How to patch Silkspan

I was thinking about using silkspan on my next airplane mostly because that is what I used 35 years ago, it brings back memories and I want to do it again. After spending several hours tonight repairing, ribs, monocoat, engine mount, tail, landing gear on my crashed airplane I got to wondering, how do you patch silkspan and keep it from looking like a bandaid? I remember the airplanes that I had in high school all looked like they had bandaids on them. I applied the silkspan and after a paint job it stuck out like a sore thumb. As long as it continued to fly and I was having fun I didn't care what it looked like. Another thing I remember was the silkspan is very sensitive to damage. The smallest little bump would make a hole. A hard landing would split the silkspan is several places. A small crash and you would have to take the airplane home in a basket.

>I was thinking about using silkspan on my next airplane
>mostly because that is what I used 35 years ago, it brings
>back memories and I want to do it again. After spending
>several hours tonight repairing, ribs, monocoat, engine
>mount, tail, landing gear on my crashed airplane I got to
>wondering, how do you patch silkspan and keep it from
>looking like a bandaid? I remember the airplanes that I had
>in high school all looked like they had bandaids on them. I
>applied the silkspan and after a paint job it stuck out like
>a sore thumb. As long as it continued to fly and I was
>having fun I didn't care what it looked like. Another thing
>I remember was the silkspan is very sensitive to damage.
>The smallest little bump would make a hole. A hard landing
>would split the silkspan is several places. A small crash
>and you would have to take the airplane home in a basket.
>
>Gary Weaver

Some new stuff called POLY-SPAN much better IMHO.

Silkspan is an extremely forgiving material, which is not difficult to patch at all. The secret to having it not show is to get an appropriate "pre-finish" on the patch.

Once you have doped the patch into position and it is tight and has several more coats of dope, here's a very quick way to get the finish back to snuff for a color coat over it. Spray several heavy coats of Krylon Primer over it and its edges. Then wet sand it with #400 or #600 sandpaper, using Prepsol I (the clear stuff) as the wetting agent. Sand it quickly, and wipe it with a soft clock - in minutes, the Prepsol will actually soften the sanding sealer.. (Don't let that disturb you.)

When it is all dry and clean, it will be degreased as well and ready for a fresh coat of color dope.

Now, you can get back to that smooth, non-fuzzy silkspan surface in a couple of hours this way, but I don't recommend it for anything but a fairly small patch. Reason is that the material, which fills so beautifully, is HEAVY. This is moderated somewhat by a lot of it sanding away, but it's still not the finish you want over a large area. Dope/lacquer/epoxy all go over the Krylon Primer without any problems, with good adhesion.

Now, the other way, if you're not repairing something that is already painted, is to go back to the multi coat processing using talc/dope, with the same level of preparation you would do from raw wood and balsa.

It all boils down to getting the paper filled properly, and the surface prepared.

As for Polyspan, clearly it has strength and puncture resistance, but I've heard several horror stories about it, and if it gets sanded INTO, well, you think silkspan is tough to make a hidden patch on! Unlike silkspan, whose fuzzy surface can be restored with dope and filler easily, Polyspan isn't so easily corrected.

Good luck!

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"Life's Tragedy is that we get old to soon and wise too late." -Benjamin Franklin

>Sand it quickly, and wipe it with a soft clock ...

Cuckoo, Grandfather, or can a plain Timex do....?

Wipe with a soft croth..

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"I have two very rare photographs. One is a picture of Houdini locking his keys in his car. The other is a rare photograph of Norman Rockwell beating up a child." -Steven Wright

>Wipe with a soft croth..

Larry, Larry, you have been sitting too close to an open tube of glue. First it is a clock you are wiping it with and now it is a croth. Next you will tell us this was all a bunch of crock.

>
>Some new stuff called POLY-SPAN much better IMHO.

Who sells poly-span?

Tom Morris is the cheapest supplier that I know of, and he sends a detailed description of how to apply it. It dopes on, and it's heat shrunk with low heart (it will "run" like panty hose if it gets too hot), and it is rather difficult to get around tight corners like some wing tips. But it can be done, and it is MUCH more punctire resistant than silkspan.
It is a polyester (?) lining material.
Bill <><

>Tom Morris is the cheapest supplier that I know of, and he
>sends a detailed description of how to apply it. It dopes
>on, and it's heat shrunk with low heart (it will "run" like
>panty hose if it gets too hot), and it is rather difficult
>to get around tight corners like some wing tips. But it can
>be done, and it is MUCH more punctire resistant than
>silkspan.
>It is a polyester (?) lining material.
>Bill <><
>

Is Tom Morris online?

Does he have a catalog?

If you tear the patch edges, rather than cutting them, the patch will blend into the background better.

... Another thing I remember was the silkspan is very sensitive to damage. The smallest little bump would make a hole. A hard landing would split the silkspan is several places. A small crash and you would have to take the airplane home in a basket.
>>Gary Weaver

This sounds like you may have applied the silkspan with the grain running chord wise.

I've been using Sig Plyspan, which is very similar to the old medium-weight silkspan (also call SGM for small gas model.) It comes in various colors. It is very tough when doped with plasticized dope. I have had several airplanes survive medium-range crashes with no damage to the covering. The advice on tearing edges is good. Also if you have a big patch, recover the whole section, so that the edges are on ribs, spars, etc. and can be carefully sanded down.

Here's a trick I learned from hanging out with free-flight people. If the silkspan is a tear, and all the material is still there;

Don't put a patch on it. Instead brush some thinned clear dope over the tear and immediately stretch some "cling wrap", or whatever they call the plastic kitchen stuff that comes in a roll. If you do it just right, the dope will soften the silkspan and you can persuade the silkspan edges to sort of stick to the underside of the cling wrap. The torn edges will (almost) come together and will stay there. When dry, remove the cling wrap and lightly spray some more clear over the wound. Not as strong as a patch, but the result doesn't show as much.

If you cover the open areas with light polyester film first, and then apply the silkspan with a coat of water-based polyurethane you get a much more durable finish. Make sure there is no oil on the film, scuff it lightly with Scotchbright, and the silkspan will stick just fine. I though this was a great original idea, until I was talking to Keith Renecle at the WC's. He said the Russians had been doing this for 15 years or so!!

>I was thinking about using silkspan on my next airplane
>mostly because that is what I used 35 years ago, it brings
>back memories and I want to do it again. After spending
>several hours tonight repairing, ribs, monocoat, engine
>mount, tail, landing gear on my crashed airplane I got to
>wondering, how do you patch silkspan and keep it from
>looking like a bandaid? I remember the airplanes that I had
>in high school all looked like they had bandaids on them. I
>applied the silkspan and after a paint job it stuck out like
>a sore thumb. As long as it continued to fly and I was
>having fun I didn't care what it looked like. Another thing
>I remember was the silkspan is very sensitive to damage.
>The smallest little bump would make a hole. A hard landing
>would split the silkspan is several places. A small crash
>and you would have to take the airplane home in a basket.
>
>Gary Weaver

One thing to note, Gary, is that the dopes of today are much different. I had the same experience with silkspan in my younger (high school) days. The stuff was brittle and would simply explode even in a small crash. The problem, it seems, is the dope, not the silkspan. Matt finishes all of his planes these days with dope and silkspan. Nothing underneath it and pure butyrate dope throughout. We used to use SIG and then used the flex stuff for undercoats. Now we use strictly Brodak and never add anything but thinner. Matt "crash tested" this finish a couple of times and it is surprising how minimal the damage is even in a hard crash. One plane went straight in, the wings broke off, but except for the bay where the break occurred there was no damage elsewhere.

For repairs, tear the edges of the patch, cut back to the next rib if a large repair, and simply apply the patch, seal it with clear, sand the edges, and finish as normal. You will not see the patch when done and the stuff will last. Matt has over 1500 flights on his present ship, and the stuff is holding up just fine.

Is there a recommended "plasticiser" that can be added to non Brodak dopes?

>Is there a recommended "plasticiser" that can be added to
>non Brodak dopes?
>
>Tom

Dave Brown sells a plasticizer, but you can also get this at an automobile paint supplier. Get the stuff made for lacquer so they can spray paint bumpers. This will work in your dope.

SIG Lite Coat is already plasticized as is their color dope. Sometimes a little extra helps, but this stuff is far different from what we used in the 50s. That stuff just made your silkspan brittle.

For small punctures or tears, you don't need a patch at all. Just get a blunt nosed paintbrush, bend the paper close together so that you have a "scar" line, and dab alot of Clear onto it. Thicker stuff that is going bad is the best.

This will pull the paper together like magic, and, in some cases, you can barely see the tear line.

On my free flight planes, I pull the tissue edges up out of the hole and use a bead of balsa cement to pull the edges together. It's amazing how the gap between the edges closes as the balsa cement contracts as it sets.

On my control line planes, holes are normally accompanied by broken ribs and spars which require more extensive remedial surgery than a bead of balsa cement.

I use cellulose dope here in the UK as all of my planes are currently powered by diesels. I am not sure if the balsa cement repair is compatible with butyrate dopes.

>I am not sure if the balsa cement repair is compatible with butyrate >dopes.

It is on the ones where I have done that same treatment.
Bill <<>