vent hole shapes?

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dr wogz

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Is there thought / theory on vent hole shapes?

I was just thinking, we all (should) have a vent hole in our tubes, and drilling one is the easiest solution. But, some drill bits tend to chew cardboard. What if I cut a hole with a knife (X-Acto type).. But that would make a square ' rectangular hole. Or maybe triangular... Would it matter? What about a diamond instead of a square? And if a triangle, pointy end up or down? if down, and with a square, would the blunt edge cause whistling? If a triangle with the pointy end down, would that be the best, aerodynamically, to not 'force' air into the tube?

What about if you cut a 3-sided square, leaving eh 4th side still attached, and press it in to the tube / body cavity. if done on the bottom edge, again, might make a flap that keeps turbulence out..

Am I overthinking it?

I'm a little rusty on my Bernoulli..
 
I assume you really mean vent hole (as in pressure venting to prevent separation), and not altimeter ports, correct? I can't see how the shape of a pressure relief vent hole could possibly matter. It is just letting air out as air pressure builds.

Altimeter ports, of course, have a very specific purpose which is most easily achieved using the number, size and shape recommended by the manufacturer.
 
I thought I posted this the HPR fourm..

Bat-mite, yes, venting to prevent pressure differentials, but then again, any hole in the air frame. I guess as well, that the hole really doesn't see much 'moving air' due to laminar region / flow..

just curious if a shape had any effect..
 
It very much has an effect, not sure I could predict what. Equilateral triangle point down, less pressure than circular. Equilateral triangle point up, more pressure than circular. Somebody want to do an article?
 
It very much has an effect, not sure I could predict what. Equilateral triangle point down, less pressure than circular. Equilateral triangle point up, more pressure than circular. Somebody want to do an article?

Nope, just drill, baby, drill !
 
Step bits and Forstner bits will help you drill cleaner holes than universal bits.
 
Curious as to the placement and number of vent holes. Two on opposite sides, two at opposite ends? The engine bay cavity vent on the F-15 is triangular skinny point forward and vents out along the trailing edge of the last engine panel for equalization. Would ejection charge pressure be negatively affected? Doubtful. Would a hole be drilled in the centering rings where pressure would vent to the back to vent the tube and the motor cavities?

Screen Shot 2017-11-24 at 8.11.11 PM.jpg
 
Curious as to the placement and number of vent holes. Two on opposite sides, two at opposite ends? The engine bay cavity vent on the F-15 is triangular skinny point forward and vents out along the trailing edge of the last engine panel for equalization. Would ejection charge pressure be negatively affected? Doubtful. Would a hole be drilled in the centering rings where pressure would vent to the back to vent the tube and the motor cavities?

I'm really lazy - recovering from turkey overdose - search for NACA submerged duct.

[edit]
So lazy I didn't read above posts...

Anyway, research has been done. If you like math, go here:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090012113.pdf

some pictures:
https://rxspeed.com/thelab/behind-the-speed-naca-duct
 
Just drill the holes and then fill holes with epoxy and re drill the holes most of the time they turn out much better.
 
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