On the integrated aerodynamic design of a propeller-wing system

In this study, potential cruise efficiency gains of a propeller-wing system are investigated through the consideration of the integrated aerodynamics of propellers and wings during the design process. The baseline propeller-wing system is a variant of NASA’s X-57 Maxwell in cruise configuration. The design space considered consists of the number, location, rotational direction, and diameters of propellers as well as the wing chord distribution. The objective is to maximize the aerodynamic efficiency as measured through the trimmed averaged propeller power and is pursued with an evolutionary algorithm. The aerodynamic analysis is conducted with a higher-order free-wake potential flow method that is supplemented with a profile drag estimation through strip theory in order to account for viscous effects. In agreement with the literature, the results indicate that larger diameter propellers rotating up-inboard at the wingtips are the most aerodynamically efficient option; however, only modest penalties exist for well designed multi-propeller systems. In addition, when the design space is restricted to smaller, more heavily loaded propellers, a local optimum exists with the propeller hub much closer to the root of the wing.