What size (and how many) holes for an Altimeter 2 on a 4" fiberglass Nike Smoke?

[dbrent]

I know Apogee states in there Altimeter 1 tutorial that 4 - 1/16" dia holes are sufficient for pressure equalization, but I assume thats only accurate for models up to a certain size. What about large airframes? I have a 4" Nike Smoke and it seems to me that if the area inside the tube is significantly larger, that the pressure equalization holes need to be larger also ( or you would need more of them ).

Is there a rule of thumb here?

Thanks,
Don

Then again maybe I should buy a fiberglass coupler and make a small E-bay.

 

[GaryT]

See Vern Knowles Site

A good rule of thumb for the static pressure port is to use a 1/4" diameter hole for every 100 cubic inches in the altimeter bay compartment that is being vented.

 

[dbrent]

See Vern Knowles Site

A good rule of thumb for the static pressure port is to use a 1/4" diameter hole for every 100 cubic inches in the altimeter bay compartment that is being vented.

Thanks! That was exactly what I wanted.

Next question:
Does the presence of these holes affect the amount of ejection charge you would use?

 

[GaryT]

The sizing chart I refereed you to is for the static port holes for your Av-Bay, Are you planing DD or SD? For SD on a 4" kit a single 1/8 hole approx 1" below the NC shoulder should suffice for the Altimiter1 or 2.

With that one 1/8 hole your BP charge won't have to be altered.

 

[dbrent]

Are you planing DD or SD?

Definitely single deployment... I've actually come up with a rough design to incorporate a small compartment (big enough for a Jolly Logic altimeter) into the shoulder of the nose cone which is about 4in long. I'm hoping this smaller compartment will equalize sufficiently with smaller (perhaps 1/16"?) dia holes.

Don