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. 

Tried the Topgloss BR

Lots of pigment in there and it is glossy, but the finish is nothing to be impressed of. I used the correct roller and finished off with a broad soft brush, as described in the manual. The problem is it is way too viscous to be smooth. Right now it seems back to polishing if not the second coat becomes much better tomorrow evening. Maybe some thinner will help, but to me it seems like it cures too fast.

The only good thing seems to be that it sticks to unprimed aluminium just as good as the primer.

Ailerons, primer and top coat

Bought Topgloss BR (Polysiloxane) at COOP along with some rollers and other stash. Then I went to the drug store and got some 60 ml syringes so I can accurately mix smaller amounts of the Topgloss. The syringes were surprisingly inexpensive, 3.5 NOK or about 0.4 Euro a piece.

Finished deburring the cutouts in the ailerons and measured up all the rivets for the ribs. Then I scuffed a test sheet of aluminium to test the Topgloss. I primed half of it with the vinyl primer and left the other half, just to find out how the Topgloss is with primer and without primer. I let it dry until tomorrow. The sheet is actually a faulty piece of RV horizontal stab skin. I really miss my old priming booth when testing all these primers and coating.

I haven't heard anything from Jotun about using Topgloss BR with no primer, so I just have to try it and see how it goes. If this works out, I will coat the whole plane with Topgloss instead of polishing. I'm not too keen on coating the whole plane with this vinyl primer with rattle cans though. If a primer is needed, then my old Monopol wash/etch primer gives a really smooth and thin coat, if it is compatible with Topgloss. But it is also possible to thin out the canned version of the vinyl primer and spray it on with air and achieve the same thickness as the wash primer (30-40 micrometers). Theoretically a 35 micrometer primer covered with a 35 micrometer Topgloss BR gives a total added weight of approximately 2 kg. This weight penalty is nothing when knowing that the polysiloxane is better than any polyurethane out there. In the cockpit I can also use Topgloss BR, hopefully with no primer.

Then the whole plane will be "Pegasus Grey" with tips and cowling in "Draco Red" and maybe with some trimmings in Draco Red as well.

Cut the openings in the ailerons and Polysiloxane

Cut the openings in the ailerons, only deburring left. Also bought a new orange from Hagmans. It was a bit more difficult to get a good finish, but the amount of pigment was abysmal also here. 4 coats of orange, and I still can easily see through it, it's ridiculous. Obviously I am doing something wrong here.

Looking a bit closer at Duplicolor web site what I have to do is first a plastic primer (also for fiber glass), then a white general purpose primer (white primer for bright colors), then the color itself (2-3 coats) and then a 2k transparent epoxy coat (2-3 layers) to achieve mechanical and chemical strength. This is not exactly straight forward and easy anymore, and with all those coats, it gets heavy. I begin to understand why people like Latex paint or real aviation products. The problem for me is that aviation paint products are practically speaking impossible to get. They can be sent from UK or USA, but the cost becomes ridiculous because they are labelled hazardous goods.

Anyway, I had a real eye opener this evening: Polysiloxane coatings. Going for the Jotun Yachting line of products, I only need one coat of Vinyl Yacht Primer (spray or brush) which I already have, and one coat of Topgloss BR, and it will last forever. Topgloss BR is a new 2k polysiloxane coat especially made for brush and roller. It is supposed to be completely smooth and shiny, even when applied with brush and roller, which in fact is the preferable method. Polysiloxane is superior to urethane in all aspects as well as being non toxic, no isocyanates. Polysiloxane coats are completely resistant to UV and oxidation. Generally a coat of polysiloxane is more corrosion resistant, more weather resistant, higher chemical resistance, more temperature resistant, and more glossy than the usual 2 step epoxy primer and urethane top coat.

The "old" Jotun Yachting method was epoxy primer and urethane top coat. The new preferred method is 1k Vinyl primer and a top coat of 2k polysiloxane. The Vinyl primer is preferred because it is smoother (but also needed for wood). So I wonder, on an airplane it should generally be enough with only a coat of polysiloxane with no primer or anything. In fact what the vinyl primer does is only to make a smooth surface for the polysiloxane top coat when using brush and roller, but it could also be that Jotuns formulation of polysiloxane requires a primer for adhesion? I don't know, but my guess is that using polysiloxane directly on aluminium would require 2 or 3 coats because it spreads so thin. And then it is faster and better to use the fast drying vinyl primer that is smooth and can be smoothed further by sanding. The spreading is incredible. 1 liter last for 30 square meters, film thickness of 30 micrometer. The older urethane top finish have the same film thicness, but only goes for 16 square meters due to higher VOC content.

I have read several places that people are using some new paint system and using only brush and rollers, Sprite Aviation for instances. This can only be polysiloxane coatings I guess.

So I ended up "Acetoning" all the orange paint off the tips. From now on there will be only polysiloxane coats on the Onex, with some Vinyl primer here and there (if needed). But this also means that I have to wait until I have more surfaces to cover because the paint is 2k. Another thing is that Jotun don't have orange, they only have a whole bunch of modern non-colors and "Draco Red". So Draco Red it is. Under the inner wing section and on the underside further back I will have some gray polysiloxane to protect the aluminium during the winter.