Lower Fuselage Joint – Part 1

With all the bulkheads now complete, I could move away from the workbench and onto the airplane as I began Section 2, Chapter 9 of the Builder’s Manual.  As the title suggests, this is the point where I permanently bonded the 2 fuselage halves together.

Let me preface the chapter by saying this was a major task, and took way, way, way longer than I imagined.  I partially attribute this to the weather turning colder, and my generally lower enthusiasm for working in a cold garage.  Regardless of my own desires for comfort, working with epoxy resin requires an environment of at least 70°, so a space heater was now a necessity if I was to continue working through the winter.  But you can read about that in my Building in the Winter entry.

Before actually bonding anything together, the normal first step would have been to align the 2 fuselage halves. Recall, however, that I took care of that a few months earlier when I was still awaiting the arrival of my epoxy (see Aligning the Fuselage Halves) so I could jump right into the joint (sounds like a blues song).

The basic concept of the fuselage joint was pretty straight forward;  a single ply of fiberglass is laid up across the joint valley, then some foam core is bonded in, and another ply of fiberglass covers the whole mess.  After that, I could cut off the flange (mohawk) and fill the remaining gap flush.  Sounded simple enough, but it sure took a long time – highly attributable to my meticulous manner I suppose.

Typical of composite construction, when two pieces are to be joined together, the core is tapered down to zero so that a solid laminate joint can be achieved.  I referred to this area as the “valley.”

I started by sanding the valley area by hand to remove any imperfections and high spots.  Next, some light weight filler (epoxy/microballoon mixture (“micro”)) was applied to any small voids or low spots so that I wouldn’t have any trapped voids in the joint.  After a full cure, the filler was sanded smooth and flush.

Then comes the messy part: a heavy ply of fiberglass, about 12″ wide, is laid up across the joint (is it “laid up” or “layed up?”) and allowed to cure with a top layer of peel ply.  After cure, the peel ply was removed.  I started at the nose and worked my way aft over the course of a few days.

Layup over the lower fuselage joint.