Ejection Charge Re-Visited

[Kyle Parsons]

Concerning the charges do not seperate your charges to two canisters. Atleast dont split up the calculated charge in half. If you need 4 grams for your main, dont put two grams in two canisters. Put 4 grams in each. What I do, which is usaully using two different electronics is put two canisters one for each electronics at the calculated size. So if you need 4 grams I’d put two canisters of 4 grams. The chances they both go off at the same time are VERY unlikely. I think for the Uproar project we argued over too do two canisters or one, its personal preference.

[Warren B. MusselmanModerator]

With redundant charges and altimeters, you can be sure that they will NOT fire simultaneously – especially if you use different altimeter brand/models (smart idea by the way). As I said, I use a calculator based on internal volume and # and size of shear pins to determine my charge size and than I effectively double that amount (Note, I only use composite tubing, with paper or phenolic you might want to back that off substantially).

If I know that one of my altimeters will always fire later than the other (I do – and plan on it), the second charge I make even 20% larger just in case the first charge fails to push things all the way out. If you properly deploy on the first charge, it won’t hurt because you’ll have the open end of the airframe to dissipate the extra force and if you haven’t fully deployed, it might be just what you need to fully kick things out – especially if your coupler/airframe joint is a bit loose and jams a bit.

Again, I don’t build anything with paper of phenolic so be aware that you could just blow your rocket up or at least blow a nice hole in the side.

Most of all – ground test if you’re nervous about it being a successful deployment.

By the way, my L3 was not ground tested. I was just extremely anal about getting a smooth coupler/airframe joint that was held together not by friction, but by shear pins. I calculated the correct amount of BP and essentially (on Art Hoag’s advice) doubled the charge size. A perfect deployment.

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