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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Rocket Camp Keeps You Busy

I feel guilty for not blogging much recently. Between teaching rocket camp, my day job, and preparing to move to Boston a week from Tuesday, I don't have much free time.

But camp has been going well. Several parents have told me that their kids have learned a lot. Which is great - and sort of surprising. These kids have absorbed a lot of technical information. Sometimes I've mentioned something once on one day, and half the kids don't look like they're even listening, and two days later, I'll ask a question, thinking I'll need to re-teach the information - but the kids know it! Concepts like total impulse and center of pressure are not easy to grasp at first, but these are some smart kids.

Anyway, rather than writing up each week in separate posts, I'll take what I've learned about teaching rocketry when I'm all done, after Friday. While this blog is partly for people who are n00bs to rocketry, maybe there are a few more experienced rocketeers who are n00bs to teaching rocketry, and maybe my experience will help you prepare.

In any case, I was able to get a little painting done. Ivy Tech has a really nice spray painting booth, and I was able to get Keith's Rocket painted. I'm pretty proud of it.

I'd originally bought the copper paint for the fins on the 3D Rocketry Nautilus II, but that rocket was lost before it was finished. Still, it looks great! I'm going to have to build one of these for myself.

The rocket has a payload compartment. Four small holes - known as static ports - allow you to fly with a barometric altimeter, such as the Jolly Logic. An altimeter needs to breathe to function, so you put static ports in your rocket to allow the payload compartment to equalize in pressure with the air outside the rocket.

I have four more Donor's Rockets to finish painting. I hope to launch these next week - after rocket school!

Here, the Ivy Tech Rocket Kids launch one of Chad's rockets:

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