Experimental optimization of UAV-Scale cycloidal rotor performance
Copyright 2018 by AHS International, Inc. All rights reserved. This paper focuses on systematic time-averaged thrust and power measurements to optimize the performance of a cycloidal rotor operating at Reynolds numbers between 100,000 and 300,000. A cycloidal rotor is a revolutionary horizontal axis propulsion device that has proven to benefit from increased maneuverability and aerodynamic efficiency at micro air vehicle (MAV) scales. The current study aims to characterize the performance of a cycloidal rotor at significantly larger UAV-scales. Towards this, experiments were conducted for a range of rotational speeds across different blade pitch amplitudes for rotor configurations with varying airfoils, number of blades, and chord-by-radius ratios. Studies found that an airfoil thickness as high as 25% of chord were capable of efficiently generating thrust and thicker airfoils provide efficient operation over a larger range of pitch amplitudes. Increasing number of blades resulted in increased aerodynamic efficiency despite a reduction in thrust per unit blade area. Optimal pitch amplitudes varied based on rotor thrust (or inflow), but centered about a pitch amplitude of 30. The cyclorotor demonstrated high CT values, even an order of magnitude higher than a conventional helicopter rotor due to the efficient use of the three-dimensional area. At UAV-scale Reynolds numbers, cycloidal rotors' aerodynamic efficiency was found to be less sensitive to chord-by-radius ratio with the exception of higher pitch amplitudes (40), where efficiency increased linearly until a chord-by-radius ratio of 0.5 and then remained constant. Increasing the chord-by-radius ratio does provide a means to increase thrust at a constant rotational speed without sacrificing thrust per unit area or power loading.
Proceedings of the AHS International Technical Meeting on Aeromechanics Design for Transformative Vertical Flight 2018
author list (cited authors)
Kellen, A., & Benedict, M.
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