Improving UAV Safety During Piloted Flight Phases by Keeping the Autonomous Controller in the Loop

摘要

This paper presents the results of placing an H-infinity controller in the loop with the human pilot of a 33% scale Yak-54 UAV. An H-infinity controller is used because it is already present onboard the aircraft for use by its autonomous flight mode. The goal of the research was to improve the safety of the aircraft above that of the open loop aircraft. However, simulation of the control system with the H-infinity controller in the loop with pilot commands revealed surprising drawbacks. With the controller tuned to provide responses of similar magnitude and mode shape to that of the open loop aircraft, the system experienced a 0.2 to 0.3 second pure delay due to the presence of the H-infinity controller. Analysis shows this delay renders the control system response similar to that of an inebriated pilot. Changing the controller to reduce this delay resulted in exaggerated responses that could send the aircraft into unsafe flight regimes. In either case, the mismatch between pilot inputs and aircraft responses creates a risk of PIO. As a result, the Aerospace Department has decided not to implement this control scheme on a flight test aircraft due to the significant flight risks.