Center Section Bottom Skin

I flipped the center section over so I could start working on the bottom skin.  This was a real exercise of persistence.  I put clecos in the front bulkheads and then at the baggage bulkhead, only to realize that the holes in the seat ribs between them were way off (by about a 1/2 of a hole).  It looked like the distance between the bulkheads grew by 1/16" between when I match drilled and when I riveted the ribs in.  I pulled the front bulkhead clecos out to see if I could massage things together - in the picture you can see the forward edge where the skin and the bulkhead flange should be even.  It doesn't look like a lot, but a half of a hole might as well be a mile.

It took the better part of an hour of trial and error, but I finally found a pattern of clecoing things together that allowed me to gently pull everything in line and even.  I suppose it's a good thing that the skins are so tight, but boy does it make it tough to get them pulled together with the parts.

The baggage bulkhead was originally a full hole out of alignment, so I decided to rivet that line first.  I was able to do everything except the very middle rivets.  I can reach those, but controlling the rivet gun is easier said than done when you can't put proper pressure on it.  I'll probably enlist Rose to help when I get to the middle.

After the baggage bulkhead line was done I moved to the seat ribs.  It is very slow going simply because it's kind of an awkward position.  I got two ribs done and then called it a day.

Center Section Rib Riveting

Back to some real work today!  With everything primed, the center section can start to go together for good.  I started by dimpling all of the holes on the bottoms of the ribs (for the bottom skin).  The forward most section of the seating area that is underneath your legs has a floor that is removable since the controls pass through the area, so instead of being riveted on it gets nutplates and screws.  Nutplates are simple, but pretty fiddly to attach - each one has to be dimpled (as well as the rib flange) and then held in place while the rivets are squeezed.  I attached the nutplates to the center two baggage area ribs as well.  That area is used as a tunnel for controls and wiring, so again is screwed on.

Next up was riveting the seat ribs to the aft bulkhead.

In addition to the rivets, each rib also gets a bolt at the top and bottom.  As far as I can tell, this isn't for strength, but purely because the top and bottom portion of each rib line up with the bulkhead web as well as the thick doubler (not sure what it's called, but the big chunk of aluminum that forms the I beam).  A rivet would have to be extremely long to make it through all of this, so a bolt is used instead.  There are quite a few places I've seen that do this.  I got all of the bolts in and torqued them down.

Lining the seatback bulkhead, seat ribs and baggage ribs all up was easier said than done.  Some seat ribs are riveted to the bulkhead by themselves, others are riveted in conjunction with a baggage rib, and yet others get spacers held in place before riveting.  It took me a couple of ribs to figure out the secret sauce.  Once I did, things went together fairly easily.  I couldn't really get the squeezer to work in the tight quarters, so I just used a long rivet set on the gun and bent each rib out of the way to get at the rivets.

The outside seat ribs get two rivets and a bolt at the seatback bulkhead.  As I was getting ready to put the right rib on, I noticed that the bolt hole was pretty badly out of round.  I'm not sure how I didn't see that before.  It's supposed to take a 3/16" bolt, but I decided to open the hole up to 1/4" instead.  That size of bolt is overkill, but considering it goes through the bar that the rear wing spar bolts into, I'd rather have a tight fit than a smaller bolt that has play in it.  Opening up the hole meant drilling the bars and bulkhead as well as the spacer and rib.

Just as I was getting ready to finally rivet that outside right rib on and put in the new bolt, I realized my mistake.  I had placed the parts down, then spun the center section around so I could get at the outside easier.  Soooo, the right became the left.  Long story short, I originally upsized the correct side of the bulkhead (easy, because I was correcting an ugly hole), but I upsized the wrong rib.  To fix that I had to also change the left side from 3/16" to 1/4" so everything would match up.  Not a big deal, just time consuming.

The last thing I did for the night was put the forward section of the front bulkhead in place by clecoing on the vertical spacer that goes between it and the side skins.  Next up will be flipping the whole center section over so I can rivet the bottom skins on.

Center Section Priming

The primer finally arrived!  Lesson learned - order directly from Stewart Systems, not Aircraft Spruce.  Apparently because the primer is water borne, Aircraft Spruce isn't able to get primer shipped to them in bulk during the winter for fear of it freezing. Stewart, on the other hand, is more than happy to ship it themselves, because for small amounts of it they can put heating packs in the boxes.  So my bright idea of just ordering from Aircraft Spruce because I had free shipping on my order turned into a month delay and me having to pay for shipping anyway!  Oh well, it's here and I'm ready to get back to work.  I never thought I'd be looking forward to priming (that enthusiasm didn't last long - 4 hours standing on concrete and bent over a spray table is rough on the body!).

I scuffed and cleaned all of the seating and baggage area ribs, then set up my table over by the open garage door with the infrared heater shining on it.  While the heater doesn't make priming at 40 degrees just as fast as priming at 75, it definitely speeds the process up over not having it.  The bare aluminum doesn't absorb the heat very well (the shiny surface reflects most of it), but once it's got a tack coat of the grey primer on it, the metal heats up within minutes.

I batched the baggage area parts (and a few other odds and ends) first, then while each coat was drying I scuffed and cleaned the seat ribs.

It seems a little silly that 4 ours of priming is what gave me a month of downtime, but that's the breaks.  I could have continued on with spray can primer, but for the cockpit area I really wanted primer that was a bit tougher.  The Professional series Rustoleum is the best spray can primer I've tried so far (although it's not self etching, so you still have to scuff), but at least in the short run it is still quite soft and easy to scrape off.  I have a feeling it will actually continue to cure and get harder with time, but I don't know for sure yet.  I tested a piece after a week and it was still pretty soft.  The Stewart is fine within a day, and after a week it's very tough.  On the next plane I won't have any qualms using spray can primer for areas that don't get touched all of the time though, like tail and wing parts.  Granted, assuming I'm not having to store the plane outside in Seattle at that point, I would probably just spray mating surfaces and call it a day.  For this plane, I know I'm probably going to be sitting in less than ideal conditions for a while, so even though I think it's overkill, the full primer treatment still makes me feel better.

Tailcone - Bottom Skin

It's been a while since I've done much.  I'm still waiting on Aircraft Spruce to send me more primer so I can prime and assemble the center section.  I called them and they said they haven't received any primer from Stewart because of the cold temps (it's a waterborne primer, so freezing is an issue), but they could have Stewart drop ship it to me with a heat pack.  Not sure why they didn't tell me that originally when I called, but oh well.  I have always bought the primer directly from Stewart, but this time chose not to simply because I had a big order with Aircraft Spruce and it was already enough to be free shipping.  I figured why not just order primer from them?  What could go wrong?  I'll give it a few more days and if I don't receive the primer I'll probably just go the rattle can route so I can keep moving.

Today I got Rosie the Riveter to help me with the bottom/side skin joint of the tailcone.  It went very quickly - maybe an hour to get the entire thing done.  She's quick with those rivets!  I do still need to rivet the curved portions at each bulkhead.  I tried back riveting the curves, but the angle of it caused me to mess up almost every rivet.  I'll have to drill 3 or 4 out and redo them with the gun and bucking bar.