side skins (section 29) part #5

Total time: 1245.3
since last time: 8 hours
section 29 total: 126.1 hours

It is with great pleasure that I declare section 29 complete! Since last time I bolted in the gear mounts and riveted in the last rib in the front side skins.

The only issue is a little bit of oil-canning in the front side skins just under the rib and just over where the floor panel rivets on. Both sides have the same behavior. I believe this is the result of the skins not being bent perfectly. This caused them to pull the lower channel slightly out of alignment as the skin was riveted in place. Then once the skin was riveted in (with the lower channel slightly out of alignment) the channel was pushed back into place in order to rivet the floor panel in. But by pushing in the lower channel the skin is now being ever-so-slightly reshaped after it is riveted to all the skeleton and the oil-canning is born.

For the sake of future builders who might also not have perfect bends in their skins, I believe the problem could have been prevented by a) having perfect bends in the skins, or b) clecoing in the floor panels immediately after the skin gets riveted to the lower channel (You can’t rivet the side skin to the channel with the floor in place). This should guarantee that the skin is exactly right as it is being riveted from bottom to top.

In my case, I will probably bond a j-channel stiffener to the inside of the skin where the oil-canning happens and thus eliminate said oil-canning.

 

side skins complete
side skins complete
gear mounts bolted in place
gear mounts bolted in place
Gear mounts in place
Gear mounts in place
section 29 done
section 29 done
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side skins (section 29) part #4

Total: 1237.3 hours
section 29 total: 118.1 hours
since last time: 35.2 hours

We’ve been making very slow progress. But we finally have something resembling an airplane. The side skins are on and the floors are in. The only thing left in this section is the main gear mounts.

The only issue we had was that the outboard floor holes didn’t align properly after the side skins were riveted in place. This was likely the result of the bend in the skin not being perfect and/or the twist in the lower channel not being perfect. This turned out to be fairly minor. Some pressure on the side of the skin to rotate the channel a little bit allowed clecoes to be inserted and the floor then riveted. Because I was a little uncomfortable with pressure being necessary, I decided to put in three extra rivets on each side (where the floor panel mates to the lower channel.)

I also decided to paint the top of the floor panels. Originally I was only going to prime the bottoms, but decided that because wet shoes would regularly be on these floors, I decided to prime the bottoms and prime and paint the tops.

And I also got to use my new pneumatic rivet puller. I bought it a couple months ago after looking at the bags and bags of pop rivets that came in the fuse kit. Putting in the floors today went very quickly and easily thanks to the new tool (and Zach’s help).

 

side skins (section 29) part #3

Total: 1202.1 hours
section 29: 82.9 hours
since last time: 36.5 hours

I didn’t get as much done in the past month as I had hoped. But that’s for a very good reason. Meet Melody. She was just born this past January and airplane production has ground almost to a halt. To be fair, the very cold weather has had some impact (thanks Polar Vortex).

Melody
Melody
The family
The family

All the parts have been prepped and some primed and we’ve started getting things riveted together. There was some (successful) effort to avoid making the same mistake that was documented in a a previous post (see here and here). But nothing very dramatic as far as the prep goes.

Line it up and clamp
Line it up and clamp
Match drill holes to longeron
Match drill holes to longeron
Everything lined up and drilled
Everything lined up and drilled
Dimple side skins
Dimple side skins

There are some deviations from the plans worth mentioning. I’m installing a parking brake valve (no picture yet) and I’ve installed an access panel into the side of the tunnel. This is to allow easier access for service and inspections of the fuel pump and possibly the fuel filter after we’re flying.

Tunnel access panel
Tunnel access panel
Tunnel access panel
Tunnel access panel
Tunnel access panel
Tunnel access panel

Then following the plans I modified a bucking bar. I haven’t seen yet where this special bucking bar will be used, but it doesn’t matter. It was great fun doing it.

Modify bucking bar
Modify bucking bar

One difficulty came from installing a few pieces out of order. Details unimportant. I ended up with two holes on each side that were really tight. No way to get a squeezer or a bucking bar in place, so I used some cherry-max pop rivets – only I realized after putting in all four that I used flush rivets where there were no countersunk holes. The rivets had to come back out. Two came out without a problem and two came out with a mangled hole. The mangled holes (one on each side) I drilled out and used AN3 bolts. Ugly, but effective. And the ugly doesn’t matter since the bolts will be completely hidden when all is said and done.

Bolt where rivet belongs
Bolt where rivet belongs

And that’s it for now. Just a few pics of the finished and attached mid-fuse longerons and forward fuse channels.

Getting the skeleton riveted together
Getting the skeleton riveted together
Upper channel to firewall
Upper channel to firewall

 

side skins (section 29) part #2

Total: 1165.6 hours
side skins: 46.4 hours
Since last time: 19.6 hours

Last time I documented a fix to the center section longerons where they attach to a gusset (see here). I had a lot of trouble drilling them properly and in the end decided to reorder the gussets and longerons and do the whole thing over again. Ralph Hoover (EAA tech advisor) came by to give me some tips and help me not make the same mistake again.

Originally the gusset had been riveted to the bulkhead channels in a previous step, which is what made fitting the longeron to it so difficult. This time, after removing the damaged gussets (the right side gusset didn’t have to be removed since it wasn’t that bad, but I ordered a new one and replaced it too), we only cleco’ed the gussets in place, fit the longeron to the gusset and clamped it real good. Then we pulled out the clecos and drilled it while on the bench, so no need for bodily contortions or mirrors. Very easy. When it comes time to rivet, I’ll do it the same way and rivet the gusset to the longeron first with it on the bench and then rivet the gusset to the side channel.

Since last time I also twisted the four front ribs according to plans and shaped the bottom front side skins. Forming the side skins was more difficult than forming the aft side skins. This time you have to use clamps to hold the bars in place and can’t cleco to the skin. On the first one I did it just like depicted in the plans – very dificult with clamps popping off and slipping. On the second skin I put a bunch more clamps on the bars and it went much more easily.

Ralph helps me redo longeron
Ralph helps me redo longeron
new longeron and gusset in place
new longeron and gusset in place
new longeron and gusset in place
new longeron and gusset in place
new longeron and gusset in place
new longeron and gusset in place
Twist forward ribs
Twist forward ribs
Form forward skin
Form forward skin
Form forward skin with lots of extra clamps
Form forward skin with lots of extra clamps
Form forward skin with lots of extra clamps
Form forward skin with lots of extra clamps

 

 

side skins (section 29) part #1

Total: 1146 hours
Side skins: 26.8 hours

The infamous section 29. There seem to be a great many issues associated with section 29 of the plans: difficult tasks, errors in the plans, unusual build materials, etc. I’ve gone and looked at a whole bunch of other build logs, in order to prepare for these issues. No doubt, I’ve saved myself a lot of headaches by doing this. However, it hasn’t stopped me from finding all new difficulties.

The first things to do were to bend longerons (1/8 inch thick angle aluminum) to the contour of the airplane sides. This is done by matching the angle aluminum to a template and repeatedly putting it in a vice at the proper place and hitting it with a mallot. Back and forth back and forth – and make sure it only bends in one axis. Bending 4 longerons took about 5 hours. Then they were clamped to the template and holes drilled.

bending and drilling longerons
bending and drilling longerons

 

Next I constructed a special wooden clamping block to facilitate bending the skins in the right way. The plans say to use hardwood. I went to Home Depot to get a 2×4 of hardwood, which of course they don;t have. I bought a 2×4 of “premium pine” and built the block, but before using it, I asked around and was urged to use actual hardwood. So I tracked down a lumber yard and ended up spending $26.00 on a 2×4 (4 feet long) of poplar and I built another block. I’m pretty sure the pine block would have worked just fine. And it would have been $23 cheaper.

Clamping blocks (one pine and one poplar)
Clamping blocks (one pine and one poplar)
Preparing to bend right skin
Preparing to bend right skin

 

Next I get the skins and longerons on the structure and match drilled the skins.

side skins on for test fit
side skins on for test fit
side skins on for test fit
side skins on for test fit
side skins drilled
side skins drilled

 

And this is when the fun began. ….. A simple step: match drill the gusset in the side channels up through the longerons. This is what it is supposed to look like (right side):

What it's supposed to look like
What it’s supposed to look like

This was accomplished by clamping the longeron to the gusset, bending the skin down and using a long drill bit to drill up through the bottom. This was the second side I did. When I did the left side, I thought it was a good idea to use a mirror and a 90 degree drill and it almost went well. This is what the gusset and longeron looked like after I did this:

Damaged gusset hole
Damaged gusset holes
Damaged longeron hole
Damaged longeron hole

Yea. The drill bit wandered and eventually went through the longeron at an angle, chewing everything up in the process. All along I thought it was going in nice and straight. But the mirror had shifted and this is what you get. It was a bad idea to do it this way. … So this is how I fixed it.

1. Fabricate a doubler to go under the gusset holes (especially the damaged hole), and another to span the damaged longeron hole on the top:

doubler under gusset
doubler under gusset
doubler over longeron
doubler over longeron

2. Fabricate a spacer to fit between the two doublers where they extend beyond the gusset.

spacer
spacer

And finally this is what we have in the end (note that the black spot is marker, not a gap):

The final fix result
The final fix result
The extra parts fabricated for the fix
The extra parts fabricated for the fix

 

Update: So many people suggested that I simply scrap the damaged longeron and gusset and start over that I couldn’t ignore it. Although I maintain this fix is most likely sufficient, I have enough doubt that I decided to reorder all the parts and do it over again (and I plan to get some help from Ralph, my tech advisor, to prevent the same mistake again this time). In fact, I’m going to redo both sides. The right is pretty good, but the edge of two holes in the longeron are closer than they should be. All in all, I’m glad about this decision. There is an expense getting these parts shipped and all, but oh well. It would be unwise for me not to defer to the judgment of so many more experienced builders.

Another update: Van’s replied that my repair was most likely sufficient and Ralph (EAA tech advisor) said the same. However, but that given the ease with which a proper fix could be done and the low cost, he advised to fix it right and offered to help – which he did. See here.