Most studies investigate hybrid electric aircraft by comparing their respective performance over their design mission. However, most missions flown are less demanding in terms of payload and/or range. Kerosene aircraft can adapt their fuel load, yet battery-equipped aircraft have to make the best of an already installed battery. This paper compares the performance of battery-equipped hybrid electric regional propeller aircraft (parallel, serial/parallel partial hybrid, or serial powertrain) over their entire payload-range envelope, relative to a kerosene aircraft designed according to the same specifications and performing the same off-design missions. The payload-range envelope is determined by intricate combinations of sizing limits of powertrain components in terms of power and energy. All hybrid electric aircraft are heavier than their kerosene counterparts and less energy efficient on their design mission. However, over a 600 km range, a 60% fuel saving can be achieved at lower payloads. Full-electric cruise may be possible for all payloads up to ∼500  km
for all architectures when a battery-supplied power ratio of 20% in cruise flight is selected for the design point. The results demonstrate the off-design sensitivity to 1) selection of the powertrain architecture, 2) selection of the design hybridization strategy, and 3) selection of the design mission.

The objective of the EU-funded research project CHYLA (Credible HYbrid eLectric Aircraft) was to identify opportunities or limitations/challenges for the applications of key radical hybrid-electric technologies and areas suitable for scaling them over different aircraft classes. This was done using a ombination of conceptual aircraft design supported by sensitivity studies, credibility-based MDO and assessment of a regional operative scenario. This article summarizes the key findings from the project and presents the landscape of technology application areas. Notably, the regional and commuter classes present the largest design space with significant fuel-saving potential depending on the mission.

The impact of the ICAO code C gate span limit is assessed on the sizing of a serial Hybrid Electric Aircraft (HEA) of increasing Degree of Hybridization (DoH). For a set of Top Level Aircraft Requirements (TLARs) similar to the ATR-42, it is shown that the increase in MTOM due to the presence of the battery is such that only a maximum DoH under 30% can be achieved before the wing span of the serial HEA reaches the 36 meters gate size. The same aircraft is fitted with Leading Edge Distributed Propulsion (LEDP) to increase the wing loading and relieve the span constraint, though this introduces limitations regarding the available wing volume. It is shown that a combination of high wing loading and of low volumetric energy density for batteries compared to jet fuel can lead to the available wing volume being too small for the required volume of the energy carriers. Finally a value in wing loading is found which simultaneously meets the span and wing-volume constraints. The higher DoH enabled by LEDP leads results in a 33% reduction in fuel burn compared to the fuel-based reference aircraft, while the overall energy consumption is increased by 6%.

This study aims at providing a landscape of opportunities and limitations for hybrid-electric aircraft (HEA) and hydrogen-powered aircraft by investigating several technological combinations applied to three aircraft classes: Regional (REG), Short-Medium Range (SMR) and Large Passenger Aircraft (LPA). The preliminary sizing of HEA using different hybrid-electric powertrain architectures, combined with various distributed propulsion layouts is conducted. The resulting HEA are then compared to a conventional design, on the basis of several performance metrics, for variations in harmonic range and passenger capacity. Throughout the design space considered, it is found that opportunities for radical aircraft design are scarce and offer limited prospective.

Various research initiatives in hybrid-electric/sustainable aviation typically address only a single vehicle or single vehicle class. However, novel propulsion and energy solutions can be expected to be differently applied in different vehicle classes. The objective of the EU funded research project CHYLA (Credible HYbrid eLectric Aircraft) is to identify areas suitable for scaling, as well as limitations or challenges for development for the applications of key radical technologies on different classes of aircraft. This article provides an overview of the design approach followed for the CHYLA project, as well as initial radical designs and comparison to the CHYLA baselines. These provide the starting point for both the sensitivity study which will be presented in a later scalability assessment and economical assessments in the CHYLA project. A variety of regional, short medium range and large aircraft has been designed, all according to the same TLAR yet without detailed tuning of important power control variables. Results are distinguishable between concepts and provide sufficient detail to capture the necessary effects. The reduction of fuel consumption will require detailed assessment and fine tuning, though reductions may be achievable for regional and possibly SMR aircraft.

This study aims at providing a landscape of opportunities and limitations for hybrid-electric aircraft (HEA) and hydrogen-powered aircraft by investigating several technological combinations applied to three aircraft classes: Regional (REG), Short-Medium Range (SMR) and Large Passenger Aircraft (LPA). The preliminary sizing of HEA using different hybrid-electric powertrain architectures, combined with various distributed propulsion layouts is conducted. The resulting HEA are then compared to a conventional design, on the basis of several performance metrics, for variations in harmonic range and passenger capacity. Throughout the design space considered, it is found that opportunities for radical aircraft design are scarce and offer limited prospective.