CHAPTER 34 - Jigging the Bulkheads

The firewall parts came back from the painter and it was a simple matter to finish off the assembly. The recess was put together with high-temp RTV in the joints and 3-3 rivets and a squeezer. Then RTV was run around the edge of the opening, and the recess clecoed into place. I'm putting the recess on the aft side, between the firewall and stiffeners per the option in the instructions. Next, the stiffeners were back-riveted one at a time and finally the weldments. In the first photo you can see the finished firewall in place on the jig, You might be able to see the red line in the center below the top (bottom in photo) stiffener; unfortunately you can't see the cross line or the laser pointer - I need a photography class. Anyway, that mark sets the centerline and height of the bulkhead, which is then adjusted around that point with a level.

Wait! What about the center support for the rudder pedals that is attached to the vertical stiffener next to the recess? Well, since I wanted to sandwich the recess and couldn't remove it as in the Orndorff videos, I had to leave the stiffener (and it's lower bracket) unriveted. In the second photo you can see the telltale row of clecos and the close-up shows the RTV around the recess and firewall joints.

The F604 bulkhead was already primed, so I could go ahead and put it in the jig while waiting for the F605 parts to come back. First, with Judi's help, I clamped the bulkhead to the longerons after marking the location according to the plans. By the way, the video is in error here in that George makes his F604 plumb - I don't know if they caught it because my video is pretty old, but it actually has different measurements top and bottom to set the wing incidence. When I set the bottom measurement, there was a gap of 1/8" between the longerons and F604 because they were cut straight at the 23" callout and the longerons have a bend there. I marked where I'd have to trim the F604, removed it, and trimmed it - making up the F604F pieces to match. Then I clamped it back in place and got Judi to hold the bottom measurement at the spar while I nailed a support board to hold it in place. The photos show it in place and centered (the blue twine is a plumb line; I just moved the bulkhead until the laser dot was on the twine) but the longerons are not shimmed or clamped yet. I will set the height and level the bulkhead laterally as I clamp the longerons. The close-up of the bulkhead/longeron joint shows the F604F part in it's final location. Matching it's upper end to the upper end of the F604Ds worked very well in making it conform to the longeron upper surface.

The next photo shows the laser level at the rear of the jig. It is set so that it just clears the crosspieces while it is level. The highest crosspieces just touch the light line; others are slightly below which will call for shimming of the longerons to level them. Being a level line, plumb measurements at the bulkhead can be assumed to be at 90 degrees to it, and it also establishes the centerline. The last couple of bulkheads will get a hole drilled in them to allow the beam to pass through; I can always put a rivet in the hole later if I desire. You can see a couple of nails holding the rear longerons apart so they don't interfere with the beam; they were slightly overbent per the instructions.

The next chapter continues with the forward structure, done while waiting for parts to come back from the painter.