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Old Dec 19, 2011, 05:23 PM
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Coat the inside of the plane with thinned epoxy?

I'm working on a Pulse 125 XT ARF which will be powered by a DLE 20. It's been suggested to me by an experienced builder at our club that every accessible wood surface inside the plane should be coated with thinned epoxy to strengthen the structure against the extra vibration that a gas engine will introduce. So, I have either one or four questions:

1. Do you agree?

If yes,

2. What type of epoxy would you use?
3. What would you use to dilute the epoxy?
4. What ratio of epoxy to diluting agent would you use?


Cheers!

John.
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Old Dec 19, 2011, 05:41 PM
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did he say to to do anything for the servos from the extra vibration. I didn't realize gas engines introduced additional vibration. Since I fly glow I only coat fore and aft of the firewall (tank area) with epoxy... full strength. Brush it on lightly then hit with a covering gun which turns it more liquid and it penetrates everywhere and kicks off quickly.
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Old Dec 19, 2011, 05:41 PM
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Coating a wood surface in glue isn't going to do diddly. Epoxy only increases strength when it's used to soak into fibers such as with fiberglass. On it's own it's heavy and brittle and adds very little strength. So all that you would accomplish is to make your model heavier. The wood fibers of the various materials used in the model are already held togehter by their own natural "glue" just fine.

If the model design requires extra structure to deal with the engine's vibration then it should be done properly by adding either more smartly applied wood or by using the epoxy to actually bond in some additional layers of fiberglass cloth over the existing wood. This coating of cloth would act much like additional plywood doublers and tie in the wood on either side of the usual joints.

But it WILL add considerable weight in doing this. If the model does not have a bad reputation when used with this engine then you may just be adding weight that it doesn't need.

And finally there's the issue of how to thin an epoxy without losing strength in the glue. While it is possible to thin epoxy with denatured methyl alchohal this does reduce the final strength of the glue. The more alchohal you use the less strong the epoxy is after curing. So there's a double whammy to the idea of coating the wood. Now you've thinned the epoxy to spread it around but you weakened it to allow you to spread it.
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Old Dec 19, 2011, 07:37 PM
Out of Time
United States, TX
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Quote:
Originally Posted by grosbeak View Post
I'm working on a Pulse 125 XT ARF which will be powered by a DLE 20. It's been suggested to me by an experienced builder at our club that every accessible wood surface inside the plane should be coated with thinned epoxy to strengthen the structure against the extra vibration that a gas engine will introduce. So, I have either one or four questions:

1. Do you agree?

Cheers!

John.
Nope. Don't agree one bit.
You're just adding unnecessary weight, and a LOT of it at that.

You're better off filleting joints, and adding some extra stringers around the engine area.
Additionally, you might want to reinforce the gear mount by using good ply to better handle the weight of the gas engine.
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Old Dec 19, 2011, 09:50 PM
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I fully agree with all posters above. But epoxy is good to protect the wood from oil in spilled fuel. A coating is needed only around engine and fuel tank. Yes, it is heavy but at least your fuselage doesn't rot in a couple of months. Of course you will need fuel-proof paint or clearcoat for the outside of the fuselage in any case, so might use that on the inside as well.
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Old Dec 19, 2011, 11:44 PM
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Nope that's one big load of horsesh*t.

Bruce, (as always) is on the money. listen to him.

I would only add thinned epoxy to areas of raw wood around the engine mounts and firewall, to stop fuel soak.
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Old Dec 20, 2011, 04:51 AM
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If anything breaks from vibration its going to be a joint. I see the odd post where someone complains about an ARF unassembling itself at a joint, most often the firewall, sometimes the landing gear attachment point.

Epoxy and fibreglass strips to reinforce a joint can be useful, if you can get access to it from the inside.
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Old Dec 20, 2011, 05:18 AM
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Disagree, unless building an airplane that will also be flown from water; but still do not agree about using epoxy, as it is heavy! For this, I would use Balsarite.

The glue in the joints is all that is needed for the strength of the structure.
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Old Dec 20, 2011, 09:08 AM
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Properly applied, epoxy adds very little weight. Just use a good epoxy paint such as Klass Kote for easy application, low weight and very high durability.
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Old Dec 20, 2011, 11:38 AM
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Quote:
Originally Posted by Rodney View Post
Properly applied, epoxy adds very little weight. Just use a good epoxy paint such as Klass Kote for easy application, low weight and very high durability.
As a coating for sealing the wood against oil soaking I agree. But the point of the OP was to coat the wood to add STRENGTH. For that it's useless.

The DLE is a gasoline and oil engine. The beauty of these big gassers is that it takes little to fuel proof the firewall and other structure. An oil based polyurethane varnish, such as Flecto Varathane, does a wonderful job and is easier to apply than trying to thin down epoxy. And it's both cheaper and not as heavy as epoxy. While you're at it be sure to varnish over any exposed wood on the wing saddle or slide on facings of the fuselage and wings. Engine oil can be carried back and soak in through this joint.

If the design of this ARF allows you to get into the nose area and assuming this big DLE is at the larger end of the engines used in it getting into the nose and reinforcing the joints with fiberglass tape and epoxy would not be a bad thing at all. But in this case you'll use pure non thinned actual laminating epoxy. You can get this proper laminating epoxy from a place that sells boat repair supplies or a fiberglass products supplier. West is one noted name but it doesn't need to be their resin. For this use any of the laminating epoxys will work just fine.
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Old Dec 20, 2011, 02:50 PM
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I didn't have any "denatured" alcohol on me recently when I was building my first built up balsa r/c, but I tried diluting epoxy with plain old iso rubbing alcohol and it seemed to work. Made the epoxy into a kind of slurry that went farther and was less sticky. I just used it on the inside of the fuel tank compartment and it dried normally and is just a thin shiny coating inside.
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Old Dec 21, 2011, 02:37 AM
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perhaps polyurethane would work for coating parts that will get oiled soaked or to strengthen the mocelor maybe shelach ?
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Old Dec 21, 2011, 08:02 PM
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Mocelor?
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Old Dec 22, 2011, 12:20 PM
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Quote:
Originally Posted by seeingeyegod View Post
I tried diluting epoxy with plain old iso rubbing alcohol and it seemed to work. Made the epoxy into a kind of slurry that went farther and was less sticky.
Before I learned about denatured alcohol (pre-internet days) I tried rubbing alcohol, all it did was make a mess. The epoxy never cured properly. I believe they cut the stuff with water as you can get various percentages of the stuff. Most is around 60-70% I believe. I get the 90% stuff for bending balsa.
Never had a problem since I started using denatured.

From what I remember reading the 2 are very similar or almost the same, (one is derived from the other?) but I sure can smell the difference, and notice when used as a cleaning agent, and mixing with epoxy.
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Old Dec 22, 2011, 03:45 PM
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Originally Posted by rcav8r2 View Post
From what I remember reading the 2 are very similar or almost the same, (one is derived from the other?) but I sure can smell the difference, and notice when used as a cleaning agent, and mixing with epoxy.
This topic has come up a few times recently....

Denatured alcohol (also called methalated spirits or 'meths' for short) contains ethanol and a chemical, and sometimes also a colouring, to deter people from drinking it. The ethanol content is why is can be used as a solvent.

Isopropyl Alcohol (IPA) is a different substance and is great for cleaning and de-greasing. I always keep a can for de-greasing plastics or metal that I am going to epoxy or solder. It also gets sticky label marks of off items.

Rubbing alcohol is an often incorrectly used term for a mixture that is used for massaging and muscle treatment. It contains IPA and a blend of oils and fragrances which would make your model smell nice, but also become a little slimey. IPA is often incorrectly called rubbing alcohol (probably because rubbing alcohol contains IPA among its ingredients).
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