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  #1  
Old 06-09-2018, 03:51 PM
BigRIJoe BigRIJoe is offline
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Default Altimeter 2 Vent Holes

I'm mounting a Jolly Logic Altimeter 2 in a BT-30 payload section. How many and what size vent holes should the payload section have?
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Old 06-09-2018, 04:16 PM
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BEC BEC is offline
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How long is the payload section?

That said - unless it's huge - all you need are three or four large pinholes.
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Old 06-11-2018, 04:21 PM
BigRIJoe BigRIJoe is offline
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Well it's a 5 inch section of BT-30. And aren't pinholes, by nature, "small"?
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Old 06-11-2018, 07:48 PM
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Well, yes. But I’m thinking use a fairly large T-pin rather than a small sewing pin. In other words, something on the order of 1/32 of an inch in diameter or perhaps a little smaller. As a long time aeromodeller I have lots of big T-pins and I use one like that for this purpose.

Basically what you are trying to do is provide enough of a leak path for air inside the payload compartment to get out and allow the pressure to equalize at apogee before the model has fallen back so much as to mess up your reading unacceptably. If you do the math and assume a ballistic path (and neglect drag), you fall back 16 feet in the first second after reaching apogee (1/2at**2) where a in this case is the acceleration due to gravity. In the first half second it’s 4 feet.

So you want the payload compartment to “leak down” pretty quickly.
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Old 06-11-2018, 09:10 PM
astronwolf astronwolf is offline
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You need only make a couple "small" pin holes, at most. You may not need any pin holes at all.
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Old 06-27-2018, 08:46 PM
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Newbomb Turk Newbomb Turk is offline
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This is all very interesting. I've never used an altimeter before, but would like to try one.
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