07-08-2012, 10:40 PM
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Incurable SEMROC Fan
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Join Date: Mar 2005
Location: Twin Falls, Idaho, USA
Posts: 2,318
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Semroc Groonies: *Marginally* stable?
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Originally Posted by Carl@Semroc
The Starlight is another old design that was probably marginal at the time. With no nose weight, Rocksim gave a margin of .54 using a C6-5 and a margin of 1.27 with the added .2 oz. weight. I never saw a Starlight back then that was unstable, but we still added the weight for margin in our release.
I have been trying OpenRocket on our designs and the results are always more conservative. I do not know where the differences are. We always select Rocksim stability equations instead of Barrowman equations for stability calculations.
Perhaps OpenRocket uses the older, less accurate equations. Probably half of our kits would be marginal or unstable if we used Barrowman, yet they clearly are not. (Well the Mars Lander is clearly marginal and should never have been released.  ) |
The RockSim file for your Saki Groonie has had me shaking my head, given the following figures, *with* nose weight:
Empty -- 1.15 calibers
A8-3 -- 0.78 marginal
B6-4 -- 0.75 marginal
C6-5 -- 0.68 marginal
But you *say* it flies okay "in the real world?" 
It makes me want to push that motor mount back until the engine hook lines up with the main body tube, instead of having it recessed.
Just sayin'.
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__________________
Jay Goemmer
"Centuri Guy"/"Tau Zero"
YORF Member 28
Semroc SAM #0029
NAR 86131
"I think about organizing things all the time. Never seems to happen. I find something that piques my interest and I'm off on a quest. Or a Centuri.  "
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Bill “Wallyum” Eichelberger re: Estes Flutter-By
03 Sept 2014
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