Effects of Asymmetric Blade-Pitching Kinematics on Forward-Flight Performance of a Micro-Air-Vehicle-Scale Cycloidal-Rotor
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Experimental time-averaged force measurements and flow visualization studies were conducted on a micro-air-vehicle-scale cycloidal rotor to investigate the effects of asymmetric blade pitching kinematics. The effects of mean pitch angle (or asymmetric pitching) on rotor lift, propulsive thrust, and power were examined. At low-tomoderate advance ratios, increasing the mean pitch angle decreased both lift and power, but it did not significantly affect propulsive force. For relatively low phase angles, the rate of decrease in power was greater than the corresponding decrease in lift; therefore it might be more power efficient to operate with asymmetric pitching kinematics at low-to-moderate advance ratios. However, an important limitation of highly asymmetric pitching kinematics was a decrease in rotor lift production. For a cyclocopter micro-air-vehicle (MAV) with fixed peak-topeak pitch angle and rotational speed, it is possible to achieve steady level flight (trimmed forward flight) using the mean pitch angle For a cyclocopter micro-air-vehicle (MAV) with fixed peak-to-peak pitch angle and rotational speed, it is possible to achieve steady level flight (trimmed forward flight) using the mean pitch angle as the two primary control variables. Flow visualization experiments identified blade stall on the upstream blade as a limiting factor of highly asymmetric pitching kinematics. The downstream blade was shown to experience a highly unsteady flow environment, and a blade?wake interaction was observed for the symmetric pitching case the azimuthal location of this blade?wake interaction varied, depending on the value of the mean pitch angle.
