Parametric Study of Aft Rotor Optimization in Stacked Propeller Systems for Urban Air Mobility

Abstract

As Urban Air Mobility (UAM) vehicles become a key area of interest for sustainable and efficient short-range transportation, there is a growing need to optimize propulsion systems for performance. Counter-rotating stacked propellers present a promising alternative to traditional single-rotor systems, offering potential benefits in thrust generation, efficiency, and swirl minimization. This thesis explores the aerodynamic performance of these stacked systems, with a focus on how aft rotor parameters—axial spacing, radius, RPM, and blade count— influence overall system performance. Using CROTOR, a range of configurations were analyzed and compared to baseline single-rotor setup. The results demonstrate that tailoring the aft rotor radius and RPM in response to the axial velocity distribution can improve normalized thrust by up to ≈3.5%. Furthermore, lower aft blade counts were found to achieve higher efficiency. These findings contribute empirical insight into stacked rotor dynamics and provide a foundation for deriving sizing heuristics that can streamline design of optimal eVTOL propulsion systems.