What is a kite?
A kite is simply a wing on a line; a description that presumes nothing about the material, shape or design of the wing itself. The wing can range from a rigid body, much like a sailplane, to a fabric structure that gains its shape by the force of the wind. Trade-offs exist in both cases, and the best kite for power generation is still an open question. The Tensairity kite, which is being developed at EMPA, lies somewhere in between these two extreme cases; aiming to combine the structural rigidity and aerodynamic efficiency of a sailplane with the low weight and transportability of a soft kite. Shown below is the 160m2 kite used by Skysails GmbH to pull cargo ships [1] (top left), a rigid glider prototype from Ampyx Power [2] (bottom left) and the EMPA's Tensairity kite prototype [3] (top right). Also shown is a concept 'airborne wind turbine', courtesy of Joby Energy [4], which we also consider a kite (bottom right).
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