Altimeter air hole

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Patternflyer

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Ok, maybe I’m way over thinking this, but as I wait for my Altimeter 2 to arrive in the mail, I decided to start prepping my Alpha III for it. I decided to go with a single 1/8” hole just under the nose cone insert. Well, guess what’s nearby? The shock cord mount. So, overthinking things as I tend to do, I thought “why not place a nice clean rivet or grommet on the body and run it through the shock cord mount to give the mount some extra security as well?”

After thinking all day about it, I came up with this. I drilled a 9/64 hole through the body and shock cord mount. Then took an R/C servo grommet and split the back side into 4-5 tabs. Ran the grommet through and bent the tabs back on the inside. I covered the tabs with glue so things wouldn’t snag on the way out during ejection. Made for a nice clean installation, provides outside air for the altimeter, and better secures the shock cord mount.E5CBF51E-D041-4767-BC89-FA0BBF4000D3.jpeg11C62EEB-708E-4144-AEA5-838424A87905.jpegA880FAC7-860C-4B9C-8473-A2523D30B869.jpegBEC7A4C5-DAB5-40F9-AA06-E16C273D8BEB.jpeg274749FB-5E60-4427-A45E-BB96D2160ABE.jpeg
 
For the amount of air one could expect to escape from an Alpha III as it climbs to lower pressure, your vent hole is more than plenty big, but I like the clean look with the brass grommet. Unless I am going for a super clean look, I make my altimeter vents by poking a pilot hole with a thumbtack and then widening it by pushing in a narrow screwdriver shaft or a construction nail.
 
Depending on which way the wind is blowing relative to the hole as the model sits on the pad, you may want more than one so that air blowing in or across the hole won't change the pressure inside and confuse the altimeter.

In Alphas I use three 3/32 inch holes at about that same distance below the nose cone/body tube joint. I use a sharpened brass tube to cut/punch them while supporting the tube on the inside. Then I harden the holes with a little thin CA and sand a bit if needed.

A Perfectflite Firefly, a FlightSketch Mini or an Altus Metrum MicroPeak can be tucked up inside the nose cone of a Alpha III, if wrapped in some padding. I use fleece pouches my wife makes for the purpose. Tether them to the screw eye.

Hopefully the 'chute won't catch on that brass bit on the way out.....
 
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