Comprehensive Study on Toroidal Propellers: Design, Aerodynamic Characteristics, and Acoustic Performance

Toroidal propellers are being experimentally adopted in electric vertical takeoff and landing (eVTOL) for their claimed advantages in aerodynamic efficiency and noise reduction. However, as their design methodology and performance characteristics remain insufficiently understood, comprehensive research is required to evaluate their potential. This paper presents the design methodology of an 8-in. toroidal propeller and compares its aerodynamic performance and underlying mechanisms with conventional two-blade and four-blade propellers. The designed toroidal propeller is optimized, and the acoustic characteristics of various propellers are investigated. It is found that the unoptimized toroidal propeller produces higher thrust than the two-bladed propeller (though less than the four-bladed one) but exhibits a disproportionately larger increase in torque, resulting in lower efficiency due to imbalanced pressure distribution between the forward and backward blades. Aerodynamic performance is improved by increasing the local pitch angle of the backward blades by 5–7 deg. The optimized toroidal propeller achieves low noise comparable to the conventional four-blade propeller and lower than both the unoptimized toroidal propeller and the two-blade propeller in acoustic performance. These findings provide insights for understanding, application, and optimization of toroidal propellers. Since these results are simulation-based, future work will involve experimental validation to corroborate computational findings and further explore the real-world performance.