Mid Fuse Ribs & Bottom Skins 26-1 to 26-7-3

With the mid fuselage bulkheads assembled, I moved on to section 26 of the plans and started working on the ribs that connect the bulkhead. After locating all the parts, I went through the usual motions of deburring all edges, and drilling and countersinking the necessary holes.

Right inboard footwell rib subassembly with attachments clecoed in place

Left inboard footwell rib subassembly

Seat belt anchor clecoed in place

For the outboard seat rib subassemblies, the end of the seat belt attach bar needs to be radiused to fit against the inside of the bottom rib flange as called out in the plans.

Parts clecoed to form the left outboard seat rib subassembly...

...and the right outboard seat rib subassembly

Outboard seat belt anchor clecoed in place

Seat belt attach bars were clamped next to each other to facilitate countersinking the holes near the ends

Countersinking the reinforcing angle nutplate attach holes, once again clamping the two angles next to each other to facilitate countersinking the holes at the ends

Seat rib subassemblies were clecoed to the aft center section bulkhead, and bolt holes were match drilled from the spar into the ribs

The inboard seat rib subassemblies fit perfectly against the wear strip that was attached to the top flange of the aft center section bulkhead

The F-1015A and F-1018 seat ribs need to be fluted so that the bottom flange matches the curve of rivet holes in the bottom skin. This is called out for the F-1015A rib in the plans, but not explicitly for the F-1018 rib. However, this must be done on both pilot and copilot sides so that the rivet holes line up.

F-1015A and F-1018 ribs on the bottom skin prior to fluting. Note the flanges do not line up.

Here it is easy to see that fluting is required since the rib flange extends beyond the edge of the skin

F-1015A and F-1018 ribs after fluting the bottom flange, matching the curve in the skin. Only the BOTTOM flange of the ribs is fluted.

After fluting all bottom flange rivet holes line up perfectly with the corresponding holes in the bottom skin

Moving on to the outboard baggage ribs, I match drilled the step mounting brackets to the ribs, first making sure that the brackets were oriented correctly per the plans.

In the correct orientation, the predrilled hole in the step mounting bracket is at the top, and the tube is parallel to the web of the spar

There are 4 additional holes in the step mounting bracket that do not exist in the outboard baggage rib. These were match drilled to #31 and reamed to #30

All holes match drilled and final sized to #30

After completing all match drilling, countersinking and deburring, I turned to dimpling all holes as required. The plans do not specify every hole that needs dimpling, but a lot can be inferred from the rivet spec diagrams at the end of the section.

Rivet holes dimpled in the outboard seat ribs

Inboard seat rib spacers labeled to ensure they get located with their matching rib

I built a couple of small stands that I will used to place the mid fuselage vertically for riveting the skins later. I decided to cleco parts together now to help understand and verify that I was dimpling the correct holes