Static port locations and altimeter chambers

I saw this link: https://www.adeptrocketry.com/staticports.htm which basically says to get accurate barometric altimeter readings you need to put your altimeter in a chamber sealed off from the engine and the "static port" holes into the chamber need to be sufficiently sized and 4 tube diameters behind the nose cone.

Everything they say makes sense from a tracking the entire flight perspective, but it seems excessive if the goal is to track the apogee for a number of reasons:

1. Once deployment has occurred, the altimeter will separate from the rest of the rocket body and no longer be affected by any of the factors listed. As long as deployment is close to apogee, one should get a reading by that point.

2. Even before deployment, once the rocket has slowed as it approaches apogee, the air-flow over the nose cone factor will go away, so having the static ports down the tube will no longer matter or be necessary.

3. Even before THAT point, once the rocket thrust has ended, the vacuum factor will dissipate fairly quickly, long before the rocket has finished coasting, assuming appropriately sized static ports.

Do others agree that for tracking apogee, the concerns listed at that link are a bit excessive?

(for what it is worth I'm going to put it in a chamber just so the ejection charge doesn't harm the altimeter, but the static ports will only be 2x the diameter behind the cone, which they say is OK for "lower speed rockets" (can anybody quantify that, is a 425 mph "lower speed" because it's not approaching super-sonic or is that still a "high performance" rocket?), so I wanted to validate my assumptions that it won't affect my ability to measure apogee.)

Thanks in advance to everyone who replies. I may be new, but I'm loving everything I'm reading. Learning a ton!

Everything Adept states, is dead nuts on.... you are forgetting the main point:

If anything causes a false reading while under full thrust , which usually ends in the first few seconds of flight, all hell can break loose & cause a premature apogee reading. This will fire apogee charge while at full speed, with disastrous results.

Yeah it won't matter when your slowing down or near apogee...... but you got to get there first!

kencraw said:

Everything they say makes sense from a tracking the entire flight perspective, but it seems excessive if the goal is to track the apogee for a number of reasons...

Click to expand...

Remember that Adept always focused on barometric-only sensors, so all their data came from there. Most modern electronics use both a barometric and an acceleration sensor. IMO, the baro sensor should only be used to read altitude at apogee, at which point the velocity is low enough that none of the placement issues matter that much. The only important thing is that the hole be there at all, so pressure can equalize.

Jim, you're talking about a setup when the altimeter is responsible for setting off the deployment charge, like a dual deployment, yes? If so, that makes a lot of sense. That would be pretty jarring to the whole setup. I'm just looking at a simple tracker with a traditional motor-based deployment charge, so I don't think that's relevant to me, unless I'm misunderstanding. Although it's a good thing to keep in the back of my head as some day I'd like to try a dual deployment setup.

kencraw said:

Jim, you're talking about a setup when the altimeter is responsible for setting off the deployment charge, like a dual deployment, yes? If so, that makes a lot of sense. That would be pretty jarring to the whole setup. I'm just looking at a simple tracker with a traditional motor-based deployment charge, so I don't think that's relevant to me, unless I'm misunderstanding. Although it's a good thing to keep in the back of my head as some day I'd like to try a dual deployment setup.

Click to expand...

If you are just using a tracker.....put it anywhere you like & it should work fine...as long as it's not in carbon fiber.
I house many of mine in the NC.

I misunderstood, thought you were flying an altimeter, as all the notes you referenced were regarding them.

JohnCoker said:

Remember that Adept always focused on barometric-only sensors, so all their data came from there. Most modern electronics use both a barometric and an acceleration sensor. IMO, the baro sensor should only be used to read altitude at apogee, at which point the velocity is low enough that none of the placement issues matter that much. The only important thing is that the hole be there at all, so pressure can equalize.

Click to expand...

Kinda...Sorta...Mosta [LOL

Some of the latest releases are still Baro only, MissleWorks RRC3's & 2+ ....Perfectflite Stratologgers, just to name a few. They do however have built in Mach-lockout features, negating false reading problems for high speed flight [mach]

edit: the RRC3 even has an algorithm built in, to allow for placement in a nose cone. It will "quarantine" any screwball readings until apogee, when it will function normally. This is besides the standard mach lock out feature.

Sorry Jim, I mis-spoke. When I said "tracker" I meant "altitude tracker", not thinking about the other electronic devices with a beacon for finding a rocket after it has fallen to the ground that are called trackers. Sorry about that (is it obvious yet I'm a newbie?).

Your original understanding was correct. I'm talking about an altimeter, but one that is only used to record altitude, specifically the apogee altitude, not one that is used to deploy the parachute. My parachute will be deployed by the motor's delayed deployment charge, not by electronics and it seems the issue you were pointing out was related to a setup where the electronics were responsible for deployment. Was my understanding correct?

Yes, good luck with your project!:wink: