Baro Altimeters in the Nose Cone

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Hybrid33

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Looking for Help from You folks that have done this and had a high degree of success.
Basically I am asking for the complete list of things I need to know to use a barometric altimeter in the Nose cone of a Rocket.
3.9" Rocket both conical and ogive shapes will be used.

1) Best position for altimeter forward end or Aft end of Cone?
2) Best location for vent holes?
And any thing else I have not listed.
Thank You !
 
A baro altimeter doesn't really care where you put it in the nose cone or AV bay. Put the holes in the switch band behind the nose cone if you're doing HED, if you're not then put them through the shoulder and the tube (assuming you have screws or shear pins to hold them in position). You want to get the holes as far back as possible from the tip of the nose cone, but a few cm's probably won't make much difference in you readings.
 
I have done this without issue on several rockets, but only with the ogive, and from 54mm to 4".

As Cris said, you want it somewhere after the transition; I have followed a general inch rule. I don't like to locate them in a spot where I have to drill through both the airframe and nosecone. This is a personal preference because I don't want to add any complexity in lining things up during prep. I have always kept mine located on the nosecone as the ogives have a flat spot before it gets to the shoulder. The issue as described to me is you want to locate the holes after the transition, which has something to do with the laminar flow and pressure differentials...or something like that.

I have flown with this up to Mach .8 without issue and I am guessing that velocity as well as design plays a role in the success of this config, so YMMV.
 
The only real issue I have found with nose cone mounted baro alts is that the data is pretty noisy, but the apogee detect and reporting are good. All of my nose electronic bays have the holes on the ogive base or on the crayon bank rockets on the flat below the conical section. Its definitely better for data purposes to get the static ports away from the NC transition, but the alt will still work just fine.
 
I have always put my sampling ports in the nose cone itself, right in front of the shoulder. Never any issues. In a 4" nose cone you can easily fit everything in the shoulder itself, add a switch band and put sampling ports there. Unless of course you need the room in the nose cone for a parachute or what not. I've done one rocket with the access hole for my screw switch through the shoulder and nose cone. Turn on the switch and twist the nose cone to cover the hole so the altimeter doesn't rely on that hole, only the sampling ports. I don't know if it makes a difference, I just do it.
 
The thing with the baro alt. as Rich said, the data gets noisy. If you want accurate baro data from your flight, the nose cone is probably not where you want the altimeter and if you do put it there, vent hole placement can be critical to accuracy. Although you might want to go to accelerometer based altimeter for that. If all you need is peak altitude and accurate deployment at apogee and main, the nose cone works fine and vent hole placement is much less critical because the desired events are occurring at relative slow speeds.
 
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