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Coat the inside of the plane with thinned epoxy?

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Old 12-19-2011, 03:24 PM
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grosbeak
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Default 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 12-19-2011, 03:49 PM
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Default RE: Coat the inside of the plane with thinned epoxy?

Quote:
ORIGINAL: grosbeak

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?
Not entirely. The use of an epoxy or urethane sealer in areas around the fuel tank and Engine are a good idea. Applying epoxy to a surface elsewhere can in fact be more detrimental than beneficial. Depending on the product used, the epoxy can make the surface brittle and cause cracking or warpage of the surface layer due to shrinkage whilst curing. In the case of lite ply etc as is used in many of our planes, this can be a problem.


Quote:
2. What type of epoxy would you use?
Go to the local fibreglass materials supplier and get soem laminating epoxy or some saturation epoxy if you wish to do it properly. This is better than "adhesive" epoxy which contins thixotropes to "thicken it.
If you are just using it for fuel proofing, go to a good paint supplier and get some urethane sealer. It is much easier to use.


Quote:
3. What would you use to dilute the epoxy?
If using proper laminating epoxy, there is rarely a need to thin it at all but if you do wish to to ensure good penetration, add Laquer thinner or acrylic paint thinner to the epoxy after you have mixed the epoxy.


Quote:
4. What ratio of epoxy to diluting agent would you use?
Usually between 10% - 15%. It is not really critical.


I am not familiar with the Pulse airframe but on many others, I have been known to add some tristock or some woven glass cloth in higher stressed areas. Make sure the firewall is pinned securely.
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Old 12-19-2011, 03:53 PM
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Default RE: Coat the inside of the plane with thinned epoxy?

John, thinned epoxy is not going to add any strength. What you may want to do is hit any of the glue joints you can get to with thin CA. You will want to seal the area around the carb to keep it from getting gas soaked but that engine runs fairly dry.
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Old 12-20-2011, 06:45 AM
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Default RE: Coat the inside of the plane with thinned epoxy?

I have found that the best way to do the inside of any model, gas or glow, is a good epoxy paint. If you use a light color, it also helps for visibility issues when installing equipment later. When HobbyPoxy was available, that is what I used but it is no longer regularly available if at all. Klass Kote is a very good alternate brand but rather costly (but worth it). There are probably other brands to but I have not tried them.
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Old 12-20-2011, 06:51 AM
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Default RE: Coat the inside of the plane with thinned epoxy?

1. Nope
2. Standard hobby epoxy. I use 30 minute in my building. I have no use for 5 min or so, that gets used for fuel proofing only. When thats out, then I use my 30 minute.
3. Denatured alcohol from the hardware store.
4. Enough to make it a little runny. I dont do this for strength, just fuel proofing. I fuel proof the tank compartment, then drill a drain hole incase the tank splits or stopper leaks.
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Old 12-20-2011, 08:04 AM
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Default RE: Coat the inside of the plane with thinned epoxy?

Hi!
1. Of course not!! Epoxy doesn't do any good on the inner surface of the fuselage.
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Old 12-20-2011, 10:19 AM
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Default RE: Coat the inside of the plane with thinned epoxy?

While somewhat beside the point, I do believe that epoxy inside the plane (especially on ARF's) can be beneficial as it will seep into any poor joint and reinforce them, especially if you use a slow epoxy and then immediately warm the area very well with a heat gun. The heated epoxy will become quite thin and capillary into any small gaps or crevices and definitely strengthen the area. The heat will also accelerate the cure time. The heat also works well with epoxy paint if you want to speed up the cure time. I also recommend the weep hole at the lowest point in the fuel compartment to drain any accidental fuel spills. Just make sure there is a clear path to it (not blocked by sponge rubber padding or such).
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Old 12-20-2011, 11:22 AM
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Clay Walters
 
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Default RE: Coat the inside of the plane with thinned epoxy?

Recommend sealing the firewall and tank compartment top to bottom with finishing resin. And if vulnerable I also coat along the wing saddle.

http://www3.towerhobbies.com/cgi-bin...?&I=LXK304&P=7
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