Experimental study on the thrust vector characteristics of a six-bar cycloidal propeller under different advance coefficients and azimuth angles

Cycloidal propellers have a unique combined revolution-pitching motion of the blades. This motion gives them excellent thrust-vector control capability. However, it also causes periodic fluctuations in the thrust vector, which creates challenges for vehicle maneuvering. To clarify the effects of the advance coefficient and the azimuth angle on the time-averaged thrust vector characteristics and thrust vector stability of a six-bar linkage cycloidal propeller, a comprehensive experimental study was carried out. A kinematic model of the six-bar linkage cycloidal propeller was first established, and the blade pitching laws under different azimuth angles were obtained. After that, an experimental apparatus was developed based on key-phase detection technology. A thrust vector stability index, 𝑆 , was also introduced to provide an overall assessment of thrust vector stability. The experimental results show that the thrust vector response of the six-bar linkage cycloidal propeller is clearly asymmetric for positive and negative azimuth angles with the same absolute value. This is because the flow fields under these azimuth-angle conditions are not symmetric. When the advance coefficient 𝐽 > 1 . 7 , positive azimuth-angle conditions have a weaker regulating effect on the thrust direction. In contrast, the thrust direction response becomes excessively strong at 𝛾 = − 2 0 ° and −30° when 𝐽 > 1 . 2 . Furthermore, for 𝐽 > 1 . 0 , thrust vector stability is better at positive than at negative azimuth-angle conditions.