A Cycloidal Propeller Using Dynamic Lift

The highly efficient locomotion of birds, insects and fish is based on unsteady fluid dynamics. In recent years, research has focused on tapping into the potential that rests within these unsteady aerodynamic processes. However, most of the dynamic pitch and heave patterns encountered in nature are difficult to produce in an air vehicle that is propelled using rotating shaft power from an engine. To address this problem, this research assessed the feasibility and performance of a cycloidal propeller designed to utilize unsteady aerodynamic lift. A cycloidal propeller consists of one or more propeller blades mounted perpendicular to a rotating disk (see Figure 1). Contrary to current technical implementations of this type of propeller, dynamic pitch changes of a single blade mounted eccentrically to the propeller shaft in order to produce free leading edge stall vortices in the fluid are investigated. To generate thrust, a flow pattern that is the inverse of the von Karman vortex street is created in the fluid. The resulting time averaged flow field distant from the propeller is that of a jet. This type of propeller is particularly suited for low flow speeds, where state of the art propellers become inefficient due to flow separation on the blades. Potential applications include micro air vehicles that may use this device for propulsion as well as vertical take off and landing, and high altitude long endurance (HALE) aircraft that need to produce lift and thrust at low Reynolds numbers efficiently. The ability of a cycloidal propeller to produce similar efficiencies as dynamic pitch and heave motions reported in literature is demonstrated in this work.