Fuselage

The next step is to drill the J-channels to the side skins and bulkheads. But before you do that, you must check the fuselage for any twist. You don't want to build any twist into this structure! The manual is quite adamant about this, and I know how important it is to have a structure that's straight and true. So how do you do that? You level the assembly and hang a plumb bob on the front end, and another one on the back end. If the structure is straight and true, your plumb bobs hang exactly vertical on the ends. Any twist would be revealed.

I got a little more elaborate than a simple visual check. I taped my ruler onto the front of the F-706 lower bulkhead and centered it on the square opening. The plumb bob is hanging right behind this opening, and you can see its pointed end hanging down right behind the ruler. Using some shims, I adjusted each side by shimming it up or down until the plumb bob hung perfectly in the middle. I was able to get the structure straight this way within 1/64 inch. The rear plumb bob, not shown, was similarly evaluated but there's no need for a ruler on the back end. When both plumb bobs were good, I started drilling the J-channels. I checked them again periodically throughout the drilling to make sure nothing shifted or moved.

I drilled every 4th hole at first, making sure the line drawn down the middle of the J-channel showed through the holes. Then I went back and drilled the rest. Here's the right side, all finished. Then I used my #40 reamer to drill the rest of the bulkhead/skin holes out to full size.

Here's the left side, all drilled. Now I think I'll flip this over. I need to drill all the holes on the bottom out to full size with my reamer, and it will be so much easier if it's upside down. Then it all comes apart for... you guessed it... the usual deburring, dimpling, scuffing and priming. Then finally, it will be time to rivet this thing together for good.

<< Previous | Home | Next >>