A tethered automatic unmanned aerial vehicle system comprising at least the components: - an unmanned aerial vehicle, wherein the unmanned aerial vehicle is a multi-copter with a body, - a ground station, - a flexible tether that is connectable or that is connected to the unmanned aerial vehicle and to the ground station, such that the unmanned aerial vehicle is tethered to the ground station, wherein the unmanned aerial vehicle comprises an angle-sensor configured and arranged to determine an angle of incidence between the tether and gravity or a horizontal plane or the body of the multi-copter, such as to determine from the detected angle of incidence at least an angular position of the unmanned aerial vehicle with respect to the ground station, wherein the ground station is configured to preload the tether, when the system is in operation, such that the detected angle of incidence is indicative of the angular position of the unmanned aerial vehicle with respect to the ground station or gravity, characterized in that the ground station comprises a preload assembly with a movable member (203.1) that is arranged in contact with the tether and that is configured to alter a tether path length of an adjustable tether path in the ground station, wherein the movable member (203.1) is arranged translationally movable on a guide of the preload assembly that allows the tether path length in the ground station to be adjusted in length by moving the movable member (203.1) along the guide, such that a load on the tether can be adjusted by moving the movable member (203.1). - an unmanned aerial vehicle, wherein the unmanned aerial vehicle is a multi-copter with a body, - a ground station, - a flexible tether that is connectable or that is connected to the unmanned aerial vehicle and to the ground station, such that the unmanned aerial vehicle is tethered to the ground station, wherein the unmanned aerial vehicle comprises an angle-sensor configured and arranged to determine an angle of incidence between the tether and gravity or a horizontal plane or the body of the multi-copter, such as to determine from the detected angle of incidence at least an angular position of the unmanned aerial vehicle with respect to the ground station, wherein the ground station is configured to preload the tether, when the system is in operation, such that the detected angle of incidence is indicative of the angular position of the unmanned aerial vehicle with respect to the ground station or gravity, characterized in that the ground station comprises a preload assembly with a movable member (203.1) that is arranged in contact with the tether and that is configured to alter a tether path length of an adjustable tether path in the ground station, wherein the movable member (203.1) is arranged translationally movable on a guide of the preload assembly that allows the tether path length in the ground station to be adjusted in length by moving the movable member (203.1) along the guide, such that a load on the tether can be adjusted by moving the movable member (203.1). wherein the unmanned aerial vehicle comprises an angle-sensor configured and arranged to determine an angle of incidence between the tether and gravity or a horizontal plane or the body of the multi-copter, such as to determine from the detected angle of incidence at least an angular position of the unmanned aerial vehicle with respect to the ground station, wherein the ground station is configured to preload the tether, when the system is in operation, such that the detected angle of incidence is indicative of the angular position of the unmanned aerial vehicle with respect to the ground station or gravity, characterized in that the ground station comprises a preload assembly with a movable member (203.1) that is arranged in contact with the tether and that is configured to alter a tether path length of an adjustable tether path in the ground station, wherein the movable member (203.1) is arranged translationally movable on a guide of the preload assembly that allows the tether path length in the ground station to be adjusted in length by moving the movable member (203.1) along the guide, such that a load on the tether can be adjusted by moving the movable member (203.1).