Haoxiang Ma Mou Chen Qingxian Wu Disturbance Observer-Based Safe Tracking Control for Unmanned Helicopters with Partial State Constraints and Disturbances. 2056-2069 2023 November 10 IEEE CAA J. Autom. Sinica 11 https://doi.org/10.1109/JAS.2022.105938 db/journals/ieeejas/ieeejas10.html#MaCW23