Ejection charge appears to have bulged the body tube.

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

jahall4

Well-Known Member
Joined
Jul 21, 2014
Messages
1,241
Reaction score
217
Technically this occurred on a non-HPR launch, but given the size of tube (4”) and the use of an ejection charge I thought I’d post here.

I’m guessing someone has seen the pattern before?
IMG_3357-2.jpg

But what about this? Appears to be gouge inside the tube at the same location.
IMG_3364.jpg

The charge was 2g of 4F. Any suggestion on:
1) How to keep this from happening again
2) Affecting a repair since there must be some weakening of the tube.
 
What aspect of it? The components? How it was packed? Where are you headed?
 
Yes and no. The paint might not have adhered to the tube and the interior shot might have been from some of the deployment hardware dinging the tube. I have shockwave patterns on the surface of highly rubbed lacquered surfaces of cardboard rockets.
It's on several and I believe it's unavoidable. Unless the tube is torn somewhere, I'd expect it to be flyable in the condition it is. You could try ground testing with less powder and see what response you get. Kurt
 
That's just it it does appear to be "torn" you can see where the seam in the tube is just in the tiniest amount separated, forward and aft of the area where the paint has been "blown" off. The gouge on the inside goes deep, almost through the tube. You can see this along that forward seam.
 
Just trying to visualize the order of components, how it would have been loaded in relation to where the charge was.

I agree that it definitely looks like something gouged the inside of the tube, just trying to think about what could have been hard / sharp enough.
 
I was using a 2.1g Pratt Ejection Canister and I suspect the laundry ended up along side the canister pointing aft. According to Doug Pratt the position of the canister in the tube should be of no consequence, but here is the caveat... The canister "exploded" shattering itself. Doug claims in the last quarter century he has never seen that happen and its a first for me having used his 1.5g canisters a few times.

IMG_3354.jpg

So, did an overly energetic discharge create a shock wave of sorts along that section of tube? That's what I hoping to determine. Surely this has happened to someone else.

What was "sharp enough"? Maybe fragments of the ejection canister?
 
I was using a 2.1g Pratt Ejection Canister and I suspect the laundry ended up along side the canister pointing aft. According to Doug Pratt the position of the canister in the tube should be of no consequence, but here is the caveat... The canister "exploded" shattering itself. Doug claims in the last quarter century he has never seen that happen and its a first for me having used his 1.5g canisters a few times.

View attachment 288669

So, did an overly energetic discharge create a shock wave of sorts along that section of tube? That's what I hoping to determine. Surely this has happened to someone else.

What was "sharp enough"? Maybe fragments of the ejection canister?

I use Doug's canisters, but he is wrong about the orientation not mattering. Here is the best advice I can give you, and I have been using his canister for 15 years.

Orient them so they blow along the lof the rocket. In my 3" and under rockets I just extend the all thread running through my electronics bay a couple inches beyond the bulkhead, and tape the canisters to them with aluminum tape.
 
Last edited:
Orient them so they blow along the lof the rocket. In my 3" and under rockets I just extend the all thread running through my electronics bay a couple inches beyond the bulkhead, and tape the canisters to them with aluminum tape.

If your saying orient them longitudinally that's what I do too. Can't really do it another way in smaller diameter rockets.

Have you ever had one of them "explode" / shatter?
 
That was an XLEC-1 w/ 2.1g of 4FG and the insertable plug? How did the ground test go?

My ( completely uninformed ) guess : your canister was upside down nestled right up to the wall and the plug had nowhere to go but that CR, kablammo.

Interior damage from a fragment, exterior damage from the bulge. Wouldn't be surprised to find a few unscorched holes in the laundry, as well?

For a repair, gluing a coupler in there should get the job done.
 
If your saying orient them longitudinally that's what I do too. Can't really do it another way in smaller diameter rockets.

Have you ever had one of them "explode" / shatter?

A few of them, but most of the time the top just popped open. Since I began taping to the all thread nothing has shattered.
 
Have you ever had one of them "explode" / shatter?

Yes, fracturing the side of phenolic airframe. I then did several ground tests with 1.0 & 1.5 bp charges.
Placed them in a fiberglass tube to simulate airframe. 3 tests, all shattered.
After seeing all the shards of sharp plastic,I quit.
Was not a Pratt...Just a generic version like the ones BP comes in with AT reloads.
I quit using them years ago and went with nitrile glove fingertips to hold bp. Nothing to cause any damage with them.
 
Last edited:
That was an XLEC-1 w/ 2.1g of 4FG and the insertable plug? How did the ground test go?
My ( completely uninformed ) guess : your canister was upside down nestled right up to the wall and the plug had nowhere to go but that CR, kablammo.
Interior damage from a fragment, exterior damage from the bulge. Wouldn't be surprised to find a few unscorched holes in the laundry, as well?
For a repair, gluing a coupler in there should get the job done.

If XLEC-1 means the XL canister then no it was LEC. Ground test went fine, but then again I used SEC at it's capacity of 1.5, which was adequate, but could have been a little more energetic IMHO. So erring on the side of caution (better a rake than a shovel, right?) I bumped it up to just under 2g for the flight.

Here is the ground test using a full SEC. Note I'm only testing the charge size, not the position of the canister. The altimeter firing was tested independently in a vacuum chamber:

[video]https://dl.dropboxusercontent.com/u/6960195/2016-04-15_18-45-54.mp4[/video]

No holes in the laundry, but I'm thinking along the same line as you. I don't think the cap was blocked per se, but I do think it was secured to well creating too much containment at least for that style of canister.

I'm prepping the tube for the coupler now.
 
And I like that idea but they are pain to assemble and you still have an igniter to buy.

I use the ejection canisters myself but I also make a canister holder that can double as a charge well from 3/4" Aluminum rod drilled out for the ejection canister to fit inside, and a hole drilled near the bottom for the wire to pass through. All of my airframes are Loc tubing and using a canister holder/charge well I have yet to blow an airframe out. The ones in the left two pics are some made for me by a friend from our local club on his lathe for some 6ml centrifuge tubes I use for my L3 project, the one attached to the AvBay is the 3/4" rod drilled out with a 1/2" hole for the small charge canisters.

As for the repair a section of coupler will do the job just fine if you have room and can get it in there.

HPIM3462.jpgHPIM3463.jpgFrenzyXLAvBayLid.jpg
 
The airframe or just the canister?

The canisters. I set up a section of plywood, placed a towel on it. Then stood up the glass airframe with charge inside.
After firing, the airframe would jump off leaving all the shards on towel for inspection.
 
The canisters. I set up a section of plywood, placed a towel on it. Then stood up the glass airframe with charge inside.
After firing, the airframe would jump off leaving all the shards on towel for inspection.

...and how where you containing the BP? Just the canister cap? plug? wadding? Tape? etc...
 
I use the ejection canisters myself but I also make a canister holder that can double as a charge well...[/ATTACH]

I'm using the canister only when the rockets configuration is not conducive to a typical charge well, but it looks like I'm going to have to come up with something similar so the canisters does not rest against the inside of the body tube.

Although I wonder if a few layers of simple duct (or even electrical tape) wrapped around that canister would keep it together. It may still shatter, but the cylinder created by the tape would not only contain the pieces, but it would necessarily have to direct the charge in doing so. The idea comes for Doug's video about pyrodex use. I don't se how the canister failed to shatter if is not for the tape wrapped around it.
 
I'm using the canister only when the rockets configuration is not conducive to a typical charge well, but it looks like I'm going to have to come up with something similar so the canisters does not rest against the inside of the body tube.

Although I wonder if a few layers of simple duct (or even electrical tape) wrapped around that canister would keep it together. It may still shatter, but the cylinder created by the tape would not only contain the pieces, but it would necessarily have to direct the charge in doing so. The idea comes for Doug's video about pyrodex use. I don't se how the canister failed to shatter if is not for the tape wrapped around it.

One thing that came up in another thread was not using the cap on the vial, instead just pack dog barf on top the charge and put a single layer of tape over the end. Evidently this will direct the gases more longitudinally with the canister.
 
One thing that came up in another thread was not using the cap on the vial, instead just pack dog barf on top the charge and put a single layer of tape over the end. Evidently this will direct the gases more longitudinally with the canister.

Yep, despite Doug's claim that it should not shatter and his direction to really wrap the thing up when using pyrodex I'm coming to the conclusion that a plug (or barf) AND the cap AND tape (even a little) is overkill since all you want to do is hold the BP against the igniter.

I really like using classic 3M yellow ear plugs. Using the cap AND the tape is probably creating the problem. Use one or the other not both, maybe?
 
...and how where you containing the BP? Just the canister cap? plug? wadding? Tape? etc...

1.5 bp dog barf.....close lid, one wrap of electrical tape. Hung on Av-bay like a flight. empty payload section attached.

Basically rocket flight ready, laying horizontal on plywood. No NC...no electronics. Just charge wire fished out of vent band to light with 9v. In front of empty payload, a towel over bush to act like a net & catch all ejected material.

Many folks use these, just not for me. I like the gentler approach of nitrile.
Once mastered these are quite simple & fast to make.
Besides the plastic holders don't hold enough for my larger rockets. The nitrile do ...up to 8grams.
 
Last edited:
I'm using the canister only when the rockets configuration is not conducive to a typical charge well, but it looks like I'm going to have to come up with something similar so the canisters does not rest against the inside of the body tube.

Although I wonder if a few layers of simple duct (or even electrical tape) wrapped around that canister would keep it together. It may still shatter, but the cylinder created by the tape would not only contain the pieces, but it would necessarily have to direct the charge in doing so. The idea comes for Doug's video about pyrodex use. I don't se how the canister failed to shatter if is not for the tape wrapped around it.

This is my method using 777 powder in microfuge tubes, but even then I got a ding in an airframe (4" cardboard with a layer of fiberglass). It knocked the paint off a small area, like yours, but either the hit was tangential enough that it didn't scar the airframe, or the fiberglass did a good job of maintaining structural integrity. I think this is the price we pay for the convenience of microfuge tubes and (in my case) smokeless powder use.
 
This is my method using 777 powder in microfuge tubes, but even then I got a ding in an airframe (4" cardboard with a layer of fiberglass). It knocked the paint off a small area, like yours, but either the hit was tangential enough that it didn't scar the airframe, or the fiberglass did a good job of maintaining structural integrity. I think this is the price we pay for the convenience of microfuge tubes and (in my case) smokeless powder use.

I'm glad that someone else has seen this effect. I your case, though, you are taping up the whole canister to achieve the higher pressures need to properly burn the 777 correct?
 
I'm glad that someone else has seen this effect. I your case, though, you are taping up the whole canister to achieve the higher pressures need to properly burn the 777 correct?

Not smokeless but I've been using 1.5g FFFF BP tamped with wadding in micro centrifugal vials on my 4" LOC Fantom, and I noticed a very small ding on the inside of the payload bay on one occasion. So far had no further damage by clipping off the lid tab and the hinge of the vial lid, and rounding them off with a file. My thinking was that when it blows there's fewer sharp corners.
 
I'm using the canister only when the rockets configuration is not conducive to a typical charge well, but it looks like I'm going to have to come up with something similar so the canisters does not rest against the inside of the body tube.

Although I wonder if a few layers of simple duct (or even electrical tape) wrapped around that canister would keep it together. It may still shatter, but the cylinder created by the tape would not only contain the pieces, but it would necessarily have to direct the charge in doing so. The idea comes for Doug's video about pyrodex use. I don't se how the canister failed to shatter if is not for the tape wrapped around it.

Yes, Use tape on the end only. NO caps. Cut them off and discard. One can wrap several layers around the tube and I believe it can help hold it together. Now, the only issue is if one uses a "blow up" the tube arrangement for the apogee charge with a long lead wire. If the canister is free and cocked to the side, it could blow out the side of a cardboard rocket. I had that happen twice before I got smart.

Blow down the tube is fine if the drogue is easy to extract out of the rocket tube. Kurt
 
Back
Top