SECTION 13: MAIN SPAR

Build Instruction Updates

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Before You Start

Modifications to Consider

Some people decide to install extended-range fuel tanks. At least for some options (SkyDesigns Installation Hints) it will save you some time to start making the necessary modifications now.
Consider buying two pre-tapped AEX tie-downs

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Note: steps 5-8 may be less confusing with a bit of context. You are using the spar flanges as templates for drilling the J-channel stiffeners. They will not be attached to the spar in the end. After you finish step 8 you will not need the J-channel until a later section. You can debur and prime now or later.

Figure 1 shows an "extra" hole on the flange. It is not used anywhere, does not need countersinking.
Step 7: Study figure 2 which points out that the long stiffeners align at the outboard end while the short stiffeners align at the inboard end.
Step 8: See this FB thread regarding how to manage the imperfect overlay of the long and short stiffener.
- For the 3 areas not to match drill: Ignore 13-2 Figure 2 (very unclear), they are clearly marked in 13-5 Figure 2.

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Step 2: "Machine countersink those rib to spar flange attach rivet holes that are in line with the nutplate attach rivet holes and are inboard of the most outboard fuel tank attach nutplate."
- See Plane Lady's youtube video explaining which holes (starting at 11:25)
- She diagrams the holes at 15:00 in the video. Essentially, they are the holes between the fuel tank nut plates (forward row nut plates) that would be covered by the fuel tank flange.

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Step 4 has you installing AN426AD4-6 rivets, but the rivets are not part of the SB kit (as of 3/2022).
- Some builders indicate that the rivets are included in the SB kits.
Step 6, check this FB thread on the tie down bracket and a potential gap between the skin and the bracket.