Good few days at the shop since my last update.
Now that I know the final position of the fuel tank in the wing bay, I can finalize the "packing" around the tank that prevents it from moving around left and right inside the wing.
The space between the tank wall and the rib is a bit larger than a couple strips of cork will fill.
A grabbed a small block of wood I had lying on the bench and discovered it makes a good model for the size of high density foam block I plan to use.
Also with the tank in final position, I can confirm the hole drilled in the lower wing skin for the fuel drain is centred on the fuel drain bung. To see this closely without flipping the wing over I used a remote mirror and zoomed in with my cellphone camera:
The image is a bit blurry, but the bung is perfectly centred on the pilot hole in the lower skin.
The drain fitting is a 1/2" nut, so I want the hole in the skin large enough to allow a 1/2" socket to turn the drain fitting into the bung when installed, or easily pulled in the future for maintenance if required.
Drilled the drain hole out to just larger that the diameter of the 1/2" socket. It clearly fits cleanly in the hole from below.
The drain plug put in the drain bung on the tank. This is just finger tight, eventually it will have thread sealant and tightened accordingly.
Once fully threaded into the bung, the drain plug will sit just proud of the lower wing skin providing easy access for testing the fuel for contaminants during pre-flight checks.
Like on the right wing, I needed to trim some of the trailing edge away from the wing tank bay. Laid out the trimming line using painters tape and drilled A5 holes at the corners for strain relief.
Used a scrap board of thin plywood to protect the rear channel and ribs underneath the trailing edge while drilling the corner reliefs and cutting along the painters tape edge with a Dremmel cut-off wheel. Much easier that using metal snips in these tight confines.
Finished drilling out the trailing edge to rear channel holes.
Lifted the upper wing skin, deburred all the holes and primed the trailing edge where it tucks under the upper wing skin.
Brought the threaded fuel neck, threaded tank flange, drain bung and fuel sensor mounting plate home so I could measure them and create 2D CAD drawings of the gaskets I wanted to make. To save some material I nested the fuel drain bung gasket inside the fuel sensor plate gasket (the inner rectangle gets cut out as extra anyhow).
Exported the 2D CAD file to a SVG (scaled vector graphics) file that can be used by the CriCut machine to make perfectly sized gaskets.
Did a cut test of the sizes on card stock and although the cutter depth should have been a bit deeper (to make cleaner cuts), then general fit is perfect for each fitting.
Found a supplier able to provide square foot sheets of Buna-N rubber at 1/16" thickness. Bought 2 sheets for less than $13 total including tax.
Buna-N or Nitrile rubber is a durable and fuel/oil/chemical resistant material commonly used in the petrochemical industry for making gaskets and o-rings. This material is perfect for my application.
The reason I chose a 12" x 12" sheet is that it is the maximum width the standard strong grip adhesive CriCut cutting mat will accept.
Concerned that the edges of the Buna sheet might catch on the positioning rollers of the CriCut machine, Brenda recommended I tape the edges down with painters tape as a precaution.
A Google search revealed that CriCut recommends a "Deep Point" blade for rubber sheets - the standard cutting blade is designed for lighter weight materials Brenda picked up a Deep Point blade at the craft store.
The adhesive mat with Buna sheet loaded into the CriCut machine without issue - a good first sign this was going to work.
For those who haven't seen a CriCut machine in action, here's a video of it in action cutting my gaskets.
Once complete, the mat returns to the loaded ready position. (I didn't let the video run to the end). If you look closely, you can see where the cutting head did it's magic.
Brenda helped me take the finished gaskets off the mat - very pleased how they came out!
Perfect dimensional gaskets for each assembly! Very VERY cool!
Once back in the shop, I proceeded to drill the gaskets out for mounting. I wasn't sure the CriCut could carve holes with this small a diameter, but it probably could. I wanted to match them however with the threaded holes already on the drain bung.
The easiest was to match up the holes was to clamp the drain bung onto a spare board with the gasket blank sandwiched in between, then drill out the gasket mounting holes just slightly smaller than the machine screws - this will ensure the gasket stays tight on the screws.
For the fuel sensor plate gasket, I built a temporary "box" of 2 x 2 blocks to support the gasket blank while I drilled the location of the gasket mounting holes..
Started with A3 holes which match the sensor plate and the fuel tank.
Gasket laid in position on the fuel tank over the sensor hole.
Fuel sensor plate clecoed back in place on the tank with he gasket sandwiched between.
Mounting holes were then drilled out to 5/16" diameter, the size required for the well-nuts that will be used to secure and seal the sensor plate.
Each mounting hole upsized to 5/16" then fastened with a well-nut as I went.
Complete fit up of fuel sensor plate (fuel sensor to be re-mounted in plate).
Pulled the assembly apart for deburring and noticed that my original inner line doesn't match the inside edge of the gasket?
Also noticed that some of the mounting holes in the gasket were too close to the edge of the gasket to effect a good seal. As a result one of the holes torn a bit too. Looks like I made a measurement error creating the 2D drawings in CAD. Thankfully I only cut one sensor plate gasket like this. I'll update the CAD drawing to widen the gasket and cut a new one for this tank and a proper one for the other tank.
Setting that aside, I drilled out the mounting holes in the threaded tank insert next, using a scrap of 016 aluminum as the backing plate (standing in for the fuel tank).
Threaded tank fitting now riveted in final position with the gasket. Sealant will be added to the rivet tails that secure it.
Outside front corner of the wing tank. Sealant will be added to the rivet heads on this side as well and won't be seen once the tank is inside the wing.
Test fit of threaded fuel filler neck and cap confirms inside flange still fits correctly. Thread sealant will be added here too. That should complete a fully sealed fuel fill assembly on the tank.
Fuel bung mounted on underside of tank with gasket. More sealant here on the machine screw tails and around the perimeter.
Next up, re-do of fuel sender plate gasket (CAD drawing already corrected, cutting to be completed still) and final seal up of tank edges. Once that sealant cures, the tank will be final mounted in the wing bay and cork strips added on top to support the upper wing skin.
Very happy with the gaskets and how they turned out and I'll probably use the same method to cut some cork supports as well.
Stay tuned for more, thanks for following along.
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.