Saturday, June 8, 2019

Building a sleeker new probe

I finally decided that I am going to steer away from "reliable" altimetry (i.e. altimetry that you can use for separation between aircraft, or report to ATC, or whatever). At least, we can put that aside for now. This means our barometry need be only good enough for estimating true air speed. Which means we can use a more convenient method of getting the static pressure than the messy aluminum tube that sticks out.

Again, one day we may reconsider, but for now, I think this is the sweet spot to make progress.

To that end, I redesigned the probe nose to have a series of radial holes part way down, judging that these would give an adequate estimate of static pressure. I then assembled that into a probe. Here are the steps.

First, we scuff a piece of 3/32" diameter brass tubing with sandpaper to give it a good gluing surface:

We then cut it into six 3/4" lengths, and clean up the cut ends:

We put them in alcohol to clean them, and take them out and dry on a clean paper towel without touching:

We then sandpaper and clean out the holes and edges in the new probe nose and a mounting ring:

One by one, we pick up each little brass tube with pliers, dab with a drop of CA glue, and insert it into each of the six holes in the nose so about 1/4" is showing:

We then screw and glue, with CA glue, the mounting ring onto the back of the nose. First we screw it down with a tiny gap, put glue into the gap, then close the gap by tightening the screws:

We then thread the tubing, this time using the brass tubes as "nipples" in the probe nose. This is an improvement over the previous system, where we had to glue the tubing directly into the nose. Note one hole is too close to the XBee -- we will fix that in a new rev. :)


This is the completed probe, and a comparison with the previous one. Stay tuned for reports!

No comments :

Post a Comment