Hover Performance and Swashplate Design of a Coaxial Rotary Wing Micro Air Vehicle

Rotary wing Micro Air Vehicles (MAVs) are especially well suited for a broad range of missions that fixed wing MAVs cannot accomplish. A robust agile vehicle with efficient rotors is required to make this configuration practical. Experimental studies show that for a variety of rotors at low Reynolds numbers (Re<50,000), poor performance was consistently measured. The current investigation explores the influence of a series of parameters such as airfoil camber, number of blades, and rotor spacing on single and coaxial small-scale rotors. Figure of merit was measured experimentally, and downwash velocities were measured for a single rotor. A Blade Element Momentum Theory model was used to calculate the airfoil characteristics from the hover tests. Downwash measurements were incorporated in the model in order to predict coaxial rotor performance and to design a lower rotor twist distribution that would yield a better rotor performance. A simple and robust swashplate suited for coaxial and single rotor configurations was designed and implemented in the lower rotor of a coaxial MAV. Weight penalty with respect to a prototype without lateral control was 17%. Flight testing of the prototype was successful showing the appropriate control authority provided by the device.