Securing ejection charges

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Absent Minded Professor
Aug 22, 2015
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Last year I started experimenting with dual deploy. I packed my charges using charge wells and glove tips on different occasions. I had good results when I packed the wells with dog barf and covered them with tape. For the glove tips, I placed the tips containing the BP in the well and secured them with tape (no dog barf) and had bad results, likely caused by the BP not being compressed enough.

I'm interested in trying to use Eppendorf tubes for my next build so I don't have to use charge wells. But how do I secure them to the bulkhead on the av bay? Surely tape wouldn't be sufficient for a high G flight. I'm imagining the tube with the drogue charge dangling from the e-match wire and the disaster that could ensue.
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I use eppendorf tubes all the time. I have free tubes from the lab, so why not?

I simply secure mine using a small strip of duct tape. Tape the tube to the bulkhead. Works fine for me.
Masking tape should work fine. What is the bulkhead material? The smoother it is, the better the tape will stick. Masking tape holds very well to fiberglass. If it is unfinished plywood then I would sand it with 220 grit sandpaper first.
I use the epi tubes (sometimes it's nice to work in biology in this hobby!), but put them in charge wells. I tried using them once taped down, and the tube cap/part chipped the paint on my fiberglassed Frenzy (no tube damage, but it seems that the force was pretty strong, and had I been in a cardboard tube, may have blown the frame out). I then started using CPVC pipes screwed down, but then blew one of those up, so I switched to copper. Have not flown as much as I want, but so far no more issues. Maintains the directionality of the charge, and contains any of the shrapnel that might be thrown off (my tubes are also wrapped in electrical tape).
I have a small machine screw poking out of my bulkhead. I zip tie my charges to that.
I have a small machine screw poking out of my bulkhead. I zip tie my charges to that.

I'm just surprised that tape is sufficient. I like Matt's this idea. Maybe I'll use a screw eye.
How about a nylon/plastic cable clamp. Can either screw it down or have a stud in your bulkhead and use a knurl nut.
I have tied them to various things in the payload bay with cable ties, or glued them to bulkheads.

For my 54mm MD I made some inserts for my avionics bay to hold the charge vials inside the avionics bay. These suit 2.5ml centrifuge vials. The aluminium inserts are glued into the bulkhead with epoxy. The igniter wires exit the pointy end of the vial and go through the aluminium retainer. The base is gas sealed with a dollop of hot-melt adhesive before the vial is pushed into place. This method was used to free up space in the payload bay and also direct the charge a little better.
I use the glove-tip and charge well method, with no dog barf. I do TWIST the glove tip though with the BP and ematch in it, and then fold a piece of painters tape over this ematch/glove tip bundle to keep it all twisted and in place. This then goes into the ejection charge well. And this gets taped in there. The glove tip is tight against the black powder because of the twisting and stays in place because of the tape.

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I leave my squibs hanging. Never had a problem with it, and I've pulled some G's.
If one uses the plastic tubes freed in a cardboard rocket, if the tube fragments, there is the danger it will blow out the side of the cardboard body tube of the rocket.

If I fear that, I put a long screw on the bulkheads and ziptie the tube on the screw. Since the drogue chute is generally small, blowing down is not that big of a deal as
it's usually easy to "pull" the harness and the smaller drogue out of the sustainer.

Also with larger plastic tubes with screw on caps, I tried drilling a "restrictor/vent" hole in the screwon caps to hold the dog barf in on the powder and fortunately did testing out in the
open and not in a rocket. The tubes "shrapnelized" the vast majority of the time so don't attempt that either.

Kurt (I've blown out two sidewalls in the past) Savegnago