Has anybody ACTUALLY seen a rupture of a tube on a cluster rocket from simultaneous black powder ejection charges?

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BABAR

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From time to time in discussion of black powder clusters, there is this “fear” that if, say all three motors have the same delay and their ejection charges fire simultaneously, it will “overpressurize” the body tube and rupture it before the nose cone and laundry come out (which should completely decompress the compartment.)

various solutions such as using asynchronous ejections (e.g., C6-3, C6-5, C6-7 motors) or using some plugged motors (plugged by manufacturer, of course ;) , let’s avoid that rabbit hole), or venting some of the motors away from the main compartment, or ejecting the motors (mentioned only for context, again let’s not go down that hole)

just curious, has anyone personally experience or personal SEEN this happen, or is it really a theoretical concern?
 

Steve Shannon

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I have not seen such. I have seen holes in tubes from ejection charges, but as far as I recall they were all charges in charge holders placed right next to the paper body tube.
 

OKTurbo

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I haven’t seen it happen, but it’s been close on one of my cluster rockets. I’ve built a few Thrustline Mike IX‘s. They had to be retired because the thin BT80 tube was getting very weak just forward of the motor mount tube. At recovery, you could still feel the heat from 3x D12-5’s and their ejection charges.
 

rharshberger

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I have, it was on my SA-3/S-125 standoff scale. The booster was a 3 motor cluster, the second time it flew the two C6-5 ruptured the cental 24mm motor tube. Build thread below. The rocket used dual 18mm for thrust and rear ejection for the first stage and a gap staged 24mm for first stage thrust and to light the second stage, the 24mm MMT was standard motor tubing not BT50H, the repair replaced it with heavier tube. The rupture may have been assisted by the fact that the ejection charge pressure was not moving through a straight tube, but had to turn a corner or two.

 

BABAR

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I have, it was on my SA-3/S-125 standoff scale. The booster was a 3 motor cluster, the second time it flew the two C6-5 ruptured the cental 24mm motor tube. Build thread below. The rocket used dual 18mm for thrust and rear ejection for the first stage and a gap staged 24mm for first stage thrust and to light the second stage, the 24mm MMT was standard motor tubing not BT50H, the repair replaced it with heavier tube. The rupture may have been assisted by the fact that the ejection charge pressure was not moving through a straight tube, but had to turn a corner or two.

Okay, so it IS a real concern, it just theoretical. Of course, based on your post, it was apparently a beautiful rocket with bad juju from the get go!
 

rharshberger

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Okay, so it IS a real concern, it just theoretical. Of course, based on your post, it was apparently a beautiful rocket with bad juju from the get go!
My thoughts are this; the hibachi effect from multiple charges firing simultaneously or in very close succession can rapidly weaken a cardboard tube eventually leading to a pressure rupture as the tube is weakened. How many flights does that take, I dont have an answer.
The SA3 failure was a simple over pressurization based on what I was seeing.
 

PatD

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My thoughts are this; the hibachi effect from multiple charges firing simultaneously or in very close succession can rapidly weaken a cardboard tube eventually leading to a pressure rupture as the tube is weakened. How many flights does that take, I dont have an answer.
The SA3 failure was a simple over pressurization based on what I was seeing.
OOOOOHHHH! When I lived in an apartment I loved the hibachi effect. Chicks thought hibachi chicken and vegies were groovie. 😂
 

SharkWhisperer

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Pat, that's borderline delinquent, and probably factually inaccurate. It's much more likely that they found the "over pressurization" effect to be "groovie"!

And anybody wonders why we're geeking on a model rocketry forum late nights...
 

icyclops

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just curious, has anyone personally experience or personal SEEN this happen, or is it really a theoretical concern?
[/QUOTE]

Nope, never seen that happen.
 

rharshberger

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just curious, has anyone personally experience or personal SEEN this happen, or is it really a theoretical concern?
Nope, never seen that happen.
[/QUOTE]
did you read the thread I linked above...Yes I have personally seen it on one of my rockets.
 

caveduck

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I've personally seen tube ruptures from *single* BP motors. The ejection charge energy is pretty variable due to differing confinement, over the years I've seen plenty of them go off pretty forcefully. And typical Estes tubes are not very sturdy.
 

dhbarr

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I had one where the charge was loud enough the launch announcer asked if I had doctored the charge. Fortunately that was one I had already made a zipper stuffer tube repair on, as I suspect it would have blown out the sidewall otherwise.
 

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