Stuck motor took paper with it.

Antares JS

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After flying my Loki motor today, I couldn't remove it after the flight, and ended up removing the aft snap ring and pushing everything out the aft end of the motor to clean it in place. When I got home. I used a piece of wood to ram the motor out and this was the result.

20220108_195048.jpg

Obviously, some paper from the motor mount tube bonded itself to the motor case and this is why it got stuck. It did take some effort to clean the stuck paper off the motor. I am thinking this probably has something to do with my sanding the motor mount tube out to get the Loki case to fit in the first place.

I would appreciate it if someone can tell me if they have had a similar experience or if someone has any tips on preventing this from happening again.
 

heada

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Was there any glue or sanding sealer or paint inside the MMT? The heat from the motor could reactivate the glue and then when it cooled, bonded with the paper. If there was a dab of glue in there, that could explain difficulty inserting it too.
 

Antares JS

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Was there any glue or sanding sealer or paint inside the MMT? The heat from the motor could reactivate the glue and then when it cooled, bonded with the paper. If there was a dab of glue in there, that could explain difficulty inserting it too.

Thats what I was thinking too, but this was the rocket's third flight. The aerotrch motor cases used on the previous two flights were a bit tight but removable in the field. If there was a dab of glue, I would think this issue would have come up before now.
 

heada

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Soak the case in warm water. The paper should pretty much fall apart and show whats under it. Paper doesn't bond to anodized aluminum by itself. Has to be something there under the paper. Might have been on the case and not the MMT.

Efit: just saw where you said you cleaned it already. Was there anything under the paper?
 

Antares JS

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Soak the case in warm water. The paper should pretty much fall apart and show whats under it. Paper doesn't bond to anodized aluminum by itself. Has to be something there under the paper. Might have been on the case and not the MMT.

Efit: just saw where you said you cleaned it already. Was there anything under the paper?

No, it took some effort to clean off but it left no residue. Really weird.
 

Halvey

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That's great. Had to recently sand out a Cesaroni case to get a engine load to fit inside. Sanded just enough to get a regular/slightly tight fit. The fit is perfect in the MMT's I have. Still unnerving after seeing this. More build notes.
 

Halvey

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It probably built or pulled moisture in that tube area, after firing then cooling, swelling the minimally thinned case and heated the motor tube glue or ??. Forced reaction. Very weird.
 

RocketRev

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You said you had to sand the I.D. of the MMT in order for the motor to fit, right?

If so, was it a brand new sheet of sandpaper or a previously used sheet/piece of sandpaper?

If used, there may have been some residue of glue or epoxy from your previous sanding work still on the sandpaper that was inadvertently left inside the MMT after you sanded it to get the motor to fit. That residue in a tight fit between the Loki motor case and the MMT, heated up by the motor's hot temps certainly could be the cause of your MMT becoming bonded to the Loki motor case.

Even if it was a brand new never previously used sheet/piece of sandpaper, there is the glue between the sand and the paper of the sandpaper to consider.

If it was my rocket, I'd replace the paper MMT with a PML phenolic MMT as the easiest solution to the problem. Don't tell anybody, but I used to routinely replace my LOC paper MMTs with good old PML MMTs. I had to sand the inside hole of the centering rings like crazy as the PML MMT had a slightly larger O.D. than the LOC MMTs, but that was normal.

Brad, the "been there, had the paper stick to the motor case" "Rocket Rev.," Wilson
 

RocketRev

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Just had another idea. Did you ever friction fit a motor case into this MMT? If so, that can leave glue residue inside the MMT as well.

TTFN... gotta go to church.

Rocket Rev,. out for now.
 

Antares JS

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If so, was it a brand new sheet of sandpaper or a previously used sheet/piece of sandpaper?

Used, but it was never used to sand glue.

Even if it was a brand new never previously used sheet/piece of sandpaper, there is the glue between the sand and the paper of the sandpaper to consider.

This seems like the most plausible idea so far. There were areas on the sandpaper where the sand had completely worn away when I was done. I had to go at that ID pretty vigorously to get the case to finally fit.

If it was my rocket, I'd replace the paper MMT with a PML phenolic MMT as the easiest solution to the problem. Don't tell anybody, but I used to routinely replace my LOC paper MMTs with good old PML MMTs. I had to sand the inside hole of the centering rings like crazy as the PML MMT had a slightly larger O.D. than the LOC MMTs, but that was normal.

I like this idea. I'm not a fan of bare phenolic airframes (tendency to shatter) but PML phenolic does make for great motor mount tubes that never shrink or lose their shape. My PML rockets are the only ones where I have never had a problem with the motor fitting.

Just had another idea. Did you ever friction fit a motor case into this MMT? If so, that can leave glue residue inside the MMT as well.

I never rely on friction fit for reloadable cases, so no.
 
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