Nose cone AV bay. Sample hole??

Where should I put the sample hole for a Baro altimeter that is sealed in the nose? I don't have the slightest idea and need answers fast. Please help.

Joker050608 said:

Where should I put the sample hole for a Baro altimeter that is sealed in the nose? I don't have the slightest idea and need answers fast. Please help.

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In the nose cone shoulder. Drill hole(s) through the body tube and shoulder. Make sure you have enough friction to keep the nose from turning and closing off the holes during flight.

Buckeye said:

In the nose cone shoulder. Drill hole(s) through the body tube and shoulder. Make sure you have enough friction to keep the nose from turning and closing off the holes during flight.

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One or two? And I'm guessing just above the shoulder wouldn't be ideal?

Buckeye, have you already tried it?
I'm wondering if speed and air deflection can alter the altimeter's readings.
If someone tried it, please let us know your experiences.

I wouldn't be too concerned with turbulent air causing any changes. This rocket won't really see subsonic transitions.

What size nosecone and what altimeter?

markkoelsch said:

What size nosecone and what altimeter?

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It's a 3" loc oglive. With an RRC2+ and might use a stratologger for redundancy. The length is a little over 12".

The general consensus is that the number of holes doesn't matter, just the area. However, Adept used to recommend an odd number of holes (1 or 3, never 2).

I generally use one largish one (1/4"), which is also the hole through which I turn on the switch.

Joker050608 said:

It's a 3" loc oglive. With an RRC2+ and might use a stratologger for redundancy. The length is a little over 12".

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I would probably go 3 1/8" holes. That is a swag guessing on cone volume.

Wayco said:

I have a "NightBow" style night rocket with a 4" nosecone 16" long. Has an altimeter, several batteries and lighting in the nosecone. Many successful flights. I drilled three 7/32" holes about an inch below the shoulder for static ports and used three 2/56" shear pins. The N/C alone weighs 1 lb. 6 oz. and I estimated the volume. If you do drill through the shoulder, I recommend using shear pins to prevent it from moving.

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My nose cone comes in just over one pound. So I will have a couple shear pins in there. Was thinking of just one 1/4" hole directly over the Baro sensor. Should be able to access the switch here too.

Crumb fire said:

Buckeye, have you already tried it?
I'm wondering if speed and air deflection can alter the altimeter's readings.
If someone tried it, please let us know your experiences.

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Sure. Many times. The recorded data during ascent may be a little off, but as the rocket reaches 0 velocity at apogee, the drogue charge will fire just fine and max altitude will be correct.

Think about a DD rocket tumbling down drogueless. Lots of airflow chaos, turbulence, and separation around the static port holes. The altimeter still reads the altitude just fine and deploys the main.

For a simple subsonic flight, I would be comfortable even putting the vent holes in the nose cone itself - not at the tip, or near curvature, but near the straight part at the bottom.

Location of ports really doesn't make a difference with the filtering on modern altimeters. They run filters as the norm, and besides: you're not going to get a scavenging effect at apogee, when the rocket's barely moving, so your drogue event is going to be just as if you had the altimeter in the more traditional middle-of-the-rocket configuration. From that point, you're not going to be going fast enough to do anything other than sample until main deployment (if you're even doing DD). Don't worry about it.

Size of ports, well... that does tend to correspond w/ av-bay volume. Sounds like you've already got wiring in there. Do you have another, similar, empty nosecone? Fill it with water and pour it out into a measuring cup. Convert oz to mL, if necessary, then mL to cu in, if you need to. The clear plastic or Pyrex measuring cups typically have mL graduations anyway. Once converted, you should be able to cross-reference to find appropriate-sized static ports. I would suggest 3.


Later!

--Coop

If you are putting the sampling port in the shoulder portion of your nosecone I would recommend that the holes in the airframe be the correct diameter (for example, 3/32" diameter) and the hole in your nosecone be larger (for example, 1/4"). This way if your nosecone moves just a bit, it will not block any of the ports. I would also drill out your sampling holes in your airframe two drill bit sizes smaller to start. Do this with your nosecone held with some masking tape. Then take the nosecone out and use some very thin CA and wick into your sampling holes. Drill with the next size drill bit. Wick more CA. Drill with your final size bit and sand the inside and out. You should be able to get some nice crisp edges this way.

Edward

I have a 3" dia 24" long (including NC) rocket that has the Av Bay in the nose and flies an RRC3. The vent holes are drilled on the surface of the cone, just above the bulkhead I installed. I haven't had any issues with deployments, readings, etc.