I didn’t take any pictures, but tonight I primed the gap seals for both wings. I used my standard primer the Stuart Systems EcoPoxy water-based epoxy primer. I am using high air pressure, lots of air, and minimal paint flow. It means I’m slowly building up layers, which makes for a better finish, I think. The downsides are that I’m often waiting for the compressor to catch up, so it’s slow, and paint particles get blown all over the garage. I have a fine layer of primer on many things in the garage. The high airflow seems to also dry the paint very quickly. So most of the paint particles being blown around are dry by the time they settle on things, and it’s more of a dust than a layer of paint.
Gap fairing dimpling
Today I dimpled the gap fairings for both wings. The plans are not very detailed, but some common sense seems to be in order, I think I have dimpled the correct sides of the parts.
I also found a couple of steps of didn’t realize I needed to complete. I short row of countersinks in the wings, and the j-channel for the outboard bottom wing skins. The j-channel isn’t drilled, and is supposed to be match drilled using the spar. I’ll need to match drill it against the skin, which should be ok, but would have been easier before I dimpled it.
Leak tested right tank, primed bottom skins
Two days ago I set up a tank test on the right wing tank. This time I carefully checked the tank fittings to ensure I had the correct amount of torque. I pumped a little pressure into the tank and left it for a couple of days. The water level in the manometer has tracked the temperature changes very closely, and I’m sure the tank is not leaking.
Tonight I primed the bottom skins for both wings. I have other parts ready to prime too, but I’m out of bench space, so will save that for tomorrow. It’s easy when only priming gone side of the parts, especially when they are flat and rectangular.
Priming the bottom wing skins
Additional molex connectors for extra wiring runs
The last two days I spent time making some mount brackets for extra molex connectors in the wing root. I needed to have at least some modifications to account for the pitot heater wiring (3 wires), but wanted to also mount a molex connector for the extra wiring I’ve run through the wings. This will make it much easier to install additional electrical devices in the wings later.
After checking with Vans, that I could safely rivet through the torque tube mount bracket, I cut out some small plates from a sheet of 1/16 aluminum. Then I marked the location for the molex connectors, cut them out with a drill and Dremel tool. Once I had a good fit for the molex connectors, I located them, drilled some holes, deburred, primed and riveted the plates into position. I have one connector on the right wing for the three spare wires, and two connectors on the left wing; one for the pitot tube wiring and one for the spare wiring. I used a bigger molex connector for the pitot tube wiring since this will carry 10A on two of the wires (power and ground for the heating element). The spare wiring will carry much lighter loads, as the wire is a smaller gauge.
Securing wing wiring
Today I spent some time tidying up and securing the wiring runs in the wings. This was mostly a case of installing zip ties and de-slacking the runs. I also installed some heat shrink to each of the molex connectors and installed some spiral wrap in areas where there’s a possibility of rubbing on bolts on the wing spar, or screws from inspection plates etc.
Pitot Mast Install
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.
Pitot Tube Mast Powder Coat
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.
Bottom skin drill/debur/dimple
The last two nights I spent time deburring and dimpling the outboard bottom wing skins. Not much to report, just some tedious work getting this completed.
The right wing skin done and temporarily installed with a handful of clecos. This keeps the skin out of the way while doing the left skin.
Pitot tube mount install -part 2
Today I cut out the pitot mast hole in the left wing bottom skin, dimples the pitot tube bottom skin holes, and countersunk the rib angle holes.
The longest job was cutting out the hole for the mast in the bottom skin. I started by removing the bottom skin from the wing, then drilled the #19 holes in the skin. These are where the screws will pass through the skin and into the mast’s flange. These holes were a pain to locate because I had dimples the backing plate. That enlarges the holes, and leaves a lot of slop when match drilling. I managed to get it pretty accurate, so then I moved on to cutting out the mast slot.
I drilled and then step drilled holes at each end. Then I used a hand nibbler to cut the material away. With a rough cut in place, I switched to running a grinding bit on my drill and cut away more material. Then I finished it up with a file, and checked the mast’s clearance frequently. By being fairly careful I ended up with a good looking hole that seems square and symmetrical.
I deburred the holes I made in the skin, and then dimples them all. I was anxious to get that done without cracking anything, and was successful. Then I dimpled the backing plate and countersunk the holes on the angle.
The pitot tube mast is basically ready to install now. I need to powder coat the mast, which I’m hoping to accomplish this week, then this is ready to be riveted together when the bottom skin is installed.
Pitot tube mount install
The last month has been busy, and I wasn’t able to make much progress on the airplane. Yesterday and today I worked on the pitot tube mount install, and a couple of other odd jobs.
I enlarged a set of systems holes in the left wing ribs so I could run a pitot and static line from the wing root to the ADAHRS, that will be installed in the left wing (two of them actually).
I decided to replace the pitot mount plate that came with the Gretz mount, because it needed more joggle, but was already dimples which would interfere with the joggling process. A secondary issue was that it wasn’t really wide enough for the 14, due to the rivet spacing on the wing spar.
I ended up making two, because the first wasn’t quite wide enough, but it was easy enough to cut out on the bandsaw, mark, drill, joggle, cut out the hole for the pitot mast, and then dimple. I had to make a tool for joggling, based on an idea from EAA Hints for Homebuilders. It came out perfectly, and it’s going to be great.
I installed a piece of angle onto the appropriate rib, then fitted the bottom skin and then match-drilled holes into the skin from inside. This necessitated a new drill, so I picked up an electric angle drill from harbor freight. It worked great until the battery ran out, and I realized I didn’t have a battery charger for this brand. So annoying! I will try to get one tomorrow.
Then I switched to another job, drilling, tapping and countersinking the pitot mast, prior to powder coating. The mast is steel, so countersinking takes a bit longer, but it’s also easier to control. The hard part is countersinking the curved leading edge of the mast. I ended up free-handing this, as I found I could see a little easier than if I had used the caged countersink. The end result was ok; not perfect, but good enough… I doubt I’ll spend much time looking at the pitot tube!
