Kitesailing Improving system performance and safety J. van den Heuvel B.Sc. August 2010 Kitesailing Improving system performance and safety Master of Science Thesis For obtaining the degree of Master of Science in Aerospace Engineering at Delft University of Technology J. van den Heuvel B.Sc. August 2010 Faculty of Aerospace Engineering Delft University of Technology ⋅ Delft University of Technology Copyright J. van den Heuvel B.Sc. All rights reserved. Delft University Of Technology Department Of Aerospace for Sustainable Engineering and Technology The undersigned hereby certify that they have read and recommend to the Faculty of Aerospace Engineering for acceptance a thesis entitled “Kitesailing” by J. van den Heuvel B.Sc. in partial fulfillment of the requirements for the degree of Master of Science. Dated: August 2010 Readers: Prof.dr. W.J. Ockels Dr.-Ing R. Schmehl Ir. J. Breukels P.D.C. Smit Summary In the world of high performance sailing people are using state of the art technology to push the limits in speed and performance. The introduction of the sport kitesurfing has shown the power that kites can generate. It has meant a revolution in the world of surfing. Kitesurfing only exists since 15 years and began to expand around the world only since the year 2000. Already in 2008 the 50 knots speed sailing barrier has been broken by a kite surfer being the first sailing system to do so. This is less than ten years after the sport started to become public in the world. This illustrates the potential in performance for the use of kites. Kites also offer the possibility of a revolution in other fields like sailing where systems are currently developed to provide propulsion for commercial vessels to save fossil fuels. Kite systems are also developed for clean energy production where wind energy at high altitude is harvested. These High Altitude Wind Power systems can also be applied to ships offering the possibility of sailing at a course of 0 degrees into the wind on pure wind energy. In this research the kite system is evolved such that the performance and safety is increased for kitesailing and energy production. Kitesailing offers higher sailing speeds and more extreme maneuvers compared to conventional sailing. Using kites for sailing has four main advantages over conventional sailing: A larger sail area for the same boat is possible ● Higher true wind speeds are present at a kite ● Higher apparent wind speeds are created by flying cross-wind patterns (sinussing) with the kite ● A kite has more degrees of freedom to perform extreme maneuvers ● This report shows the results of the research that is focused on two goals: Improving the performance of a kitesailing propulsion system and improving the safety. Three different aspects play a dominant role in the development of the system. Improving the L/D ratio of the kite allows for sailing higher upwind. Scaling up the kite increases the pulling force which results in faster sailing. Safety is the most important factor of all that will determine if kitesailing can be practiced by the general public. These three areas of research apply Kitesailing vi Summary equally to the fields of electricity generation and the large systems for commercial sailing. The research of every one of these aspects starts with a theoretical investigation after which new theories are developed and new designs being produced. Actual tests on the beach and during sailing show the improvements that have been made. To increase the performance and safety the following set of requirements is determined: 1. The kite is not allowed to generate more than 450 N in the center of the wind window while it is fully depowered for an 18 ft catamaran 2. The kite must have the possibility of creating zero lift on every position in the wind window. 3. The kite should be able to handle pulling forces of at least 3000 N. 4. The scaled kite must be able to handle twice the aerodynamic load per square meter without buckling compared to the original kite. 5. The L/D ratio of the kite should be as high as possible for sailing upwind. The goal of this thesis is to determine what parameters should be focused on to effectively increase the performance of kitesailing and to design, produce and test a new kitesailing system that meets these requirements. From the sailing system analysis it follows that the focus should be on increasing the lift of the kite by either increasing the lift coefficient CL,A or the surface area SA for effectively improving the overall performance of the sailing system. The surface area is the most promising way to effectively increase the sailing speed. Increasing the kite area from 13 m2 to 25/,m2 increases the sailing speed by 30% on an upwind course. A 50 m2 kite doubles the sailing speed upwind compaerd to a 13 m2 kite. A bridle analysis and design program has been written with two different methods to deter- mine the discrete force distribution on the bridle points of an existing kite. The calculated aerodynamic loads on the tips using an aerodynamic lift distribution proved to be too small. The bridles designed using the original geometric bridle layout gave good general shapes of the kite during flight. A bridle configuration is designed which completely fulfills the requirements of supporting the kite such that it has its design shape during flight and of offering the possibility of zero lift on every position in the wind window. With this capability to depower the size of the kite can be made much larger than the sail area used on a conventional 18 ft catamaran and still keep within the safety requirements. Even in wind speeds of 15 m s the kite area can still be increased to 45 m2. ~ Rules of thumb have been derived for scaling of a tube kite. A new 25 m2 kite is designed, produced and tested. Tests have shown that this kite can easily cope with the design loads of 3000 N without buckling of the leading edge. The maximum lift coefficient of CL max 1.1 of tube kites is already comparable to those of other ”flying wing airfoils”. Therefore this area is difficult to improve. The L/D ratio offers greater possibilities. ( ) > For improving the L/D ratio, four concepts have been analyzed: Kitesailing vii Adding a lower skin ● Adding an elliptical leading edge ● Adding winglets ● Increase the aspect ratio ● Adding a lower skin and an elliptical leading edge both improve the L/D ratio with almost 50%. Increasing the aspect ratio by 80% increases the L D max with the accompanying lift coefficient by 33% and the maximum lift coefficient CL max. The canopy tension also increases by 250%. Adding winglets is not usefull as long as( the~ ) aspect ratio can be increased. ( ) Field tests with a lower skin on a Naish Aero 4 m2 tube kite have shown that this concept can be successfully applied. The leading edge can be made with a minimum amount of foam of only 18 mm of maximum thickness on a 5 m2 tube kite. Kitesailing results In 2009 and 2010 the ”‘Round of Texel”’ was sailed with the Hobie Tiger kitesailing catamaran. The lap times of the kitesailing catamaran and the fastest competitor using conventional sails on that day are given by following table: Table 1: Laptimes of the record runs of the kitesailing catamaran and the fastest competitor using conventional sails in 2009 and 2010 2009 2010 Kitesailing 4:45 4:00 Conventional 2:07 2:30 It shows that the difference in lap time between the kitesailing system and conventional system between 2009 and 2010 has been decreased by one hour and ten minutes. Kitesailing viii Summary Kitesailing Acknowledgements This project could not have been successful without all the help from so many people. I want to thank my supervising professor Wubbo Ockels, the chair holder of ASSET who has set up a great working environment for research on kites. Roland Schmehl for his great effort in getting the final details worked out and pushing me to take that extra step. I also owe many thanks to Jeroen Breukels who has provided me with great feedback for many months and to Pepijn Smit who has taken the effort to take a seat in my graduation committee to give his insights with his great expertise on kite designing. I thank Edwin Terink who has helped me so much on moments when technology resisted me, by keeping a close eye on my graduation schedule and by supporting me with his engineering capabilities that go far beyond mine. I also thank all others at ASSET who have helped me so much on numerous occasions and for giving me great new insights and who have been involved in having great lunches with lots of laughing: Stefan de Groot, Roland Verheul, Lyssandre Rammos, Aart de Wachter, Rolf van der Vlugt and Barend Lubbers. Also Nana Saneeh for arranging so much paperwork during my stay at ASSET. Of course my family and friends are not forgotten for their great support and enthusiasm which has helped me greatly, with Gerben as my kitesailing budy with whom I experienced already so many adventures. Shashika has a special place among all for her love and great support and the many meals she cooked for me so that I could work through the evenings to get the best result. I thank you all. John August 2010 Kitesailing x Acknowledgements Kitesailing Contents Summary v Acknowledgements ix Nomenclature xv 1 Introduction 1 2 Existing kitesailing systems 5 2-1 Traction-based kitesailing .