Worked on the F-904 bulkhead this week. This assembly is really beefy - the wing spars bolt into each side. The two major fore and aft bulkheads actually came with the wing because they are precision match drilled to the wing spar and are shipped as a unit.
Here's the assembly clecoed together just to get a feel for how everything goes together. The 4 small ribs are where some cover plates will be bolted - fuel lines run through holes in the ribs. The fuel selector and fuel pump will mount in a center section between the two large ribs. We're looking at the forward side of the bulkhead.
Once it was all clecoed together, Van has you install the main spar bolts (*very* tight fit - they are precision bolts and the holes have been reamed to the exact size) to hold everything in alignment, then match drill the F904C/D left and right components to the F904A & B bulkheads.
There are also a number of holes which are either enlarged or laid out and drilled for 5/8" nylon bushings. These are used for rudder cable and wiring bundle runs. These are drilled with a step drill for a nice clean hole.
Here is the aft bulkhead's corresponding holes after drilling with the step drill. The holes will receive a nylon bushing and will be used to for wire runs.
The control column assembly mounts to the aft side of the aft bulkhead. The two F633-L/R brackets need to be match drilled and machined down to size for lightening.
Here I'm match drilling the F633-L to the aft 904 bulkhead (match drilling means you back drill through an existing hole in the bulkhead into the bracket). This ensures proper alignment of the holes. I put a centerline down the back side I can see through the hole to make sure all is lined up correctly.
Once they were match drilled, I used to band saw to trim off the extra metal (Van's has a cutting diagram) then spent a couple of hours filing and polishing to get to this:
Not sure I'd do it again - took a lot of work to drop a few ounces, but I'm pleased with the result, so no regrets.
Since I had the control column mounts done, I went ahead and put the control assembly together. Van recommends doing it while there is plenty of room to work. Once it's all together it's set aside until it's needed much later in the project.
Here I'm working on finding all the bolts and working out how it all fits together. Although most of the parts are prefabbed and powder coated (they are steel), a number of holes have to be drilled to size and the bushings need to be final ground to fit.
There are specific numbers and thicknesses of washers used to ensure no slop in any of the parts. Really fun trying to work all these washers in such a tight spot. I can see why they have you do this while it's easy to get to (although you'll still have to do it in a tight spot later, since there is no way to leave this bolt in place).
Here's the entire assembly after putting everything together and getting it all lined up.
The column mounts on the back side of the bulkhead. The columns come up through the seat floor (so the stick ends up being just aft of your knees) and your legs go over the bulkhead. I had to put it on the floor to see how it all worked. The controls feel just like the demo plane I flew in - absolutely smooth as butter and no slop whatsover. Wonderful feel.
Once all the fitting is done the sides are riveted on.
Finished up the week fabricating and drilling the attach angles that will serve as doublers behind the ribs mounted to the forward bulkhead.
