Autonomous Takeoff and Flight of a Tethered Aircraft for Airborne Wind Energy

Abstract

A control design approach to achieve fully autonomous take-off and flight maneuvers with a tethered aircraft is presented and demonstrated in real-world flight tests with a small-scale prototype. A ground station equipped with a controlled winch and a linear motion system accelerates the aircraft to take-off speed and controls the tether reeling in order to limit the pulling force. This setup corresponds to airborne wind energy systems with ground-based energy generation and rigid aircrafts. A simple model of the aircraft's dynamics is introduced and its parameters are identified from experimental data. A model-based, hierarchical feedback controller is then designed, whose aim is to manipulate the elevator, aileron and propeller inputs in order to stabilize the aircraft during the take-off and to achieve figure-of-eight flight patterns parallel to the ground. The controller operates in a fully decoupled mode with respect to the ground station. Parameter tuning and stability/robustness aspect are discussed, too. The experimental results indicate that the controller is able to achieve satisfactory performance and robustness, notwithstanding its simplicity, and confirm that the considered take-off approach is technically viable and solves the issue of launching this kind of airborne wind energy systems in a compact space and at low additional cost.

A Small-Scale Prototype to Study the Takeoff of Tethered Rigid Aircrafts for Airborne Wind Energy

“…Overall, the described hardware solution and the corresponding control approach achieve the desired, conflicting goals of limiting the tether pull while avoiding an excessive reel-out of the line, which would lead to entanglement very quickly. A movie showing the winch behavior (in combination with the glider autopilot described in detail in [16]) is available on-line [15].…”

“…the pilot inputs are fed directly to the actuators), to fly-by-wire (with low-level controllers that stabilize the glider pitch and roll, and the pilot providing references for these angles), to fully autonomous. The modeling and automatic control of the glider is described in detail in a separate contribution [16].…”

“…The system modeling, identification and controller design aspects related to such an autopilot, as well as the obtained experimental results, fall beyond the scope of the present paper, whose focus is on the prototype hardware and ground station control. The autonomous take-off and flight of the aircraft are therefore subject of a separate contribution [16]. The paper is organized as follows.…”

Set Membership Identification of Linear Systems With Guaranteed Simulation Accuracy

“…Here, we present the results obtained with the proposed identification approach applied to data acquired from realworld test flights of a small-scale prototype of an autonomous tethered aircraft, used for Airborne Wind Energy (AWE) generation, see Fig. 10 and [10]. We focus on the identification of a model of the roll-rate dynamics of the aircraft, resorting to a data set collected during several experiments.…”

Cascaded Pumping Cycle Control for Rigid Wing Airborne Wind Energy Systems

“…Although the reliability of the control system plays a paramount role that decides upon the success of this new technology, most of the available literature focuses on flight path optimization instead of the development of more robust control solutions. One recent control approach that is not dedicated to flight path optimization is presented in [9]. In the paper, the authors focus on take-off and landing control, including a transition to a loiter-like figure-of-eight flight pattern on a constant tether length using linear controllers.…”