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Author Topic: Finshing resin in place of silkspan  (Read 1321 times)

Offline Matt Colan

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Finshing resin in place of silkspan
« on: July 03, 2009, 07:26:01 PM »
On Grandpa's P-47 he's still finishing, he had the paint peel off the wheel skirts.  He decided to put on finishing resin on it, instead of building it up with silkspan and clear.  He put a coat of the finishing resin on it and primed it.  I've never felt a finish so smooth on a plane before paint.  He didn't weigh it before or after, but I weighed a first set he made, and the present set and it weighed only a tenth of an ounce heavier than the first set.

I'm thinking of using the finshing resin on the stab and elevator on my cobra.  I would think that finishing resin would be fuel proof, since I coat the engine compartment with it anyway.  I would also think that it would make the stab and elevator ultra strong.  And also once you have the resin on it, it would be ready to be primed and then put paint on it.

What does everybody else think?

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Offline Mark Scarborough

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Re: Finshing resin in place of silkspan
« Reply #1 on: July 03, 2009, 08:50:15 PM »
IMHO, he finishing resin is not inherently a bad idea, but I dont think it will do what you anticipate. It will make the surface more resistant to denting, but it will not strengthen the stab in any meaningful way. Using silkspan and dope creates a "skin" that acts as a stressed member of the structure and will in fact strengthen the tail significantly in ways that matter because it is acting as a stressed skin. beyond that, finishing resin will be a fair amount heavier for no appreciable strength increase,, my vote is nope,, use the silkspan and dope. There is also the issue of dissimilar products. finishing resin is not designed to recieve dope, it will work in some cases, but its another variable in the finishing process that can come back to haunt you.
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Offline Randy Ryan

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Re: Finshing resin in place of silkspan
« Reply #2 on: July 06, 2009, 06:02:47 AM »
I'm with Mark, though you could try CF veil. I used it on my Gladiator and noted a marked improvement in stiffness, that's a good thing.
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Offline Don Hutchinson AMA5402

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Re: Finshing resin in place of silkspan
« Reply #3 on: July 06, 2009, 08:58:08 AM »
Some years back I ran a series of tests to compare the structural stiffness gained when using silkspan vs. carbon mat as a covering material. A series of coupons were tested for bending, twisting and breakage using the same number of coats of clear dope to apply. The results showed that they were almost exactly the same, one sample might go one way and the next duplicate test item may go the other way but differences were insignificant. The test data were published in Stunt News about 10 years ago.
Don
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Offline Larry Fulwider

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Re: Finshing resin in place of silkspan
« Reply #4 on: July 07, 2009, 07:02:33 AM »
Quote from: Don Hutchinson on July 06, 2009, 08:58:08 AM
Some years back I ran a series of tests to compare the structural stiffness gained when using silkspan vs. carbon mat as a covering material. A series of coupons were tested for bending, twisting and breakage using the same number of coats of clear dope to apply. The results showed that they were almost exactly the same, one sample might go one way and the next duplicate test item may go the other way but differences were insignificant. The test data were published in Stunt News about 10 years ago.
Don

Don --
Do you have the issue date of the article? I'd love to read the entire thing from the archives, despite your good summary above.

Do you know if anyone has done the "other half" of the test -- testing finishing epoxy vs cured dope on either substrate? Not hardness of finish, but specifically bending stiffness (not breaking strength) where the finish side is the side under tension?

   Larry Fulwider
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Offline Willie Johnson

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Re: Finshing resin in place of silkspan
« Reply #5 on: July 07, 2009, 05:19:28 PM »
Try finishing resin with light fiberglass -  .56 or .73 oz/sqr yd.
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Offline Don Hutchinson AMA5402

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Re: Finshing resin in place of silkspan
« Reply #6 on: July 07, 2009, 09:03:16 PM »
Larry-
Sorry, I don't have the date of the issue with my tests in it. Probably around 2000 +/- a couple of years. Have colllected far too much extra baggage over the years and passed the old issues on to a friend. A clue would be the Doctor article by Ted Fancher where he talked about the carbon mat. That is what gave me the idea to test the material so it will be some time after that was published.

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Offline John Miller

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Re: Finshing resin in place of silkspan
« Reply #7 on: July 09, 2009, 09:25:03 AM »
Isn't it funny, how old things become new again?

Using poly epoxy over .5 - .75 oz FG was all the rage back in the late 70's - 80's.

If you can get access to copies of Stunt News from that period of time, there were many good "How To" articles. Windy, if memory is correct was a proponent of this type of finishing.

It offered a strong, solid base coat. It could be easily stripped, if needed, and worked well for repairs.

If done with care, weight was fine.
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Offline john e. holliday

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Re: Finshing resin in place of silkspan
« Reply #8 on: July 10, 2009, 09:24:09 AM »
As stated earlier, finishing resin, the type that uses an activator will come out heavy if not done properly.  I quit using it years ago.   This was not the epoxy resin that is available.  DOC Holliday
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Offline Pinecone

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Re: Finshing resin in place of silkspan
« Reply #9 on: July 10, 2009, 11:54:11 AM »
This came up recently.  Al Rabe still uses the light FG cloth and resin for flaps.

I did this on my Twister in progress.  .50 ounce cloth, and WEST epoxy.  Then auto primer, sand and repeat.  Looks nice.
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Offline Matt Colan

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Re: Finshing resin in place of silkspan
« Reply #10 on: July 14, 2009, 04:14:26 PM »
Grandpa weighed his Big Job fuselage before he put the resin on, it weighed 6.5 ounces.  He put the resin on and two coats of primer, and it gained 4/10 of an ounce.  Almost nothing.  I'm sold!!! #^  #^  #^
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