Tube volume and force of ejection charge?

Before reading the thread about Estes motors more powerful (and inconsistant) ejection charges, I was wondering if there was any rule of thumb on ejection charge and body tube volume. After reading that thread, I realize that all bets may be off, but still there must be some common sense rule about how small a rocket can get before vent holes are needed, or how big it can get before and inside tube must be used.

Any comments?

My LJ II seems to eject just fine with a single D12-3 motor and it's a 4" Estes BT101 with an inside length of about 10".

Hmm, I bet someone will be able to give guidelines. There are calculators for this sort of thin, but you would need to know how much BP is in the motor. Personally, I have had more problems with BT-20s than any other tube size

there is a very good thread on this , I can't find it but this will provide a good start

For Estes ejection charges

D size engine =.85 grams
A,B,C,=.5 grams

Originally posted by tdn
I realize that all bets may be off, but still there must be some common sense rule about how small a rocket can get before vent holes are needed, or how big it can get before and inside tube must be used.

Click to expand...

I say that the smaller doesn't really need vent holes, since it'll all get vented out the top anyways. Use a long shock cord. Bigger, you could just add a bit of BP to the top and secure it with tape, but use VERY little, until you KNOW how much you'll need.

Stymye listed a good starting point. Use that along with EMRR's Ejection Charge Calculator to determine if you need to add any. Don't EVER try to take any away!!!

Jason

just a point of experience... I had a 2" diameter 3ft long tube, With one C6 engine that ignited and low a behold there was enough force to push out all the recovery system...it actually pushed it out pretty fast...so that give a bit of a visiual.
...just my $.02

-matt