Autonomous take-off and landing of a tethered aircraft: a simulation study

The problem of autonomous launch and landing of a tethered rigid aircraft for airborne wind energy generation is addressed. The system operates with ground-based power conversion and pumping cycles, where the tether is repeatedly reeled in and out of a winch installed on the ground and linked to an electric motor/generator. In order to accelerate the aircraft to take-off speed, the ground station is augmented with a linear motion system composed by a slide translating on rails and controlled by a second motor. An onboard propeller is used to sustain the forward velocity during the ascend of the aircraft. During landing, a slight tension on the line is kept, while the onboard control surfaces are used to align the aircraft with the rails and to land again on them. A model-based, decentralized control approach is proposed, capable to carry out a full cycle of launch, low-tension flight, and landing again on the rails. The derived controller is tested via numerical simulations with a realistic dynamical model of the system, in presence of different wind speeds and turbulence, and its performance in terms of landing accuracy is assessed. This study is part of a project aimed to experimentally verify the launch and landing approach on a small-scale prototype.Comment: This is the longer version of a paper submitted to the 2016 American Control Conference 2016, with more details on the simulation parameter

Airborne Wind Energy Systems: A review of the technologies

Among novel technologies for producing electricity from renewable resources, a new class of wind energy converters has been conceived under the name of Airborne Wind Energy Systems (AWESs). This new generation of systems employs flying tethered wings or aircraft in order to reach winds blowing at atmosphere layers that are inaccessible by traditional wind turbines. Research on AWESs started in the mid seventies, with a rapid acceleration in the last decade. A number of systems based on radically different concepts have been analyzed and tested. Several prototypes have been developed all over the world and the results from early experiments are becoming available. This paper provides a review of the different technologies that have been conceived to harvest the energy of high-altitude winds, specifically including prototypes developed by universities and companies. A classification of such systems is proposed on the basis of their general layout and architecture. The focus is set on the hardware architecture of systems that have been demonstrated and tested in real scenarios. Promising solutions that are likely to be implemented in the close future are also considered

On sensor fusion for airborne wind energy systems

A study on filtering aspects of airborne wind energy generators is presented. This class of renewable energy systems aims to convert the aerodynamic forces generated by tethered wings, flying in closed paths transverse to the wind flow, into electricity. The accurate reconstruction of the wing's position, velocity and heading is of fundamental importance for the automatic control of these kinds of systems. The difficulty of the estimation problem arises from the nonlinear dynamics, wide speed range, large accelerations and fast changes of direction that the wing experiences during operation. It is shown that the overall nonlinear system has a specific structure allowing its partitioning into sub-systems, hence leading to a series of simpler filtering problems. Different sensor setups are then considered, and the related sensor fusion algorithms are presented. The results of experimental tests carried out with a small-scale prototype and wings of different sizes are discussed. The designed filtering algorithms rely purely on kinematic laws, hence they are independent from features like wing area, aerodynamic efficiency, mass, etc. Therefore, the presented results are representative also of systems with larger size and different wing design, different number of tethers and/or rigid wings.Comment: This manuscript is a preprint of a paper accepted for publication on the IEEE Transactions on Control Systems Technology and is subject to IEEE Copyright. The copy of record is available at IEEEXplore library: http://ieeexplore.ieee.org

Aeronautical Engineering: A special bibliography with indexes, supplement 62

This bibliography lists 306 reports, articles, and other documents introduced into the NASA scientific and technical information system in September 1975

Modelling and analysis of rotary airborne wind energy systems : a tensile rotary power transmission design

Airborne wind energy is a novel form of wind power. Through the use of lightweight wings and tethers it aims to access locations out of reach to current wind harvesting devices, at a lower cost and with a lower impact on the environment. There are multiple airborne wind energy systems currently under development, one group of these, referred to as rotary systems, use multiple wings networked together to form rotors. This thesis presents an analysis on the design and operation of rotary systems, with a particular focus on the power transmission from the airborne components down to the ground. There are various power transmission methods used for rotary systems, among them tensile rotary power transmission uses multiple networked tethers held apart by a small number of rigid components to transfer torque from a flying rotor down to a ground station. The aim of this research is to improve the design and operation of rotary airborne wind energy systems that incorporate tensile rotary power transmission, and to assess system performance based on mathematical modelling and test data. It focuses on the Daisy Kite system design, a rotary system, being developed by Windswept and Interesting. Included in this thesis work is the development of three mathematical representations to support systematic analysis and design improvement. The first representation, a steady state model, is used to analyse rotary system design. The second and third models are dynamic representations of varying complexity. Also included is an experimental campaign conducted on the Daisy Kite in collaboration with Windswept and Interesting. Field tests are carried out on nine different Daisy Kite prototypes at their test site on the Isle of Lewis, Scotland. Measured data is collected for the various prototype designs under different operating conditions. The measured data is used to assess the reliability of the three mathematical representations. This allows the models to be validated and compared to one another in terms of their accuracy and computational efficiency. During the experimental campaign several design and operational improvements are made that increase the power output and lead to more reliable operation. The mathematical representations are used to identify key design factors and to optimise rotary system design. Improved understanding and design of the rotary airborne wind energy system has been achieved through this holistic investigation.Airborne wind energy is a novel form of wind power. Through the use of lightweight wings and tethers it aims to access locations out of reach to current wind harvesting devices, at a lower cost and with a lower impact on the environment. There are multiple airborne wind energy systems currently under development, one group of these, referred to as rotary systems, use multiple wings networked together to form rotors. This thesis presents an analysis on the design and operation of rotary systems, with a particular focus on the power transmission from the airborne components down to the ground. There are various power transmission methods used for rotary systems, among them tensile rotary power transmission uses multiple networked tethers held apart by a small number of rigid components to transfer torque from a flying rotor down to a ground station. The aim of this research is to improve the design and operation of rotary airborne wind energy systems that incorporate tensile rotary power transmission, and to assess system performance based on mathematical modelling and test data. It focuses on the Daisy Kite system design, a rotary system, being developed by Windswept and Interesting. Included in this thesis work is the development of three mathematical representations to support systematic analysis and design improvement. The first representation, a steady state model, is used to analyse rotary system design. The second and third models are dynamic representations of varying complexity. Also included is an experimental campaign conducted on the Daisy Kite in collaboration with Windswept and Interesting. Field tests are carried out on nine different Daisy Kite prototypes at their test site on the Isle of Lewis, Scotland. Measured data is collected for the various prototype designs under different operating conditions. The measured data is used to assess the reliability of the three mathematical representations. This allows the models to be validated and compared to one another in terms of their accuracy and computational efficiency. During the experimental campaign several design and operational improvements are made that increase the power output and lead to more reliable operation. The mathematical representations are used to identify key design factors and to optimise rotary system design. Improved understanding and design of the rotary airborne wind energy system has been achieved through this holistic investigation