All I had to do today to get the center section ready to mate with the aft fuselage was match drill the seat and baggage floors to the ribs then put the optional 5th point mounts in for the seat belts. Normally all of that would be pretty quick, but Van's didn't prep a lot of things they normally do, so it made for a bit more work than I was expecting.
I started out by match drilling the seat and baggage ribs to the floors. My first gotcha was in the tunnel section of the seating area. The seat pans here get attached with nutplates, but unlike most areas Van's didn't pre-punch the holes in the ribs for some reason. The screw holes in the seat pans were also not the right size, so they had to be upsized as well. The tunnel uses two different nuplates - you can see that half are the typical type with the screw hole in the middle of two rivets, but a few are nutplates where the screw is on the end of the nutplate and the two rivets holding things on are on only one side.
I still haven't quite figured out what the story is with two of the holes at the front edge of the seat pans. Most of the holes alongside the front edge are for screws that go into nuplates attached to the bulkhead flange, but the two middle holes have no nutplates to mount to. I triple checked the plans and they are indeed supposed to be left like this. I'm sure buried in the drawings somewhere is something that will clue me in as to what goes here, but for now it's a mystery.
One of the biggest time sucks today was in how often I clecoed all of the seat pans down, only to find a reason I needed to pull the clecos out. I bet I had it all together and pulled apart at least a half dozen times. One of the things that caused some trouble was the pre-cut notches for the main seatbelt anchors. All four of them are cut so that they rub against the anchors and make it difficult to slide the seat pans into position. I finally took a file to all of the notches and opened them up another 1/8".
The outer two seat ribs have blank flanges and have to be drilled to match the seat pan pieces. Since the ribs are curved, this was easier said than done. I had to pull the seat pans out many, many times to get things lined up.
I had already fluted the bottom side of the ribs in order to get the curve it needed to match the bottom skin, but I hadn't fluted this top side yet because I wasn't sure where the holes would be. I put the seat pan on top of the rib and marked where the holes were so I could make sure not to flute in those areas. It took a few iterations to get the curve right. The web of the rib also needs to stick out beyond the seat pan. Van's recommends using a piece of .032 sheet as a spacer. I think the point of this is simply to ensure that the rib web is what the fuselage skin will press against vs letting the edge of the seat pan hit the side skin and chew into it. After I got the ribs curved and rivet holes drilled, I did the same for the front portion of the rib flange. It's the same process, but this portion of the rib isn't riveted to the seat pan. The front pieces that make up the seat pans are held on with screws and nutplates so they can be removed for access to the controls. I'll still need to drill the rib flanges for the nutplate rivets and attach the nutplates down the road.
I've had the pieces for the removable section of the center seat ribs sitting on my bench for a long time. They won't be put in place until the controls are in, but I decided to go ahead and rivet them together.
The section of flange that I cut out from the ribs is simply riveted to an attach bracket. The bracket gets bolted to the rib web, allowing the seat pan to still screw into the nutplate in the flange.
Now for the maddening part! On the advice of just about everyone, I decided to purchase the optional 5th point "crotch strap" mounts for the seat belts. Even though the 9A is not aerobatic, the crotch strap is hugely beneficial and I think should be standard equipment. Having the 5th harness point keeps the lap belt from riding up during an accident, which can make a significant difference in overall trauma and safety. I've also heard many people mention that it makes a big difference in turbulence as well (the RVs are pretty light planes, so they can get bounced around pretty good).
This was one of those tasks where reading the page of directions made it sound super easy! All I had to do was locate the anchors between a couple of ribs, drill them, and rivet them in place. Easy! Maybe a picture will show how "easy" this really was. Somewhere in that mess of scrap angle and half a dozen clamps is the actual mount. The top of the mount needs to be level with the top of the ribs (the seat pan will get screwed to it), plus it needs to be vertical. None of that sounds difficult to accomplish, but the tight quarters really made it tough. The biggest issue I had was that even my angle drill was too big to get a drill bit parallel to the web of the mount (the angle drill isn't too long - the problem is that the head of it is still fairly thick, so if the hole is close to the web of a piece, the drill bit can't go in without being pushed out at an angle).
With all of the clamps removed, you can see what this is supposed to end up like - simple! The mount is made up of two pieces (the piece of aluminum in between them is just a temporary spacer). The holes on either side where the clecos are are the ones that gave me fits. There was just no easy way to get a drill in there. I finally just had to let the drill bit go in at an angle. I think given that the material is so thin, it should be fine. An angled hole in thick material is a major problem, but I think I'll be okay here. This took so long, this is where I stopped. I still need to match drill the mounts to the seat pans, drill a hole for the bolt of the actual seat belt hardware, then pull it all out and prep it for riveting. Of course then there is the passenger side to do, but I imagine that will go much quicker now that I've struggled with one side.
