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Altimeter Vent Hole Location

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Brian-Tampa

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Hi,
Just started laying out my fiberglass 4" DX3 for drill holes (launch lugs, vent holes)

Where is the proper location for the vent holes in the payload bay?

I know to stay away from other objects to facilitate clean airflow, but there seems to be several schools of thought on the placement on the airframe.

I usually place them back about 5-6" aft of the nose cone/payload airframe seam.

I have heard of putting them just aft of the nose cone, about 1-2" aft of the nose cone/payload airframe seam.

I have also heard of putting in the middle of the payload space. For instance, if the payload volume is say 14" in length, then put the vent holes at 7" of this volume length.

What is the correct method?

Any help would be GREATLY appreciated!

Brian
 

DAllen

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Read up in your manual for your altimeter. As I recall, Perfectflite recommended staying away from transitions and nosecones by one body tube diameter as a rule of thumb. 4" rocket = sample holes need to be 4" away from the base of the nose cone longitudinally. BUT, I know folks have had great success with alt bays in their cones so there's that.

I just put the sample holes right smack dab in the middle of the ebay for simplicity. I don't think there really is a right or wrong answer here just so long as the holes are big enough to allow for free airflow to the alts with consideration to the size of the ebay. Also, I would recommend putting in 3 holes evenly spaced around the rocket diameter just to make sure a cross breeze cannot go straight through. And that's one of those things I am not sure is entirely but I just do it cause its a simple precaution to execute.
 

David Schwantz

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For a neater appearence I like to aliiiign my vent holes with my fins, 3 fin gets 3 holes, 4 fin gets 4 holes. Sized accordingly. 1" switch band, holes are centered on the 1/2". I like to make sure thy arrrre drilled so as either the main nor the drogue will block the vent holes.
 

Voyager1

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Many people have screw switch access holes around the avbay switch band that can also double as pressure vents. All my dual deployment avbays have this arrangement and I have never had an issue. It is often recommended that an odd number of holes is used.
 
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Steve Shannon

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It almost sounds like he’s not asking about vent holes for the altimeter pressure sensor. I think he’s asking about vent holes to equalize pressure in his payload bay/parachute compartment.

If that’s so, placement is not critical.

If you mean the vent holes for your altimeter, those need to go in the av-bay, usually a caliber or more away from obstructions or protuberances like rail guides. More importantly, keep the hole edges clean, not ragged.
 

Buckeye

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For venting airframes, it doesn't matter.

Frankly, the need for these airframe vent holes is overstated. Most rockets have enough leakage and not enough pressure differential to separate themselves. Hell, Jolly Logic Chute Release doesn't even mention needing vent holes for its altimeter!
 

cerving

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Anywhere works fine, try not to cover it up with the laundry if possible. And like Buckeye said, there's probably enough leakage in your airframe anyway... although if you're flying with a "whomp" motor (VMax, ST, etc.) you definitely need a vent hole.
 
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