Conceptual design of UAM powered by fuel cell and battery hybrid propulsion system

Abstract

In this paper, a novel conceptual design method of Battery-FC hybrid propulsion multirotor UAM was proposed. The proposed design method largely follows the process of "Design step – Design selection step". In the design step, each UAM is designed with varying hybridization ratio ranging from 0 to 1. The first half of the design step aims to calculate the power required for flight, and in the latter half, various elements are designed based on the calculated power and according to the hybridization ratio. In the design selection step, the design that does not pass discard criteria is discarded, and the most cost-effective design among the remaining designs is selected as the final design. A case study was conducted to identify the utility of the proposed design method and to verify the influence of each design variable. As a result of comparing the UAM designed according to the proposed method with published specifications of representative commercial UAM, there was a deviation of about 5%. The optimal hybrid ratio was when the fuel cell output power equal to the power for cruising flight and the battery supplement additional power for ascending and descending. This configuration could significantly reduce the take-off weight of the UAM, which led to a significant reduction in LCC. Hybrid configuration could flight much farther than battery-only and reduce LCC by about 1/3 of FC-only. 11C-rate discard condition satisfied both the safety and economic aspects of the battery. Each time the number of passengers was increased by one, the LCC increased by 15%, but the LCC burden per passenger decreased. As time goes by, LCC decreased according to changes in energy prices. A further research can be conducted with a conceptual design method for Regional Air Mobility (RAM) or other types of UAM, such as Lift & Cruise and Tiltrotor.