Self-stabilizing propeller

Abstract

Object and purpose of research. The solution discussed in this paper is applicable to the propellers (including those with oscillating blades) operating in fluids, and is intended to ensure self-adjustment of blades to the optimal attack angle. Subject matter and methods. Blade self-adjustment to the optimal attack angle was achieved through one of the properties of the boundary layer for viscous flow around the foil system: this layer acquires different thickness at the opposite sides of foils with non-zero installation angle, thus becoming an asymmetric displacement body. The propeller intended to use this property had its blade and a stabilizing foil attached to a common axe so that the rotation axis of both the blade and the foil was between the application points of the hydrodynamic resultant force (i.e. centers of pressure) for the blade with and without the stabilizing foil. The locations of pressure centers were calculated as per the linear theory. This property of the propulsion system was confirmed experimentally. Main results. It was experimentally demonstrated that proper selection of the rotation axis coordinate in a viscous fluid creates a zone of stable attack angles. This zone also exists for symmetric foils arranged one after another with non-zero installation angle. It means that these foils could be used in a fin-type propulsor, but this will require a control device preventing blade lock due to reversal of oscillation direction. In the suggested solution, blade axis is connected with driving rods by means of steering arms, and the driving rods themselves have guides locking blade tips when oscillation direction changes. Conclusion. The solution suggested in this paper has been experimentally validated, and it paves way to introduction of simple but efficient fin-type propulsors. Following this design, the author suggests a flipper with increased propulsion efficiency in a wide range of speeds, as well as a propulsor based on hinged hydrofoils: this design does not need propeller to maintain the speed.