Requirements and design of powertrains for eVTOLs

The potential future of personal transportation and taxi services may be in some sectors beneficially amended with electric vertical take-off and landing (eVTOL) aircraft. Currently, dozens of companies are actively engaged in the development of eVTOLs, with the imminent commercialization of several vehicles. This article delves into the requirements, the present trends and powertrain technologies surrounding VTOL flight mechanisms. The main challenge for eVTOLs is that the propulsion system becomes part of the primary flight control system and therefore is critical for controlling the vehicle. This puts much higher demands on availability and safety of the powertrains than in conventional aircraft. Furthermore, as mainly propellers and fans are used for control that feature a constant or only slowly varying pitch angle, the thrust has to be dynamically changed using motor speed changes resulting in demands on motor acceleration and deceleration which are far beyond those of other transportation applications. Finally, if lift-to-cruise eVTOLs are considered, conflicting requirements are put on the powertrain, where high power is required for rather short times during take-off and landing whereas a rather low continuous power at high powertrain efficiency is needed during the prolonged wing-borne operation phase. This article provides an overview of regulatory and flight physics for eVTOLs. Thus, requirements for the electrical powertrain are deployed with focus on battery, electric motor, thermal management and HV circuit. As in the case of ground-based vehicles, all these parts must be carefully selected, designed and co-optimized i. a. with focus on weight, energy or safety, but on trend with much more challenging aviation standards to be met.