Effect of Unsteady Blade Pitching Motion on Aerodynamic Performance of Microrotorcraft

The improvement in aerodynamic performance of microscale rotors using unsteady blade motion is investigated using numerical simulations and experimental work. The basic idea is to use dynamic blade pitching motion to delay the onset of stall, enhance the lift, and increase the envelope of operation of small-scale airfoils operating at the low Reynolds number and low Mach numbers that are typical of microrotorcraft. A 22-cm-diam twobladed microrotor system featuring piezoelectricaly actuated controllable twist rotor blades was developed and tested in hover. The piezoelectric actuation system had sufficient control authority and was able to generate up to ±2.3-deg blade unsteady tip twist deformations under rotating conditions. Excitation of the blade in torsion resulted in significant improvement in the microrotor thrust in the poststall regime. (At 24-deg rotor collective pitch, up to 11% improvement in rotor thrust was demonstrated.) The experimental measurements also showed good agreement with numerical predictions for the effect of dynamic blade pitching on the thrust output and power consumption of the microrotor.