Super Big Bertha - Prepping the Payload for Altimeters

 

To fly an altimeter in the payload section of the #estesrockets Super Big Bertha #modelrocket, the payload really should be vented using static ports. This will allow the payload section to depressurize as the rocket ascends, so the altimeter can correctly read the air pressure outside the rocket and determine altitude.

Some people, including some very knowledgable rocketeers with experience in using altimeters for competition rocketry, claim payload sections don't necessarily need venting. There is often leakage of air pressure through places like the nose cone shoulder. But this one is quite airtight - the nose cone pops quite loudly when I pull it off. So I'm going to assume altimeters aren't psychic, and add static ports - it can't hurt.

I usually put three static ports on three-finned rockets and four on four-finned models. I don't know why - I just prefer things to match, I suppose. Longtime readers know I can be a fussy builder. It's your hobby - build it the way you like.

After consulting several static port calculators online, I determined I would need four 1/8 inch static ports on the Bertha. It's best to have them far from the nose cone. The joint between the nose and body tube can increase turbulent airflow over the ports if they are near the nose, and this may affect the accuracy of the reading the altimeter takes. So I drilled them near the bottom, through both the tube and the coupler.

I marked the spots first in pencil, then with a push pin, and finally drilled them out.

The drill will leave some jagged bits around the hole. Static ports should be smooth and round on the outside to reduce turbulence.

To smooth the holes, wick some water thin CA glue into the drill hole. Once it's cured, you can sand the opening smooth and clean up the hole with the drill bit.

After sanding the outside smooth, there's a bit of jagged paper left in the static port.

A second pass of the drill bit should clean up the static port leaving a clean, round hole.

Final smoothing and rounding may happen after primer.

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