Wing Fuel Tank 18-2-1, 18-2-5 to 18-4-8, 18-5-3, Fuel Return
I continued working on the left fuel tank by countersinking the row of holes in the skin that attach to the baffle, skipping every 10th hole. This was relatively straightforward once I had the countersink cage dialed to the correct depth.
The only issue I encountered was while working along the bottom of the skin, I could not get the countersink pilot through the hole, as the baffle and skin holes did not line up perfectly. At first I decided to start reaming these holes, and while this worked, I wasn't happy with removing 1-2 thousandths of material on one edge of the baffle holes to get the countersink pilot to fit through.
Instead of reaming, I decided to remove all clecoes from the bottom baffle flange, and recleco the skin to the baffle, this time taking extra care to ensure the holes were lined up from the start. This worked much better, and I was then able to countersink without needing to do any reaming
The reason this worked was that clecos don't fill the entire hole, and in this case were holding the pieces in slight misalignment. I may order some skin pins to use in future as they are meant to hold pieces together to a tighter tolerance, and would have helped to avoid such issues.
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| Countersinking the skin to baffle holes, checking each hole with a rivet for correct depth |
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| All holes countersunk along the left fuel tank skin to baffle |
Next I countersunk the nutplate attach holes in the Z brackets. This again was relatively straightforward, however I had to pay special attention to the holes nearest the edges, making sure I held the countersink cage square to the edge. This avoided over countersinking due to tipping of the cage.
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| Z bracket held in vice with a piece of 2x4 to help clamp it securely for countersinking |
With the countersinking done on the left fuel tank, I started preparing the ribs and stiffeners for the right fuel tank. The same process of straightening flanges, deburring edges, fluting and reaming all holes was followed as for the left tank.
I also took care of deburring edges and reaming holes in the right tank attach bracket and right tank baffle prior to beginning assembly of the right tank.
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| Right fuel tank parts prepped and ready for initial assembly |
Disassembly of the left fuel tank, followed by assembly of the right fuel tank went smoothly. For the right fuel tank, I tried to follow the assembly order (rib attachment in particular) outlined in the fuel tank assembly video that Van's published a couple of years back. That video will be incredibly useful when it comes time to apply proseal for final tank assembly as it is filled with useful hints that will hopefully save a lot of time and potential mistakes.
By following the assembly order in the video, I was able to get the first rib in place without issue since the cradle helps hold the skin in alignment close to that first rib. All other ribs went in easily, except for the inboard root nose rib which was still somewhat tight, but with some patience (and creative choice of words!) I was able to cleco it into place.
Next I match drilled the holes into the right fuel tank top stiffener, clecoed the baffle and Z-brackets into place, and proceeded to countersink the skin to baffle holes. This was quick and easy having done it once before. This time I made sure that the baffle was aligned with the skin holes on both sides prior to starting.
Finally, I reamed all screw holes in the right tank skin to #19.
With the right fuel tank assembled and drilled, I next took time to debur all holes in the left fuel tank parts and skin.
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| Right fuel tank assembled, and left fuel parts waiting for hole deburring |
With the right fuel tank assembled and drilled, I next took time to debur all holes in the left fuel tank parts and skin.
The only holes I decided not to debur were the interior skin to baffle holes on the tank skin. These were previously countersunk from the exterior side which results in a somewhat thin edge remaining. I didn't want to make the edge any thinner by deburring, so instead prior to tank sealant application, I will instead just scuff along these holes with a ScotchBrite pad to preserve them as much as possible.
For my RV-10, I have decided to install the SDS EM-6 electronic fuel injection and ignition. This requires fuel return lines to send excess fuel back to the tanks. I figured that this would be a good time to plan for installing the return line flanges so that they are in place when I complete the tanks.
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| All holes deburred except skin to baffle holes on the interior of the tank skin |
For my RV-10, I have decided to install the SDS EM-6 electronic fuel injection and ignition. This requires fuel return lines to send excess fuel back to the tanks. I figured that this would be a good time to plan for installing the return line flanges so that they are in place when I complete the tanks.
I had previously ordered 2 extra VA-141 flanges from Van's, and following instructions for fuel return line placement, I marked a location for the flanges on each of the left and right tank aft root ribs
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| Right fuel tank. Fuel intake on the left, and fuel return placement on the right (held with magnets). I had to make sure there was enough clearance from the aft skin stiffener, and I also temporarily attached the fuel vent line bracket to ensure adequate clearance from that as well. |
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| Fuel return flange location marked for reference |
After removing the right fuel tank aft root rib, I proceeded to drill the center hole for the fuel return flanges. Marking the center point as accurately as I could, I then drilled a #30 pilot hole and used a step drill in the drill press to upsize it to 3/4".
As this hole is very close to the rib flange, I also had to make sure that the step drill bit was pulled out far enough from the drill chuck to ensure that the chuck would not hit the flange while drilling.
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| Flange center hole position marked |
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| Drilling the flange center hole from the exterior of the rib so that it could be clamped and held flat |
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| Flange center holes after drilling and deburring. Both came out nicely and were located in the correct position for the flange. |
I finished up the return line holes by match drilling the rivet holes from the flange into the rib.
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| Match drilling return line flange rivet holes to the root rib |
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| Return line flange holes completed. Flanges will be attached later with rivets and tank sealant |
Next I countersunk the holes in the fuel cap flanges for a dimpled skin. I found it easiest to clamp the fuel tank flange, supported by a piece of 2x4, in the vise. With this setup, countersinking was easy!
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| Fuel cap flange secured in the vise while countersinking |
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| Fuel cap flanges ready for installation |
I also countersunk the nutplate attach holes in the fuel tank attach brackets for the dimpled shims. No issues here other than being careful with holes at the ends of the flanges. I also dimpled the nutplate attach holes in the shims, again being careful with the holes close to the edge.
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| Countersinking the nutplate attach holes in the fuel tank attach brackets |
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| Brackets and shims, nutplate attach holes countersunk and dimpled respectively |
Build Hints
- If final sized holes don't line up well after clecoing parts, try removing clecos and realigning to see if that helps. Clecos don't fill the entire hole, and this can cause a very slight misalignment of parts, barely noticeable until you try to insert a drill bit, reamer or rivet.
- Refer to Van's incredibly useful fuel tank assembly video for tips and insights on fuel tank construction, and in particular working with tank sealant.
Time Taken: 23.6 hours
Dates: November 21 - December 9 2023
Wing Fuel Tank Total Time: 38.7 hours
RV-10 Build Total Time: 542.7 hours
Priming Total Time: 50.9 hours (not included in build time totals)