Balsa wood is the most common material used on models and can be cut in two ways. Many kits come with die-cut fins, but when custom designing fins, a fin pattern must be made.
The anatomy of a fin:
Creating fins from patterns: after deciding on a fin design trace the pattern onto the balsa wood using a metal straightedge (when possible). Keep in mind that the leading edge of the fin must be parallel to the grain of the wood. Use a sharp modeling knife to carefully cut the fins out of the balsa.
Shaping fins for maximum performance: most instructions will say to sand all of the fin edges square. Shaping the fins decreases aerodynamic drag, allowing the model to fly higher and faster.
 Rounded Edges |
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Smoothing The Fins: Even after sanding, balsa is not as smooth as it can be. Sanding sealer can help to smooth out the woodgrain, and create a much more efficient rocket.
Start out by sanding the fins with extra-fine grain sandpaper. Once this is completed, apply a thin layer of sanding sealer to all the balsa surfaces. Be sure to let the sealer dry, and then sand again with fine sandpaper. Repeat these steps a few times t o ensure that all the grain has been filled in.
Attaching the fins: most models come with fin alignment guides that can be cut out of the manual, and used to mark the body tube. When designing a rocket, it is sometimes possible to use these guides to mark the body tube. Below are fin alignment guides of different type. To use, print out the image and place the bodytube directly on top of the image. the lines show where the fins should be placed.
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To glue the fins to the body tube, start by applying a layer of glue to the root edge of the fin. With the tube inverted (nose down), place the fin on the marking line and hold it there for a few minutes. Once the glue is set, repeat this with the rest of the fins. Allow the them to dry at least 24 hours before continuing with construction.
Glue fillets help to reinforce the fins. Apply several thin layers of glue along the root edge of the fin. Be sure to allow the fillets to dry in a horizontal orientation so that the glue does not run.
