Preface the first set of flat outputs allows realizing one of the first "free-floating" versions of the classical hybrid force-motion control for standard grounded manipulators. Based on these results we designed two types of controllers. The first is an easyto-implement controller based on a hierarchical approach. Although it shows good performance in quasi-static conditions, actually the tracking error increases when tracking a dynamic trajectory. Thus, a second controller more suited for tracking problems has been designed based on the dynamic feedback linearization technique. Two observers, for the 3D and 2D environments, respectively, have been designed in order to close the control loop using a minimal sensorial setup. We showed that the tether makes possible to retrieve an estimation of the full state from only an IMU plus three encoders for the 3D case, while from just an IMU for the 2D case. Parts of those results were extended to a novel and original multi-robots case as well. We considered a multi-tethered system composed of two aerial robots linked to the ground and to each other by two links. The theoretical results on generic tethered aerial vehicles were finally employed to solve the practical and challenging problem of landing and takeoff on/from a sloped surface, enhancing the robustness and reliability of the maneuvers with respect to the contact-free flight solution. This work has been supported by the European Union's Horizon 2020 research and innovation programme under grant agreement No 644271 AEROARMS. We would like to express our deep gratitude to Dr. Anthony Mallet for the excellent and continuous maintenance of the software and hardware framework. Without his precious work, the several experiments conducted during this work would not have been possible.