Hybrid design: camber inducing techniques
A. First of all I needed to test my concept of effective 3D billow. I understood the C-quad design and started making something like it. But I did not like the way the C-Quad packed. Learning from other stuntkites and the Velcro spine enclosement I modified each spar-end with one so spars could be tensioned or removed without the bridle coming loose. The method of attaching the bridle to the LE also provided me with a solution for the LE bridle wear. It flew reasonably well and it packed away like any other stuntkite, could even strap to the back axle of my buggy!
B. The zero thickness where battens are located between cells on the C-quad provided flight stability but I felt that it could hinder it's maximum lift performance so I started designing the sail for a smooth topskin. Keeping the battens in the same plane as the LE I simply used partial ribs to achieve the aerodynamic billow shape. I made the sail and framed it but never got the time to bridle it during three months before my wedding. I might bridle it in future just for comparison with later models.
C. I did not stop thinking... This is where the windsurf sails really got me wondering about hybrid sail design. The chord being the shortest line between the LE and the TE meant that a batten under tension along the camber line would have the same shape as the camber of partial rib that supported it. This meant a few improvements as the billow wasn't so variable anymore and that the sail would keep it's shape better under all conditions and wasn't a factor of the airpressure on the skin. I never made this to test the concept but went straight to the next being a simpler version of this concept.
The spar-ends have also been modified to incorporate the same technique used on windsurf sails to place the battens under tension using a friction clip and Velcro. During this design I also started getting rid of all frame connectors. I broke quite a few during testflights with type A and got tired of replacing them all the time. Noticing the fact that windsurf sails had no connection between batten and mast I tried to achieve the same.
D. Most foil profiles had a reasonably straight line from about 15%-20% past maximum thickness towards the TE which meant that the partial rib or riblet would only need to support the first 50% of the profile and that the batten under tension could do the rest. I also started using marine sail battens instead of carbon or fibreglass spars/rods in this design. This is my current project and I'm currently in the bridling stages and hope to have the picture of it flying and a review published soon after this.
E. Future project using preshaped-battens to provide the cambered shape with little or no tension and no ribs/riblets. Hang gliders have been using this technique for years now. I did not like the idea of flexing the foil into shape with the bridle and sail tension as it meant the kites performance would vary for different conditions which was even worse than the induced billow technique in type A. Preshaped battens would solve this while simplifying the design tremendously.
