Can ejection charges be packed too tight?

More specifically Pyrodex in surgical tubing. I recently had a flight that failed to eject the parachute. I used two (one backup) 3g Pyrodex charges tightly packed in surgical tubing. A few months ago I flew the same rocket on identical charges (except they may not have been as tightly packed) and it worked flawlessly. (I also ground tested before this flight and 3g was more than enough) I cut open one of my older (very tightly packed) charges and the Pyrodex seemed to fuse into a solid ball. Could this effect the rate at which Pyrodex burns? My theory is based on the fact small granules burn faster than a solid piece of propellant. Can you pack BP or Pyrodex so tight you decrease the burn rate of your charges? So far this is my only theory as to why my previous flight failed a badly.

I wouldn't pack them until the day of flight.

Tighter is better, with pyrodex ghe tighter its confined the quicker and more efficiently it will burn, BP is the same but less touchy about how tight.

Here is one of my charges I found after being cut from the surgical tubing. I think it's safe to say this was my issue..

Did it get wet?

Pyrodex works great in antique firearms.

Not so much for ejection charges. It's a progressive propellant, designed to burn under pressure, inside a barrel. It burns much too slow for ejection charges.

Especially when it's damp.

No moisture, just being packed super tight in surgical tubing and sitting around for a few months. It burned fine, except for the fact it burned like a slug of propellant rather than an ejection charge :/

Makes one wonder how moisture permeable the tubing is over time?

Banzai88 said:

Makes one wonder how moisture permeable the tubing is over time?

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That also seems like a good theory.

The tubing to not that permeable, but the means of closing the ends around a pair of wires probably is permeable, unless a sealant is used.
The tubing probably leaches a fair amount of chemicals into the powder if it is new. If you can smell the tubing, it is still gassing out a fair amount of something.
I have not yet experimented with surgical tubing. I have with glove fingers, and was dissappointed.

I have wondered this same thing. On my L3 attempt, I used the exact same setup as my test flight. I used ejection canisters that tested perfectly with a multimeter, fresh batteries on the altimeters, and black powder from Aerotech. Both of my drogue charges failed to fire. The altimeters show that they fired, but they did not.
I've since rebuilt the rocket and am getting ready to do my L3 launch again, but have wondered if I had the powder packed too tight. It has never made sense to me that both drogue charges failed to fire even though they both tested positive, and the altimeters indicated they were good and fired.

ckjohnson said:

I've since rebuilt the rocket and am getting ready to do my L3 launch again, but have wondered if I had the powder packed too tight. It has never made sense to me that both drogue charges failed to fire even though they both tested positive, and the altimeters indicated they were good and fired.

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One should always try to fire the charges by direct contact to the battery you were using, after a failure such as yours.
That will rule out :
1. having enough current
2. bad matches.

At the least you will know if matches fire.

If they do fire...you probably had a bad connection.

PS were those canisters utilizing a resistor or match?

Igotnothing said:

The tubing probably leaches a fair amount of chemicals into the powder if it is new. If you can smell the tubing, it is still gassing out a fair amount of something.
I have not yet experimented with surgical tubing. I have with glove fingers, and was dissappointed.

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Been using both for years, NEVER had an issue from being prepped months in advance , let alone from any chemical reaction. BUT either must be sealed correctly with tape around the wire [glove tips],or wire ties around the tubing at minimum.

To use pyrodex you must contain it extremely tight. In either glove tips or tubing you must wrap with several layers of electrical tape or what happened above is the inevitable.

There is a section in the sticky at top of this high power page "build darkstar etc'' look in index on how to properly do glove tips for charges.[#70-71]

I'm going to ground test again before the next launch. I'm using different initiators on each altimeter now to reduce the chance of failure. I'm also planning on putting another altimeter in there, just as a backup of the backup. 😉

ckjohnson said:

I'm going to ground test again before the next launch. I'm using different initiators on each altimeter now to reduce the chance of failure. I'm also planning on putting another altimeter in there, just as a backup of the backup. ��

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That should not be necessary, you can cover your butt by just using 2 initiators placed in each charge.

If that doesn't do it .......you have other SERIOUS issues.

I've heard nothing good regarding using pyrodex for charges. why not just use BP?

IMHO---Black powder is best as Im sure most agree. But its easy to go to the sporting goods store and get Pyrodex. If you have a can of it (as I do) you want to use it. You paid for it so you want to use it. But take a little BP from a reload and a little Pyrodex sometime and test burn them one at a time- you will see and hear why BP is better.( be careful though) use a long match or fuse and safety goggles*** replace the BP you took from the reload with pyrodex- the very small amount wont make any noticeable diff. Mixing is not advisable but Ive done this regularly with E-F-G reloads and now have a few grams of BP stash****. The BP does emit more gas and gives a nice "poof" as it burns which makes it more desirable for ejection. I have used Pyrodex a number of times in F-G-H reloads for motor ejection and DD and had a couple of" instances" I could attribute to Pyrodex . If I had a choice** I would use BP every-time. For safety. We don't want a 5lb rocket coming in ballistic because you used pyrodex and it wasn't packed right.****** Use all safety precautions please when messing with BP or Pyrodex.

blackjack2564 said:

That should not be necessary, you can cover your butt by just using 2 initiators placed in each charge.

If that doesn't do it .......you have other SERIOUS issues.

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+1, and couldn't agree more.

I'm as 'Type A' as they come. Just started dual deployment this year (a whole 2 flights under my belt...). However, I did a lot of reading and asking questions on TRF, and lots of ground testing. During my testing I ran into a series of e-match failures (shortly after the manufacturer identified they had a problem with a batch - several other TRFers reported similar). This led me to making my charges with 2 e-matches per and testing the resistance of every one. Just be sure to test that your deployment altimeter is capable of firing both channels with 2 e-matches/initiators per. In regards to Pyrodex vs BP, all my reading /searches on TRF found too many reported difficulties with Pyrodex. Sourcing BP was more of a challenge than Pyrodex, but worth the piece of mind.

Thanks for the great ideas guys! I'll check in and see about using two initiators per charge. I'd use a dozen altimeters to ensure a successful L3 flight at this point.

ckjohnson said:

I have wondered this same thing. On my L3 attempt, I used the exact same setup as my test flight. I used ejection canisters that tested perfectly with a multimeter, fresh batteries on the altimeters, and black powder from Aerotech. Both of my drogue charges failed to fire. The altimeters show that they fired, but they did not.
I've since rebuilt the rocket and am getting ready to do my L3 launch again, but have wondered if I had the powder packed too tight. It has never made sense to me that both drogue charges failed to fire even though they both tested positive, and the altimeters indicated they were good and fired.

Click to expand...

Did you measure the resistance of the matches before and after the flight?

The reason I ask is because as improbable as it may seem, you could have been a victim of bad matches. I had a flight where I used commercial matches, each one from a different manufacture and from batches I've used successfully before. Both matches showed about 1 ohm resistance before the flight. Neither fired. Amazingly, the rocket fell flat and was undamaged. Post flight, the altimeter was beeping altitude like a nominal flight. Both matches read open like they had fired. My only conclusion was that both matches failed in the same manner, as improbable as that may seem.