Fuel Tank Extensions

Early on I decided that I would build in extended fuel tanks. It was not until I actually received my kit that I realized that there are a couple levels of how much you extend the wing tanks. I finally decided to only extend my wing tanks by 1 fuel bay. Some people extend them by 2.

Lon and Pam Kelly went with 1 fuel bay extensions in N123PK. This gives them a 92 gallon fuel capacity. Assuming a 14 gph fuel burn with their IO-550, this gives them 6 hours flying time with slightly less than an hour reserve. They typically plan cross country trips in 3 hour legs. I imagine that Terry and I would be doing the same, and that going beyond 92 gallons would be pointless and a fair mount of extra work.

The ES Fastbuild wing kit is built for 4 fuel bays in each wing. The plans only calls for 4 fuel bays per wing. However, Lancair builds in a shear web between ribs BL 97 and BL 120. The space between BL 97 and BL 120 is not a fuel tank as is because there are no fuel flow tunnels cut in rib BL 97. Modifying each wing to have a #5 fuel bay is very simple ( if the fuel caps, fuel tank vent tubes, and fuel probes have not been installed ). A summary of the needed steps are:

Cut 4 fuel flow tunnels in BL 97. Finish the rib edges in the fuel flow tunnels with an epoxy/micro filler.
Install the fuel caps in fuel bay #5 instead of #4.
Run the fuel vent tubes to fuel bay #5 instead of #4.
Seal fuel bay #5 just as needed with fuel bays #1 through #4.
Extend the fuel probes into fuel bay #5. ( this assumes that you purchased fuel probes that are long enough to accommodate the extension )

Those that wish to extend their tanks further and have a #6 fuel bay will need to follow a slightly modified plan, but there is considerably more work involved. The steps are:

Cut 4 fuel flow tunnels in BL 97, and BL 120 each. Finish the rib edges in the fuel flow tunnels with an epoxy/micro filler.
Install the fuel caps in fuel bay #6 instead of #4.
Run the fuel vent tubes to fuel bay #6 instead of #4.
Seal fuel bay #5 & #6 just as needed with fuel bays #1 through #4.
Extend the fuel probes into fuel bay #6. ( this assumes that you purchased fuel probes that are long enough to accommodate the extension ).
Build a shear web extension between BL 120 and BL 139.5. This should be done after the aileron idler, bellcrank, and push rods have been installed in the wing to make sure there will not be clearance problems. If you do have clearance problems, the shear web can be angled in toward the spar on the outboard end of the shear web segment. If you have to angle the shear web in to avoid a clearance problem, the shear web will likely have a slight curve to the top and bottom.
Create a capstrip that is form-fit to the skin along the shear web extension you created.

To guide me while making cuts for the fuel flow tunnels, I drew a half circle outlines with a Ultra Fine Point Sanford Sharpie Marker. To create a template for drawing consistent half circles for the tunnels, I cut off a half inch segment of PVC pipe with my electric miter saw. Then I cut the PVC ring I created in half by holding the small piece between two 2”x4” scraps. This left me with 2 PVC half circles, one of which is also included in the picture. It only took me about 3 minutes to make this template. I then held one of the pieces against BL 97 in the right places, and marked the outlines. I removed the fiberglass and Nomex core material with a circular rotary saw bit in a Dremel Advantage tool. Then I used a diamond grinding bit in a Dremel MultiPro to refine the edges. Now I need to fill the tunnel edges with epoxy/micro. It was very helpful to have separate rotary motor tools with the separate bits chucked up so that I could switch back and forth as needed quickly.

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