So I was at Folly Beach on Friday the 17th in 10-12 MPH winds. I launched my 9 foot Tyvek Delta kite to watch the center spreader bar snap cleanly in half when the kite achieved maximum height and wind resistance. The broken dowel punctured the wing when the kite folded in half. The kite will be easy to fix, but I was concerned with how easily the dowel snapped.
The diameter is 7/16" or about 1 cm and is the one I am pointing to in the photo. I think bamboo might have a stronger strength to weight ratio. I might try some since I just got 500 stakes for a different project.
NOOO!!! that is terrible! I always thought of those spars as over-built, and have flown in higher winds... Its telling that it happened right at the ferrule. A stronger alternative would be to not use a ferrule on the spreader, or to use a three-part spreader with two ferrules, so the ferrule isn't right in the middle, where maximum stress concentrates.
Bamboo has a much better strength to weight, and its flexibility is superior for a spreader. A whole culm is problematic because it doesn't bend evenly, and ferrules can crush the hollow cylinder. I'd try to match two culms and put their wider ends in the middle. The bottom of the culm might be thick enough not to be crushed, but perhaps consider filling the culm with either a dowel or maybe epoxy before putting it in the ferrule. Or maybe try a fiberglass spreader (ick!).
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