Dynamics and anti-disturbance control for tethered aircraft system

Tethered aircraft system has been widely investigated because of its extensive application in hose-drogue autonomous aerial refueling, aerial towed decoy, and towed aerial recovery drogue, etc. Yet, due to the system nonlinearity, unknown airflow disturbances and unmeasurable tether tension, the anti-disturbance control of the tethered aircraft system is still a difficulty, which has not been well solved in the existing literature. In this paper, by introducing the elasticity and length variation of the tether, the system model composed of the multi-link tether model and the 6-degree-of-freedom dynamics of the tether aircraft is accurately established, and the reachable domain of the tethered aircraft is carefully analyzed. Then, the system nonlinearity is handled by applying a new coordinate transformation, and the lumped disturbances are estimated by extended state observers. Finally, an extended state observer-based adaptive dynamic surface control approach is employed to guarantee the accurate tracking of the tethered aircraft under airflow disturbances. In comparison with PID method and active disturbance rejection control method, simulation results demonstrate that the proposed control method has better tracking ability under airflow disturbances, specially gust.