altimeter in nosecone

Has anybody done this? Where do you put the vent hole? Seems like you could put it back on the tube where the NC shoulder is, and use a shear pin to keep it aligned. I thought though, that there might be less turbulence and the bass of the nosecone, just above where the body meets. It's a mega mosquito nosecone if that makes a difference.

I tend to put a vent hole right above the shoulder. Put it in the shoulder and you run the risk of twisting the nose cone and blocking off the vent hole.

kzimmerman said:

Has anybody done this? Where do you put the vent hole? Seems like you could put it back on the tube where the NC shoulder is, and use a shear pin to keep it aligned. I thought though, that there might be less turbulence and the bass of the nosecone, just above where the body meets. It's a mega mosquito nosecone if that makes a difference.

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I haven't personally done it 'in' the nose cone, but it's been done by others numerous times. I have the JL AltimeterOne, and it just rests on top of the parachute, which is obviously very near the top. I went on the advice from others to put the vent holes -at least- 1Cal behind the shoulder of nosecone, where the air has time to 'settle' more. Understandably, directly at the base of the NC, is a more turbulent area.
Also, make sure your holes are large enough. I made 3 little tiny 1/16" holes, and the altimeter did not seem accurate, until I made the holes larger.

This is a rrc2, using it to set up a cable cutter for dual deploy, not one of the little altitude sensing ones. It needs to be protected from ejection charges, hence inside the nosecone. I cut off part of the base of the nosecone, and am putting a bulkhead in it's place to allow access and for the attachment point for the shock cord and the ejection charges (one at appogee, one about 300'-500') I've modified the thing to take up to 3 grain 29mm motors, and beefed up the airframe to suit. So, I'm going to be pushing a lot more altitude potentially, hence the desire for dual deploy.
Blackbrandt, the shear pin was to prevent the nosecone from spinning. My concern was for the position that would allow for the best reading in an area that has a fair degree of turbulence.

kzimmerman said:

Has anybody done this? Where do you put the vent hole? Seems like you could put it back on the tube where the NC shoulder is, and use a shear pin to keep it aligned. I thought though, that there might be less turbulence and the bass of the nosecone, just above where the body meets. It's a mega mosquito nosecone if that makes a difference.

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I would stick the holes (min 3 120° apart or equally spaced if more than 3) on the flat part of the nosecone, about an inch above the shoulder. I have 3 rockets with converted nosecone AV bays and they work fine.

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I have put the altimeters inside the Nose cone and put the holes just above the shoulder too, so far they seem to work fine, however I have not flown a configuration with two (one in body and one in nose) to verify how accurate the one in the nose is for recording puposes. I know they worked at apogee, and again at the main deploy altitude. Static port can be seen in the last photo on the Red Crayon just above airframe to nosecone juncture (Red Crayon suffered a fatal crash due to a long delay, no electronics involved).

kzimmerman said:

This is a rrc2, using it to set up a cable cutter for dual deploy, not one of the little altitude sensing ones.

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Wut? The RRC2 is an "altimeter", and thus senses "altitude" via air pressure. A vent hole is needed.

The pressure gradient around the nose cone may affect the altimeter's reading up to apogee, but that is all. The apogee will be measured correctly (zero vertical velocity), as will the main parachute setting altitude (relatively low velocity). Go for it.

I got bad readings with a single hole in my Leviathan NC. I ended up putting three small holes 120-degrees apart.

Here's a similar solution to the above, but I couldn't afford the volume loss that comes from gluing the retaining bulkhead up at the shoulder so I glued mine to the base of the cone and built a tray/frame to carry the altimeter and a balance weight. (This is for a 2.6" Madcow BOMARC which needs lots of nose weight anyways so I wasn't too worried about about adding too much structure.) You can't see it in the photos, but there's also a second bulkhead glued at the front of the cone to ensure that the tray stays well supported on the center line.





I went with three equally spaced 3/32" static ports drilled about 1/4" up from the shoulder. I'm using this arrangement to ensure ejection is triggered at apogee, but I expect it would be equally capable of triggering a cable cutter on the way down.

Allright, well there seems to be a general consensus. I'll give it a whirl with the holes at the bottom of the nosecone, just above the shoulder. I'm building another one with a loc 54mm nosecone with the eggfinder in it, hopefully this will all work out!