Productive weekend after a busy work week

Holiday season and IT change freeze is generally over and I'm back into the swing of ongoing projects at the paying job and was gone on the road all week.  It was great to be back in the shop this weekend working my other (non paying?) job.

The more this aircraft comes together, the more complex the order of operations seems to become.  I probably spend way more time figuring out not what to do next, but what should come next.  Every drilled hole connects something to something else, and I have to always be cognizant that I don't drill something before all parts of that particular joint/juncture/assembly are ready to be positioned.  So far so good, but I've got many, many things in the future to consider as I work.

As the greater fuselage assembly comes together I need to decide how to fit and add the tinted Lexan rear cabin windows.  These windows are is one thing that doesn't actually join with something else.  Just a row of rivets around the perimeter of the window opening holding the Lexan in place (remember, these windows are not pressurized or designed to open and close, essentially just portholes to let the light into the rear cabin area).  As the appearance of the rivet lines on the outside edges of the windows is what shows, I think it best to layout and drill the holes in the fuselage cabin skin, then drill through the Lexan window.  The windows will be added after painting of the plane is complete, but I want to fit them soon before the cabin is closed up and access will be more difficult.

The rivet line needs to be 10mm outside the window opening, the window Lexan is 20mm wider:

I want the rivet line to exactly match the window curvature, 10 mm outside.  I could cut yet another cardstock template and trace it, but I thought why not make a simple tool that can mark the edge with a fine tip Sharpie, so this is what I came up with.

I cut a simple triangle from a scrap piece of 025 aluminum.  Two A4 solid rivets are the edge guides and the hole for the Sharpie exactly 10mm offset below that.  I used longer rivets and the rivet squeezer to just pinch them enough that they hold in their holes tightly:

Here is the backside.  I rounded the tips of the triangle and bent them forward slightly so the tool rides smoothly across the skin. 

Here's a short video of how it works.  Careful with the volume on the video - Ron is working with the grinder in the background and I didn't get a chance to edit out the audio before posting!

https://youtube.com/shorts/OqJJnmhwhU0

I might remake the tool and use a smaller Sharpie hole as I don't like the thickness of the rivet layout line this one leaves:

Finished adding the rear horizontal bulkheads.  The required "L" angles are added to the top of them where the top fuselage skin will connect.  This is also where the fore and aft horizontal tail supports get mounted once the tail is ready for fitting, so it's a "no rivet zone" until later:

This middle cross "L" doesn't have a bulkhead to connect to, but is an important support for the entire tail structure.  It's going to be fun to add later once the top skin is on! - more on this later in the build

Rear cabin uprights now in place between the rear cabin windows with a couple of clecos to hold them.  This helps square up the sides more and eventually will make up the rear half of the vertical flapperon push rod tube covers.  Also in the picture is the centre bearing support channel.  I have it propped up close to where it belongs, but will wait for the control rod placement before drilling the rivet lines on it.

Speaking of control rods, I got more hardware and 4130 tubing of various sized from Aircraft Spruce this week, all part of the control system.  I'm planning on dual control sticks so I had to add some more to my original order plans:

Also picked up the 3mm tinted Lexan sheet for the rear cabin windows.  I realized when I got it home that it is not only tinted, but it also has UV coatings.  Not required, but nice to know it will be better able to withstand sitting in the bright sun when I fly to Tahiti (just kidding) :)

Another weird camera angle?  The top right longeron looks like it is huge and touching the ceiling - it is not.  I clamped the main wing spar channel in place to get a feel of where it will sit once the top skin is in place and how the cabin side channels meet up to it.  Not pretty, but this fit up confirms the side skins are equally matched on their respective lower longerons.  This is only a temporary fit to check things out and won't allow the top skin to be rolled out, so I took it down immediately after the picture was taken - couldn't take a chance of it falling and punching a hole through the bottom skin either!

As I rolled the top skin on top of the upright fuselage sides I realized that there isn't much room to brace  the top skin on and any slight outward swing of the upper longerons would allow the top skin to fall inside.  To prevent the longerons splaying outwards, I tied them together (see the orange twine below) in a narrower width than the upper skin.  I also added the the upper skin stiffeners to help as I rolled it out:

It's starting to look like a fuselage!

I'll need to fire out the best way to add the upper fuselage skin diagonals.  Like the sides, they overlap the longerons on the inside of their curvature, but at least with the bottom and side skins, I had access by reaching over or around to fit them:

With a little of wiggling and sliding back and forth, I got the top skin aligned in the proper position relative to the front edges of the side skins.  The forward edge still needs to be trimmed - I left it long when I was laying it out to ensure fit before trimming if needed (see order of operations comment above).  I temporarily clecoed the forward upper fuselage doublers in place to check fit:

Blue line on the left is approximately where the front edge will eventually be trimmed back to - 30mm forward of the rivet line for the skin/main spar joining point.  Blue line on the right is a marked to show the trimming of the skin where it meets to the upper longeron edge.  This will be trimmed later as well:

​With the forward upper fuselage doublers in place, I now know where I can trim the outside edge of the skin - it has a notch that matches the doubler, but I can't make that cut until I trim back the longeron and the skin will lay completely flat on the longeron - yet another C before B but only after A order of things:

Picture of the right cabin side which shows the eventual notch to be cut out - this too will be more clear later:

Now with a confirmed location of everything, I can safely cut the longeron to match the cabin sides.  Trace a line with a fine Sharpie:

To avoid damaging either of the fuselage skins, I tied back the the side skin with orange twine and propped up the upper skin on top of cleco I inserted in the hole - perfect!

Used the Dremel tool with a cutoff wheel to trim the longeron back close to the line:

Untied the side skin, laid it flat against the longeron and clecoed it in place - still some minor trimming to do:

Slow work with a sanding drum on the Dremmel and some careful filing by hand and he longeron is now matched to the side skin:

Now I can fit the rear wing attachment plates to the front side of the cabin upright channel at the front edge of the side skin:

With the wing attach plate in place and confirmed flush with the cabin side skin I finished pilot drilling several of the cabin upright channel holes to finalize its position on the skin.  The attach plate will be drilled to the channel later, after back drilling the existing holes through the main spar channel when it is in place - then, with it secure in place, I can square up the cabin before finish the drilling on the uprights - man, that's a lot of steps in order to get this in place, but probably one of the most important connections in the airplane, so it's worth the extra effort to think it all out.  The cabin upright channels  still need the inside corners bent, but that will happen when I fit the rear upright covers, another thing to keep my mind occupied I suppose.

Lots more to come soon, including more bending, drilling, deburring, priming, head scratching, followed by more bending, drilling deburring, priming and riveting.  Always learning, but also always getting closer!! :)

Thanks for following along!