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BP capacity of forward closure on 38mm.

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Fuddrucker

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Does anyone know the capacity of the forward closure on the 38mm canisters. I am trying to find out how many grams of BP it will hold.

Another way I could put it is,,,has anyone ever used a 38mm in a 5.5" frame and used the standard BP charge to pop the nose. No electronics, no extra BP, just what the closure would hold. I am wondering if a 38mm closure would have enough charge to pop the cone on a 5.5 dia. rocket I am planning. The actual space to pressurize would be about 22". Using a ejection charge calculator, I would need 4.62 grams of BP for 18 PSI.

Thanks!

...Fudd
 

Justin Horne

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Well, i'm sure you aren't getting 4.6 grams in! I'm thinking maybe 1.25 if you packed it to the top..
 

Elapid

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in a standard AT 38mm forward closure and got 1.5g full to the top.
 

n3tjm

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Is the rocket an I-ROC? That sounds like the size of the I-ROC's chute compartment. You will have no problem with the 38mm (and 29mm) forward closures :). I have flown my I-ROC's with both 29 and 38mm motors with out problems :).
 

Missileman

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Are you sure you need 18 psi on a 5.5" rocket?
I read something recently (can't remember where now)
The larger the diameter the less pressure you need.
The way it figures is this, figure the square area of your nosecone.
Figure that every square inch has this same pressure applied.
As you can see if you do the math 18 psi on a 5.5" rocket is really alot of force applied to the cone vs. a smaller diameter rocket.
 

n3tjm

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BP amounts have always been confusing for me. Because I heard both stories. My rule... the bigger the tube, the more poweder. Sure, there is more force in that cone.... but it will take energy to deliver that energy to the nose cone; plus you are also moving the heaver recovery harness that you would have with larger diameter rockets....

Does that make sense?

I don't know... been up for 17 hours...
 

DumasBro2

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You can also increase the capacity by usinga couple wraps of masking tape around the knurled part of the closure then tape across the top to seal it off.

steve
 

Fuddrucker

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Originally posted by n3tjm
Is the rocket an I-ROC? That sounds like the size of the I-ROC's chute compartment. You will have no problem with the 38mm (and 29mm) forward closures :). I have flown my I-ROC's with both 29 and 38mm motors with out problems :).
It's not the I-ROC, but the scratch build I am making is about that same size. I am going to put a 54mm mount in it, but I also want to fly it on 38mm motors as well and that was why I was wondering if the 38 closure would be ok for it. I am thinking of making it my level 2 cert. rocket and want to be sure I have covered all my bases.

...Fudd
 

Fuddrucker

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Originally posted by DumasBro2
You can also increase the capacity by usinga couple wraps of masking tape around the knurled part of the closure then tape across the top to seal it off.

steve
Thanks for the great idea!

...Fudd
 

Fuddrucker

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Originally posted by missileman
Are you sure you need 18 psi on a 5.5" rocket?
I read something recently (can't remember where now)
The larger the diameter the less pressure you need.
The way it figures is this, figure the square area of your nosecone.
Figure that every square inch has this same pressure applied.
As you can see if you do the math 18 psi on a 5.5" rocket is really alot of force applied to the cone vs. a smaller diameter rocket.
Now that you mention that, I too remember reading something about that. I think it was in the last issue of Sport Rocketry (had Jim Flis on the cover I think, or at least someone holding a Duece's Wild). May have also been on RocketryOnline's website. Anyway, it makes sence. On that theroy I am also reminded of tires. The larger the tire, the less air pressure you need to make it firm. I don't really think I need 18psi, that is just what the calculator gave as a PSI option. The other option was 15 PSI and it said I need like 3.82. If I use the ejection charge calculator from RocketryOnline, for 10lbs of pressure, I need 2.58 grams.

Thanks for the measurments and the replys. I feel confident now that it will be fine. I think I worry too much!

...Fudd
 

utahrc

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I've got a Polecat Aerospace 5.5" Skeeter that blows the nose just fine with the 38mm charge. I've seen several of their 5.5" Nike Smoke's do the same. As long as you've got the chute packed loosely and the nosecone on just tight enought that you can lift the rocket by it but still shake it off you should be fine.
 
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