2.6.0 Filling & Sanding Wings & Winglets

The first part of the process is to slather on Velocipoxy Microballoons. I mixed it to the consistenacy of mayonnaise but it still ran down creating a mess. Darn gravity! It actually looks kind of shiny after that first coat is applied! Because I used so much I mixed it in that white bucket, poured it on, then used drywall taping knives to smooth it out.

The underlying fiberglass needs to be smoothed out and "finished". This is the beginning of that process on the upper side of the left wing. I use Velocipoxy "Micro-balloons" here to fill in the fiberglass in preparation for an epoxy primer coat to be added later.

After this is applied and cured the sanding process begins. This is what the wing looks like after the first sand is complete.  This photo happens to be the bottom of the wing though.  It’s no longer shiny but it is much smoother! And take a look at the floor - you can see the fine dust covering it!

Here's the bottom of the left wing multiple sandings and fill applications of the epoxy gel coat. It's hard to tell from the photo but at this point the wing surface is about as smooth and level as I can make it. The epoxy primer, to be added later, will finish out the smoothing process.

Here's a photo of the finished surface for the top left wing.

And we start the process all over again for the right wing. This is the first coat for the top side of the wing.

Once everything is sanded as best as possible, it’s time to start cutting up the wings and winglets to make ailerons and rudders. Yeah, after putting in all of this effort we now start cutting and slicing it all up! That’s a bit scary!!! The book actually recommends applying an epoxy primary coat at this point but everyone that I talked to at Oshkosh said to hold off doing that until later.  More filling needs to be done once everything is cut out so there’s really no point doing it now. Aileron construction starts here!

Skip ahead a few years (yeah, the wings were built back in 2016/2017 and it’s now 2021!) and I’m back to finishing the wings and canard this time in preparation for a prime coat and eventually paint. The old sanding tools and dust mask are back in use! Because the goal now is to get these surfaces ready for real paint, I upgraded my sanding tools and techniques. I spent a bunch of time watching YouTube videos - the pros who do cars and such - and learned quite a few techniques. Because the wings have been sitting around for a few years, I started by re-sanding what I already had.

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It may look smooth, but it isn't!

I really thought I had these surfaces smooth. I’d sanded down to 320 grit and while it felt smooth, the truth is, it really isn’t. One of the tips I learned is to use what’s called “guide coat”. This is a very fine black powder (you don’t need much!) that gets spread over the surface you’re trying to smooth out. Then, using a relatively fine sandpaper (I used 220 grit on some DuraBlock sanding blocks I purchased), the trick is to sand over the guide coat using a ‘Z’ pattern. The high spots continue to get sanded but guess what? The low spots don’t and they stay black! You can easily see that in the photo below. In my case, the low spots are mainly along the wing spar. To fill that in I mixed up some Velocipoxy and Micro and carefully filled those in. That epoxy mixture is pretty stable, in other words, it doesn’t shrink too much during cure, but even so, subsequent coatings of the guide coat continued to accentuate any remaining low spots. It’s also very useful for showing pin holes!

In the photo below you can see a few areas that got filled in (mainly the aft part of the wing) that now sand out the dark. But I still need more fill along the spar line.

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The low spots are all dark. They need more filling and sanding!

I spent some $$$ on a Dura-Block sanding kit, along with a bunch of different rolls and grits of sandpaper. These are what the pros use and I have to say that they do work. Finish work is still hard though. Every time I think I’m finished I find more minor bumps. Ugh!

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In order to make any progress with finishing the wings and other parts of the airplane, high-quality sanding blocks are required. Dura-Blocks, along with various grits of sandpaper, are what the pros use. I bought the kit from Amazon as well as the longer block. They really work, even though finish work is still a pain in the butt! :-)

So, the top of the left wing seems to be about as smooth as I can get it. Nevertheless, I’m sure that once I put the primer on it, I’ll find more bumps and low spots. In any case, I decided enough was enough which meant it was time to flip the wing over and start to work on the bottom side. In order to do that, I needed to build some really high stands (saw horses???) to put the wing on so that I can flip it over without smashing the winglet. In the photo below I’ve got the stands in place and my neighbor and I used the shop crane to lift it up high to get it on the stands. That actually worked really well!

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Lifting the wing onto the really high saw horses so that it can be flipped upside down for finish work on the bottom.

Once the wing was right side up on the stand, it was a relatively simple matter for the two of us to flip it upside down. In fact, we just rolled it over using the leading edge on the winglet side and the spar on the other side. Of course, because this is so high, I now have to do finish work standing on a ladder. Oh well!

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And here it is upside down! Those winglets need a lot of clearance!

I’ve just started this process. More to come, for sure! Once I’ve got this as smooth as I possibly can I’ll apply some PolyFlex UV Primer over the wings which will also help to fill in pinholes and any remaining low spots. That stuff also gets sanded and requires at least two or three coats.

Jump ahead one month and guess what? The left wing is finished! It took quite a few coats of PolyFlex (along with more filling and sanding) to get everything as good as possible, but I finally said that "enough was enough" and I moved it off to the side and covered it for protection. Here it is, off to the side, awaiting reinstallation on the fuselage. Of course, I haven’t even started the right wing yet!

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The left wing is finished - literally! I've gone as far as I plan to with primer for this wing.

So, the left wing and canard are finished, but now it’s on to the right wing. More of the same - filling and sanding! I’d been using a Harbor Freight orbital sander, which worked nicely, but as with all Harbor Freight stuff, it’s not the highest quality. I was not able to attach it to a vacuum so the little cloth bag had to catch the dust. It did ok, but wasn’t the best. Then, it started overheating to the point that  even with leather gloves on, it was almost too hot to touch. So, time for a replacement. Home Depot had a special on a Bosch variable speed orbital sander, model ROS20VSC. Wow - what a difference! This one comes with a carrying bag for storage, has an attachment so that it can be hooked up to a vacuum, and never gets hot, even after more than an hour of continuous use. It’s always worth it to spend a few extra bucks. I’m now really spoiled!!!

Prepping the right wing for finish work.

More photos later as I continue to make progress on the right wing.

ui© John Trautschold 2018