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  #1  
Old 09-28-2010, 09:35 PM
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Feyd Feyd is offline
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Default New Design - Tube Type

I kind of like tube-fin rockets even though I've never built or flown one. Here is an interesting three-engine 18mm cluster for you all to check out. Lots of tubes :-)

Seems to fly pretty well on pretty much any 18mm engines I put in it.
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  #2  
Old 09-28-2010, 10:16 PM
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I've built the Quest Totally Tubular, and my own No Tube Left Behind, and I find they're OK to a degree. There does seem to be an 'upper limit' to the length of the fin tubes -- beyond some length relative to their diameter, they stop being effective. Haven't figured out the ratio yet...

Looks good!
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  #3  
Old 09-29-2010, 06:27 AM
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Thanks for the comments... I'm kind of anxious to see how it actually flies. But I'm not looking forward to cutting all of those side tubes! The angle cuts for the transitions will be a challenge too.
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  #4  
Old 09-29-2010, 08:15 AM
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For a moment, I couldn't see what you were talking about (the comment about side tubes). How many are there? (Between the low res image and the black color it is kind of difficult to tell.) BTW, I'd consider that more of a ring fin design rather than a tube fin, but that's really just semantics. From what I understand, Craig is right about the length of tube fins and stabilizing efficiency. I think I remember someone mentioning somewhere that about 2X the diameter is about as long as they should be - any longer and you start getting compression effects inside and air doesn't flow through as well.

Something you might want to consider with those side tubes is vented ejection (think of the Estes Trident). Same as a baffle and no (or very little) wadding needed.

Greg
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Old 09-29-2010, 08:26 AM
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Yea... I tried putting tube fins on this one and the weight ratio was all off. I'll have to look at it again.
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  #6  
Old 09-29-2010, 09:34 AM
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As far as the vented ejection goes... I'm not sure I want to drill a bunch of holes in the transitions I have a central tube going from the engine mount area to the first "payload" section where the parachutes are. If I build this I'll put a baffle in that tube.
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  #7  
Old 09-30-2010, 12:40 PM
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Quote:
Originally Posted by Feyd
...If I build this I'll put a baffle in that tube...


Just insert this in an appropriate location:

SEMROC #16 Ejection Baffle
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  #8  
Old 09-30-2010, 12:52 PM
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Custom's now OOP Serval was my all-time favorite tube-finned rocket.
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  #9  
Old 09-30-2010, 04:06 PM
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Oh yea, I've used Semroc's baffles and I'm very happy with them. Definitely I'll use a baffle instead of wadding
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