Ejection charges??

so i've been pondering the ejection charges for my L1 rocket, and one question keeps coming to mind...how much do i really need for the apogee charge? it'll be falling drogueless so it's just like 10ft of recovery harness (not gonna call it shock cord when there's no stretch), so i really just gotta get it to pop open and move a foot or 2 away im guessing? i just need to get it out, i don't need a big pop cuz i'm not pushing out a parachute or anything.

other the other hand

my main chute is packed kinda tight, but still loose enough to pull without too much stress, so i'll have to really test that one, but am i right in thinking that the powder for my apogee charge really only needs to push the two parts apart and pull a few feet of cord out? or should i get it to get to unravel the cords and snap taught with a little force?

and i know everyone's going to say enough to get it to all come out, but i really don't think i need all of it to come out when the booster side is heavier anyway and will unroll all the cord in descent. :O

Ground test!!! I would use enough to get it to the end of the harness without a lot of shock. To much shock and your nose cone and main will have a tendency to keep moving and deploy.

You can always fan fold the harness and tape it every 4 - 5 folds. It will have to break the tape, reducing energy and shock. Any tape that doesn't break on drogue deploy will break when the main opens.

Watch closely how it falls drogueless. If the fin can spins/flutters and stays above the upper section, depending on the balance of the upper section, it can go nose down and fall ballistic, pulling the fincan behind it. If that happens, you greatly increase the chance of the fin can falling through and fouling the main when it deploys. You really want the fincan even or below the rest of the rocket on the way down and I would strongly suggest a drogue if it doesn't fall that way.

i'll second the ground test.
a friend had a level one rocket that was using dual rear ejection (upscale gemini DC), he ground tested that baby three times.
he's also had enough lawn darts to earn himself the nickname captain of the lawndart team, nearly all his lawndarts are due to not having enough ejection power (has a tendancy to build big light rockets that usev Estes motors, and still does not use stuffer tubes or breaks the rocket half way.

Third vote for ground test and the measure passes. The only other option is to blow it out or blow it up. I recommend against going high on the charge.

I will 3rd a ground test..But, really only on your main charge..The apogee charge, I agree with you on, can be just enough to seperate the pieces a foot or so and let gravity do the rest of the work extending the cord..For the main charge you will want to use enough charge to push the parachute completely out the tube..I generally go with a charge size half the body tube diameter in grams of BP(4" tube=2grams of BP) which has worked successfully so far for me..

*facepalm* yes i'm going to be ground testing lol. my quesiton was just on the strength of the ejection that i'm going to be looking for

also jon, you're the 4th vote :wink:


thanks guys, just waiting for the BP to arrive and i'll take a vid if i can get the video camera to do what i want