Effect of Axial Spacing and Rear-Propeller Pitch on Performance of Coaxial Propellers

As electric aircraft receive more attention, efficient electric propulsion systems become increasingly important. In this study, a coaxial propeller system based on a popular model propeller is considered. The effects of various design choices in such a propulsion unit are studied using computational fluid dynamics. The inter-propeller spacing is analyzed, as well as performance of lower propeller with different pitches under conditions of thrust-, rpm-, and torque-matching with the upper propeller. Propeller spacing has shown relatively little effect on overall performance, when upper outflow is fully developed. Depending on a matching metric, different pitch variations of lower propeller were found to correspond to optimal thrust-power ratios. Computational data for propeller characteristics and illustrations of flow fields and pressure distributions on propeller blades are presented in the paper.