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Old 12-19-2006, 12:12 PM
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CPMcGraw CPMcGraw is offline
Join Date: Mar 2005
Location: Mobile, Alabama
Posts: 5,357
Exclamation New Plan -- Flitter

Another in the Schoolyard Sounders series. The model has reasonably good performance of 460' altitude and a Dv of 10-11 FPS. Only one motor is called out -- the A3-4T; all others produce very high Dv numbers. The model has a 1.75 stability margin with this motor in place.

Included below is the suggested fin cutting pattern. Some may ask "Why do I use so many pieces to create such a small fin?" The answer has to do with the grain direction around the outer edges. You want the grain parallel to the outer edges as much as possible. This is not as critical with a traditional solid-slab fin because the bulk of the fin adds to the strength; with an open-frame fin, you don't have the extra bulk to resist warpage and breakage. Running small strips of balsa around the edges, parallel to that edge, adds tremendous rigidity with little to no penalty in weight. Think more in terms of building a Guillows or Comet rubber-band model airplane than in building a rocket fin. Same principle.

One suggestion: The fins are called out as 1/16" balsa sheet, but start your construction with 3/32" sheet and sand the surfaces down to an average thickness. Finish by laminating paper labels to both sides of each fin, sealed with thin CA.

Length: 15.49"
Diameter: 0.908" (ST-8)
Fin Span: 4.85"
Weight: 0.82 oz

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Attached Files
File Type: rkt Flitter.rkt (126.4 KB, 76 views)
Craig McGraw

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