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  #1  
Old 09-21-2017, 02:29 AM
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Default 1972 D12-3. Should I fly it?

I'm thinking of flying a junk rocket with a D12-3 made in April 1972 at our club launch this Saturday.

What say you? Should I do it? What do you think will happen if I do?

This D12-3 has been in my possession since it was first purchased at a hobby store. There was a time in the 80's that it spent two or three years in the attic, but since then it has been in a fairly constant normal indoor environment. My theory is that thermal-cycled motors can return to stability over long periods of time.

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Old 09-21-2017, 08:08 AM
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Quote:
Originally Posted by Royatl
I'm thinking of flying a junk rocket with a D12-3 made in April 1972 at our club launch this Saturday.

What say you? Should I do it? What do you think will happen if I do?

This D12-3 has been in my possession since it was first purchased at a hobby store. There was a time in the 80's that it spent two or three years in the attic, but since then it has been in a fairly constant normal indoor environment. My theory is that thermal-cycled motors can return to stability over long periods of time.


If your attic is like mine, that sucker has spent three years cycling from 75 at night up to 150 degrees in the day during the summer and down to the 30's or less in the winter. I'd only fly it if you like seeing roman candles.
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Old 09-21-2017, 10:36 AM
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I've launched many old 1970 engines with great success.
But, my engines were stored indoors in an air conditioned closet.
The best answer to the old D12 is "I'm thinking of flying a junk rocket."
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Old 09-21-2017, 10:39 AM
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Quote:
Originally Posted by Royatl
My theory is that thermal-cycled motors can return to stability over long periods of time.

Then you need to design an experiment to test that hypothesis. I say fly it. My prediction, based on absolutely no data, is that it will not cato.
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Old 09-21-2017, 12:10 PM
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I thought the issue with thermal cycling was the differential diametrical change between the case and the propellant slug (due to different coefficient of thermal expansion of the materials) which allowed the propellant to de-bond from the paper case. During the burn, when it reached the OD of the slug there is a sudden large increase in surface area, causing a pressure spike which leads to CATO.

I don't see how this could self heal...but I've wondered if you could put an epoxy fillet at the back of the motor to keep the slug in, like the old EnerJet motors???
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Old 09-21-2017, 03:17 PM
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I don't see how this could self heal...
I'm pretty sure it can't I think Roy was just having a little fun with us

Doug

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Old 09-21-2017, 03:25 PM
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Please fly it, and shoot video. I love a good pyro show.
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Old 09-22-2017, 05:58 PM
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Quote:
Originally Posted by LeeR
Please fly it, and shoot video. I love a good pyro show.


Come to Minooka, IL and I'll fly a junker with an E60-6 before or after and the wife can video it.......
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Old 09-21-2017, 04:43 PM
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Quote:
Originally Posted by Doug Sams
I'm pretty sure it can't I think Roy was just having a little fun with us

Doug

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No, this is an observation. I've seen lots of old motors that I would have thought would blow, work perfectly. And a thought experiment. If dissimilar substances bond at high pressure in seconds, could they also rebond under lower pressures over longer periods of time? Maybe a couple of years, or even five years, is not enough, but ten, thirty, or in this case, forty-five years might be perfect.
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Old 09-22-2017, 10:17 AM
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Quote:
Originally Posted by Royatl
No, this is an observation. I've seen lots of old motors that I would have thought would blow, work perfectly. And a thought experiment. If dissimilar substances bond at high pressure in seconds, could they also rebond under lower pressures over longer periods of time? Maybe a couple of years, or even five years, is not enough, but ten, thirty, or in this case, forty-five years might be perfect.
My thinking is that it could re-seal, and perhaps be tight enough to fly without catoing, but I'm doubtful of it actually rebonding.

The pressure and conditions at the time of manufacture result in bonding, but I'm skeptical it can re-bond at the much lower pressure of simply getting warmed up in a field box, for example.

That said, this is a perfect question for Ed Brown

Doug

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