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Fuel proofing plastic parts

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Old 09-25-2018, 04:57 AM
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mscott23
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Default Fuel proofing plastic parts

I am about to begin to build an F4B-4 from RCM plans from 1995. There is a cowl and dummy engine in the project which i have found from Williams brothers. The entire dummy engine assembly is plastic and would fit this 1/6 scale model well. My concern is that this model will be using a 90 four stroke glow engine which will spatter fuel on the plastic. Anyone know of a good way to fuel proof plastic parts or should i be concerned at all about this. Thanks in advance
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Old 09-25-2018, 08:50 AM
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Most dummy engines are mounted ahead of the glow power plant. I don't think that you have much to worry about. If you feel the need, a clear coat could be sprayed over the dummy, providing some protection.

I would use Minwax Polyurethane. Others may suggest a clear epoxy.
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Old 09-25-2018, 05:06 PM
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Thats a good point Tom. I will probably paint the dummy engine but the minwax Polyurethane is a good idea. Thanks for your reply
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Old 09-25-2018, 05:14 PM
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Originally Posted by TomCrump View Post
Most dummy engines are mounted ahead of the glow power plant. I don't think that you have much to worry about. If you feel the need, a clear coat could be sprayed over the dummy, providing some protection.

I would use Minwax Polyurethane. Others may suggest a clear epoxy.
Rustoleum clear is another good choice and my spraycan favorite. Minwax poly works great also. Epoxy is excellent but requires spray equipment many donít have.
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Old 09-27-2018, 05:14 AM
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Had a Williams rotary living in front of/around an OS 45. Did a clear coat of dope with an air brush. Not a problem until it hit the ground in an un-lady like fashion.
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Old 09-27-2018, 06:17 AM
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Yes no amount of clear dope will solve an unfriendly landing
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Old 09-27-2018, 06:20 AM
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sounds like i have a few options to skin this cat. Just gathering info now. I'm still looking into how available the dummy rotary engine is through Williams Brothers. At one point i was told that Williams Brothers had gone under but they seem to have resurfaced in Texas.
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Old 09-27-2018, 09:46 AM
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I tried Rustoleum clear several years ago and it was not fuelproof. Mayb the formula has changed since the New?.
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Old 09-29-2018, 07:29 AM
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Originally Posted by mscott23 View Post
sounds like i have a few options to skin this cat. Just gathering info now. I'm still looking into how available the dummy rotary engine is through Williams Brothers. At one point i was told that Williams Brothers had gone under but they seem to have resurfaced in Texas.
Give William's Bros a try. It is still a going concern and having spoken on the phone with they guy that now owns it he seems a nice fellow who deserves our support.
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Old 10-01-2018, 06:49 AM
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Thank you for that Thats a great point, I will contact them and get their opinion when i'm ready to purchase. So looking forward to this project
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Old 10-01-2018, 07:18 AM
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if you have spray equipment, the best bet is to use an automotive two part polyurethane. in the past, I have been able to get it in a rattle can from various auto parts dealers that sell paint. it comes with a small glass ampule in the can that you must break by smacking the can on a hard surface and then shaking the snot out of the can. the stuff works good enough. I know I can get it from NAPA dealers, I would think any parts house that sells paint would have a version from whomever is their stocking paint vendor.
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Old 10-05-2018, 05:02 AM
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When you get the Williams parts, take a piece of the plastic sprue and drop it in a small jar of fuel and see what happens.
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Old 10-05-2018, 06:13 AM
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Originally Posted by Appowner View Post
When you get the Williams parts, take a piece of the plastic sprue and drop it in a small jar of fuel and see what happens.
I would expect it to eventually melt.

What is the object of this test ?

Last edited by TomCrump; 10-05-2018 at 06:18 AM.
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Old 10-05-2018, 09:41 AM
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Originally Posted by TomCrump View Post
I would expect it to eventually melt.

What is the object of this test ?
To gain an idea as to just how resistant to the fuel the plastic really is.
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Old 10-06-2018, 07:40 AM
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Originally Posted by Appowner View Post
To gain an idea as to just how resistant to the fuel the plastic really is.
I took a look at the Williams Bros site and saw that the engine kits are made from polystyrene plastic. Alcohol (methanol) shouldn't bother it. Gasoline might eventually attack it. I'm not sure about nitromethane. It is a pretty strong solvent but comprises a relatively small portion of the fuel we use. I suppose the bottom line is that people have successfully used Williams Bros engines on glow powered airplanes for decades. I agree that fuel proofing the paint is probably the bigger issue. One upside of using a four stroke is that it is often easier to point the exhaust pipe toward the rear of the airplane, away from the cowl and dummy engine. It is also reasonable to remember that it will only ever be perfect once. It all goes downhill after the maiden flight. This is not necessarily a bad thing and in some cases adds to the character of the airplane. It is just a recognition that clean up and touch up is an ongoing part of maintaining a scale plane. I hope to see a picture of the F4B-4 one of these days. It's a neat airplane.
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Old 10-08-2018, 05:15 AM
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Your comments are all correct and dipping a piece of the plastic in fuel is a good test. This plane will definitely run a 90 four stroke so pointing
the exhaust away from the dummy engine will be easy. This will be version 2 of this plane. I originally built it in 1997 from RCM plans and after a 15 year hiatus I plan on rebuilding it. I'm having a real tough time posting a pic of the original i built. I will keep trying
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Old 10-08-2018, 05:33 AM
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that is a great idea
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Old 10-15-2018, 10:48 AM
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Tested by me with up to 30% nitro, comes in satin or clear, it works,,
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