Correct. Maximum flow and minimal filleting. I am open to reducing the width from 12/16 to 11/16" if you think it would help that much. But I don't. Keep in mind it almost doesn't matter how much volume there is with 1, 2, or 3 ejection active tubes. The net pressure from the charge is similar and the momentum of the payload section in this case coming off and with a small tightly wrapped (relative to the 2.25" tube) drogue or main, it will be reliably deployed.

Jerry

http://v-serv.com/usr/kits/rearejection.htm

Well - I hope we can agree to disagree....

I made a mock up of the 0.75 wide slot. You can see it is fairly wide compared to the body tube. And when mated with another tube, there is a major gap that needs to get covered and sealed....

As to whether there is 1, 2, or 3 active tubes - each tube contributes 38 cubic in. which is 20% of the total volume (with 3 active tubes). Since the pressure is based on the volume it acts upon, it does matter how many tubes are used.

With 0.75 x 1 port (per the instructions), there is a total of 2.25 sq in of ports. For the tube area, this is 8%. And there is still over 130psi in that motor pod that has to go through these ports.... I'm still concerned about that motor pod blowing up....

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I got my vinyl today from Stickershock!

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Two comments. How wide would you make the slots? 5/8"? I could provide silk or some other fabric to cover the gap when gluing to maximize slot area while keeping length to a reasonable minimum. Isn't your ejection charge too large if it is generating 130 psi on such a large volume? I assume 1/2g charges. I use 3F and AT uses 4F.

BTW Les you got U.S. Rockets Trident 2.25 #001.

Jerry

Actually, I having trouble wrapping my head around this. Part of the problem is some things don't scale up. For true cylinders, whether they be 1" diameter or 10' in diameter, they meet tangentially with only "one point" (or maybe I should say 1 line) touching, This makes it difficult to widen the slot without creating the gap. One approach would be to glue a dowel between the tubes to cover the gap. I sketched adding a 1/8" dowel on the left and a 1/4" dowel on the right (both in red) against the 3/4" wide port.

For the 1.2g, that is the amount of powder in a 29mm CTI load (what I generally use).
Excluding any issues with passing the gasses through the ports, the TOTAL volume of the motor pod, 3 ducting pods, and passenger pod is equivalent to a 2.25" diameter tube x 48" length. With 1.2g, this would create a little less than 12psi to eject the chute - a little light (I typically plan on 15) but if the cone is not too tight it would probably be OK. The pressure will probably be reduced some due to the impact of the static pressure having to feed through the ports. Hence there may only be 10psi or less to actually move the laundry and cone. Now I get a bit worried....

In terms of the 130psi - that was calculated without the ports. So now we have the 1.2g in the 2.25 tube but the motor pod is only 4" long (between the top CR and the nose cone) instead of the equivalent 48". For a typical rocket with a 2.25 diameter, the ejection charge would push against the 3.8 sq in of nose cone to push it out. With a 48" equivalent length the pressure wave would expand throughout the entire volume. But here the gas is constricted and has to fit through the ports which are smaller. And the ports don't actually move like a cone would, where the movement helps to reduce the pressure. The cone moves up enlarging the volume (probably insignificant effect) until it is off the tube allowing the gasses to expand into the atmosphere (very significant). The rocket may not see the full pressure because the cone came off before full pressure was achieved.

Back to the motor pod vs the 3 duct tubes and passenger pod. I calculated the total volume of all the pieces at around 190 cubic inches. The motor pod alone is only a bit over 15 cubic inches. This is less than 8% of the total volume, yet the ejection charge occurs here and then through the ports has to feed the other 92% of the volume.

Bottom line - Will sufficient pressure be relieved through the ports before the ejection pressure spike causes a rupture of the motor pod. THAT I CAN"T ANSWER. I don't have the knowledge to calculate the dynamics of the gasses vs the structural integrity of the cardboard.

I am open to suggestions or inputs from others who can help figure this out.

The easy way out is to use the dual deploy option and bypass the ducted ejection.
I admit I would RATHER use the ducted ejection to be a true Trident, just.......I also don't want it to be raining down in pieces........

forgot my pix...

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I would probably remove about half of that.

1/8" precut dowels are a stock part for us. It would be trivial to include 12 of them per kit.

The 1x32.5 foot version would not pass gas. It would dual deploy all near the top.

Jerry

If you noticed in the pix, for a 1/8" dowel the 0.75" cut extends past the dowel. In this case the port size would have to be cut back to less than 0.5". In reality given slop in measurement or cutting probably closer to 0.4" max.

With the total volume, 0.6g (half) will generate only 6 psi to push the cone off and the laundry out.
Dropping down to only one duct tube we get back to 10psi - but now there is only 1 port to relieve the pressure

And the motor pod (again, neglecting the ports) could see 73 psi.