I started today by installing the crotch strap brackets.  I’m either going with Hooker or Crow harnesses, but either way, the spacing between the brackets has to be increased to 5/16″ (instead of the stock 1/8″ spacing).  Mike Bullock already determined the best way to accomplish this and documented it here, so I’m just going to copy his method (thanks Mike).  I put a center line that is aligned with middle nutplate, then measured 7/32″ forward and 3/32″ aft of this line and put additional marks.

The front side of the bracket is positioned with the web flush with the forward line and drilled to the adjacent ribs.

Instead of cutting a 5/16″ spacer, I just used a couple of AN5 bolts which are 5/16″ in diameter.  I taped them in place and clamped the aft side of the bracket against the bolts and against the seat pan, then drilled the bracket to the adjacent ribs.

The prepunched holes in the seat pan need to be drilled to #19 for #8 screws.

Here is the backside, showing good edge distance on the #19 holes.

After repeating the process for the right bracket, I finished up a few remaining tasks such as drilling the seat ribs to the aft side of F-704, match drilling all ribs to bulkheads, and drilling out the forward tooling holes to 5/8″ for wiring runs.  I then disassembled the center section and started prepping the individual components.

First up is to debur and dimple the holes in the bottom flanges of F-704.  Remember that the holes we countersunk in the bottom skin have to be skipped when dimpling so that the floor stiffeners can lay flush against this flange.

Neither the instructions nor the plans make any mention of these holes in the top flange of the aft side of F-704, but the seat pan that sits above this is removable, so this must just attach the top of the seat ribs to the F-704 flange.  Since the seat pan needs to sit flush against this flange, I countersunk this for an AN426AD3 rivet.

Finally, I started deburring all of the components.  I made it through the F-704 and F-705 bulkheads and six of the eight seat ribs before running out of steam.  I should be able to finish deburring the rest of the center section components tomorrow.

I finished deburring and dimpling the remaining center section components and stayed up until well after 2 AM (on the 29th) getting everything cleaned and primed.  I’m exhausted, but wanted to finish this so that I can begin final assembly tomorrow.

I started final assembly of the center section this morning.  First up is to rivet the crotch strap brackets to the appropriate ribs.  I used solid rivets here instead of the blind rivets called for in the plans.  These can all be reached with the squeezer when the ribs are out in the open like this.

These pairs of ribs can then be riveted and bolted to the aft side of F-704 (bolts go through the top and bottom ends of the forward flanges of these ribs and through the thick spar carry through bars).

Now the rest of the ribs can be riveted on.  I also final torqued all of the rib to F-704 bolts and lacquer sealed them.

F-705 and the baggage ribs can then be riveted on.  Because of the rear spar carry through, spacers, etc., the lengths of the rivets varies pretty significantly through here, so pay close attention to the rivet callouts.

While access is good, I bolted on the control mounts and lacquer sealed them.

Since everything is now bolted to the aft end of F-704, there is no reason not to bolt the two halves together.  I reinserted a couple of close tolerance bolts to ensure perfect alignment, then installed the two AN4 bolts and spacers.

Here is a closeup of one of the spacers and the installed bolt.  I had to use three washers under the nut (the maximum allowed) to cover the grip (this bolt is a little long like this because it also holds part of the gear weldment on nosedraggers).

I riveted together the connecting straps for the modified seat ribs and temporarily installed them so the ribs are more rigid during the next few steps.

I also installed the one leg nutplates in the top of the crotch strap brackets.  This would have been easier to do before riveting these to everything else.

I deburred and dimpled the bottom skin and shot a little self-etching primer on the parts that will be covered by the corner ribs and F-704.

Finally, I clecoed the bottom skin to the center section skeleton.  This is ready to rivet; I need to see if I can find a riveting partner sometime in the next couple of days.

Jenn graciously offered to help me rivet part of the center section (after midnight no less).  We made it through a fair amount before Jenn’s wrist hurt too much from operating the gun.  Hopefully we can finish this up tomorrow so that I can start working on joining the center and aft fuselage segments.

The canopy rails need to be modified.  The plans specify slightly different modifications for the tip-up vs. the sliding canopy.

I’ve measured out and marked the areas to be removed.

The cutoff wheel makes quick work of making distortion free cuts in the rail, but it can get away from you, so I kept it back from the line 1/16″ or so.

After a few minutes of filing, here is the finished result.  The top edge of the slot will be seen in the cabin, so I made sure it is perfectly straight.  The other side will be under part of the canopy latch, so it doesn’t matter as much if it is absolutely perfect.