redundant charges

Has anyone had a problem with redundant charges using surgical tubing involving "sympathetic" ignition? I.E. one charge igniting the other? My best guess is to wrap the backup in foil tape and separate them as much as possible in the harness/chute stack?

Does it matter? The purpose of the redundant charge is to mitigate the failure of the primary charge. The goal is to have an ejection. Yes, having both go off sympathetically will cause a bigger bang but your tubes and cords should be able to withstand it.

Wallace said:

Has anyone had a problem with redundant charges using surgical tubing involving "sympathetic" ignition? I.E. one charge igniting the other? My best guess is to wrap the backup in foil tape and separate them as much as possible in the harness/chute stack?

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I have had this happen with glove fingertip charges. I don't use surgical tubing charges. On my last flight I tried to mitigate this by putting the charges in a glove palm with some dog barf, but I couldn't tell if it was successful or not.

PhlAsh said:

Does it matter? The purpose of the redundant charge is to mitigate the failure of the primary charge. The goal is to have an ejection. Yes, having both go off sympathetically will cause a bigger bang but your tubes and cords should be able to withstand it.

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It does matter if the charges should go off simultaneously, resulting if snapped harnesses, mains deployed at apogee, etc. I have had this occur when dual altimeters from different manufacturers do not have enough time set between deployment events. YMMV....

PhlAsh said:

Does it matter? The purpose of the redundant charge is to mitigate the failure of the primary charge. The goal is to have an ejection. Yes, having both go off sympathetically will cause a bigger bang but your tubes and cords should be able to withstand it.

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Brilliant, I am kicking myself for that thought having not occurred to me.

It may be worth considering redundant ignition, but single charge. Make the charge such that it will get the job done. What is the likely failure point - that the charge goes off but fails to cause a separation, or that the charge fails to go off? The latter is far more likely with correctly sized charges.

Gerald

I'm a redundant charge user, especially after this:
[youtube]8kEMGniMe0g[/youtube]
Around 39-42 sec... sometimes things get stuck, especially on large diameter airframes.

To OP: I make my charges using the ejection lighter/cardboard tube combos that Wildman's sells and tape them a few inches apart on my bulkplates. No sympathetic ignitions so far.

That likely would have completed separation via drag, but we'll never know. In any event the charge was a bit too small. I don't advocate borderline charges. Regardless,

Welcome back!
Gerald

I agree with pondman, it does matter.


I have experienced an over-energetic apogee event that resulted in my nosecone pins shearing and my main deploying. This resulted in a 3. 46 mile recovery. Unless your recovery system is immune to this then I would try to mitigate both charges going off simaltaneously.

mpitfield said:

I agree with pondman, it does matter.


I have experienced an over-energetic apogee event that resulted in my nosecone pins shearing and my main deploying. This resulted in a 3. 46 mile recovery. Unless your recovery system is immune to this then I would try to mitigate both charges going off simaltaneously.

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That is exactly what I am attempting to avoid. Anyone have any real world experience with say, physically separating charges via harness/kevlar or foil tape on the backup?

I've flown quit a few of the surgical tube charges. I've not had or heard of surgical tube charges having this problem.

I have had this issue with thin vinyl glove finger tips. At LDRS I was test flying some altimeters and was using the thin vinyl glove material. I tripled up the vinyl by using full length fingers and tied it up and then folded it back over itself, tied it and then folded it over again. Then wrapped it in masking tape. (I had four charges in a 3' cardboard rocket) and did not need/want it to become a chain reaction.

Tony

I prefer redundant ematches, not charges.

I use centrifuge vials exclusively. The few times I used multiple charges (4 channel altimeter), there was no chain reaction.

Buckeye said:

I prefer redundant ematches, not charges.

I use centrifuge vials exclusively. The few times I used multiple charges (4 channel altimeter), there was no chain reaction.

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So just hot glue over the wire pass through and snap 'em shut? Or were they taped up also?

I have a 2.5" rocket, single deploy that uses redundant charges. RRC2, Apogee, then 1000 feet. My normal charge is 1 red cap (I use volume measurements, I have thousands of these little red caps from a previous project). My back up charge is 1.5 red caps. I use 3/8" OD x 1/16" wall, 1/4" ID tubing. They end up being 1.5-2 inches long, including the ends which are zip tied off. I drop both of them right on top of my electronics bay, no shielding except some dog barf tossed on top. I pack the kevlar cord, then my inverted piston on top of that. It ends up being a really tight space.

I've flown that rocket at least 15 times, ~2,500' each time - you can see all the events. I have never had a sympathetic ignition of my backup charge. I've always been able to see (and hear sometimes) the 1000' charge go off during descent when the rocket is under parachute.

I've flow the surgical tubing charges exclusively since Tony shared the idea with the world - mostly in cramped recovery quarters. I've never noticed in any of my altimeter data a sympathetic ignition - I've been able to see the pressure spikes in the data when they go off.


Edward

Wallace said:

So just hot glue over the wire pass through and snap 'em shut? Or were they taped up also?

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Hot glue and snapped shut. No tape. 1.25g charges.

Has anyone tried more commonly available vinyl tubing? If so, To what result?