Drilled mid wing spar

Still have to drill up all the steel at the tips. I'm not sure if it's best to take them now, or after the spar is riveted. Have to sleep on it.

The 3 in 1 paint is really good, and readily available locally and exist in many colors. Just have to make sure it cures for 3-4 days and it is like stone and stick like glue. It is matt/satin and very easy to spray. Gray and orange with this satin finish will look cool. Regarding paint, I think I have 4 options now. 3 in 1 which I can do myself. Jotun Topgloss BR which I also can do myself, but I'm still not convinced the end result will be OK due to milkyness when polished. Polish it (combined with 3 in 1). The last option is to fly it to Lithuania/Poland when finished and paint it there by professional aircraft painters, much cheaper than to do it in Norway. 

Right wing rib and mid spars deburred

Deburred the left wing ribs and primed the mating surfaces. Deburred the center wing webs.

Left wing finished updrilled

Right wing skeleton finished

Finished the right wing spars and ribs, riveted and bolted together ready for fitting of the skin.

Tried to spray on the Jotun Topgloss BR (Polysiloxane) with a new and much better spray gun. The result was very bad. If it is me who is terrible at spraying, or that the paint is not formulated for spraying, I don't know, probably both. It was full of pin holes or fish eyes (I really don't know the difference), looked awful even where no pinholes were seen. But I rubbed the half of the test piece with Biltema rubbing again, and it was all shiny again. Have to get some Biltema Hard Wax tomorrow and see if also that makes it all milky like the two other waxes I tried.

The 3 in 1 paint is very good. It dries in 10-15 minutes, but then it is rather soft. After 3-4 days it gets all hard and nice. J. S. Cock also has a special primer for aluminium. It is the same stuff as this 3 in one, but specially formulated to stick on very smooth surfaces, aluminium and stainless steel in particular but also glass. It is only on larger cans, not rattle cans.

I have this booklet "How to paint your own airplane" by EAA. What a total waste of paper! All it say is Acid etch, Alodine, epoxy primer and polyurethane top coat. Yes, it works and the result will be top, but the problem is that: 1- Acid etch will creep into joints and corrode your airplane from the inside. 2- disposing used Alodine is almost impossible due to hexavalent chrome. 3- Urethane is poisonous and requires a booth and a breather. 4- Epoxy primer isn't even necessary. Doing all this with all these extremely nasty chemicals is not something to do in your home. A heated garage will work, but the main point is that the only corrosion that will exist on a painted surface of aluminium is filiform corrosion, and to prevent it does not require all these stages. The corrosion that causes most problems is galvanic corrosion, and none of this will do anything to prevent it. Besides, these products are impossible to obtain locally, for me at least.

If I should go for Polyurethane, the process will be scuffing with scotchbrite, etch primer or epoxy primer, topcoat. That will last for ages without any filiform corrosion and the finish will be top. If that was to corrode, it would be due to galvanic corrosion caused by fasteners and similar. This will also require a booth, but it is somewhat doable because I can get the stuff locally. But, the equipment (booth, spray guns, breathers etc) seems like a whole lot of money and time for a one time process, that may turn out bad. Sending the airplane to some professionals may very well be a better solution.

What I (still) hope to do is use this Polysiloxane with paint and roller. Then wet sand with 1000+ grit, Biltema rubbing and wax it. It is only this waxing part that is a problem right now, maybe I can do without waxing? For primer I have four choices; Epoxy, etch primer, Vinyl (Jotun) or Polyester (JSC). Epoxy and Vinyl I know will work, etch primer and polyester I have to try first. All this I can do at home, and the end result will be like polyurethane, in some aspects even better (UV). In the cockpit I will use 3 in 1 rattle cans with a top coat of clear satin enamel, or maybe 3 in 1 spray gun with the special reducer that gives a harder satin finish instead of the matte finish.

The other choice is polish.

Priming and test

Primed the rib doublers and mechanism using this 3 in 1. The rest of the ribs will only be primed on the mating surfaces with vinyl.

I also made a test piece from some scrap 6061. The plan was to put in on my boat, but then I remembered my boat is on land this winter for a little fix up this spring. It's only a few meters from the sea, so I will put it there anyway and let it stay for some years. I just have to test how this 6061 and stainless rivets holds up in a real marine Norwegian atmosphere. So I made some holes and riveted a few rivets.

Half of the piece is primed with Jotun Vinyl primer. From left to right: [-, Duralac]  [-, -]  [primer, Duralac]  [primer, -]. The lower rivets are solid AN rivets for comparison.

I also looked at the Jotun polysiloxane test pieces. It has really cured by now and can withstand Aceton, ethanol and xylene just as good as my old epoxy primer. It is impervious to UV and really hard, similar to polyurethane. It really is high gloss as well. If I could just find a way to put it on so it looks remotely acceptable... Have to try to spray it on tomorrow using my primer gun and see how it goes, but I am afraid it is too viscous. 

Deburring ribs

Deburred all the ribs for the right outer wing.

Found a new (for me at least) paint system. It is called "3 in 1" from Power Coat. It is a modified polyester paint used in the industry for all kinds of things, mostly metals, and is supposed to be very good. It works as a primer and top coat. It can be bought as aerosol and in ordinary cans for roller or spray. Tried it on some scrap aluminium, and will see how it turns out. Polyester is I believe the same as gelcoat. The paint is 1 part, but a special catalyst can be mixed in to increase shine and hardness.

Right outer wing

Finished drilling all the holes in the right outer wing. The paddle hinge reinforcement did not have any pilot holes, so it was done the "old fashion" way.

Aileron paddles (finished)

These paddles needed lots of modifications. The Aurora bearings also must be installed, and Kerry sent a mail late last night (Norway time) that this will be a very tight fit, possibly moving the hole for the bolt longer out. So I took one bearing just to see how it fitted.

The one and only paddle that was according to plans, looked like it would fit exactly, but the one with the hole filled would have no chance of fitting. So I drilled out the rivet, countersunk also on the other side, and riveted a new one in. Then I filed off the excess and had a nice "foot" with two perfectly flush surfaces.

To be sure the bearing would go clear of the foot, I dremeled the hole a bit oval, then drilled #13 and reamed up to #12 for the AN-3 bolt. In the end I had a hole that was offset enough to give a clearance of about 1 mm (checked with bushing and AN bolt into the bearing). Finally a set of paddles that fits and is according to plans.

Aileron paddles

According to Kerry the drawings are correct and should be followed regarding the paddles. OK, this means that only one single paddle of the four are correct, and that is the left hand inboard. The ones marked outboard paddles has a hole in the "foot" that is not supposed to be there. The right inboard paddle is a copy of the left, and therefore has the hole for the aileron push rod on the wrong side (when on mounted on the right hand side). No big deal, I think it will work no matter how they are mounted as long as the hole for the push rod is correct on both sides, and the extra holes on the "feet" are filled up. Anyway, I shuffled the inboard and outboard paddles so they will be 100% according to the drawings. This means I have to make one new hole and fill up two other. The holes in the feet are 1/8, and I meant to use a flush 1/8 solid rivet, but I managed to countersink a bit too much, so I went up to 5/32 and countersunk a bit too little so I could file them 100% flush when set.

I don't really like the mechanism with a steel set screw in the aluminium paddles. A little moist and salt and this is bound to corrode both at the threads of the set screw and in particular at the contact points between the tip of the set screw and the paddle, and there really is no good way to prevent this. Nothing dangerous, but I suspect these will need to be adjusted often to keep the mechanism nice and tight. Duralac can't be used here as it hardens too much (it is meant for permanent fasteners). A much better design would have been the paddles also were made of steel. This way the steel and aluminium could be insulated at the rivet joints which is perfectly doable.

Aileron paddles and mechanism

I need more clamps to be able to drill all the 1/8 holes on the spars for the outer ribs without getting burrs in between the already riveted parts on the spar.

So I started on the aileron paddle mechanism for the folding of the wings. The 4 paddle blocks shall have two bearings each. The holes for these bearings are not honed or reamed to correct size, but are approximately 4-8 hundreds of a mm too small. I should have a reamer to do this, but a reamer this size costs 150 $. The drawings say use a reamer or sand it slightly. So I sanded and sanded and sanded... which was very fiddly because the hole is only approx 17.45 mm. Eventually I got them up to 17.5 mm, the bearings I measured to 15.52 mm, so this should be a nice fit. Here I really think Sonex should have reamed this part up to correct size. The block itself is (as all machined angle components) are really first class pieces of machined aluminium, and a press fit bearing is a close tolerance fit that requires reaming. Manual sanding and measuring and trying the pieces will do, but the amount of work is at least a factor 1000 compared to reaming. I thought about simply heating the blocks to let the temperature increase the holes, but Kerry (Sonex) said that heating should absolutely NOT be done, because the bearings will not stand the heat.

For the paddle mechanism, the drawings and the machined angled paddles does not add up at all. The machined angled parts have two identical inner paddles and two identical outer paddles while the drawings call for different LH/RH outer paddles and different LH/RH inner paddles. Very confusing, but both ways will work even though the end result will be different. There were also lots of trimming to be done on the already machined mating ribs to make the paddles fit.