Altimeter vent holes

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Brian-Tampa

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About halfway finished with my new EZI-65 build. I am going to utilize a Jolly Logic Altimeter 3 for this rocket. Any ideas for vent hole sizes in the main air frame and how many?
Also, my friend suggested rather than use air frame vent holes why not drill small holes in all 3 centering rings?
His reasoning was that with all 3 centering rings having holes in them, the payload section would be vented.
Has anyone done this? Is this a plausible method? Please help!!
Thanks in advance
Brian
 

micro

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The problem with that idea is that you'll be venting to the low pressure area developed at the aft end of the rocket, throwing your numbers way off. You'd probably still be able to discern the apogee but not worth it I'd say.
 

BEC

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Regardless of the size, you want the vent holes to be in a surface parallel to the direction of flight and away from discontinuities like nose cone joint, rail buttons, and such.

Putting them in the centering rings so that the outside pressure "seen" is in the base of the rocket is going to mess up your data. At least in looking at the post-flight graph you'll be able to see if the low pressure area at the base of the rocket messed up even your apogee value or not.

Neil gave you a couple of good suggestions.
 

Brian-Tampa

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Regardless of the size, you want the vent holes to be in a surface parallel to the direction of flight and away from discontinuities like nose cone joint, rail buttons, and such.

Putting them in the centering rings so that the outside pressure "seen" is in the base of the rocket is going to mess up your data. At least in looking at the post-flight graph you'll be able to see if the low pressure area at the base of the rocket messed up even your apogee value or not.

Neil gave you a couple of good suggestions.
Thanks for the input, it makes perfect sense to now.
 

Brian-Tampa

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Regardless of the size, you want the vent holes to be in a surface parallel to the direction of flight and away from discontinuities like nose cone joint, rail buttons, and such.

Putting them in the centering rings so that the outside pressure "seen" is in the base of the rocket is going to mess up your data. At least in looking at the post-flight graph you'll be able to see if the low pressure area at the base of the rocket messed up even your apogee value or not.

Neil gave you a couple of good suggestions.
Thanks for the great info, I really appreciate the advice.
Brian
 

Brian-Tampa

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The problem with that idea is that you'll be venting to the low pressure area developed at the aft end of the rocket, throwing your numbers way off. You'd probably still be able to discern the apogee but not worth it I'd say.
Your info was invaluable, as several other members came up with the same answer too.
Thank you for the help.
Brian
 

BEC

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I greatly appreciate the input.
In sizing my ports, what would I be using for size to determine volume? The entire lower airframe volume or the area forward of the of the top centering ring?
Whatever defines the actual volume the AltimeterThree will be in. You can deduct some for things filling up the space (like recovery equipment) but for this purpose as long as they're big enough you'll get reasonable flight data. There is such a thing as too big I have been told, but I don't have a sense for what that looks like. You probably need to be off by a factor of several if not an order of magnitude for it to be literally "too much".
 
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