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Ejection Charge Vent-hole design

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Astrofox

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Recently I obtained a LOC 163 kit. However, when I opened the kit I found that the plywood disk given to me to allow for ejection charge gasses to pass and pop the 'chute didn't come with any holes. I figured this wouldn't be much of an issue since it would require a drill and some spare time to fix. However, I have been wondering if there are any general rules of thumb for the size of a hole to allow for ejection charge gasses to pop the nosecone off instead of accidentally ejecting a motor or motor adaptor. Considering that this is on such a small scale too, what do you think might be the best way to ensure that the screw-in eye bolt is secure/the disk (with ejection holes) won't break under a relatively high-ish load? I plan on making an e-bay for the rocket at some point to house a tracker/altimeter for much more intense flights.
 

crossfire

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Are you talking about a vent hole in booster tube. Your MMT should li d be totally open. You should be able to see motor in MMT from looking down from top of booster tube.
 

Voyager1

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Are you talking about this disk? If so, then you can base your hole size on the scale of this one.
 

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Astrofox

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Are you talking about this disk? If so, then you can base your hole size on the scale of this one.
Yep, that disk in particular. I was wondering if there were any specific dimensions/spacings for those holes or if I could instead make something of my own design without compromising the integrity of the disk too much.
 

Voyager1

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Well, if that’s the same disk as yours, then I would just copy that one as it is. If that’s a 38mm diameter body, then it appears that those holes are about 5-6mm. So, I would drill 6 holes at 6mm several mm in from the edge, as in the image, plus the hole for the eye bolt.

Those holes were dimensioned to have a total aperture sufficient to allow the ejection exhaust to escape without building up too much pressure in the booster tube. You want them large enough to vent the gases, but not too large that the disk structure is compromised.

When you’ve drilled the holes, I would coat the disk with epoxy before installing it, to protect it from the hot exhaust and burnt charge.
 

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