Drilling the J-channels4h
September 24, 2022
Today I drilled the J-channels to the skins and bulkheads.
The first order of business was to put the aft of the fuselage on top of the tables. The plans tell you to remove the twist before drilling the J-channels to the skins, and I thought it would be easier to do that when the fuselage rests on the straight top edges of the skins.
Once everything aligned (I used a plumb bob to see if the top and the bottom tooling holes align -- as per plans), I drilled every 5th hole in the J-channels.
It all went well, except that on one of the J-channels, I did not align the channel well enough and the very second hole was quite off the center. I remade the part using one of the two remaining pieces. I think, I only need these two pieces to make much shorter top channels. Since I only drilled two holes before I ruined the part, it should be long enough to make one of the two top channels, so I should be okay.
The aft part is where clecos were necessary to align the side skins and the aft bottom skin. Since these clecos were exactly in the holes I was supposed to use to drill the channel, I removed the bottom aft skin. This allowed me to drill the bottom channels to the side skins first, then use clecos to force everything back together.
In the end, everything aligned well. Not too much force was required to put the bottom aft skin back into place.
After that, I put the fuselage back on the sawhorses.
However, this is where I got a small issue: when I drilled the J-channels through the flanges of the F-711 bulkhead, two of the flanges got very small edge distances.
I kind of knew that these flanges would get marginal edge distances (the original part have pretty short ones as well), but did not do anything about it. This was a mistake, when I formed the aft part of the F-711 bulkhead, I should have moved the flanges up a little.
A potential repair I am considering is to put a doubler across the three rivets.
After drilling all the holes in the J-channels, I installed both of the ELT mounting brackets (the left and the right). They install between the J-channels behind the F-706 bulkhead.
The way you install them is you drill the holes in the bottom channel first, using the bracket as a template. However, my tight-fit angle drilling attachment would not fit to drill these holes. So, instead of drilling the holes in place, I marked their location first.
Then I pulled the J-channel out of the fuselage, attached the bracket to it using the marks to position it, and drilled using a regular drill.
After that, I put the J-channel back, clecoed the bracket to it, then used the opposite side bracket to mark the holes on the top of the channel to drill, and drilled them.
The end result.
I don't know what am I going to use the left bracket for (the right one I am going to use for the ELT), possibly, for the controller board of FlyLeds (which is what I am currently considering for the lighting). There is not much reason to put the controller there, but maybe it will reduce the number of wires going to the panel area. The board only needs three wires: ground, position lights supply, and strobe lights supply.