Hi, Im working on my final generation rocket for my rocketry class and I'm on the Avionics team, the avionics system we selected is the RRC2L and it has no information about vent holes in the manual. I've seen sources saying I should have a 1/4" hole for every 100 cubic in. but the diameter of our avionics bay is only 3 in and the height is 6.5 so it only has a volume of 46 cubic inches, so what should I do for the vent holes? Also I need to show work for the calculations page so if you could explain ant simple calculations or a rule that would fit into my situation it'd be greatly appreciated.
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Page 3 in the RRC2L manual has this:
I usually only have one or two holes in my 3" stuff with short bays. Usually one about 1/4-3/8", and maybe another on the opposite side.
I usually use at least one vent hole for switch access, so they tend to be larger (and less of them) than the book recommends.
I usually only have one or two holes in my 3" stuff with short bays. Usually one about 1/4-3/8", and maybe another on the opposite side.
I usually use at least one vent hole for switch access, so they tend to be larger (and less of them) than the book recommends.
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The formula is also in the manual.
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Yep...Per Missleworks:
If I were doing it I'd "try" to have three ~1/8" holes. That rarely works with my switches, so I compensate by using the missleworks guide and the cross sectional area provided in the recommendations. Two 1/4" holes provide more cross sectional air venting than three 1/8".
Usually, large holes have less edge effects (at the hole), and will behave better from a cross section standpoint than small holes.... The problem is windage. If you get them too large, you can see odd behavior in the electronics because the large holes cause turbulence, pressure drops, etc....
Don't get carried away, but I wouldn't worry about a single 3/8" hole (especially if you can locate the electronics a little away from the hole, or backward facing, etc...). Much bigger holes than that, and I can't help, at least for 3" rockets.
Maybe others will reply.
If I were doing it I'd "try" to have three ~1/8" holes. That rarely works with my switches, so I compensate by using the missleworks guide and the cross sectional area provided in the recommendations. Two 1/4" holes provide more cross sectional air venting than three 1/8".
Usually, large holes have less edge effects (at the hole), and will behave better from a cross section standpoint than small holes.... The problem is windage. If you get them too large, you can see odd behavior in the electronics because the large holes cause turbulence, pressure drops, etc....
Don't get carried away, but I wouldn't worry about a single 3/8" hole (especially if you can locate the electronics a little away from the hole, or backward facing, etc...). Much bigger holes than that, and I can't help, at least for 3" rockets.
Maybe others will reply.
I copied and pasted this from the Perfectflite StratoLogger SL100 manual pdf.
Hopefully the row spacing doesn't "blow-up" once I post it.
It's not MissileWorks, but it should reflect the same pressure issue.
Edit: I just now looked, it did reformat... I don't feel like redoing the spacing, but you should be able to down load the manual at their website.
http://www.perfectflite.com/Download.html
Static Pressure Sampling Holes
You must drill one or more clean-edged holes in the airframe
into the avionics bay to allow outside air pressure to be
sampled by the altimeter (see table below for recommended
sizes). These holes should be as far away from the nosecone
shoulder and other body tube irregularities as possible (at
least 4 to 5 times the body tube diameter or more) to minimize
pressure disturbances being created by turbulent airflow over
the body tube. Sand the area around the hole as necessary to
eliminate flashing or raised edges. Best performance will be
achieved by using four smaller holes distributed at 90 degree
intervals around the airframe’s circumference instead of a
single larger hole. When using four holes, each hole should be
½ the size of a single hole as noted in the table. This will
minimize the pressure variations due to wind currents
perpendicular to the rocket’s direction of travel.
With any high performance rocket, pay particular attention
to the size and placement of the holes – do not make them
too large or too far forward! If your rocket has an irregular
nosecone (e.g. Honest John, Nike Smoke) you should move
the holes even further back.
AvBay AvBay Single Port Four Port
Diameter Length Hole Size Hole Size
1.6” 6” .032” .020” (small pinholes)
2.1” 6” .048” .025”
3.0” 8” .113” .057”
3.0” 12” .170” .085”
3.9” 8” .202” .101”
3.9” 12” .302” .151”
5.5” 12” — .286”
7.5” 12” — .5”
Single Port, hole size = Diameter * Diameter * Length * 0.0016
Four Ports, each hole = Diameter * Diameter * Length * 0.0008
Hopefully the row spacing doesn't "blow-up" once I post it.
It's not MissileWorks, but it should reflect the same pressure issue.
Edit: I just now looked, it did reformat... I don't feel like redoing the spacing, but you should be able to down load the manual at their website.
http://www.perfectflite.com/Download.html
Static Pressure Sampling Holes
You must drill one or more clean-edged holes in the airframe
into the avionics bay to allow outside air pressure to be
sampled by the altimeter (see table below for recommended
sizes). These holes should be as far away from the nosecone
shoulder and other body tube irregularities as possible (at
least 4 to 5 times the body tube diameter or more) to minimize
pressure disturbances being created by turbulent airflow over
the body tube. Sand the area around the hole as necessary to
eliminate flashing or raised edges. Best performance will be
achieved by using four smaller holes distributed at 90 degree
intervals around the airframe’s circumference instead of a
single larger hole. When using four holes, each hole should be
½ the size of a single hole as noted in the table. This will
minimize the pressure variations due to wind currents
perpendicular to the rocket’s direction of travel.
With any high performance rocket, pay particular attention
to the size and placement of the holes – do not make them
too large or too far forward! If your rocket has an irregular
nosecone (e.g. Honest John, Nike Smoke) you should move
the holes even further back.
AvBay AvBay Single Port Four Port
Diameter Length Hole Size Hole Size
1.6” 6” .032” .020” (small pinholes)
2.1” 6” .048” .025”
3.0” 8” .113” .057”
3.0” 12” .170” .085”
3.9” 8” .202” .101”
3.9” 12” .302” .151”
5.5” 12” — .286”
7.5” 12” — .5”
Single Port, hole size = Diameter * Diameter * Length * 0.0016
Four Ports, each hole = Diameter * Diameter * Length * 0.0008
Last edited:
I wrote too much about venting for Apogee's Peak of Flight newsletter awhile back. It is here: https://www.apogeerockets.com/Peak-of-Flight/Newsletter543
There is a link to an Excel spreadsheet down in the "how big do the vent holes need to be?" section that goes to the only calculator that I've come across that takes into account the expected speed as well as the volume of the compartment. This can be important since what you really want is the pressure inside to track the pressure outside with little time lag. https://www.offwegorocketry.com/userfiles/file/Calculators/Static Port Holes.xls
There is a link to an Excel spreadsheet down in the "how big do the vent holes need to be?" section that goes to the only calculator that I've come across that takes into account the expected speed as well as the volume of the compartment. This can be important since what you really want is the pressure inside to track the pressure outside with little time lag. https://www.offwegorocketry.com/userfiles/file/Calculators/Static Port Holes.xls
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