Autonomous Take-Off and Flight of a Tethered Aircraft for Airborne Wind Energy

TL;DR

This paper presents a control system enabling fully autonomous take-off and stable flight of a tethered aircraft for airborne wind energy, demonstrated through real-world tests with a small prototype.

Contribution

It introduces a simple, model-based hierarchical controller for autonomous take-off and flight of tethered aircraft in airborne wind energy systems.

Findings

Controller achieves stable, figure-of-eight flight patterns.

System demonstrates robustness and satisfactory performance in real tests.

Proves viability of low-cost, compact airborne wind energy launch methods.

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.