| Resumo : |
This research introduces a novel concept of Lighter Than Air (LTA) vehicle, the tethered airship. It is a self-propelled airship that has an anchorage system, being able to perform free flight and also anchor to a surface for a period of time. While anchored, this vehicle can remain stationary in a certain region in a passive way, similar to a tethered balloon, or perform navigation within the limits determined by the length of the tether, or also hover in a desired position using its own control system. A theoretical investigation is also presented. The equations of motion are described and the linearized model is obtained by the finite difference approach. The decoupling between the longitudinal and lateral-directional motion and a linear stability analysis are performed. The lateral-directional motion presents an unstable mode for different wind speeds. A study of the dynamic characterization is carried out and a new classification for the flight modes of the longitudinal and lateral-directional motion of a tethered airship is proposed, differentiating the flight modes of this new platform from the free airship and the tethered balloon. In addition to proposing a novel concept of LTA platform and presenting a theoretical investigation, this research presents the development of an autonomous tethered airship, involving constructive adaptation, integration of the embedded system in the air vehicle, implementation of the control laws and the validation of the developed platform through in-flight test campaigns. The experimental setup and the detailing of the flight control system are described. A system identification methodology for the tethered airship is approached aiming to obtain a high fidelity model. The deviations from sensor measurements and aerodynamic parameters are estimated. The stability of the system is achieved by designing a Stability Augmentation System (SAS) and the gains are obtained using the LQR technique. The dynamic stability of the open and closed loop system is analyzed in the domain of time and frequency, comparing simulations with flight test data. The architecture of a Guidance, Navigation, and Control (GNC) system is proposed and validated through flight campaigns. The result of this development is a stable tethered airship with autonomous functionalities, performing autonomous takeoff and landing, hovering at desired altitude, and autonomous navigation using waypoints, improving the autonomy level of the airships. |