Flight-Path Reconstruction and Flight Test of Four-Line Power Kites

Abstract

A flight-path reconstruction algorithm for tethered aircraft, which is based on an extended Kalman filter, is presented. The algorithm is fed by the measurements of a set of onboard and ground-based instruments and provides the optimal estimation of the system state-space trajectory, which includes typical aircraft variables such as position and velocity, as well as an estimation of the aerodynamic force and torque. Therefore, it can be applied to closed-loop control in airborne wind energy systems and it is a first step toward aerodynamic parameter identification of tethered aircraft using flight-test data. The performance of the algorithm is investigated by feeding it with real flight data obtained from a low-cost and highly portable experimental setup with a four-line kite. Several flight tests, which include pullup and lateral-directional steering maneuvers with two kites of different areas, are conducted. The coherence of the estimations provided by the filter, such as the kite state-space trajectory and aerodynamic forces and torques, is analyzed. For some standard variables, such as kite Euler angles and position, the results are also compared with a second independent onboard estimator.

Aerodynamic characterization of a soft kite by in situ flow measurement

“…11). This is in line with the mass distribution used by Bosch et al (2013) and the average ratio of 3 : 1 for the forces in front and rear bridle lines measured by Hummel (2017) for different kites at various power settings. Starting from an initial guess for the line angle λ 1 , we calculate the angle λ 2 and the respective angles for the steering lines.…”

“…Because the membrane wing is continuously deforming during operation it is not as straightforward as for a rigidwing aircraft to define the orientation of the kite relative to the flow. One option is to use the inflated center strut as a reference component to mount the flow measurement equipment (Borobia et al, 2018;van Reijen, 2018). Mounting the equipment directly on the suspended KCU is not considered to be an option because this relatively heavy component is deflected substantially when flying sharp turns (Fechner and Schmehl, 2018) and can also exhibit transverse vibrations.…”

“…In the absence of reliable velocity measurements, van der Vlugt et al (2019) describe an approach to estimate the lift-to-drag ratio of the airborne system components from measured force and position data. Borobia et al (2018) have mounted a Pitot tube directly on the center strut of a small surf kite to measure the relative flow speed. Together with data from other onboard sensors, this has been used to feed an extended Kalman filter to get an optimal estimate of the aerodynamic force and torque generated by the kite as well as the relative flow velocity vector and other kite state variables.…”

Aerodynamic characterization of a soft kite by in situ flow measurement

“…In lack of reliable velocity measurements, van der Vlugt et al (2018) describe an approach to estimate the lift-to-drag ratio of the airborne system components from measured force and position data. Borobia et al (2018) have mounted a Pitot tube directly on the center strut of a small surf kite to measure the relative flow speed. Together with the data of other onboard sensors, this 20 has been used to feed an extended Kalman filter to get an optimal estimate of the relative flow velocity vector and other kite state variables.…”

“…One option is to use the inflated center strut as a reference component to mount the flow measurement equipment (van Reijen, 2018;Borobia et al, 2018). Mounting the equipment directly on the suspended KCU is not considered to be an option because this relatively heavy component is deflected substantially when flying sharp turns (Fechner and Schmehl, 2018) and can also exhibit transverse vibrations.…”