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Is ejection charge strong enough to eject capsule?

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PAL9000

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Hi. My brother and I are building a rocket that will eject a capsule containing an egg. We plan on attaching the capsule to the bottom of the nose cone, which will fall free of the rest of the rocket using its own parachute.
We aren't sure if the ejection charge will be strong enough to push out the capsule+nose cone along with the other main parachute (plus wadding paper).
The rocket is two BT-80 body tubes coupled together.
We have attached details of the rocket.
Do you think an E12-6 motor will eject the capsule+nose cone, or is the rocket too long for the ejection charge to travel 28 inches to eject that combined mass (130.6g)?
Thank you!
 

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NAR29996

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Hi. My brother and I are building a rocket that will eject a capsule containing an egg. We plan on attaching the capsule to the bottom of the nose cone, which will fall free of the rest of the rocket using its own parachute.
We aren't sure if the ejection charge will be strong enough to push out the capsule+nose cone along with the other main parachute (plus wadding paper).
The rocket is two BT-80 body tubes coupled together.
We have attached details of the rocket.
Do you think an E12-6 motor will eject the capsule+nose cone, or is the rocket too long for the ejection charge to travel 28 inches to eject that combined mass (130.6g)?
Thank you!
I'd use a stuffer tube to reduce the volume that you need to pressurize. IOW, Increase the length of the motor mount tube until it reaches the coupler.
 

gna

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I'd use a stuffer tube to reduce the volume that you need to pressurize. IOW, Increase the length of the motor mount tube until it reaches the coupler.
+1
I would use another centering ring on the motor mount tube near the end. How is the main parachute attached to the rocket body? I don't see a shock cord. Also, what are you using for fins? It says "cardboard," but I'm guessing that's not right.

I think an E12-4 might be a better motor choice.
 

Zeus-cat

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I'm not sure an E12 will provide a safe flight. Two BT-80 tubes and an egg means this will be a heavy rocket for an E12.
 

gna

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I think it will be fine. I threw together something similar in OR, using Estes tubes and nosecone, and it seems to be fast enough off the rod. I figured 42" 3/16 rod. I also used 1/8 balsa for the fins.

If it were my rocket, though, I would make the fins a bit bigger so it's stable without the load. I'd worry that they wouldn't have enough force to counteract the weight if it got off track. I'd probably make them TTW and paper them, too.
 

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gna

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Here's an edit, with larger fins and tabs, stuffer tube up to coupling and centering ring butted up to bottom of coupling, It flies OK on an E12-4, both with and without the payload.
 

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RocketTree

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Reduce the internal volume as much as possible, and it should be fine. Might also be important to keep deployment speed as low as possible. If you get really ambitious, determine the charge pressure with online calculator. The charges are usually powerful in the BP motors.
 
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