Exploration of Off-Design Performance for Hybrid Electric Regional Aircraft

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.