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Old 03-23-2016, 12:50 PM
Kevin Huddleston's Avatar
Kevin Huddleston Kevin Huddleston is offline
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Default Pressure vent holes

Hello all. In a 5.5" dia. rocket that is also dual deploy, would you still add pressure venting ports just below the shoulder of the NC and just above the motor mount? Would such holes require more BP for the deployment charges? How do you know how big to make the vents...or do I need them at all?

Thanks!
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Old 03-24-2016, 08:48 AM
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tbzep tbzep is offline
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Quote:
Originally Posted by Kevin Huddleston
Hello all. In a 5.5" dia. rocket that is also dual deploy, would you still add pressure venting ports just below the shoulder of the NC and just above the motor mount? Would such holes require more BP for the deployment charges? How do you know how big to make the vents...or do I need them at all?

Thanks!

Any time you are hitting higher altitudes you need vent holes to prevent the NC or payload section from popping off while still ascending. It won't make a lot of difference where they go as long as they are between the bulkhead and the first separation point. I used to put them just above or below one of the launch lugs/buttons since the lugs already affected the looks of the rocket in that area anyway.

Obviously, you still need vents in the payload section to prevent the NC from popping off, whether or not you use a barometric altimeter. If you use a barometric altimeter, you need to be a bit specific about the location so the air flow over the vents won't affect the altimeter readings.

A single 3/16" hole is all I ever used on my HPR stuff to equalize pressure. If you feel a little paranoid, hide a second hole somewhere down the launch lug/button line. Unless your ejections are just barely getting the chute out, you won't need to worry about additional BP. If in doubt, do a ground ejection test. It will only cost you a few cents and you get a better perspective on ejection charges.
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Old 03-24-2016, 09:06 AM
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Thanks for your reply!
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