StarDotStar

I'm planning to build a couple of light weight balsa & ply nitro pattern planes this year and I was wondering/hoping if some experienced F3A builders/builders out there would chime in on this topic and offer some advice on which adhesives are best for a strong bond while at the same time keep the weight down for the various and differing parts of assembling a high quality nitro powered pattern model. Any suggestions would be greatly appreciated.

speedracerntrixie

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I'm going to use an example of what I want on hand to build a wood Dirty Birdy.


Thin and medium CA
Titebond or equivalent
Epoxy laminating resin
Cabosil
Milled fiber
Micro balloons


Most of the build would be done with the Titebond dispensed from a glue syringe. The weight savings would come from not using too much. The CA usage would be minimal. Epoxy laminating resin is great for fuselage doublers without inducing warpage. It will also be used to glass the wing center section and fuel proof the engine/fuel tank compartments. Taking the laminating resin and adding milled fiber and cabosil to form a paste adhesive is many times stronger then using straight 30 minute epoxy. In fact I haven't had " minute epoxy " in my shop in over 20 years. Laminating resin mixed with micro balloons with just enough cabosil to prevent sagging makes great wing fillets. Of course if you intend to paint, glassing the fuselage with 3/4oz cloth will be done with thinned laminating resin.

carlgrover

what he said.

carl

StarDotStar

Thanks for your feedback!

Which type of Titebond are you referring, there seems to be a few types? titebond(dot)com(dot)au

I'm curious what the milled fiber does to the consistency of the laminating resin, does it go clumpy?

Thanks

speedracerntrixie

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I have been using Titebond 2 but a buddy has been raving about Titebond 3 so I bought a bottle yesterday. Not sure when I will get a chance to use it. I need to lay up a cowl and set of wheel pants this week. I will take some pictures of my paste mix so you can see what to expect.

ini

The original Titebond is fine for wood contruction, esp. balsa. Relatively easy to sand.
II and III are water resistant. That does not bring any value in model airplane building.

speedracerntrixie

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On the subject of mixing fillers to laminating resin to replace " minute epoxy " here are a few pictures. The first are a couple of my primary fillers, milled fiber and cabosil. These two are mixed 50/50 into the resin to the consistency of tooth paste. Great for high strength bonds/filling. For a mix that doesn't require maximum strength but easier sanding is desired mix 50/50 with cabosil and micro balloons.


Milled fiber on the left, cabosil on the right.

speedracerntrixie

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Two mixes, the one on the left has the milled fiber and cabosil added. To the right mixed resin with no fillers. Notice the bubbles, I mix very thoroughly, a good mix is just as important as proper ratios.

The paste usually goes into a paper cone for dispensing.

A joint filled with the paste mixture.

StarDotStar

Thanks so much for sharing your input guys.

RESIN MIXTURE:

Is there any advantage to adding both the milled fiber & the Cabosil in preference to adding just one or the other? is there any good reason to use both the milled fiber and the Cabosil?

I hear that while adding strength to the resin mixture, I hear that Cabosil is quite heavy. So I gather it should be used sparingly where keeping weight to a minimum is important?

Referring to you pictures (Thank you for adding those!) I see the resin mixture turns white when the Cabosil and fibers are added, does the mixture dry/cure clear?

TITEBOND:

I read that Titebond lll provides a longer working time, is an interior/exterior glue, is water proof and is also FDA approved so you could always eat your lunch off your plane if you don't have a plate handy .

speedracerntrixie

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Adding both milled fiber and cabosil: The cabosil keeps the mixture from sagging, without it if placed on a vertical surface it would most likely run. Of the three fillers I use, milled fiber is the heaviest, then cabosil and then Micro balloons. The strength profile is in the same order. The filler choice is dependent on the strength required. Most times it is cabosil and milled fiber just like this picture of a landing gear plate being bonded into a fiberglass fuselage. As far as weight is concerned, using the method gives me a slight weight reduction due to being able to use less adhesive then if I were to use straight 1:1 " minute epoxy ".

dhal22

Agree on plane 'ole Titebond. No need for waterproof Titebond. I like Hysol in epoxy areas. Either get excellent control and reach by using the mixing tube or a quick squirt into a mixing cup.

StarDotStar

Thanks so much for your advice guys, it's a big help indeed!

Hopefully this information will help other modelers out there as well.

Just one thing on the bubbly resin (after vigorously mixing)... The way to remove the bubbles is to pour the resin mix into another cup, but from a height so there is only a very fine stream of resin, I find this greatly helps removing the air bubbles which of course are the enemy for bonding, but then again would be your friend for fillets.

speedracerntrixie

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Hitting the resin with a little heat from a heat gun would do the same thing. That said, removing the bubbles is not nessesary. When mixing in fillers you will mix in a certain amount of air as well, that's why adding fillers will actually accelerate the crosslink ( cure ) of the epoxy.

misterv47

I have tried them all and my favorite wood glue for pattern plane building -by far - is Elmer's Glue-All.

That said, I also use one helluva lot of epoxy. I use Elmers any time I can to save weight, then epoxy for the things that have to be extra strong.

For building I use West Systems GFlex 205 epoxy. This stuff is the best thing ever.. except..

One thing I do that is unusual is to avoid plastic film coverings entirely, in favor of 3/4 oz. fiberglass cloth and epoxy paint. To apply glass cloth I have found an epoxy that has to be tried to be believed. Instead of using resin, use epoxy. And not just any epoxy, it is only available from Wings West RC. Get it. Use it. There is nothing else out there like it. It is THIN, so it goes on the cloth easily and blots easily. By which I mean that when I apply the WW epoxy to the fiberglass cloth, after everything is wetted and in place, I use paper towels to blot off as much of the excess epoxy as I possibly can.

Really, there is nothing else like a fiberglass/epoxy finish on a wood pattern plane. It's the best of all worlds, because it is stronger, lighter, better looking, and longer lasting. YES. It is far more work, but the results are so much better that I just don't care.

kdunlap757

I have a build thread on the "other" website in the classic pattern flying section where I show how I built a .60 size nitro Nutcracker pattern model that weighs only 4 lb 3 oz primed and ready for painting. I experimented with a lot of new techniques but here are some takeaways that led to weight reduction

1) used vacuum bagging for wing and tail cores
2) Used carbon fiber veil between the wing sheeting and the core to add to the bonding strength/quality
3) Sheet the wings using west systems epoxy thinned 30-40%
4) Skin wings with 3/4 oz fiberglass thinned 30% then cover immediately with sig micro balloons. (Cuts down on the need for filling and additional layers of epoxy)
5) Used aerofill as a light weight filler. This is magic.
6) Agree with the glue recommendations in this thread.

Your biggest danger areas in adding needless weight are gluing the sheet cores and fiberglassing the wing/stabs. Don't be averse to thinning the epoxy. My biggest recommendation is to spread epoxy using a west systems foam roller. You cut these to a smaller size and can get 2 per roller. Roll until there is a slight sheen. If the epoxy looks flat or dull add a bit more. Remember you thinned and have room for a dab or two more. The thread referenced above explains all of this.

Good luck
-Ken

Pylonracr

The best method of degassing mixed resin is to put the mixing cup into a vacuum chamber and slowly pull vacuum until the bubbles are gone.

Scott