Effects of Disk Loading on Handling Qualities of Large-Scale, Variable-RPM Quadcopters

The performance of Urban Air Mobility (UAM) scale quadcopters with fixed-pitch, variable-speed rotors is examined at different values of disk loading. Three 544kg (1200lb) aircraft are considered in hover with disk loadings of 287N/m2, 574N/m2, and 861N/m2 (6psf, 12psf, and 18psf), corresponding to rotor radii of 1.2m, 0.86m, and 0.70m
(4.0ft, 2.8ft, and 2.3ft). Optimized explicit-model-following controllers are designed to meet standard handling qualities criteria using CONDUIT. In trim, it is seen that increased disk loading results in increased power, but with reduced motor torque due to higher rotor speeds. Time domain simulations are considered in order to examine the peak torque required by the aircraft, which is used to estimate required motor weight. Based on a step command in heave rate, a 54% reduction (total reduction of 40.6kg) in motor weight is seen for the 18psf quadcopter. Assuming a step change in rotor speed, the peak torque required for the heave maneuver is also predicted in closed form using an analytical model based on momentum and blade element theory. The analytical model captures the trend in peak torque during the heave rate step response, with predicted values within 12% of the values from the time domain simulation.