Next to twisting the side rails, fabricating the fiber glass frame for the canopy was the thing I was least looking forward to. Especially since I had so much trouble forming the molds for the fairings. But it turned out I was just using the wrong ingredients. It all depends on the length of the fibers in the mixture:
Fibers are of somewhat visible length, and make the mixture very hard to form. When cured the surface is very rough, solid and hard to grind. Therefore, the resin is very rigid and strong.
Flox are shorter and make a nice pastry solution that easily fills larger gaps. Other than the fibers it also forms a smooth surface if left alone for a few minutes. It is easily grindable with a rougher grit. I liked 40 to start with, but 60 or later on even 100 would certainly work as well, always depending on how big the area to form is.
Micro balloons are by far the softest and most easily formable solution. The balloons are so powdery that one needs to take good care protecting one’s lungs. As soon as I dip into my bag there forms a cloud of micro balloons in the air around it. Since the cured resin is so soft, I think there is always one or more covering layers of something harder, e.g. plain resin, needed.
In the following photo streak I will try to explain the formation of my fiber glass frame, hoping that it might help one or the other.
I thought I thoroughly taped off all surfaces before starting to work. In the end the paper covers on the side were OK, but there were two places where the resin sipped through the paper and stuck to the aluminum. Luckily, it was still blank and therefore the resin / paper mix could be broken apart with my fingernails without damaging anything on the pane.
Before I used an old candle to wax those areas that should not connect to the resin. Since that worked only mediocre I ordered a pot of wax and applied it very generously. This worked so good that when I removed the canopy in the end I had to do an extra grind run on the bottom to remove the wax in order to glue the rubber seals to the created gap (the one with the C-00003). The white on the canopy arms is white dyed resin after my first attempt to apply the first layer with the cling wrap, which didn’t work out for me. The first cling wrap was so thin that I was unable to apply the first layer straight. Thereafter, I tried a thicker wrap, but that one was so thick that I couldn’t move the layer after applied. Finally, I followed my technical advisor’s hint to just stipulate the first layer with a brush in place.
Using the brush cut to 5/8” lengths with nitrile gloves worked really fine. I used the brush to pull the layers straight which led to the fibers on the borders being pulled out a little. In the end that was no issue at all, since those parts are being trimmed off any way. My initial fear was that the fibers shifted prior to application and the cut outs would fit anymore. This turned out to be an absolute non-issue. More of an issue was the application of the first layer with little ‘sag’. Using a brush leads to quite some sag. Stability wise it certainly connects now more snug to the metal arms, but I also had to do a lot more filling. Because of the, in the end more than little, sag I decided to fill with 6oz. fiber glas strips from a roll quickly cut and applied together while doing the connecting part on top, of course, after grinding the sagged area with 60 grit sand paper and de-dusting it. As for de-dusting I always did both, wipe the area clean with a designated brush and then blew clear the part including the whole surrounding area.
While the KAI are very precise in form and location of the 13 layers, they also allow for modification as fit. Cutting the fiber glass strips from the 9oz. cloth was very challenging in terms of getting the rim neat and straight. My technical advisor recommended to use prefabricated strips of same or slightly lower weight. I used 6 oz. strips and added therefore at least four more layers. This allowed to create a very stable zipper like layer mix that nicely formed the required 2 in. radius. The first layers were wider layers that I still cut from the original 9 oz. cloth, as well as the top cover sheets. The dashes on the side indicate the growth of the fabric length with the increasing layers. In the end the KAI only ask for the first two inches, so that we started extending the layer layers way further down in order to start filling the gap towards the final form.
On the picture above one can see additional triangles I cut out to fill the aft dents not only with flex but to also use the space to add some additional fiber strength. The reflecting part left of that is some epoxy flox mixture (see description at the beginning of this post).
For my grinding block I bought a 4 in./10 cm plexiglass tube and cut out a 1 3/4” / 4 cm wide part and taped it with Mylar tape to a wood block. This way I had a grinding block that exactly followed the 2” radius requested by the KAI and made all shaping, grinding, forming and, well even pushing to the finishing cloth, a real no-brainer.
Just a word on finishing cloth: In the beginning I always used finishing cloth. It was a great help in terms of sucking up any excess resin from the fiber glass layers. Do not push the cloth down with you fingers, at least I always created dents that I had to fill later on. What worked good for me was, using my grinding block to carefully push the finishing cloth in form. I say carefully, because whilst beauting up one location you can easily add additional wrinkles in another place.
This is how the form looks like after removing the finishing cloth and before grinding. While those steps still look pretty bad, they were easily ground down with 60 grit sand paper.
This is about the stage at which I started to move up the grit from 60/100 to 100/150. You can still see a lot of spots that need filling, but there were no areas left. Honestly, I was driven by three factors: First, I wanted to prevent grinding into areas that looked fine already. Second, I was stuck so long on the work of the first pet of the paragraph in the KI that it felt about time to move on. Third, I was running out of 60 grit sand paper and tried not having to re-order another batch. Anyhow, in the end I think it was the exact right spot.
Before applying the last coats of resin, there were some places to fix. Maybe I ground a little too deep, but the KAI asked to grind until one sees the metal. So I mixed some more flox mix, but this time a little bit more liquid to fill the gap. Used a brush to apply it and stayed close by for another 20 minutes to wipe off any droplets with the brush. Ended up a lot easier than expected.
After fixing all the dents, holes, gaps etc. I reapplied the yellow electrical tape around the area of the canopy glass and the bottom and generously brushed the form in with resin only coating. Removed the electrical tape to receive a clear border and ground the whole part with 100 then 150 grit sand paper. Repeated the whole process three more times, but added white dye to the two top covers. Very happy with the form and hoping the the excess area is really larger enough for a nice cutoff in the next step.
Trimming the form with a Dremel with a diamond blade cutting disc worked great although that much precision hadn’t really been necessary as long as I left enough fiber to grind. The real form I created with my grinding block. The 2” radius tool worked great in the curvature. Started with 60 grit and worked myself down to a 220 grit to get a nice smooth trim.
I am really happy with the result so far. A little word on why I used white color and not grey like most home builders: I do not worry about reflections because my RV-12is will be equipped with a glare protector right under the fiber glass part. As for coloring my plane I plan to use a white base color with some dark blue accents. Therefore, I considered that white resin is appropriate for my specific purpose/case.
There was still some foam visible and the KAI ask to cover it with resin to increase the longevity. I decided to use fiber resin mixture as I was planning to also use it along the inside top of the metal arms to further strengthen them and really bond the metal and fiber glass forms together.
On this picture one can see how rough the fiber epoxy mix comes out. The picture bone has been taken before grinding. Although not part of the KAI, the RV-12s of my flight school both have an additional layer of fiber glass on the inside of the metal arms. I am considering doing the same, after returning from my Easter holiday.