November 15, 2019

Pitot Installation Complete, Electrical Checks OK

Although I’ve had it for a while, I never finished the pitot tube installation on the left wing. It was one of few remaining tasks to do before I close out the wing. I finished up wiring the heater controller module, then took care of the plumbing.

Pitot lines carefully bent using the same tool I used for the fuel tank breather lines. To achieve the gentle radius, I had to bend the pipe a little bit at several points.
Wiring all dressed up and secured. Deutsch DT connector used as a disconnect that will be accessible from the inspection hole. The wiring is staked down to ensure it doesn’t interfere with the aileron torque tube that comes later (with fuselage kit?)

There are a few solutions out there to link together the 3/16″ aluminum tubes from the pitot with the 1/4″ plastic tubing that goes to the fuselage; I chose to use AN style fittings on the aluminum tube, screwed into these nylon fittings that I got from McMaster. BTW, I also bought nylon tubing from McMaster to use instead of the clear vinyl tubing supplied with the sling kit.

I like these fittings because they form an interference fit on the threads, and the screw-on nut includes an o-ring and a metal gripping ring that bites into the tube to form a tight seal.

Although these nylon fittings have NPTF-type “dry seal” threads, the mating threads on the AN fitting are the NPT variety, so a thread sealer is recommended. Unfortunately I can’t use the Loctite 577 that I would normally use (it’s only for metal fittings), so a search for a thread sealer suitable for both plastic & metal fittings led me to a product from Rectorseal, T Plus 2. It’s sold at Lowes for a few bucks.

I applied Loctite 577 to the AN fitting nut, and TP2 to the threads for the nylon fitting. Leak checks were negative, with a balloon staying inflated for 24 hours. I tied together the ends of the blue and green tubing using a short section of the vinyl tubing that was originally supplied with the kit; heating it up with a heat gun made it flexible enough to fit over the stiffer nylon tube.

Soapy water sprayed onto the pressurized tubes, no bubbles
Balloon covering both the pitot inlet and the AoA sensing ports

I did electrical checks next, to ensure wiring to the lights and pitot heater were good. Lights are pretty straightforward to check. Although these Kuntzelman LTR lights are bright, I don’t like how they use a threaded lug for ground/return, which is the same lug that’s used to hold the light in place — this makes the whole wing become a return path, and I’m afraid that could lead to electrical noise problems later. I ran a dedicated return wire for the lights, so I’ll have to figure out a way to keep the lights electrically insulated from the structure. Nonethess, the lights worked fine. I used a bench top adjustable power supply to apply 12V, and according to the ammeter on my power supply, these lights draw about 1.1 amps each, pretty efficient for the amount of light they throw out!

Soon these will light up a dark runway
Bright!

For the pitot, I had to use a different power supply capable of pushing more amps, so I used a DC switching supply rated up to 10A, then I used a Seek thermal camera that snaps onto my iPhone to watch the temp rise on the pitot.

Right after power is applied to the pitot heater – tip temperature 84°F
The Garmin G3X install manual doesn’t state what the regulated temperature should be, only that the regulator “limits the maximum tip temperature to make the probe safer to the touch.”. I saw a max temp of about 124°F, which should be hot enough to prevent ice accumulation while not burning someone touching it
Drok adjustable power supply that I bought from Amazon a while ago – something I had laying around, nothing fancy

Now with these tasks done, I did some final inspections and vacuumed the inside of the wing before putting on the upper skins.

Primer applied along the rivet lines for the inner top skin
Outer skin cleco’d in place
Inner skin cleco’d in place. Holes for the ribs and spar line up fine, but the holes for the two upper stringers don’t line up so well.

Most of the holes line up ok using clecos, but the alignment is not perfect so I’m going to have to use a chucking reaming to open the holes up, which will create more metal shavings.. which means I have to vacuum one more time. So I’m going to do that, pull the skins off one more time to vacuum up the shavings, then I should be ready to rivet the skins down and move on.

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