Hover Handling Qualities of Fixed-Pitch, Variable-RPM Quadcopters with Increasing Rotor Diameter

Abstract

The handling qualities of quadcopters with fixed-pitch, variable-RPM rotors of several diameters are examined. Three aircraft sizes are considered, with rotor diameters of 1.2, 1.8, and 2.4 meters and gross weights of 136, 308, and 544 kg respectively. Each aircraft is first held to standard, ADS-33 handling qualities specifications, then Froudescaled specifications are applied in order to scale the requirements of the two smaller aircraft. CONDUIT R is used to optimize inner and outer loop controllers for actuator activity in each case. Time domain simulations are then presented in order to determine the necessary motor current margins needed. In the time domain, piloted commands and gust inputs are simulated along all axes for both the inner and outer loop controllers. Much greater current is required for yaw rate commands than for either pitch or roll commands. However, when a TRC controller is included, significantly higher current margin is needed during a small magnitude step in longitudinal speed for all aircraft sizes than were observed for the inner loop. The maneuver that requires the highest current margin is the yaw rate step for the smallest aircraft and the longitudinal velocity step for the others, regardless of Foude-scaling. Using the maximum current values from these simulations, the 136 kg vehicle requires 9.7% to 12.4% motor weight fraction,the 308kg vehicle 13.0% to 14.4% motor weight fraction, and the 544 kg vehicle requires a motor weight fraction of 16.8%. Motor weight requirements can be reduced somewhat on the larger aircraft by flying the pitch and roll axes exclusively in ACAH mode instead of TRC mode. In this case, step commands in yaw rate is limiting for the 308kg vehicle (requiring 12.0%–13.1% motor weight fraction) and heave commands are limiting for the 544kg vehicle(requiring 14.5% motor weight fraction).