Couple of updates to share. Got some work done early in March, then was away for almost 2 weeks for a work trip, then back in the shop yesterday for the day.
Both fuel tanks are now together awaiting sealant at the seams. I decided to keep the rivet spacing on the seams at 20 pitch - not required for strength, but will ensure the seams are tight and will squeeze the sealant out to the edges of the inside seam.
By placing the clecos on the inside edges of the tank I can test fit the tank in the wing.
It's a tight fit. I had to slide the rear corner of the tank inside the rear channel first, then slide the tank forward towards the spar..
With the tank forward as far as it would go, the fuel port on the tank doesn't completely line up with the passthrough hole, so some more trimming of the top forward seam on the tank was required so it can clear the wing spar.
When I originally cut and bent the tank skins I had the intention of having the tank and seams welded, so I wasn't concerned that the forward seam flange was a bit narrow. Now that I plan to rivet the tank together, the forward seam won't be wide enough to safely rivet.
To correct the issue, I cut the folded flange off, and bent a new flange that can be riveted onto the front wall of the tank and is wide enough on the other flange to accept a row of rivets to secure the top skin.
Once the rivet lines were laid and drilled out, I trimmed away the excess top skin to match the new flange. This brings the upper front edge of the tank close as I can to the plans (5mm overhang).
The right wing tank doesn't have the same flange width issue and I was able to create a rivet line in the original bent flange, then trimmed it the same way to match the left wing tank.
Got my fuel sender mounting plates back from Henri the welder. Very happy with the work he did. They look heavy, but are actually quite light and the welds are solid and fuel tight.
Next step was drilling out the passthrough hole where the fuel sender extends into the tank. A small hole saw is perfect for this.
Some simple trig math to figure out the centre of round plate. Bi-sect the circle in two places. Draw a perpendicular line from the mid point of each of the bi-sect lines. Where the perpendicular lines intersect is the centre of the circle.
Holesaw on the drillpress makes a nice clean hole:
Deburr and clean up some of the sharp edges with sandpaper and they are ready for the sending units.
Drill and tap the plate for mounting screws:
The mounting plate is thick enough to allow for four full threads to engage and holds the mounting gasket tight. I may add some thread locker when final installing these as I'd prefer not to have a nut that could come loose and fall inside the tank.
Next up I need to fabricate the rear channel fuel tank support angle. In the standard aircraft, the wing tanks are smaller and supported by a rear tank rib that runs laterally from the inboard and out board fuel tank bay ribs. With the long range tanks, an angle is added to the rear channel to secure the tank forward in the fuel tank bay.
Rather than create new from fresh stock, I realized I had some scrap ends of channel cut off the end of the rear channel when building up the wing skeleton. Although a bit thicker material, these will work perfectly.
Mark out where to cut the channel to create the angle and cut on the bandsaw:
The plans call for the angle to be mounted on the top of the rear channel, but this doesn't make sense to me as the trailing edge and fuel tank skin will then have a bump to overcome when they get attached. The only thing I can think of is that it is done that way to make mounting it easier. I going to mount mine inside the channel by securing temporarily with some epoxy so I don't need to cleco it in position as those clecos then will be in the way when I attach the trailing edge and fuel tank skin. Eventually rivets will hold it all together anyway.
With the tank rear support angle temporarily in place and the front edge trimmed correctly, the tank fits good, nice and square in the wing. A piece of adhesive cork will be put on the face of the angle (and elsewhere on the tank) to prevent rubbing:
Onto the fuel bungs.
Sometimes Google is your friend, sometimes it overcomplicates things. For the fuel drain bung, I want to secure it with five machine screws evenly distributed around the perimeter. So I searched Google on how to divide a circle into five equal parts.
I took a scrap of cardstock, and following the multistep process learned how to divide the circle, transcribe arcs off tangents, re-measure from arc to bisect angle, then scribe from intersecting angles to arc the outer circumference where the five hole locations I need will be. Really cool, bit how can I do that on the bung itself? This is too complicated for what I'm trying to do. Can someone say "Squirrel" !!
Can this be done easier with a protractor and simple math? Yes young Jedi, easier it can be (Master Yoda rolling his eyes)....
Draw a circle using a grade-school protractor. 360 degrees divided by 5 is 72 degrees. Mark five locations on the circle 72 degrees apart.
Centre the bung on the circle.
Use the five tangent lines to mark the drill holes on the bung with the centre punch at each of the five locations.
Drill the five holes.
Learn he will. Maybe.... LOL
With the bung now drilled out to A3, I centred it over the tank drain hole and secured it with clecos:
Satisfied with the location and fit, I took the bung off the tank and expanded each of the holes to 5/32 on the drill press and tapped each hole in turn to accept a 1/4 inch 10-32 stainless machine screw. The mount holes in the skin need to be slightly larger to clear the threads of the screws:
When final installed, sealant will be added underneath the screw heads and between the bung and the tank skin.
Next up, securing the fuel tank output bung fitting.
I needed to drill where the skin, tank rib and bung will meet.
With the location determined in the tank seam, I removed the rib from the tank and clamped the bung into place. I then back drilled through the rib flange and into the bung just enough to mark the location of the holes.
The bung was then put in the vice on the drill press and drilled just deep enough for tapping for machine crews the same as the drain bungs.
The holes in the skin and rib flange were opened up slightly for the 10-32 machine screws. With sealant this will secure the fuel bung very well, but I'll add some thread locker as well.
Test fit the fuel tank again with the new rear support angle and the finger strainer in place and it's coming together. Thread sealer will be added once this is final installed. Still some fitting to do in the wing bay (spar fuel tank support channels), but very pleased how the tank fits so far.
Next up is fitting the fuel sender assembly and the fuel fill neck and cap.
The fuel sender plate is inverted on the top of the tank so I can trace out the shape on the upper tank skin and determine how it will mount.
The red "panel" line represents the out dimension of the fuel sender assembly. The inner red circle is the rough estimate of where I intended the sensor to go. The inner green box roughly represents the access hole I'm going to create. I will be nice to be able to look and reach inside the tank should the need ever arise in the future. For rigidity, I may narrow the lateral width of the access hole a bit, I'll make the decision once I determine how this will be sealed and secured to the tank skin.
So this wing assembly has gone much faster than the first, but total time has been almost equal to the first as I figure out the fuel tank and associated wing plumbing. Hope to finalize this wing in the coming weeks and get the bench clear for the fuselage assembly.
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.