Investigation and Characterization of a Cycloidal Rotor for Application to a Micro-Air Vehicle

Abstract

In recent years, interest has been growing in a new class of very small flight vehicles called micro air vehicles (MAVs). The use of cycloidal propulsion for such a vehicle has some advantages over other configurations that make it an attractive alternative to fixed-wing and rotary-wing vehicles. In a cycloidal blade system, a series of blades rotate around an axis of rotation oriented parallel to both the blades and the horizon. As the blades rotate about the axis, their pitch angle is varied periodically.

This paper investigates a small scale cycloidal rotor to determine its viability for use on a micro air vehicle. An analytical model, using a combination of wind turbine theory and an indicial solution for the aerodynamic response was developed in an attempt to predict rotor performance. A small experimental rotor was constructed and tested to determine the effects of blade number, blade pitch angle, and rotational speed on thrust output, power requirements, and efficiency. While a six-bladed configuration demonstrated more thrust production than a three-bladed one, results showed lower efficiency than that predicted and may suffer from blade-wake interference. High blade pitch angles of $30^{\circ}$ to $40^{\circ}$ are necessary to meet thrust requirements for an MAV.

Experimental results are compared with predictions as well as to results from a conventional rotor to ascertain the effectiveness of the cycloidal configuration. A maximum figure of merit of approximately 0.55 is achieved during testing, comparable with the conventional rotor. However, figure of merit for the cycloidal rotor declines as rotational speed increases, severely limiting its usefulness if high efficiency is necessary. An investigation of the flow field around the rotor is conducted to achieve an acceptable quantitative picture of the rotor downwash. Results demonstrate that outflow is directed approximately $15^{\circ}$ from the vertical. Although it appears that flow may expand upon exiting the rotor, results are inconclusive at this time.

An MAV utilizing cycloidal propulsion is modeled in CATIA to determine its viability. The cyclo-MAV utilizes two cycloidal rotors, providing thrust, propulsion, and control. Complete vehicle weight is 240 grams. Based on the experimental results, it is feasible to construct a micro air vehicle using cycloidal propulsion.