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Old Jan 30, 2013, 02:55 PM
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Originally Posted by Steve Merrill View Post
I would guess it also depends on what surface you are coating. Balsa needs some filler, foam, does not? Or should I just prime everything the same?

I bought some today. Thanks!

On the stabilizer, which was 1/32" balsa sheeted foam, I just misted a couple coats of spray acrylic on the balsa to harden it up a bit and sanded. A single coat of SS filled the grain and left a good surface. I was going to stop there to save weight.

Foam needs to be filled to prevent the texture of the foam from telegraphing through. Maybe it soaks into the balsa and fills the low spots and so one coat is OK? Foam needs to be filled to get a good result with only 2 or 3 coats.

Make sure you practice on some scrap first to get used to brushing it. moving the brush SLOWLY helps a lot. I use syringes to measure the A and B to get an accurate mix. I can buy 10 ml syringes without needles at the local farm supply store for about $0.60 each.
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Old Feb 03, 2013, 02:16 PM
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Having remade the roasted tail and fuselage I finally have time to coat them with Styrospray.

To get ready, I made a fixture to hold the fuselage. Bamboo skewers pushed into the nose and tail provide axles for this simple holder. It allows me to rotate the fuselage as I apply the Styrospray. Styrospray is a 2 part polyurethane coating. Stir up the thick,white "B" component to get all the solids resuspended. Then measure out equal parts "A" and "B" (I used syringes) and mix thoroughly. I used an old Gorilla glue bottle as an applicator. Not only does it make it easier to get the right amount Styrospray on the piece but you can cap it up and save any leftovers for the next coat. Mixed Styrospray supposedly has a 3 day pot life if sealed.

Squirt some on the piece and use a foam brush to spread it around. The trick is to apply it just thick enough to self level and move on. Moving the brush slowly allows you to move it around to get uniform coverage. It starts to cure as soon as moisture in the air hits it. I coat about 4" at a time moving around the fuselage. "Tip off" that band to blend it into the previous band and move on. Going back later will just leave brush marks. When the fuselage was coated I put it into my oven to cure. The Styrospray sets up in 30 - 60 minutes and is then ready to recoat. Like epoxy, recoating before its fully cured will allows subsequent coats to chemically bond to the previous coat.
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Old Feb 03, 2013, 03:13 PM
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That is one darn good looking fuselage there. Can Styrospray also be sprayed on the plane as the name seems to define? Is it also a water cleanup?
Thanks
**Neons** Bob
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Old Feb 03, 2013, 03:23 PM
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Originally Posted by **neons** View Post
That is one darn good looking fuselage there. Can Styrospray also be sprayed on the plane as the name seems to define? Is it also a water cleanup?
Thanks
**Neons** Bob
If you go to the Industrial Polymers website they have videos about spraying it. I don't think it would make sense with something this small. The viscosity is similar to epoxy so you would use a hopper gun like they use for textured sheet rock coating. It is definitely not water clean up: water makes it cure!
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Old Feb 03, 2013, 03:56 PM
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Hi Pay ,
Looks great. Is that a foam brush I see in the first pic?

Phil
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Old Feb 03, 2013, 04:19 PM
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Originally Posted by Smokin' Beaver View Post
Hi Pay ,
Looks great. Is that a foam brush I see in the first pic?

Phil
Yes, and its densest one I could find. The job of the brush is to move the coating around not to deliver it to the surface as you would when painting.
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Old Feb 03, 2013, 05:06 PM
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That's really intriguing, Pat. It's as if the underlying foam acts like the glass cloth matrix in fiberglass, giving the SS rigidity and strength, without actually getting impregnated with SS.

I have to say I learn more watching your builds than almost anyone else's. You sure have a way with foam, glass and other non-balsa techniques.

Steve
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Old Feb 03, 2013, 07:58 PM
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That's really intriguing, Pat. It's as if the underlying foam acts like the glass cloth matrix in fiberglass, giving the SS rigidity and strength, without actually getting impregnated with SS.

I have to say I learn more watching your builds than almost anyone else's. You sure have a way with foam, glass and other non-balsa techniques.

Steve
I appreciate that Steve, but the idea for the heat molded foam came from Harpye. I just added the idea of using a solid form instead of Harpye's many 6mm depron cross sections. And that was only because I'm not very good at 3D CAD (and I don't have a laser cutter!)

Likewise, I have to give credit to Fahim at WOWplanes for discovering Styrospray and using it for covering foam airplanes.
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Old Feb 03, 2013, 09:06 PM
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Below are a couple shots of the finished tail section and fuselage. As you can see, I went with fixed rudders. After ruining the first set (scale hinging and all) I didn't feel like going through all that again!

The Styrospray added 16g to the tail bringing the total to 65g. The balsa covered EPS stabilizer got one coat and the rudders two coats. Normally, I would have covered those with 1/2 oz. cloth and WBPU. The Styrospray added about the same weight and is MUCH easier. The grain on the balsa isn't completely filled but you'll never notice it under flat paint.

The fuselage came in at 153g, 36g of which is Styrospray. I gave it three coats from nose to just aft of the wing TE and only two from there back. I've been subjecting the first (over cooked) one I made to all sorts of abuse and its plenty strong with good dent resistance. That one has only two coats.

The SS worked out to 10.6 g/sqft. on the fuselage. The first coat always weighs roughly double what subsequent coats do. The photo actually looks better than the finish is. Though the brush strokes are gone, the SS picks up bits of dust and crud from the air. The SS will need to be sanded before painting. Wet sanding works great and dry sanding with stearate-coated paper works well too.

The weight came in right in the middle of the 10-11 g/sqft. range I typically get with either 3/4 oz glass cloth/epoxy or Kraft paper/WBPU over foam. Kraft paper/WBPU adds stiffness because it shrinks as it dries - nice for wings but not really needed on the fuselage. The Kraft paper/WBPU requires lots of filling and sanding of the overlaps and would have been difficult on the 219's curved nose area. Glass/epoxy could have handled the curves but the overlaps would still need to be sanded and the whole thing filled. Since I hate filling and sanding, I think I'll be using more Styrospray in the future.
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Old Feb 05, 2013, 07:32 AM
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I got the tail section fitted. After marking my reference line I used the stabilizer's hot wire template to mark the cut out and tweeked the opening to make the stabilizer sit at the right angle with some sandpaper. I won't glue it in until after the wing is mounted. Going with the fixed rudders meant I could leave the top part of the fuselage over the stabilizer intact and still slide the stabilizer into place. The original plan was to make the stab removable to access the rudder and stab adjusters.

With the stabilizer fitted I could measure the moment of the fuselage and tail to calculate how close I'll be on my CG. With a 2200mAh battery pushed all the way forward the CG should come out right at 25% MAC. I made the bulkheads fore and aft of the wing thick enough that I could have mounted the wing up to 1/2" aft of the scale position if it looked like I would be very tail heavy. I'm glad I won't have to do that.
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Old Feb 08, 2013, 09:25 PM
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I was curious if mixed SS would still be usable after a day or two. I had about 10 ml. left in the glue bottle so I poured it out after a couple days and spread it around on some scrap foam and it set up as it should. So as long as it is sealed up it seems to last a day or two at least (not that I would intentionally mix more than I was going to immediately use.)

My wife says I'm easily amused and the photo below proves it. After pouring the mixed SS out of my applicator bottle, I set the bottle aside and let the SS still clinging to the walls cure. After a couple days I removed it by teasing it away from the walls of the bottle with a bamboo skewer. It came out basically intact. This demonstrates another characteristic of SS; it stays somewhat flexible and even in thin layers has significant tensile strength. If I would have tried this with fully cured epoxy I'm pretty sure it would have shattered.
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Old Feb 08, 2013, 09:51 PM
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I've not had much luck using foam for vacuform molds so I'll cast the mold from plaster.

To make the mold for vacuforming the canopy I need to make an impression of the fuselage. After wet sanding the canopy area, I covered it with heat shrink window insulation film. This is a thin plastic sold in home centers for insulating windows from the inside (the stuff for window exteriors doesn't work as well.) The film is there to act as a release layer for the fiberglass. I taped a piece of the film around the area I want to cover as best I could and then shrunk it down with a hair dryer. A band of tape is needed to hold the film down in the concave area just behind the canopy. There were still a few wrinkles and I hit those areas with steam from a tea kettle. Don't apply steam for more than a second or two or you risk deforming the foam underneath.

Now that my release layer is in place I'll cover it fiberglass and eventually use this female mold to cast a plaster plug to vacuform.
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Old Feb 09, 2013, 03:23 PM
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Couldn't you also just layer that area with fiberglass and epoxy and use that as your canopy? You could cut out windows and glue in clear acetate? I'm interested to see what you do next. This has been an informative thrad
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Old Feb 09, 2013, 04:38 PM
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Originally Posted by Steve Merrill View Post
Couldn't you also just layer that area with fiberglass and epoxy and use that as your canopy? You could cut out windows and glue in clear acetate? I'm interested to see what you do next. This has been an informative thread
I'm glad you've found it interesting.

I think the canopy is too curved to do it with flat sheet acetate, at least the front part. Also, since the canopy forms the battery hatch, the vacuformed canopy with a stiff floor glued in will make a strong, durable hatch.
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Old Feb 10, 2013, 04:24 PM
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With the release layer shrunk over the fuselage I'm ready to apply the fiberglass.

First, I laid down a one piece layer of 2 oz. cloth followed by 3-4 layers of 6 oz. cloth in smaller pieces. When that was cured I marked my reference line and the canopy location on the fiberglass. Then I popped the glass off the fuselage and trimmed off the excess cloth. The shrink film leaves a really nice smooth surface on the inside of the glass.

The fiberglass is too thin and flexible at this point to use as is so I added a foam frame around it to support the fiberglass when the plaster is poured. I taped the fiberglass back into place on the fuselage. Then I used the fuselage templates, adding an extra 1/4" around the outside, to make the main frames from FFF. After those were glued to the fiberglass I filled in with smaller pieces of FFF to stiffen everything up. I clamped a couple rulers to the main frames and made a cut with the hot wire to get a nice flat, stable base.

Finally, I removed the mold from the fuselage and added the dam at the back. I made an insert of scrap foam that will be suspended in the mold to reduce the amount of plaster required and give a more uniform thickness to the walls of the plug. The walls of the plug are about 3/4" thick. On a mold this small it probably wasn't necessary but on large molds that are very thick in one section and thin in others, you can get cracks when the thick portions get much hotter than the thin sections as the plaster cures.

The last photo shows the finished plug. I'll let that dry a few days and pull my canopy.
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