We took four different rokkaku kites out to the parking lot today to compare their performances. Kite 1 (photos 1, 8, 12-15) was the original rokkaku with all-carbon spars. Kite 2 (photos 1, 8, 11-12) was similar but with a modified spine. We also hung a camera off the line of this kite to film Kite 3. Kite 3 (photos 1, 8-10) had an identical canopy to 1 & 2, but instead of carbon spars, it had inflatable spars made of cuben fiber. The inflatable spars had the same curvature as the original carbons spars. Kite 4 (photos 3-7) was also made from an identical canopy and also had inflatable spars made of cuben fiber. However, these spars were 90% of the diameter of 3’s spars, and their curvature was 50% that of 3’s spars.
Kite 4 had the best performance overall, which was a surprise. The third photo shows 4’s general appearance while flying–very little deformation (the first photo shows deformation in the other kites).
Additionally, Kite 4 rarely wobbled during flight, unlike Kite 3, the other inflatable kite, which constantly swooped while flying. It is possible that part of this behavior can be attributed to a drop in windspeed by the time we flew Kite 4, but it is likely that the less-curved spars were simply more resistant to deformation from compression than the more-curved spars. Photo 4 shows Kite 4’s deformation when Don jerked the line very hard, so deformation was possible, but did not occur when flying or winching.
An additional measure of performance was the line angle of each kite. The line angle from the vertical of Kite 4 was around 29-30 degrees, whereas for Kite 3 it was around 47-48 degrees. The carbon-sparred kites had line angles closer to 39-40 degrees.
Bottom photo shows tearing at seams of untested cuben spar (original curvature, 90% diameter). We have learned that, while cube fiber is very strong, it does not react well to being sewed. We can patch defects with glue, but in the future cuben fiber structures may need to be entirely glued instead of sewed.
For video see next post.Return to News