Abstract
Abstract. We have developed a tow test setup for the reproducible measurement of the dynamic properties of different types of tethered membrane wings. The test procedure is based on repeatable automated maneuvers with the entire kite system under realistic conditions. By measuring line forces and line angles, we determine the aerodynamic coefficients and lift-to-drag ratio as functions of the length ratio between power and steering lines. This nondimensional parameter characterizes the angle of attack of the wing and is varied automatically by the control unit on the towed test bench. During each towing run, several test cycles are executed such that mean values can be determined and errors can be minimized. We can conclude from this study that an objective measurement of specific dynamic properties of highly flexible membrane wings is feasible. The presented tow test method is suitable for quantitatively assessing and comparing different wing designs. The method represents an essential milestone for the development and characterization of tethered membrane wings as well as for the validation and improvement of simulation models. On the basis of this work, more complex maneuvers and a full degree of automation can be implemented in subsequent work. It can also be used for aerodynamic parameter identification.
Highlights
With the turn of the millennium, kitesurfing has evolved into a mainstream water sport, followed by the more recent variants of land and snow kiting (Tauber and Moroder, 2013)
In terms of industrial applications, flexible membrane wings have already been used since the 1970s as aerodynamic decelerators for airdrop systems and are currently being explored for airborne wind energy (AWE) generation (Schmehl, 2018)
We have presented a unique tow test setup for automatic measurement of the dynamic properties of different wing types at full scale and under realistic conditions
Summary
With the turn of the millennium, kitesurfing has evolved into a mainstream water sport, followed by the more recent variants of land and snow kiting (Tauber and Moroder, 2013). Despite the advancements within the kitesurfing and AWE industries, tethered membrane wings are mostly still designed by iterative testing with empirical and intuitive variation of wing parameters This has led to a relatively high degree of maturity on the product level, the approach is time-consuming and expensive because a large number of prototypes need to be manufactured and tested. For this reason, we conclude that the empirical design method will only allow for limited further improvements and that it is indispensable to develop a systematic understanding of how wing performance parameters, such as aerodynamic coefficients, lift-to-drag ratio, steering forces and moments, depend on the wing design. This holds for leading edge inflatable (LEI) tube kites (see Fig. 1) and other single-skin kite types, since ram air wings have already been investigated systematically for several decades (Dunker, 2013, 2018; Johari et al, 2014)
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