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Jul 26, 2020, 04:37 PM
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Quote:
Originally Posted by tspeer
For the 250g limit, I'd use tissue paper instead of masking paper or newsprint. The same basic techniques apply.

I used medical exam table paper for my latest build. I found what worked best was to wet the foam and apply the paper dry, then squeegee the paper down to saturate it and remove excess glue. If I pre-wet the paper or worked it too much it tended to come apart. I was using thinned Varathane WBPU for this build because I didn't want the yellow color of Titebond II.

The tissue made a harder surface than the bare foam, but not as hard as masking paper would be. It sanded well and was a good surface for painting. I used thinned artist acrylic paint for color in order to save weight. The color worked out well, but it didn't cover places where the carbon spar caps were exposed. You can still see the carbon strips. I finished with two clear coats of thinned WBPU.

I'm going with this approach again in the future. The only thing I might do differently would be to use a white primer to get a uniform base before adding the color coats - if I think the plane can stand the weight.

My first try was ok. used a square piece of 3/4inch EPS insulation foam.
Weight before --- 11g.
Weight after covering one side with masking paper and wood glue 50/50--- 14grams.

It somewhat improves stiffness and prevents foam from cracking when you bend it a lot.

I also realized that if you don't need to cover conplex bends then I don't think you need to wet the paper. Also warping is probably a result of wetting and stretching the paper too much. I skipped that step and I didn't observe any warping.
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Jul 26, 2020, 04:40 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by RedLabel
My first try was ok. used a square piece of 3/4inch EPS insulation foam.
Weight before --- 11g.
Weight after covering one side with masking paper and wood glue 50/50--- 14grams.
......................................
What area was that test piece?
Jul 26, 2020, 04:46 PM
Entropy is happening!
Jim.Thompson's Avatar

Half thought through experiment.


I have an experiment in mind to make a kind of thick Depron substitute. I have some salvaged scrap low density foam sheet of about 10 mm thickness.
I'm thinking of gluing newsprint to both sides of it with PVA in the manner described in this thread, to make up a sandwiched foamboard of sorts.

If at all successful, the laminate (for want of a better word) sheet could be then used in a similar way to what Depron is commonly used.

Anyone have thoughts on this?

Jim.
Jul 26, 2020, 04:47 PM
Registered User
Quote:
Originally Posted by Jim.Thompson
What area was that test piece?
Around 50 sq inches or 320 cm^2.
Jul 26, 2020, 04:52 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by RedLabel
Around 50 sq inches or 320 cm^2.
Thanks. That is nice and light then!................
Jul 26, 2020, 05:13 PM
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tspeer's Avatar
Quote:
Originally Posted by Jim.Thompson
I have an experiment in mind to make a kind of thick Depron substitute. I have some salvaged scrap low density foam sheet of about 10 mm thickness.
I'm thinking of gluing newsprint to both sides of it with PVA in the manner described in this thread, to make up a sandwiched foamboard of sorts.

If at all successful, the laminate (for want of a better word) sheet could be then used in a similar way to what Depron is commonly used.

Anyone have thoughts on this?

Jim.
I've been thinking of a similar concept that I'm calling artificial balsa. Instead of 10 mm thickness, I want to slice a good quality foam like MPF into 2 mm sheets. Then apply tissue or 3/4 oz glass to both sides using Titebond II or WBPU. The idea is to create something akin to 1/16" balsa that can be cut with a Cricut Maker. It would be used to cut ribs for stick-and-tissue construction, or for light weight wing skins.

Instead of covering both sides, the sheet of foam could be covered just on one side and pressed by a platen so it dries flat. Then it could be used as a wing skin with the skinned side to the inside. Once applied to the wing, the bare foam can be sanded and filled, then covered to complete the sandwich.

One big question is, "What thickness of foam has the same weight as the skins?" That would determine the tradeoff between a thick foam skin and a thinner sandwich skin. If the sandwich is stronger or stiffer than the foam alone for the same weight then it would be a worthwhile approach.
Jul 26, 2020, 05:26 PM
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tspeer's Avatar
Quote:
Originally Posted by RedLabel
My first try was ok. used a square piece of 3/4inch EPS insulation foam.
Weight before --- 11g.
Weight after covering one side with masking paper and wood glue 50/50--- 14grams.

It somewhat improves stiffness and prevents foam from cracking when you bend it a lot. ...
3 g per side is equivalent to 0.4 inches of your foam. So if you sliced the foam sheet in half and skinned both sides of the resulting sheets, you'd end up with each sheet being very close in weight to the original 3/4 inch sheet. EPS isn't very stiff or strong, so I think the resulting sheets would be stiffer and stronger.

If you sliced it into three 1/4 inch sheets and skinned them, the result would be lighter than the 3/4 inch original sheet. That would make a nice material for many forms of construction.
Jul 26, 2020, 05:54 PM
Foam is where the heart is
brett.c's Avatar
Quote:
Originally Posted by Jim.Thompson
I have an experiment in mind to make a kind of thick Depron substitute.
Have you seen the green insulation foam at Bunnings?
Very similar to Depron and lighter than the orange stuff (Knauf).
You would just have to hotwire cut it to your desired thickness.

I am going to use it in future builds because once covered it would be about the same weight as the bare foam that I currently use.
Jul 26, 2020, 11:46 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by brett.c
Have you seen the green insulation foam at Bunnings?
Very similar to Depron and lighter than the orange stuff (Knauf).
.....................................
Yes Brett, however, I did not realise it was lighter than the yellow/orange Knauf foam.
Thanks for the tip. I will be buying some for sure.
Jul 29, 2020, 01:28 AM
Registered User
received some Minwax polycrylic satin.

Tried it on a 6x7" piece and it added around 2 grams with the paper and polycrylic.

Given the size I say it is very close to the wood glue.
VS the wood glue
- Polycrylic dries very fast and it is harder to apply to the paper. It was much easier with fg cloth since you apply it over the cloth and doesn't matter if it dries or becomes tacky
-Poly seemed a bit stronger.
-Poly seems to be very close or slightly lighter.

Since wood glue is safe(polycrylic is also much better than urethane still it has a bit of a smell, wood glue doesn't) I think I will stick with it and use polycrylic as a top coat if needed.


On a side note found an adapter laying around, with some nichrome wire and pvc pipes I now have a nice hot wire bow cutter and ready to roll .
Sep 08, 2020, 11:34 PM
Registered User
Has anyone experimented with adding some gelatin powder to the glue/water mixture?
Sep 10, 2020, 08:35 AM
I Look, Listen, and Learn
Timbo383's Avatar
Quote:
Originally Posted by topbrent
Has anyone experimented with adding some gelatin powder to the glue/water mixture?
Well that sounds interesting, and it has some possibilities....Who's up for doing that?


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