Lift kite operation requirements of a rotary airborne wind energy system

Rotary kite airborne wind energy system is equipped with a tensile rotary power transmission (TRPT) system that can transmit torque from the airborne components to the ground [1,2]. The TRPT section has several equally spaced connecting tethers linking all concentric rings from the top end to the bottom end, the top ring acts as the rotor with multiple rigid blades, and the bottom ring is connected to a fixed ground station. A lift kite is applied to lift the rotor and TRPT system and provide tension as the axial force, the latter directly influences the TRPT transmission performance. The lift kite plays central roles during system operation in the air, launching and landing. The aim of this work is to investigate the operation requirements of the lift kite. At any given wind speed, the equilibrium point of the system is achieved by the operation of lift kite. A small deflection angle, θ, is induced between the TRPT’s central axis and the tether connecting the rotor to the lift kite. The tension force exerted by the lift kite, Fk, counterbalances the drag force on TRPT, DTRPT , and the lumped gravitational force of the AWE system,W, leading to the moment equilibrium. To enable effective torque transmission and aerodynamic performance, the lift kite force, Fk, and its deflection angle, θ should be determined to achieve the designed TRPT elevation angle, β, and the required tensile force. Hence, both axial and normal components of Fk are determined, and considering the drag force, the requirement for the design of the lift kite and its operating altitude, Hkite, can be calculated. The understanding of the lift kite operation requirements is not only necessary for system design optimisation and control, but also critical for deployment of automated