Rocket Construction: Balsa Fins
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Most rocket bottles have curved sides which makes cutting well fitting
fins difficult.
First, I start with the outline of the rocket bottle on a piece of paper. I add a "good-looking" shape of a fin. To optimize drag, I make the outer edge (here: left edge) parallel to the rocket axis. As fin material I use balsa wood, 1.5 or 2 mm thick, depending on the size of the rocket. Before cutting with a sharp knife, I make sure the grain is parallel to the upper edge (see sketch). |
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To strengthen the wood considerably, I soak it with cyan-acrylate (CA) glue, using a double layer of household foil around the wiping finger. This glue-soaking adds only little weight. If the fins should look nice, I wrap it before in very thin red paper. This adds some more strength, forming a "sandwich" with the wood. |
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To glue it on, I tried many glues: epoxy, CA and a plastic cement, all
on the same rocket. None has been torn off yet, except by brute force.
Here you see how I attach the fins to the rockets: using a "Helping Hand", the glue can RIP (rest in peace) until hardened. The rocket body sits in a vise, loosely tightened. However, aligning the fin parallel AND vertical with the desired exactness is not easy. |
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Watch a fin being glued on with PolyURethan
glue. The PUR glue is transferred with a syringe. I made some holes through the fins close at the glued edge; the glue will penetrate through the holes, forming some sort of rivets. (I saw this tip somewhere on the net - I am happy to give credit here, but: where was it?). Watch the foam growing ... |
