Both the Estes K-36 and the Centuri Saturn V had clear add-on fins. The Estes kit used a sandwich of two pieces that the modeler glued together on three of the edges. The Centuri kit used a single sheet with a pair of slots that you bowed out to slip over. This made the fin have a slightly cambered shape and gave the Saturn a nice slow rotation. IIRC, on a single D12, by the time it ejected it had rolled somewhere between 1/2 and one full rotation. Since the real Saturn had a roll program, it should give it mission points!

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