07-07-2017, 12:40 AM
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Master Modeler
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Join Date: Feb 2009
Location: Auburn, Washington
Posts: 3,643
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Quote:
Originally Posted by blackshire
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Jason,
I have the original instructions for the first Alpha I built (probably in 1968 or 1969), which has the thin centering rings for the motor mount. I also have copies of later versions that show the thicker ones arranged as shown in the yellow "Model Rocket Manual" pages in some catalogs. That arrangement was pretty much the way it was done until the big thick single cylinder was introduced....sometime after the nose cone became plastic and the fins were being die cut.
That arrangement - as shown in your link - is actually the way I prefer to do it when I build an Alpha.....
NOTE: the fin pattern on that catalog page is NOT quite right. Or at least it doesn't quite match the SP-25 pattern, the shape of the subsequent die cut fins (which are very close the SP-25 pattern) or the current laser cut fins (which are slightly smaller and with more sweep). However, if you order laser cut K-25 fins from Semroc, that's the shape you will get (unless Randy Boadway has changed the cut files after he bought Semroc). Fin shapes are a whole 'nother long discussion
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