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  #1  
Old 09-21-2017, 03:29 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, 09:08 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, 11:36 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, 11:39 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, 01:10 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, 01:27 PM
Scott6060842 Scott6060842 is offline
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I would definitely fly it, in something you are not very fond of. Got an old "The Dude" laying around?
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Old 09-21-2017, 02:13 PM
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Tape a LONG stick to the motor "Bottle Rocket"-style and launch it from a tube.
Worst that happens is a cato that destroys nothing but the engine casing.
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Old 09-21-2017, 04:17 PM
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Quote:
Originally Posted by rocketguy101
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, 04:25 PM
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Please fly it, and shoot video. I love a good pyro show.
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Old 09-21-2017, 05:35 PM
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Quote:
Originally Posted by rocketguy101
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???



No. Understand that the bonding that occurs between the casing and the propellant (and previously pressed nozzle) occurs within seconds under great pressure.
The de-bonding occurs, as you say, from the change in diameters. If fired within a few months after this occurs, you'll get flame propagation through that microscopic separation. My theory is that if the motor now is kept in normal storage conditions, the bonding reoccurs as a function of pressure over time. After all, there is still pressure being applied, as the diameter the casing was made at, is smaller than the chunk of propellant. This might explain why a lot of the early 90's Estes E15's, which were taken from the market due to a high probability of catos, (anecdotally) work perfectly now. The cause of their problems was slightly different. They worked fine when fired within a few months after manufacture, but 'dried out' too much, and started catoing later. But it seems the longer they're just left alone, they "settle in" to their casing.

By the way, I think your idea about the epoxy fillet would just lead to either a nozzle blow out or a split casing.

But it's still just a theory
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