Mid-fuselage bottom skins complete!

The one last step in this section is a very long one - basically "rivet the whole thing together", so we started doing that. First came the TAS antenna doubler, which I wanted to rivet before attaching the skin (I'll leave drilling the TAS antenna hole for later):

TAS antenna doubler riveted in place
Then we clecoed the skins and started riveting them to the ribs and bulkheads (except for the aft/side holes that are riveted when attaching the side skins or the tailcone). Since the skin is longer than the parts, we needed to improvise a jig to hold it while we riveted:

Size comparison: mid-fuselage parts onto jig vs almost-average-size human :)

Mid-fuselage bottom skins ready to rivet
We got to a good rate of about 2 rivets/minute, which means this still took many hours of work to do all 731 rivets, but gave us good results in the end:

Fully riveted mid-fuselage bottom skins

Fully riveted mid fuselage
With this, the mid fuselage section is complete and ready to attach to the forward fuselage.

Time lapse:


Total mid-fuselage ribs and bottom skins rivets: 1151
Total mid-fuselage ribs and bottom skins time: 92.7h

Forward fuselage ready to attach

We continued riveting the forward fuselage parts, which is now about bringing large parts together:

Firewall parts mated with the forward fuselage bottom skin and ribs

This involves using a layer of sealant between the firewall bulkhead and the bottom skin - I used the 3M Firebarrier 2000, as others before me have, for some added fire protection:

Firewall bulkhead clecoed with sealant to the forward bottom skin

Once the sealant cured, I riveted the parts together:

Firewall bulkhead riveted to the forward bottom skin
We proceeded to rivet the forward fuselage ribs to the bottom skin, which required some challenging positioning (or longer arms than my wife has), so we supported the firewall bulkhead in the right places for her to put her knees down on it:

Wife trying to find a good way to buck the rivets at the bottom flanges of the forward fuselage ribs
Wood supporting the firewall bulkhead to she could support her knees on it



and with that, got the whole thing riveted:

Fully riveted forward fuselage ribs (except the aft 4 holes)

The spacing between the forward fuselage rib and the forward fuselage bulkhead (per the previous post) worked out great and I riveted the parts together:

Forward fuselage bulkhead riveted to attach angle, with proper spacing to the nutplate

We then attached the floor ribs to the surrounding parts. Some pop rivets are used in the tighter area attaching the ribs together:

Inboard floor ribs riveted to forward fuselage bulkhead and firewall bulkhead

Finally, we attached the center section bulkhead, by bolting/torquing its web to the ribs then riveting them:

Forward fuselage parts attached to center section bulkhead

Special note goes to my newest accessory, rivet set caps - I thought this was silly, but the difference in the resulting rivet heads is blatant - even the coating of the heads was entirely preserved:

Rivets done with the caps (left row) vs rivets done without it (right 2 rows)

The next step is the big attachment - mating the forward fuselage to the mid fuselage. We're doing the two sections in parallel, so we now need to finish riveting the mid fuselage.

Time lapse:


Total forward fuselage ribs and bottom skin rivets: 578
Total forward fuselage ribs and bottom skin time: 101.1h

Forward fuselage riveting

I finally started riveting the forward fuselage parts, starting with the smaller ones:

Riveted smaller parts for the forward fuselage
I riveted the attach angles to the forward fuselage ribs:

Attach angle riveted to forward fuselage ribs
which, for some rivets, was kinda tricky with the squeezer, given the nutplates were already on:

Riveting through an opening to clear the nutplate
I riveted together the bottom forward fuselage bulkheads and seat rail supports (note - those nutplates could also have come later, would've made it easier to rivet them to the skin):

Bottom forward fuselage bulkheads riveted to forward seat rail supports
then started riveting the floor ribs:

Forward bottom skin riveted to floor ribs
Before riveting the next parts - the bottom forward fuselage bulkheads - to the skin, I decided to check how they'd fit against the vertical angles, and am glad I did - they did NOT fit, due to interference with that innocent-looking nutplate, on both sides:

Bulkhead hits the nutplate edge before the holes align :/

Other bulkhead also hits the nutplate before the holes align
That side of the bulkhead had plenty of edge distance, so I trimmed off another 1/8" from them with the bandsaw+grinder:

Bottom forward fuselage bulkheads marked for trimming

Trimmed bottom forward fuselage bulkhead
I then wrapped it in tape before the final edge deburring, such that the file would remove the tape only where I actually had to re-apply primer, and protect any existing primer:

Deburred trimmed bulkhead edge with tape for selecting priming

I then used the rattle-can primer for this small touch-up:

Primed trimmed bulkhead edge
and finally riveted those onto the skin as well:

Bottom forward skin riveted to floor ribs and bulkheads / seat rail supports
While waiting for my riveting partner (a.k.a. the wife), I also fabricated the landing gear mount shims, which are used slightly later in this section:

Landing gear mount shims cut to size
Next step is partially riveting the systems brackets, then it gets interesting, by joining the skin and parts above with the parts from the firewall section.

Time lapse:



Total forward fuselage ribs and bottom skin rivets: 438
Total forward fuselage ribs and bottom skin time: 92.4h

Fuselage side skin side plate countersinking

While building the forward fuselage ribs/bottom skins, I realized the center section side plates would be quite hard to machine-countersink at the expected time (middle of section 29) with how close they are to the center section bulkhead assemblies, so I clecoed them to the skins, match-drilled and machine-countersunk them at that time:


Just a small step to save time later.

Time lapse:


Total fuselage side skin rivets: 0
Total fuselage side skin time: 10.7h

Forward fuselage countersinking, fuel pump shelf and primer

I continued by machine-countersinking the center section bulkhead to accept the skin dimples:

Machine-countersunk forward center section bulkhead holes
I also took advantage of not yet having the bottom skin on, in order to more easily attach and match-drill angles that make a shelf for the EFII install. I'm roughly following the instructions from the Aircraft Specialty hose kit, and may get the kit from them.

Aluminum angles to make a shelf for the EFII pumps

Leveling the two sides of the EFII shelf angles

We had done primer on the skins earlier in the month:

Forward fuselage bottom skin, scuffed but not yet primed

Forward fuselage bottom skin, primed

This weekend we then did another large batch of primer, to get all the parts that need to go on the skin, before the skin is attached to the forward ribs and firewall bulkhead:

Forward fuselage parts before primer

Primed forward fuselage parts

More primed forward fuselage parts

Next will be a lot of dimpling and riveting of those parts.

Time lapse:


Total forward fuselage bulkheads, ribs and bottom skin rivets: 0
Total forward fuselage bulkheads, ribs and bottom skin time: 70.2h

Mid-fuselage bottom skins ready to rivet

Finally coming back to this section and making progress!

I took a step from section 44, and drilled the mid fuselage skin nutplate holes to size - the goal is to attach the two forward-most nutplates before riveting the skin on, since they're in somewhat tight spots after the skin is installed. The others should be easy to squeeze rivets for later:


We finally primed the bottom skins:




then proceeded to remove the vynil from both for riveting:


We then dimpled the skins, and next will start riveting them on.

Unfortunately in that batch of primer I forgot to include the TAS antenna doubler, which is way easier to rivet on before the skin is in place (because the heat tee goes over it), so I'll do that batch before continuing with this section.

Also related to the TAS antenna, I was thinking of cable paths for it, and wondering if I could put the TAS in the tailcone and run the 4 cables straight back (so exiting the tunnel to the right, then going through the rear spar bulkhead. The main question I had was about drilling a big (1/2" or so) hole through the rear spar bulkhead, so I contacted Van's support and send them this annotated picture, and they confirmed it's OK to do so:

Rear spar bulkhead hole location for running cables to the back

Time lapse:



Total mid-fuselage ribs and bottom skins rivets: 412
Total mid-fuselage ribs and bottom skins time: 84.2h

Forward fuselage skins and ribs deburring, fuel return path and bottom TAS antenna location

I finished deburring the remaining parts for the forward fuselage, and dimpled the ones that were already primed (the forward fuselage ribs):

Most forward fuselage ribs deburred parts

Deburring and trimming mid seat rail supports

Dimpled forward fuselage ribs
I also did some work in planning for the fuel system. Since I plan to use the EFII System32, I followed the steps from others who have run hoses for it, and may end up getting the hose kit from Aircraft Specialty, so I followed their instructions, starting with enlarging the systems brackets holes - the original one is the right size for a 1/2" snap bushing (plus another which is meant for brake lines and thus much smaller), but I'm planning to use 3/8" fuel hoses with grommets, so I enlarged it to 5/8" for the grommet). I did this by transferring the holes to a backing piece, enlarging them to the right direction on the backing piece (away from the screw hole and away from the top bracket edge), then transferring back with a unibit:

Transferred existing holes to a backing piece

Enlarged holes in backing piece, to transfer back to brackets

Enlarged systems bracket holes

Systems bracket with grommets
Of course I did screw up and had to re-make two of those top brackets :)

I also enlarged the forward fuselage rib holes to 9/16" for the fuel return lines:

Enlarged center hole for fuel return line (before deburring)
I added a hole for those lines through the side skins and center section side plates:

Hole position on the side skin for fuel return line 
Enlarged fuel return side skin/side plate hole
Per the post on antenna positions, I made an antenna doubler for each tunnel section:

Antenna on aft tunnel doubler

Forward tunnel doubler for TAS antenna
I'm not going to install the forward doubler just yet - the aft tunnel is harder to rivet in (with the heat tee over the spot), so I'll just add that one for now).

Next up, a bit more deburring and then primer and riveting to complete this section!

Time lapse:


Total forward fuselage ribs and bottom skins rivets: 0
Total forward fuselage ribs and bottom skins time: 61.3h

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