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.

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.

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."

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.

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???

I would definitely fly it, in something you are not very fond of. Got an old "The Dude" laying around?

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.

I'm pretty sure it can't :) I think Roy was just having a little fun with us :)

Doug

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Please fly it, and shoot video. I love a good pyro show. :)

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

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.

A few years ago I bought some old built rockets off of eBay. I restored a couple of classic kits but a couple more just simple scratch-builts that weren't worth the effort, even though they're flyable. One of them has a 24mm mount. That's the one I'll use.

Interesting! Could be the makings of an R&D project. Wonder if you xray-ed thermal cycled motors early on, could you see the debonding, then over time see it go away?

Yeah, right after I posted I thought about the nozzle blowing out then thought better to blow out the nozzle than blow out the forward end and torch the rocket....maybe??

I also have an old D12-3 in my stash (stamped production date is 5-31-74) as well as my very last D13-3 (date on that one is 8-6-71). The marking on the D13 has faded quite a bit and is hard to see in the pic.

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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Put it in an old Maxi-Brute X-Wing.
The flight MAY simulate it getting blasted by a TIE Fighter.

I CAN'T SHAKE HIM! :eek:



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Come to Minooka, IL and I'll fly a junker with an E60-6 before or after and the wife can video it....... :D

Flight made! Worked perfectly (actually I changed to a D12-5 made on July 20, 1973)


So, I still have the above pictured motor, as well as a couple of D12-7's, one from 1973, and the other from 1974.