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Pressure vent holes

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LBarron

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Hi,

I have a question about vent holes for you knowledgeable folks out there. I'm planning to put two deployment controllers inside a 54mm tube (electronics bay) which will then go inside a 7.5" body tube. I know the formula for sizing the holes, and I know I should space them equally around the tube and in clean air, but I'd like to know if the holes in the electronics bay should line up horizontally and vertically with the holes in the body tube?

Any thoughts would be appreciated.
Leland
 

bobkrech

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Leland

As long as the 7.5" compartment is isolated by pressure tight bulkheads from the rest of the rocket so that ejection charges do not pressurize it, it does not matter where the vent holes are located on the smaller electronics bay tube. Naturally the hole on the 7.5" tube must be in a turbulence free region.

This arangement will act like a windscreen on a microphone and realy tend to eliminate any turbulence related phenomon from effecting the pressure gauge. Just don't forget that the area of the holes on the 7.5" tube must be much greater than the area on the smaller inside electronics bay. The the hole area to volume ratio on the 7.5" compartment must be equal to or greater than the hole area to volume ratio of the smaller electronics bay or you will add a delay constant to the pressure measurement.

Bob Krech
 

powderburner

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Bob K. made some good points, but I might add one little thought:

The arrangement you are asking about (with non-aligned holes) could also offer the advantage of keeping the interior electronics bay a little cleaner, as there would be no 'straight path' for dirt/debris to get inside and mess things up. If you make suitably-sized holes (per B.K.'s notes) the air pressure should get through just fine.
 

LBarron

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Thank you both very much. I shall drill some holes and get on with the building.
:)

Leland
 

powderburner

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are you by any chance a member of DARS?
I have been thinking of joining and (if you are a member) was wondering what you think of that org?
 

LBarron

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Hi PB,

Nope, I'm not a member of DARS. But I did attend one of their launches in Windom and found the event to be well organized and everyone to be very friendly. Also, I have emailed Tim Sapp (VP) on occasion and he has always been very prompt to reply and extremely helpful.

Right now I'm working on a liquid fuel project that falls into the experimental category and therefore is not something they would sanction. If I decide to go back to solid fuel rockets I would definitely join their group.

Leland
 
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