteries) and sustainable aviation fuels (SAF) represent a compelling alternative to the current kerosene [14,15]. Electric-powered aircraft, discussed in detail in [16][17][18], exhibit a main penalizing issue related to the low gravimetric energy density of batteries that introduces large detrimental weight increase; hence, electric or hybrid-electric aircraft may only be designed to reduce fuel consumption and related emissions for short flight distances, for aircraft belonging to commuter up to the regional category [19][20][21], whereas some benefit can be gained with much difficulty if medium-and long-range aircraft are considered [22]. However, to assess the actual emissions of hybrid-electric aircraft, the electricity production methods should be taken into account; specifically, a clear transition towards renewably sourced electricity production is compulsory for an actual general reduction in emissions [20,23,24].…”