Hover Handling Qualities of Fixed-Pitch, Variable-RPM Quadcopters of Increasing Size

Abstract

Fixed-pitch, variable-RPM quadcopters of increasing size are simulated in hover. Three aircraft sizes are considered, with rotor diameters of 4, 6, and 8 ft(1.2, 1.8, and 2.4 m) and gross weights of 300, 680, and 1200 lb (136, 308, and 544 kg) respectively. Control design is performed for each aircraft using CONDUITR, first using standard ADS-33E-PRF handling qualities specifications. Froude scaling is then applied to the specifications in order to design more comparable, aggressive controllers for the two smaller aircraft. Piloted commands and gust inputs are simulated in the time domain in order to estimate the necessary motor current margins needed for adequate maneuverability local to hover. Of the maneuvers considered, a yaw rate step requires the highest current margin for the smallest aircraft, while the longitudinal velocity step requires the highest current margin for the others, regardless of the Froude scaling of the handling qualities metrics. Using the maximum current values from these simulations, the motor weight fraction is 8.3–10.6% for the 300-lb vehicle, 11.6–13.0% for the 680-lb vehicle, and 15.8% for the 1200 lb. Motor weight requirements can be reduced on the larger two aircraft by flying with the pitch and roll axes exclusively in the attitude command, attitude hold mode, rather than translational rate command. In this case, step commands in yaw rate are limiting for the 680-lb vehicle (10.7–11.8% motor weight fraction) and heave commands are limiting for the 1200-lb vehicle (13.6% motor weight fraction). Estimated motor weight requirements are also reduced by decreasing the rotor inertia and introducing additional filtering into the aircraft commands.