burst strength of typical model rocket body tubes

eanybody know, in general, what kind of psi, typical estes,totally tubular or BMS 13mm body tubes can take before they would burst? does anybody know
what psi is generated by typical estes 1/4A-A from their ejection charges?
tia
shockie B)
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On Thu, 11 Aug 2005 22:49:01 GMT, "shockwaveriderz"

Why do you want to know? Surely a NAR member wouldn't be flying home made motors. It's against the rules.
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phil, theres nothing wrong with a NAR, or TRA member doing AR on his own time.... Thats why the NAR rewrote its membership pledge langauge. NAR rules only apply when I am on NAR-time.
anyway I am using body tubes for piston launcher tubes, and I was wondering what kind of pressurization they might be able to take.
shockie B)
wrote:

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On Fri, 12 Aug 2005 00:23:56 GMT, "shockwaveriderz"

I'm not aware of that data being available, but it would still be quite useful.
In terms of piston tubes, things are rather complex and there is little or no hard data available. First there is leakage past the piston seal to consider, that diminishes peak pressure loads. Furthermore, body tubes commonly used are quite elastic and swell up under pressure. Most piston seals are poorly designed and do not maintain a seal when the tube is expanded under pressure. This in effect is a built in safety relief valve. Thus, the fact that the tube does not rupture in use does not tell you much. Of course, I use a layer of glass over all my piston tubes. Average piston pressures can be relatively low, and even peak pressures do not seem to approach that of the motor chamber pressure. I'll skip the more complex discussion...
Pressures from ejection charges are also very dependant on specific cases. However, it's just BP so you should be able to find some helpful data.
Alan
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alan:
by "leakage past the piston seal" do you mean between the piston itself and the inner piston walls?
Assuming a minimal difference between the od of the piston and the id of the piston tube walls, I have been using either a spray graphite or a dry spray teflon, and a piston head that is 2x diameter, with the idea towards minimal friction and the spray /length both hopefully contributing to a better "seal".
I assume that by using a layer of glass, that is to prevent any possible swelling under pressure load? I had considered doing essentially the same, thing but I was just going to impregnate the tubes with a finishing epoxy, allowing it to soak in real good, to make them more resistant to any swelling.
thanks
shockie B).
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On Fri, 12 Aug 2005 02:33:44 GMT, "shockwaveriderz"

yes
Well, you might decrease the swelling by an order of magnitude or so, but there is always some swelling, and some leakage even without swelling.

You can put a thin layer of epoxy on the inside of the piston tube and lap it, to get a longer lasting tube. On the outside you can put on a layer or two of 3/4 Oz. Glass with CA or epoxy.
Or yo can just keep doing what ever you've been doing. It probably works better than nothing. Or, glue on a layer paper or use whatever materials are at hand.

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Alan Jones wrote:

I'm sure they only swell a fraction of their original volume. Any expansion they experience would probably be negigible. Any increase in piston clearance (reducing peak pressure) is also likely to be negligible, unless you're working with clearances in the .001" range.
Dave
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wrote:

Yes.
That hypothesis is case dependent, but even inferior piston launchers can be much better than nothing.

Ideally, piston seals should have clearances in the .000" range.

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IIRC, Kraft paper has a tensile strength of about 30psi. You can use standard hoop stress equations after that, I suppose, although I'm not sure how you account for the seams in a spiral-wound tube...
BillW
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Hundreds if not thousands of R&D reports must have been done on piston launchers in the last 35 years. I bet if you dig the NAR R&D archives you will find exactly what you are looking for.
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wrong. :(

Where are these archives, and how do I access them? The only "archives" that I'm aware of are private collections. You can find some NAR R&D reports in the NAR Tech Review, From NARTS, but that is only a small sampling and certainly not "the NAR R&D archives".
Alan Have shovel, willing to dig.
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Good question, but they have to be somewhere, where do all the summeries go ?
63.6 Summary Each entry shall include, in addition to the detailed report, a separate 250-300 word written summary of the report. The summaries from all the entries shall be sent to the NAR Contest Board by the Contest Director with the meet results. The NAR reserves the right to publish the summary in order to disseminate information on current R&D activities.
They must be in someones garage or storage room. find them, scan them and make a library ;-)

Google finds only some of those.

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Well, maybe dozens... Including one more this year.
--
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
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Time to check out posting to r.m.r with Google Groups after AOL killed their newsgroup support:
First, for all that you hear about piston R&D projects--and you would think there would be dozens of reports available covering every detail of piston launchers--My literature search, both of my collection of NARTS publications and on the web, turned up roughly a half-dozen reports back in early July. There may be dozens of piston reports, but they are not accessible.
None of the ones I could find said anything about pressure in the piston. I was actually specifically looking for pressure data, because my brother wanted to do an R&D on pressure. So much to our astonishment, it was up to us to come up with some sort of measurement of the pressure in a piston. We got numbers around the 5-10 psi (gauge, of course) range. There are likely higher pressures momentarily, as we only could look at pressures averaged over fair-sized intervals.
I'm not aware of any pistons that have popped a seam because of internal pressure.
I just finished putting up our R&D paper on my website this morning:
http://members.aol.com/petealway/piston.htm
I hope this is of use.
Peter Alway
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wrote:

Thanks, and congratulations.
Alan

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I've seen people use pistons that looked like they were made out of body tudes so a motor tube should be plenty strong. I don't know much about it. Check with people that to the NAR contests for altitude. They are the ones that use them.
On Fri, 12 Aug 2005 00:23:56 GMT, "shockwaveriderz"

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know
I've used them for ejection charges, packed full of 3 or more grams of BP with a ematch hot glued in one end. the hot glue end lows out before the tube gives way most times.
I would not use them for motor casings, you can get empty 13mm paper motor casings many places. heck, just use the dummy engine cases sold.
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Try http://www.rocketmaterials.com/ There is great scientific information on a variety of rocket materials including body tubes.
Dasheight

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Let's call the burst strength B, and the ejection strength E.
Then we have B < E for at least some combinations.
:-(
--
Bob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf
  Click to see the full signature.
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