Pitot/AOA

With the pitot mast powder coated, last night I finished up the pitot tube install. Since I’m using the Gretz mount, and the wings are going to be stored for a while, I’m going to keep the mast and pitot tube uninstalled until I mount the wings. At this point I’ll just get all the fittings attached to the pitot tube, and bend the aluminum tubes to clear the aileron push tube.

Having not bent any aluminum tubing before, nor flared tube ends, I had some experimenting to do. I had the tools, but hadn’t spent time learning to use them. EAA’s hints for homebuilders has a couple of great videos on this, if you can find them. I had some scrap 1/4 inch tubing to practice with. I used some scrap to make a template of the bends I needed, which allowed me to ensure I can route the pitot and AOA tubing around the elevator pushrod that would otherwise interfere with the tubes. I was also able to confirm that I will be able to pass the pitot tube through the mast, given the bends I was making.

The only real problem was working with the two tubes (pitot and AOA). Bending the first one was easy, the second slightly harder due to interference from the other tube and the tube bending tool. Following a slightly different line, I worked around the issue.

The next step was to trim the tubes to give plenty of clearance from the top skin. Tube cutter worked ok, but again some interference with the other tube created a small problem.

With the tubes trimmed it was time to install the sleeves and b-nut, then flare the ends of the tubes. Apart from the interference issue, this was an easy step.

Then I was able to answer a question that I had been contemplating, which was how to run the wiring between the pitot tube and the controller. There is a rib between the pitot tube location and the controller location. The connectors are bulky and I’d need to either cut them off and rewire after passing through the systems hole, or route them through the lightening holes in the rib. I found I could pop out the snap bushing and pass the connectors through the systems hole in the rib. This will allow me to use the systems hole for the wiring, as I can cut a slit in the bushing to pop it over the wires, then push into the systems hole.

Last night I powder coated the pitot tube mast.

Having not done any powder coating, I had to buy the tools, and then practice by experimenting on some other parts. I bought the tools from Amazon, and the powder from Harbor Freight. Powder coating is actually quite a simple process, it involves coating a part in a powder, then heating it to 400 degrees (F) for 20 minutes to melt the powder. The trick is getting the powder to evenly coat the part, and for this a special air gun is needed. The air gun uses air from the compressor, to gently blow the fine powder onto the part. Then, an electrical field draws the powder onto the part and causes it to stick. The gun plugs into an electrical generator, and charges up the powder particles, while the part itself is grounded.

To heat the part, I bough a cheap toaster oven ($30), which is just big enough for what I need.

Steeling one of the kids stainless steel mugs, I set up an initial test. I didn’t use enough powder, but it was enough to get familiar with the equipment and go through the process.

Then I moved onto the pitot tube mast. The powder seemed to stick a little better, perhaps being steel vs stainless steel, of just getting more used to the process. Unfortunately I accidentally dumped some powder onto the mast just as I was finishing up. But it was easy to just wipe the powder off and start again. Eventually I was happy with the coating, and I carefully lifted it into the oven and left for 20 minutes. I let it cool slowly, and checked on it this morning.

I’m happy with how it turned out. I could have cleaned it up a little better; some of the blue marker rose to the top of the paint. And I could have perhaps gone slightly thicker, but it looks good to me and I’m happy with how even the coating was and how it turned out.