Optimisation of a liquid cooling system for eVTOL aircraft: Impact of sizing mission and battery size

High-energy and -power density lithium-ion batteries (LiB) can enable viable electric vertical take-off and landing (eVTOL) aircraft for advanced air mobility provided that their battery thermal management system (BTMS) allows safe and efficient operations with acceptable weight penalties and capacity degradation. In this paper, we present the first optimisation of a liquid-cooled LiB BTMS for a notional tilt-wing reference eVTOL aircraft. Using an in-house developed BTMS sizing and battery degradation modelling algorithm, we investigate the effects of cruise altitude, hover duration, and battery pack oversizing on BTMS weight and battery lifetime. We minimise the BTMS weight, power, and battery temperature. The optimisation results reveal that varying cruise altitude has a negligible effect on BTMS design. While an extended hover duration does not adversely impact degradation, a considerably heavier BTMS is needed. The BTMS is about twice as heavy when the hover duration increases from one to seven minutes. Shortening the flight distance or oversizing the battery pack greatly impacts the battery lifespan. The battery capacity degradation rate halves when increasing the battery pack size by 20%.