I'm getting ready to start assembling this rocket, and I'm a little nervous about whether or not the ejection charge from Aerotech F and G motors will be enough to push everything out the top. And as I'm trying to figure this out (looking at various BP ejection charge calculators) I realize that I don't know if the tube length measurement is from the forward CR to the bottom of the parachute package, to the bottom of the nose cone, or all the way to the top end of the body tube.
The body tube is 2.6" diameter (lightweight BT-80). The motor tube, which is 7" long, is going to be cut down to 4.125", with the forward CR flush with the end.
Distance from the forward CR to the bottom of the parachute package is 14". To the bottom of the nose cone, 21". To the top of the tube, 24" (3" shoulder on the cone).
I'm working under the assumption that the three Aerotech motors I'll be using (F67, G74, G80) have a .7 gram black powder charge.
If the distance is to the bottom of the parachute package, the ejection pressure is 19 psi.
If the distance is to the bottom of the nose cone, pressure is a little over 12.
If the distance is to the top of the tube, pressure is just under 11.
If the pressure is not sufficient, I can leave the motor tube at 7" long, and glue a third ring flush with the end. If I need more length than that, I'd have to figure out how to extend the 7" tube. (I've already epoxied the ejection retainer base the to the tube, as well as the forward and aft CRs.)
BTW, the nose cone is a loose fit.
I'm attaching the .ork file if that helps. Any and all input would be greatly appreciated.
The body tube is 2.6" diameter (lightweight BT-80). The motor tube, which is 7" long, is going to be cut down to 4.125", with the forward CR flush with the end.
Distance from the forward CR to the bottom of the parachute package is 14". To the bottom of the nose cone, 21". To the top of the tube, 24" (3" shoulder on the cone).
I'm working under the assumption that the three Aerotech motors I'll be using (F67, G74, G80) have a .7 gram black powder charge.
If the distance is to the bottom of the parachute package, the ejection pressure is 19 psi.
If the distance is to the bottom of the nose cone, pressure is a little over 12.
If the distance is to the top of the tube, pressure is just under 11.
If the pressure is not sufficient, I can leave the motor tube at 7" long, and glue a third ring flush with the end. If I need more length than that, I'd have to figure out how to extend the 7" tube. (I've already epoxied the ejection retainer base the to the tube, as well as the forward and aft CRs.)
BTW, the nose cone is a loose fit.
I'm attaching the .ork file if that helps. Any and all input would be greatly appreciated.