I’ve continued with various cabin and door jobs over the past month. Mounted the door struts, and was quite surprised when the doors “worked” properly. Open the door, let it go, and the door goes up by itself. I filled over the door hinge gap covers with micro, and sanded it back to shape (no photo, but it worked out well). I also glued the Aerosport overhead on permanently, using Lord adhesive. Started doing some filling work, but then elected to put it aside for a while and catch up with fuselage work – that was the work I put aside a few months ago in order to use the last of the warmer weather before winter on the cabin top, doors and windows.
I drilled the fuselage for the engine mount, to get this out of the way before painting the interior. It is apparently quite normal for the holes in the firewall to NOT line up properly with the engine mount. I didn’t pay enough attention to this, and decided to simply follow the Van’s instructions and drill one of the top holes to size (3/8″). This turned out to be a mistake, because it established an arbitrary fixed point for that corner of the engine mount and what I SHOULD have done was to establish where the engine mount had to go with respect to ALL of the pilot holes in order to (a) take out all the pilot holes, and (b) keep the mount exactly centred. Why (b)? Because on the end of the engine on that mount there will be a hole in the cowling, and a spinner that is supposed to line up with that hole.
I should have “worked” that top hole to move the centre of the 3/8″ bolt hole about one mm toward the middle, but I didn’t. I had to stretch the mount a bit with a clamp (not much, just a bit) in order to fully cover the opposite hole. The bottom middle holes were right on the edge of the 3/8″ guide on the engine mount, so much so that I could drill a #30 hole in the centre point and not actually break into the pilot hole. I was a bit concerned about how to drill these holes without having the off-centre pilot holes “pull” the drill away from where it needed to go and start scraping material off the engine mount tubing.
To resolve this, I 3D printed a bunch of drill guides. They were just cylinders with a 3/8″ outside diameter, and a #30 hole through the middle. Using plenty of cutting fluid, I drilled #30 holes in the places where I could, and “pinned” the mount in place using the shank of long #30 drill bits. In the places that couldn’t be pinned because the pilot hole already overlapped the centre, I used “other” 3D printed drill guides of various size internal holes, and stepped up the drill size in successive operations before consuming the pilot hole. The final step was to use a 3/8″ reamer to final drill the hole, and then put the 3/8″ engine mount bolt, washer and nut in place.
By the time I got to the worst two holes – which had #30 drill bits holding the mount in location, the other bolts around the mount held it in place so well that I simply ran through the same series of drill guides, stepping up the drill sizes. The mount simply could not move, so the fact that I was breaking through the very off centre pilot hole didn’t matter at all. I was able to consume those (badly off centre) pilot holes without dragging the drills off centre, again finally finishing up with the 3/8″ reamer.
At the end I had a handful of wrecked 3D printed drill guides, but they had done the job!
I found that I had installed the incorrect sized nutplates on the Antenna inspection covers, #8 rather than #6. It was a nuisance but fairly easy to drill them all out and replace them with the correct part.
Then it was on to painting. I primed and painted all the detachable interior panels, primed assembled and painted the rear seat frames, plus the remaining control rods, rod ends and some other miscellaneous bits. After that I prepared the fuselage and painted the internal floors and baggage area. Most of these areas will be covered by an Aerosport carpet set.
Once that cures, I’ll be able to go back and mount the seat rails, rudder pedals, brake lines, fuel valve and lines, and control system so quite a lot of parts I have lying around here will go into the airframe for good.