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Old Dec 02, 2014, 02:38 AM
Scratch-builder
viper1990's Avatar
Singapore
Joined Oct 2007
81 Posts
Quote:
Originally Posted by KFC View Post
I don't look at it as wood vs. foam. I use the advantages of both materials to get the best of both worlds. Foam is great for the skin panels because it is lightweight, cheap, easy to shape, and assembles very quickly. Wood is perfect for the internal structural parts because it is strong and supports the foam. When they are working together is when the results are truly inspiring.
I have built many planes for quite some time now, with different types of foam (blue foam,EPS, depron and Pinkfoam) +wood (balsa and plywood) combination. Having reasonable prior experience knowing which material to use for certain parts of the plane can really save lots of weight without compromising structure integrity!

I couldn't agree more with your explanation.

Last but not least, after browsing through many pages in your thread, really inspires me and other modellers alike to do something that awesome in the future.
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Old Dec 02, 2014, 02:38 PM
KFC
Blue Foam Master!!!
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United States, KY, Hanson
Joined May 2007
2,648 Posts
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Originally Posted by Eddie P View Post
I really like the way you have significant material making structure or hard points where you need them and light material where you don't need the strength. think this is the true definition of "composite Structure". "Many Materials". It's a great use of the right material for the right job vs. a "foam" or "wood" build.

Also I know the build is a while ago but can you tell again what resin / coating you used to lay down the paper... did you add many "fill coats" and what sort of sanding technique did you use? Wet sand / What sort of grit? I'm curious. After my DC-8 build I'm doing right now I'd like to build another airliner I've wanted to build for a while and I will likely go in a similar route using built up wood and foam sheet composite with a glass or paper finish.

On my current DC-8 build I have decided to leave the wood overlay off the foam fuse and I'm covering the foam with either glass over the prepared surface or a composite tissue and glass over that.

Anyhow was just thinking back to your build and wondering about the specific of the covering technique you used and when your thoughts were looking back on it.
my first thought would be "never again". As with anything else in life, the results of any endeavor are directly proportional to the time and effort put into it. The paper/polycrylic covering produced what amounts to a "3 foot airplane". It looks great from beyond 3 feet away, but when you get closer, the flaws become readily apparent. Also, the covering provides almost no resistance to hangar rash. I made the choice to cover it this way because I wanted something cheap, easy, and fast (and the fact that I HATE working with fiberglass, lol). Even with all these advantages, I still made some mistakes in the process.

After filling and sanding the cracks and seams in the fuselage, I applied a light coat of polycrylic to the fuselage and then lightly dry sanded the whole thing with 220 grit paper.

I started the covering by cutting newspaper into panels approximately 8"x 12". I used a disposable foam brush to apply polycrylic to each panel just before I applied it to the fuselage and repeated this process until the entire fuselage was covered.

After the paper covering dried, I dry sanded the overlap between the panels with 120 grit paper. And this is where I made my first big mistake. I had assumed that the polycrylic would have wetted the paper in a manner similar to epoxy/fiberlass covering. Unfortunately, this was not the case, and the paper acquired a lot of 'fuzz' in the wake of the sanding. I failed to notice this until I started painting and everything went to hell. If you look through the pictures toward the end of the build, you will see the results for yourself. What I should have done was to apply another coat of polycrylic after sanding the paper and then sanding again with 220 grit paper. This would have provided a nice smooth surface to paint.

With all that being said, the A340 will be covered with lightweight glass cloth and epoxy resin. I still hate the thought of working with fiberglass, but I have done a little research and experimenting to help make the process less cumbersome. Having made a couple of test pieces and subjected them some pretty rigorous testing, I am very happy with the ability of the fiberglass covering to not only resist handling damage, but also the strength it adds to the structure without a massive weight penalty.
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Old Dec 02, 2014, 03:33 PM
Official Boat Bum
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United States, NV, Reno
Joined Mar 2000
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Hey thanks for the feed back. I can totally appreciate what you say. The first time I did a "tissue" covering job with a glass composite layer butting up to it (for the nose section as glass lays way better over compound curves). I had the same thing happen, re: fuzzing. I re wet the fuzzy paper and then went over it with wet sandpaper, 400 grit to clean it up before priming and wet sanding again with 400.

I predict, based on your talent, experience and attention to detail, that your fiberglass skills will come up to speed very quickly and probably surpass 90 percent of the modeling community.

My first "glass job" was building my own surfboards when I was a 14 and I had no internet or friends or family to show me, just a book. It turned out OK, and sanded super smooth and seemed too good to be true even if it was a little (or a lot) heavy. My second "glass job" was using .6 ounce cloth on my first scratch built airliner made of sanded extruded foam in 1996. I used Dan Parson's 0.6 ounce cloth and his favorite "Envirotex Lite" resin. Dan passed away many years ago but was a prolific builder back in the 90's as a retired guy who built and flew every day. Glassing with .6 ounce cloth is so dang easy.

Glassing with .7 is just as easy and actually better than .6oz clth as the weave is not so open and not much if any extra weight in the cloth yet "filling the weave" is easier as there is more glass material that wets out flat and allows a smooth filling process later with resin or primer (a personal choice).

Some guys glass with water based polyurethane or epoxy resin. I prefer thin viscosity laminating epoxy resin these days though I've tried most of the other resins and ways to do it. I use primer or red devil body putty to fill a lot of the weave and then primer again and when you are ready to paint it's mostly sanded off (primer and putty). Some guys just fill the weave with extra resin or resin mixed with other things. A good glass job done with care with a light coat of paint weighs about the same as a Monokote surface job but is much easier to repair and looks way more like a scale airplane surface.

My wait time between glass projects seems to be 1.5 seasons. I hate sanding so much. And there is so much sanding with a quality glass project. But when you are done it looks and flies so good that the next year the swearing stops and the desire to glass again re occurs.

PS, I think I saw you mention you had air bubbles come up under your finish before. I've had that too. To me it only has happened over a structure of extruded foam (pink or blue) especially in areas of spackel. I was wondering if it's outgassing from the foam, delaminating the glass. It seems to happen over time and in hot environments. I've never had this happen to glass layered over EPS foam though, for some reason. Or over balsa sheeted on top of any foam.
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Old Dec 04, 2014, 01:17 PM
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mike_fish's Avatar
Russian Federation, Mosk. oblast', Grigorchikovo
Joined Jul 2005
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Quote:
Originally Posted by KFC View Post
my first thought would be "never again".
Dear KFC & Eddie P. You making excellent planes!!!!
You must to immortalize that
Making molds and use sandwich technology!!! It'll be masterpiece.
I hope you will listen to my voice. In this process there is nothing difficult.
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Old Dec 04, 2014, 04:38 PM
KFC
Blue Foam Master!!!
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United States, KY, Hanson
Joined May 2007
2,648 Posts
Quote:
Originally Posted by mike_fish View Post
Dear KFC & Eddie P. You making excellent planes!!!!
You must to immortalize that
Making molds and use sandwich technology!!! It'll be masterpiece.
I hope you will listen to my voice. In this process there is nothing difficult.
I think if I ere to go through the mold process, I'd want to do it with a smaller plane. The first time with any new technique is bound to come with some mistakes. As with anything else, there is a learning curve.
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