Modeling Tethered Multirotor Autogyro with Altitude Control via Differential Rotor Braking

The potential use of tethered autogyros as energy-efficient low-altitude surveillance systems calls for control and stability analysis of autorotative flight. A control-oriented dynamic model of a tethered multirotor autogyro, introducing the flapping degree of freedom of each blade, is developed in this paper by combining the Lagrangian approach, blade element momentum theory, and catenary mechanics. The resulting model is hybrid in the sense that the aerodynamic forces are three dimensional, whereas the autogyro is constrained to move within the vertical plane. The assumption that roll and yaw motions can be controlled by lateral rotors in the full three-dimensional extension facilitates detailed dynamic modeling while limiting the number of states. The equations of motion are numerically solved, and equilibrium characteristics are explored. The trends of equilibrium data are consistent with existing results in the literature. Simulation results show that a two-loop feedback controller based on a novel regenerative differential rotor braking technique is effective in controlling the autogyro’s pitch angle and altitude while using the restoring force from the tether. To further substantiate the efficacy of the proposed controller, this paper presents a stability analysis of the system.