Do you put vent holes in 'sealed' areas of your rockets?

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Curtis Enlow

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I am doing a nose cone mod, cutting off the blown-in shock cord ring/bulkhead (which has a vent hole, BTW) and installing a bulkhead & U-bolt. As I was fitting the bulkhead I realized I would be capturing relatively dense air in the sealed nose cone at a density altitude of -1,116 feet (I'm at 72ft. alt, 42F, 30.12in/HG, 42F Dew point right now).

On a warm, sunny day the air inside could expand considerably, and then again, especially with a couple thousand feet altitude gain, at launch. So, I figured a vent hole might be a good idea to equalize the area, as there would be a lot of pressure behind the 1/8" ply bulkhead even before the forces of deployment.

Do any of you normally do this? What about fin can/MMT areas that might otherwise get sealed in? Has anyone ever had an issue with over-pressure in a sealed area or blow-out failures after repeated cycles of launching?

Thanks!

C
 

K'Tesh

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I think that you're OK, so long as you're keeping things under a mile... Beyond that, it might be a good idea.

[edit] These are just my feelings on the matter, and are not backed with any specific training or experience other than seeing what happens to Tupperware and sealed packages of film going from Montana into Denver.

[edit edit] Then again, I've never had problems with sealed packages bursting when checked into checked baggage, even for flights across the Atlantic (from JFK to the LHR), or the Pacific (Mainland to Hawaii (numerous experiences) and from SEA to PEK), altitudes there were hovering around the 7 mile range. Though the rate of change in altitude is much slower in a car or a plane.
 
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Banzai88

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Never had a problem, but I've been to just under a mile and under mach. Above that might be a different thing, but I've never heard of it being an issue.
 

DaveW6DPS

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I have never had an issue with air pressure in those areas.

Venting the body tube is a good idea to keep the captive air from pushing the nose cone out on the way up, but otherwise I haven't seen any problems.
 

Curtis Enlow

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Thanks, all! It seems the pressure differentials aren't enough to be a big issue at low speeds/altitudes, though small static ports can't hurt.
 

Curtis Enlow

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I like the idea of static ports, of course the electronics bay for recovery timers will need one, but I like the idea of a body tube port, as well.

I don't like the idea of a raw hole drilled in the cardboard but I would like to make one out of thin, polished aluminum not unlike the small aircraft one below (but with a backing plate for mounting/sealing) but am trying to think of a way of forming it to the 4" OD of the body tube short of having/finding curved steel parts and rigging some kind of press.

Any ideas?

 

dshmel

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One thing to consider. Sealed components that have vents added may pick up moisture which would be difficult to remove.
Exactly. I have some rockets with water inside that won't dry out.
 

Curtis Enlow

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Despite Mildew being the state flower, here in Washington State we, ironically, don't have a lot of humidity, especially during flying season - it's very dry, in fact. (The last few years we got less rain than LA in the summer).
 
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