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Fuel proofing an LT-40

Old 08-18-2008, 01:08 PM
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madmoe
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Default Fuel proofing an LT-40

Hi! I'm finally getting close to completing the construction of the fuselage in my LT-40 build but have a question. I know I need to fuel proof the fuel tank compartment behind the firewall, but have a few questions:

1) Do I also need to fuel proof the engine mounting area (forward of firewall), or is this protected by the covering material?
2) I had thought to use a fuel proof paint, but when I went to the my LHS, they didn't know what I was talking about. I know I can use thinned epoxy for the same purpose, but as I have never done it before, was a bit uneasy about that (afraid I would thin it too much and end up with a rubbery mess). Anyone have suggestions?

Thanks!
Old 08-18-2008, 01:45 PM
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bigedmustafa
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Default RE: Fuel proofing an LT-40

Don't sweat it! 50% alcohol and 50% 30 minute epoxy will fuel-proof your tank area and engine area nicely.
Old 08-18-2008, 01:47 PM
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Default RE: Fuel proofing an LT-40

Which type of alcohol?
Old 08-18-2008, 02:12 PM
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Default RE: Fuel proofing an LT-40

I have an LT-40 and I just used straight 30 minute epoxy painted on the entire engine compartment, fuel tank compartment, and also the piece of exposed plywood that extends out on top of the fuel compartment. It worked fine! You don't have to reduce it with alcohol at all. I used Tower Hobbies 30 minute epoxy. I just used a stiff little brush - one used normally for applying flux when soldering - and cleaned it off with isopropal alcohol beforehand and also when I was done. One suggestion is to remove the fuel tank cover when doing this or else you'll epoxy that to the top of the fuselage by accident.

If you have any other questions specific to the LT-40 ARF, ask away. I just completed assembly a couple weeks ago and have gotten a lot of tips here on RCU and RC Groups as well as from guys at the club so may be able to help you out some, even though I'm a newbie.
Old 08-18-2008, 03:20 PM
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Default RE: Fuel proofing an LT-40


ORIGINAL: bigedmustafa

Don't sweat it! 50% alcohol and 50% 30 minute epoxy will fuel-proof your tank area and engine area nicely.
50% alcohol??? That's WAY too much. It will never set up. Just a few drops will work best or just heat with a heat gun to thin ot and spread it quickly.
Old 08-18-2008, 03:31 PM
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n19htmare
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Default RE: Fuel proofing an LT-40

Don't think it matters, it'll evaporate anyways.

Denatured or isopropyl(91%+)
Old 08-18-2008, 04:18 PM
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RCKen
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Default RE: Fuel proofing an LT-40

It absolutely does matter. If you mix too much alcohol of either type (regardless of the percentage) it will make a soupy mess that will never set properly and will remain soft and gummy for the life of the model. While it's possible to thin epoxy with alcohol and have no problems, it can also be a mess if you mix too much alcohol in. As I said, it will never setup properly. The problem is that you are not just thinning the epoxy. The alcohol actually changes the chemical structure of the epoxy components, and too much will keep it from setting properly. I've had one time that this happened to me, and it too me hours to scrape all of the epoxy off in order to start again. Since then I have thinned epoxy with heat. Use 30-minute (or higher) epoxy and put a small dab of it on the area you want to fuel-proof. Hit it with your heat gun and it will thin out to the consitency of water. Use a disposable brush to cover the area you are working. Just know that the set time of the epoxy will be reduced as you heat it. I like doing it this was because the thinned epoxy wil seep into the pores of the wood and give you better protection.

Hope this helps

Ken
Old 08-18-2008, 09:43 PM
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horace315
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Default RE: Fuel proofing an LT-40

if your LHS does not know what fuel proof paint is then they aren't a very experienced hobby shop.get you a bottle of clear dope that is the best fuel proofing i have found to use,only drawback to using it is that you need a well ventilated space.epoxy works well but if you need to glue anything to it after it hardens it is a little effort to remove it in tight places to get a good bond.
Old 08-19-2008, 08:08 AM
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madmoe
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Default RE: Fuel proofing an LT-40

Thanks for all the responses! I remember using dope waaaaay back when I built a fabric covered control line plane. Do they still make that stuff? RCKen, thanks for the explanation. I really enjoy learning the WHY in addition to the WHAT. I don't have a heat gun yet (I know I need to buy one, just haven't gotten it yet). What kind of heat is needed? Would a hair dryer be sufficient.
Old 08-19-2008, 08:16 AM
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Default RE: Fuel proofing an LT-40


ORIGINAL: madmoe

Thanks for all the responses! I remember using dope waaaaay back when I built a fabric covered control line plane. Do they still make that stuff? RCKen, thanks for the explanation. I really enjoy learning the WHY in addition to the WHAT. I don't have a heat gun yet (I know I need to buy one, just haven't gotten it yet). What kind of heat is needed? Would a hair dryer be sufficient.
I've never tried a hair dryer, but it just might get hot enough. You can try it on a scrap piece of wood and see if it works.

Ken
Old 08-19-2008, 08:57 AM
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Default RE: Fuel proofing an LT-40


ORIGINAL: madmoe

Thanks for all the responses! I remember using dope waaaaay back when I built a fabric covered control line plane. Do they still make that stuff? RCKen, thanks for the explanation. I really enjoy learning the WHY in addition to the WHAT. I don't have a heat gun yet (I know I need to buy one, just haven't gotten it yet). What kind of heat is needed? Would a hair dryer be sufficient.
They still use it on full scale planes too. I think Tower carries it but I know SIG does.

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