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Box Fin Design

posted 15 Jul 2017, 07:25 by Andy Lakin-Hall

I've been looking for a new design for rocket fins, and came across the Box Fin from US Water Rockets. These have the advantages of being adjustable, and they self-align to the side of the rocket, so I don't need the fin gluing jig to hold things in place in straight alignment.

The template that USWR provide needs scaling to fit the diameter of the bottles I'm using. I used some string to wrap around the circumference of the bottle I will be using, and then used that to calculate the diameter, and then the width of the fin shape. I opened the PDF template in Inkscape and copied the fin shape from there. That was then pasted into a new Inkscape file and scaled to the correct dimensions. My printer scrambles direct prints from Inkscape, so I exported the file as a PDF and then printed that on card at 100% scale.

 I cut out the card fins and tested them against a bottle, to make sure they fit correctly.

Satisfied with the card templates, I printed out three new copies and used repositionable spray-mount adhesive to temporarily glue them to sheets of yellow corriflute.

I cut out the fins with a craft knife, scoring through the central line to make a hinge. Then I used blue PVC tape to cover the edges and join the three parts together. Here they are fitted up against a bottle to test their fit.

The new fins can be mounted the the eventual rocket, either with velcro or with bamboo skewers as described in the USWR guide.

If you're interested in the template I made, which fits standard 2litre fizzy bottles, you can find it here.