Investigation of a tensile cycloidal rotor and cam cyclic pitching mechanism

Abstract

A cycloidal rotor is characterized by an airfoil span parallel to the axis of rotation. A tensile cycloidal rotor places the airfoils under tensile forces only, thereby attempting to utilize the inertial forces on the rotor to minimize airfoil deflection and overall weight. A prototype rotor was built that meets the micro air vehicle (MAV) size constraint of 15.24 centimeters (6 inches). A new cam path design was used as a pitching mechanism, which reduced overall design weight and mechanical power requirements, and allowed for curved flat plate airfoils and angled airfoil structural supports. The cycloidal rotor was designed to pitch on both sides of the airfoils in an effort to reduce the axial force that was previously observed in mechanisms that pitch straight airfoils using an offset four bar linkage on only one side. The radial and axial strains were measured to determine the forces on the rotor, and compared well with a finite element simulation. The power-to-thrust ratio increased with RPM, which is in contradiction with theoretical rotor predictions. This indicated there are likely inefficiencies due to friction, which is supported by the measured non-zero power requirement at zero RPM.