Fitting the rear fuselage top skin. - Part2

While my wife toiled away at preparing a great Thanksgiving meal, I worked on my CX4 project. It was time to put the trimmed top skin back on and drill the holes in the stringer. Before I put the skin back on, I marked out the hole locations in the stringer and then drilled them with a #40 drill. This way I could replace the skin and hold it tight to the stringer with the straps and 1"x2" boards, reach up underneath and use the previously drilled holes as guides for drilling the skin. This technique worked great.

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I occassionally drilled a little deeper into the 1"x2" board and used a cleco to temporarily secure things.

One of my concerns leading into drilling these holes was how to secure the stringer where it butts against the forward longeron. If you remember, I chose to do my splice differently than the plans call for. I'm doing this splice from the outside with screws instead of the inside with consunk rivets. So, at this point I have to undo my splice to drill my holes. This means that nothing is holding the two peices together where the stringer butts against the forward longeron. So, I carefully held the stringer and skin in place with a clamp and twisted it inward (because the top skin wants to bow outward) until everything lined up and then drill the first hole nearest my splice and installed a cleco.  I also used a couple of wood clamps after this first hole was drilled to twist everything into alignment. This really wasn't as hard has it sounds. Just take care and drill that first hole carefully. Everything else falls into place after that.

So, once all the holes are drilled, you can remove the clecos from the underside, loosen the straps and clamps carefully and install clecos on the outside. It is one of those times you can look at your project and see that you have accomplished something of significance.

By this time, the turkey was done and I had one more thing to be thankful for!

Fitting the rear fuselage top skin.

With the rear bulkheads in place, it was time to start fitting the rear top skin. The key is to pre-drill the bulk heads where you want the rivets to go. Once the holes were drilled in the bulkheads, I used my Dremel tool and drilled the skin from underneath using the bulkhead holes as guides. I started with just the centerline holes and put cleco's in them.

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Then I clamped a 1"x2" board to each side edge and then use some straps to pull the skin down tight. Looking underneath, I was concerned about the gaps I saw near the top of the bulkheads. After a conversation with Dave Thatcher, I proceded with drilling holes and installing cleco's. What I did was, I loosened the straps until the skin laid nicely near the tops of the bulkheads and drilled the holes and installed more cleco's. Then I would draw the straps tighter and repeat the process.

I am pleased with the outcome as the gaps I was concerned with just went away using this procedure. As I tighten the strap closer to the stringer, I then used the clamps holding the 1"x2" board in place to clap it to the stringer.

Once all the holes were drilled, I then drilled them to 1/8" size and marked the oversized skin for trimming along the stringer and the F6 & F10 bulkheads.  I have now removed the skin for trimming and while it is off, I will predrill the holes in the stringer. I will also debur all the holes. Hopefully, I will be able to finish the installation over the Thanksgiving weekend.

Installing F8 & F9 Bulkheads

I finally spent time working on my project yesterday. I worked on locating and installing the F8 & F9 bulkheads. I used an 8 foot piece of 1"x2" square alum. tubing as a straight edge and placed it on top of F6 & F10 bulkheads to determine the height of F8 & F9 bulkheads. I had already used this square tubing to make sure F10 was level with F6.

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The photo above shows the assembled bulkheads, but I assembled them after the next step I'm about to describe.  I had to figure out a way to get the tops of the bulkheads to stay in position while I attached the skin. I had assembled my bulkheads by laying them on the plans. I temporarily assembled them with cleco's, but found that they were too tall to fit between the square tubing and the 2"x4". So what I did was I disassembled the top of the bulkheads and clamped them to the underside of the square tubing. I located them in a postion where the top skin would transition nicely onto the side stringer (I use a scrap peice of .020 alum. for this). I then used some scrap 1/16"x3/4" angle as temporary "holders" to keep the top bulkhead piece in place where I wanted it. Once I had drilled holes and cleco'd everything in place, I could disassemble everything and begin to figure out how to attach the remaining side and bottom bulkhead pieces, which I kept assembled.

I had to trim my side pieces so I could raise the bottoms to the correct height. I slid them between the temporary mounting angle and the face of the bulkhead and then aligned everything the way I wanted it. Then drilled holes and cleco'd things together.

Take note of the hole in the left side piece. This is the hole that the elevator push rod tube is suppose to go through. Again, I drilled this hole by placing this piece on the plans and locating it's position. As I said before, the bulkheads didn't fit until they were trimmed down. I only trimmed from the top on both side pieces on both the F8 & F10 bulkhead (instead of trimming a little off the top and a little off the bottom of these pieces), so at this point, I don't know if this hole is in the correct position. I'll let you know when we get to installing this push rod tube. If I had to do it over, it might be better to drill this hole later on.

I did try to pull the top skin down over the top pieces before attaching the side and bottom pieces, but I didn't feel comfortable in doing so. I'm now ready to try this again. Till next time...