This week I’ve moved on through the infamous section 26 of the build manual, match drilling the outer ribs, rear set and baggage area ribs, de-burring, dimpling, priming and finally riveting them in place to make up the mid fuselage skeleton. This section of the build manual is infamous not only because it misses out several necessary steps that, if not done now, are very difficult to correct later, but also because Van’s have never revised the instructions. Various builders have documented what extra steps to do, I researched this and came up with the following list, to be added to the steps on page 26-5.
- Dimple the #40 holes in the F1015A outer ribs
- Dimple the #40 holes in the inter-costal ribs that mate with the F1015A ribs
- There are three #30 holes in the side skins that are not present in the F1018 ribs. Cleco the F1018 ribs to the side skins now, final drill these holes, and dimple them with a 120 degree dimple set (they will eventually receive CS4-4 rivets).
To do the above, I laid out the F1015A and F1018 ribs, lay the side skin on top and cleco’d the ribs in place. I match drilled all of the #40 holes between them (except for the holes not to be dimpled), and used the skin as a drill guide for the three #30 holes in the F1018 rib. I then de-burred and dimpled the ribs. You need a 3/8″ female 3/32″ dimple die because of how close the holes are to the flange of the rib, and the thickness of the rib making the flange corner quite rounded.
I did look at one builder’s log where he had mistakenly placed the vertical flange of one of the outer ribs on the outside of the corresponding riser, rather than the inside. I recall wondering how anyone could make such a silly mistake, given the obvious detent in the rib. After riveting the left side F1018 outer rib in place, I stood back and looked at it – and couldn’t believe I had just made the same mistake! It turns out to be quite easy to engage the auto-pilot while riveting and overlook something like this. Easy to correct with just three rivet drillouts, but it would have been hard to fix later on when there were more things in the way.
After completing the mid fuse skeleton, I needed to stand it up on something to hang the bottom skins, which overlap the bulkhead by a few inches to overlap the forward spar. I lay the cradle I made for the horizontal stabilizer on its side (not being used right now because the HS is bolted onto the empennage), braced it to some workbench legs, and it made a perfect work position to clamp the mid fuse assembly to while hanging the bottom skins.
Next step is to match drill the bottom skins. While these are in a convenient work position I’ll also drill the necessary holes to mount a couple of antennae, and the A/C condenser.