I fabricated a spacer out of 0.020" Alclad that will go between the pitot tube backing plate and the skin. Measure, mark, drill pilot holes, rough cut, Dremel, file, deburr. Here's a time-lapsed series of shots of its creation:
As for match-drilling the backing plate to the bottom skin, the Gretz plans have you clecoing the skin to the wing and back-drilling through the plate into the skin. That would work okay if I could remove the top skin to get in there, but on the quickbuild wings the top skins are of course already permanently attached. I thought about trying to get an angle drill back in there, but that seemed like a recipe for frustration and/or disaster. Instead, I came up with this approach:
I match-drilled the pattern of the spar rivet holes in the backing plate onto a piece of bar stock I found in my scrap box, to make a stand-in for the actual spar flange. Then, I clecoed the backing plate, spacer, pretend-spar, and skin to the workbench through the spar rivet holes. After that, it was a simple matter to match drill the skin to the backing plate, right into the table. Having a sacrifical layer of MDF on top of the workbench is incredibly handy.
Here's a test fit with the skin, spacer, backing plate, and mounting angle all clecoed together. Alignment is good and the skin lays down just right with the spacer in place.
On to the pitot mast cutout in the bottom skin. No pressure, it's just a $64 replacement skin and a similar cost in shipping and handling if you screw it up. First comes starter holes with the unibit:
Then a rough pass with a carbide cutting bit in the Dremel:
Lots and lots of filing later, it fits pretty well:
The gap between the mast and the skin isn't exactly symmetrical – it's about 1/16" on one side and between 1/32" and 1/16" on the other:
I could file the sides to match, but what I'll probably do instead is just blend the mast into the wing skin with a small fillet of Proseal during final assembly. I can't think of a situation outside of major wing damage where you'd need to remove the pitot mast from the wing – the pitot tube itself, sure, but the tube can be removed from the mast just by taking out four little screws and unhooking the air line and heater wires. Good enough. It might even help to keep water from getting up into the wing that way (think about it, ice + heated pitot). Who knows?
Anyway, the pitot mounting stuff is basically done for now. Now if I could just beat the head cold I brought back from last week's ski trip.