Investigation of Rotor Vertical Offset Effects on Quadrotor Performance

Quadrotor performance and stereoscopic particle image velocimetry (PIV) flow field wind tunnel measurements presented in this work aim to quantify rotor-rotor interactions and their manifestations for various hub spacings, including vertical offset. Three quadrotor configurations were examined; the cross configuration and two plus (+) configurations. In the cross configuration, the fore rotors were lowered relative to the aft rotors. In the Plus 1 configuration the fore and aft rotors were lowered, whereas in the Plus 2 configuration the side rotors were lowered. In the cross configuration, increases in hub spacing led to decreases in the thrust coefficient (CT ) of the fore rotors for the same rotational speed. An increase in the rotor vertical separation resulted in an increase in CT of the aft rotors of up to 24%. Results showed that large vertical rotor separation and close hub spacings yielded best performance. The side rotors in the Plus 1 and Plus 2 configurations showed differing thrust coefficients based on relative rotor position and wind speed leading to aerodynamic asymmetries. In the Plus 1 configuration, the aft rotor experienced significant changes in performance based on both the hub and vertical spacings as it moved into the beneficial upwash regions from the side rotors, as evidenced by PIV flow field measurements. Performance results of the Plus 2 configuration showed positive effects of the fore rotor on the side rotors as they were lowered, exacerbating aerodynamic asymmetries. The aft rotor also experienced beneficial effects from the side rotors, which diminished as the side rotors were lowered. These results were further confirmed by measured rotor inflow velocities from the PIV. An examination of the thrust-to-torque ratios of the plus configurations indicated best performance for a rotor vertical separation of 0.5R.