What's the estimate? (I don't have an Adept altimeter and they've gone out of business)
Jasper,
Sorry for the delay . . . Adept info !
https://web.archive.org/web/20070805004922fw_/https://www.adeptrocketry.com/staticports.htm
QUOTE :
Adept Rocketry - Information on Static Ports
Copyright © 1999, 2005, All Rights Reserved
An altimeter must be installed in a “sealed” chamber with a vent or vents to the outside. A sealed bulkhead below the altimeter chamber is necessary to avoid the vacuum caused by the aft end of a rocket during flight. A sealed bulkhead above the altimeter chamber is necessary to avoid any pressure fluctuations that may be created at the nose end of the rocket. The vent (also known as a static port) to the outside of the rocket must be in an area where there are no obstacles above it that can cause turbulent air flow over the vent hole. Do not allow screws, ornamental objects, or anything that protrudes out from the rocket body to be directly in line with and forward of a vent hole. The vent must be neat and burr free and on an outside surface that is smooth and vertical where airflow is smooth without turbulence or obstruction.
Some rocketeers use multiple static ports (vent holes) instead of just one. Very strong wind blowing directly on a single static port could affect the altimeter. Multiple ports evenly spaced around the rocket tube may help cancel the effects of strong wind, the pressure effects of a non-stable (wiggly) liftoff, or the pressure effects that occur due to flipping and spinning after deployment. If you wish to use multiple ports, then use three or four.
Never use two. Ports must be the same size and evenly spaced in line around the tube.
The general guideline for choosing port size is to use one 1/4 inch diameter vent hole (or equivalent area, if multiple holes are used) per 100 cubic inches of volume in the altimeter chamber. For instance, an eight-inch long four-inch diameter tube has a volume of about 100 cubic inches. Use one 1/4 inch port, or three or four 1/8 inch ports evenly spaced around the tube. Area wise, one 1/4 inch hole is equivalent to
four 1/8 inch holes. An altimeter chamber two inches in diameter and eight inches long (25 cubic inches) needs one 1/8 inch vent hole or three or four 1/16 inch vent holes. For a chamber 1.5 inches (38 mm) ID by 4 inches long (7 cu. in.) use one 1/16 inch hole or three or four 1/32 inch holes. Keep hole sizes within -50% or +100% of the general guideline. Do not make the holes too small, and
especially do not make them too large. Obviously, a vent or vents in a BT-20 (18 mm) body tube will be quite small.
Vent holes should be a minimum of four body diameters below the junction of the nosecone with the rocket body. This is necessary with high performance (high speed) rockets. The tremendous pressure on the nosecone leeches down the rocket body as much as four diameters before it dissipates.
www.adeptrocketry.com, 11-18-05
END QUOTE :
Dave F.