Thank you Rick and Rob. This was very informative. The smooth contours of the comparative polar diagram I had found on the web site earlier suggest it was generated more by wishful thinking than by actual data points. In hindsight I am reminded again that there are no loopholes in physics. I had hoped it would have been enough to adapt current drone control systems to a tethered kite. My attention is back to the promise of the simplicity of mast laced mainsails ;-)