07-07-2017, 01:20 AM
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Master Modeler
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Join Date: Jan 2009
Location: Fairbanks, Alaska
Posts: 6,507
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Quote:
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Originally Posted by BEC
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  |
By "thin centering rings," do you mean the flat white card stock ones that--in kits such as the Astron Farside--were often glued to the BT-20 motor mount tube *and* to a BT-50 stage coupler?
I always preferred that "two doughnut-type centering rings" kind of motor mount as well (the "modern" [but anything *but* better] thick, heavy BT-20 to BT-50 motor mount 'centering sleeve' is only fit to be cut into multiple "doughnut-type" centering rings).
That "yellow catalog pages Alpha fin planform" sounds like yet another variation to add to the history mix... I wonder if that particular Alpha (those yellow pages are from the "Model Rocket Manual" catalog insert, which begins here: http://www.ninfinger.org/rockets/no...a/69est048.html ) was, back then, a sort of "school bulk rocket," where teachers would buy batches of Alpha parts and use those Alpha plans (with that included fin pattern) so that the kids could build their rockets? (I wonder this because in those days, a lot of people around the country had to buy model rocket supplies and building supplies by mail order--that 1969 catalog also offered paint, glue, sandpaper, hobby knives, and Photo-Flash "D" batteries for that reason.) |