I've been meaning to publish this edition of my blog since Monday, which was Halloween, but work commitments have kept me busy and I've also been in the shop getting stuff done!
With the lower fuselage skin almost ready for deburring and priming of the joining surfaces, I needed to get the lower fuselage access cover (the Hell Hole cover) final fit up done. I didn't time this to happen on Halloween, but it seems appropriate :)
Before taking the lower skin/longeron/diagonals apart for debur, I fitted the flap/controls mixer cross support by back drilling from the inside of the skin just forward of the hell hole. This cross member provides the rear support structure for the flight controls as they pass through the centre of the cabin space back to the flapperon mixer tube (more on this once completed) .
Also drilled out and deburred the control tube bearing hole in the centre support channel. This mounts centred on cross member to support the control tubes, but I'll wait until I have more of the rear baggage area complete to determine the correct vertical mounting position for it. Nothing in the plans shows a vertical measurement and I want to have it exactly correct so the controls don't bind. There are also some clearance holes to be made once mounted.
With all the diagonals and longerons removed, I laid the lower skin down flat and upside down on the table. The hell hole cover was placed into final position and squared to the hole, diamond bends facing out from the hole.
The goal here is to make the cover lay as flat as possible to the lower skin and use the tension created by the diamond bends to tighten the cover skin as it rebounds once attached. It isn't much, maybe 5mm of depth in the cover from corners to the peak where the diamond bends cross, but it certainly is an effective design by Zenith.
With the cover in position, I placed a bucket of clecos on the centre, which weighted down the panel flat. Then I drilled the cover down where rivnuts and screws will hold it in place, starting at the corners:
With all the holes drilled and fastened (not all shown in this picture) to the lower fuselage skin the cover maintains tension and stiffness once the weight in the middle was removed - excellent!
With everything match drilled to correct size where I can at this point, it was time to strip off the protective plastic and start deburring all the holes. I generally try to leave the plastic on as long as I can to help protect the finish of the aluminum from getting scratched - it's never perfect, but reduces the amount of scratches I'll need to remove before eventual prime and paint.
Once every hole is deburred (both sides of the skin), every inside surface of the skin that contacts another part gets a scuff with ScotchBrite, then a light spray of primer. Like all the other components I've assembled so far, grey self-etching primer in visible/outside areas, zinc-chromate green on inside surfaces.
The inside of the access hole gets the grey:
The rear inside of the fuselage and lower rear skin gets the green:
Had a couple of minutes down time while the primer cured, so I fabricated some nylon bushing plates that will be required for the flapperon mixer assembly. 40mm square, 1/8" thick.
Used a punch to centre a hole in each which eventually will be drilled out to 3/8". More on these later.
For now the lower fuselage skin gets rolled up and put back into storage so I can complete the diagonals and upper longerons for the side skins.
Laying out the right side fuselage skin on the table I needed to complete the cabin window cut-outs. I've been anxious about doing these as there is always a risk of tearing the thin fuselage skin which could render the entire skin un-useable and needing to be replaced. But like anything in this build so far, no risk = no reward, right?
Clamping the skin down to the table with a sacrificial backing board behind it and I used a bit of cutting oil to assist with the round corners:
The pilot holes I drilled previously are exactly the same on both fuselage side skins, but they are being cut individually. I was going to use the fly-cutter tool to form the corners of the cabin window cutouts, but it is too big to cut 25mm radius holes, forcing me to use a bi-metal hole saw. Much more aggressive cutting, but taking it slow and using the cutting oil worked very well.
Corner holes for the cabin window cutouts complete:
Inside hole cuts can be difficult, particularly in small areas as there is no way for the cut-away aluminum to curl out of the way of the shears as it is cut.
Getting metal shears into the 25mm radius holes effectively was too difficult, so I used a Dremel cut off wheel to first cut a relief line wide inside the window cut out. This freed up the tension in the aluminum and I could trim the outer edges of the windows smooth between the corners:
Next all cuts are deburred and sanded smooth. Eventually I'll flange the edges inwards just a little bit so the edges are tight against the Lexan windows. I'm looking into adding a silicone or rubber gasket as well which will keep out the rain and prevent any rubbing on the Lexan.
It took a couple of hours to complete the cabin window cutouts, but with a bit of patience and careful trimming, they both turned out great!
Window cutouts complete, time to start adding the vertical and diagonal stiffeners:
I've done the same as the bottom fuselage skin, adding additional opposite diagonals:
Once the diagonals are in place, flip the right side fuselage skin over and start fitting the longerons. A yet to be drilled longeron for the top edge and the lower right longeron from the bottom skin in place on the side skin for fit up. The lower one is only clamped in place at this time, it will be match drilled during assembly of each of the finished side skins to the bottom skins.
I still need to trim the forward edges of the fuselage side skins at the front cabin join location. I'll wait until later once I have the uprights and spar carry thorough channels fitted in place (just in front of the windows, better view in another picture further down):
Drilled out the upper right side longeron to A3, then alternatively to A4. A forest of clecos!
With the upper longeron final match drilled, the entire right side fuselage assembly is flipped back over and I can start to fit up some of the upright channels.
The baggage area back panel support channel shown here in rough location. I originally thought I should pilot hole fit this in place for future assembly, but I've decided to wait until the fuselage sides are mated to the fuselage bottom to see how everything fits best. Kit builders don't have these issues, they just cleco things together and right size the holes for rivets.
Test fit of other upright channels seems to confirm things will go together nicely when the time comes. The two channels at the left show where the fuselage side skin will be trimmed to match. The channel in the middle behind the first cabin window is one half of the flapperon control tube cover (more on these later).
Next up, everything comes apart for debur and priming. The repeat everything for the left side fuselage skin. With the left side done, I can start assembly of the fuselage and installation of some of the controls like the flap mixer and bearings. I'll likely be fitting the windows up as well, but the final install of the windows happens much later on in the build.
Very pleased with my progress so far on the fuselage. I got discouraged for a bit figuring out order of operations, but managed to get a process together that seems to work well so the left side should go much faster. Another bite of elephant consumed :)
Thanks for following along, more to come soon!
New here? Try starting at:
Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.