In this paper, we describe a transportation system-level model of an urban air mobility (UAM) network over a single metropolitan area. This model provides the ability to assess many parameters, including the number of vehicles needed in the system to meet demand, the number of vehicles airborne at any given time, and the length of time vehicles may have to loiter before a landing pad becomes available. We focus our initial studies with the model on exploring the UAM system-level implications of different energy storage systems on UAM vehicles. Specifically, we compare fully-battery-electric vehicles to vehicles with multiple hybrid-electric powertrains, which consist of different energy conversion systems (i.e., engines and fuel cells) and fuels. The transportation system-level model provides insight into vertiport ground infrastructure requirements, such as the number of recharging or refueling stations and the impact of various vehicle powertrains on these requirements. Ultimately, results indicate that the use of liquefied natural gas (LNG) as a fuel in a hybrid solid oxide fuel cell-battery-turbine system can result in a vehicle power system that provides lower operating costs, reduced carbon dioxide emissions, and lower power system weights than pure battery-electric solutions at the same power level while also having fewer infrastructure integration issues. Additionally, a hybrid internal combustion engine-generator-battery solution fueled with LNG provides a near-equivalent energy cost solution to pure battery-electric power systems at the same power level, but at a much lower system mass. Consequently, this hybrid architecture is expected to provide advantages for sized vehicles over other power system types.
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