Post-Motor-Failure Performance of a Robust Feedback Controller for a UAM-Scale Hexacopter

The performance of two flight controllers is compared for a 1200 lb hexacopter following single rotor failure. A nominal flight controller is tuned to meet handling qualities specifications for the healthy aircraft in forward flight, and a robust two-plant controller is tuned to also satisfy the same set of handling qualities specifications following
front rotor failure. This two-plant controller is tuned to simultaneously meet the handling qualities for the healthy and failed aircraft. In both cases, the flight controllers do not utilize knowledge of the rotor failure. The performance of the controllers is compared for single rotor failures of the front and side rotors. For front rotor failures, the two plant
controller decreases the peak pitch deviation by 3.5 and provides a more well damped response, but does not provide significant benefit during side rotor failure. Various maneuvers are also performed for each controller to evaluate the cost for using the robust controller in normal operation. The largest torque difference, a pitch doublet, requires 8 ft-lb additional torque for the two-plant controller, while the peak torque requirement for maneuvers occurs during a yaw rate step, where about 140 ft-lb of torque is required for the nominal controller (143 ft-lb for the two-plant). For both controllers, recovery following rotor failure requires substantially more torque (280 ft-lb) than the different maneuvers considered. Therefore, motor sizing is limited by rotor failure cases, not normal operation.