Steady and Transient Hover Performance Investigation of Electric Medium-sized Variable-RPM Rotor

Electric variable RPM rotors are increasingly being used for propulsion and control of unmanned air vehicles. As these vehicles scale to carry heavier payloads of 50 to 400 lbs (20 to 180 kgs) in the group 2 and 3 UAS category, there are concerns about their aerodynamic performance and handling quality degradation. First, a universal electric powered experimental testing rig designed for use on a hover tower and in a wind tunnel is described. Second, steady hover data is estimated using blade element momentum theory. These predictions incorporate an empirical correction approach and an interpolation approach to capture Reynolds number variation along the span of the blade and variation with RPM. Results show good agreement with the interpolation method for the low Reynolds number rotor tested. Finally, transient step and chirp inputs are presented. The chirp inputs were used in CIFER to validate the results of the experiment and fit transfer functions of thrust and torque due to RPM and RPM2.