The last two days were filled with wet sanding the aft top tool cowl. Last we left off, I had sprayed black primer on the surface. This was to give me a guide coat. As you start sanding the primer on the highs sands away and the low spots remain black. This gives more of a visual for places that require adding filler. The left photo was before I was “done” sanding the primer. The middle photo shows when I was starting to add filler. The right photo shows how the low spots end up looking.
As I’ve said before, you can’t sand out a low. So the visual of the black guide coat really helps. You can see the ring of black around the low spots. These “ring” shapes end up being very telling for when you have the low spot fixed. You want to fill the low slightly above the desired surface, then sand back to contour. Any hard edges, lips, or straight lines are suspect when doing this and generally means keep sanding.
The filler I am using here is called “Icing.” It is a polyester (Bondo) filler and sands easily. I wouldn’t use this much of it on a flying part, but it works here. It does kick off fast in our 116 degree heat here. So mix in small batches. You can see that most of the guide coat ends up going away when you have your surface ready to move on to the next round.
Yesterday was all sanding by hand with my long boards and sanding blocks. I have a great set of hand sanding tools with which Jon, Greg, and myself finished Betty. I do really like my hand sanding tools, and there are times and places where they are the best tool for the job. Much to Jon and Greg’s chagrin, I didn’t want any power sanding tools used with Betty.
My buddy Shawn came over yesterday while I was block sanding and asked why I wasn’t using pneumatic DA sanders. I told him that I didn’t find them to have the control and finesse that I needed when contouring. They also tend to have hard edges that make gouges and divots in an otherwise nicely progressing surface.
Shawn introduced me to interface pads for power sanders. They are foam pads that come in varying thicknesses that all but take away the ability to make divots and gouges. These pads even allow you to go around inside corners. So I went this morning to my local auto body supply store and picked up both a 3 inch and a 6 inch dual action (DA) sander, a selection of interface pads, just about every grit I thought I would need of hook and loop paper, some squeegees, more adhesive backed paper for the long boards, some pin hole filler, and a really neat new sanding block. Yea it was an expensive morning. One of these days I will put together a blog post about which tools I chose and why. There are a few features I have already come to rely on, like the “throttle.”
It was some of the best money I’ve spent on the project yet. I couldn’t wait to get back to the hangar to try them out. They made quick work of all the little areas I had to fill. By choosing very fine paper to start with, I was able to control and gauge what paper I needed. I started with 220, and eventually ended up with 120 for sanding the icing with the 3″ DA. The 6″ it seemed a little more aggressive with the same grit paper, so I was sanding with 180 with the 6″ DA.
No matter if you are using power tools or blocks, it takes a while to fill and sand all the areas that need it. Plus, try as I may, my filler application technique usually ends up causing a bit of extra sanding too.
I was also turned on to a new product by Richard, Evercoat 440. It is a micro pin hole filler. On Betty, I did the epoxy wipe method. Richard recommended I try this product as a quicker and easier way to get pin holes filled in the tool cowl. It is a product that goes on much like a wax. You put it on an applicator, rub it into the part, and buff away any residue. Sounds great in theory, and I am sure it works great, when it isn’t so hot. These products are normally designed to be used between 60 and 80 degrees F. The filler was kicking off so fast that we were actually creating lumps and bumps on our nice surface.
Not to worry, with composites anything can be fixed. So I got the 400 grit paper on my new DA and went to town. It didn’t take long and we were back to a nice surface. I could see where the Evercoat did fill some pin holes, even after the 400 grit sanding.
My chemist friend Brian, who also has a background in auto paints and body work, told me to put the Evercoat in the fridge and try it cold tomorrow. Maybe between the part being 100 degrees and the overcoat being 50, we can average to 75 for the time it takes for the product to cure. That sure would make for an easy way to fix my pin holes. I will let you know if that works.
At the end of the day today I was ready to shoot some more primer on it to act as another guide coat and to reveal any flaws. I had some grey rattle can primer. Not ideal, but will work for a guide coat. So Kevin and I sprayed a can worth on.
One thing was immediately evident. We didn’t fix anywhere near all the pin holes. But that can be fixed easily. Because the primer flashes and drys so quickly here, the primer had a sandy or gritty texture. So, my new DA and 400 grit paper to the rescue.
I did a quick sand over the whole cowl surface to get rid of the texture. It was almost as if I had started polishing it. The primer actually seemed to somewhat evenly sand, showing a more ideal contour, or less low spots.
One way to tell if you have a nicely contoured, smooth surface is by reflections on the surface. Usually you need a glossy paint to do this. But I was pretty stoked when I saw the wet rattle can primer surface that was only sanded to 400 grit make some pretty nice reflections. That is a sure sign we are going to have a nice looking cowl.
The general road map for this part is as follows: Next bodywork steps are going to be filling pin holes, a coat of epoxy primer, and polishing. If any other imperfections show up we will fix those too. Then we will pop the tool cowl off the plug and remove most of the plug. This will allow us to sand the inside surface of the tool cowl to fix any thickness and fit issues at the forward flange. From there it will be time to make a mold. I can’t wait to see how this part turns out.
Ok, the other really cool thing that happened today was I got a visitor. Dave Anders, the builder/owner/pilot/scientist/engineer of the fastest and most efficient RV4 visited the workshop. He follows this blog, and had seen my cowl progress and wanted to come visit to see it. Very cool stuff. When a person of this caliber, experience, and accomplishment is around I try to zip my trap, listen, and ask questions.
If you don’t know who Dave is, google “Dave Anders RV4,” or “Dave Anders and Kitplanes,” or “Dave Anders tri aviathon.” There is a plethora of information out there and it is inspiring to those of us who are builders.
Anyway, he and I got to visit for about an hour and a half. I gave him my tour of my new cowl shape, he gave me about a semester’s worth of education. We spent time talking about the cowl shape, composites, exhausts, cylinders, pistons, inlets, Helmholtz resonance, etc. Talking with him is always inspiring and energizing. He has a passion for the science behind how our engines and airplanes work. I can’t wait to show you all some of the things we discussed and how they will work on Brian’s Defiant.
Dave, I can’t thank you enough for the help and time you’ve spent with me. I really appreciate it and it is always educational. It is a real charge for me to get to spend time learning from your experience and the things you’ve done.