Covering advice
03-08-2003, 08:05 PM
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Covering advice
Somewhere I saw advice on covering a sheeted fuse with silkspan. Can anyone give me info on the proper way to do it? I am trying to build light. This will be my C-47 with a 45" WS
03-09-2003, 03:56 PM
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Covering advice
I've never used silkspan, but, in general, great care is needed to get a light weight, conventional finish. I've done a lot of tissue and silk covering and the following should give you a sense of how these things are done.
First, you apply two coats of dope to your airframe, everywhere that the covering material touches. Then you lay the covering down over the part and apply dope directly to the covering, with a brush. Then, with your thumb, you rub down the dope, into and through the covering so that the fresh dope and it's solvents, re-activates the dope on the frame work. Keep rubbing out till the applied patch of dope is dry or nearly so. Keep doing this in patches till the entire airframe is stuck down. It WILL look like a mess. But not to worry, the next coat of dope will smooth all out.
On compund curves, you need to apply the tissue in patches. Silk will confrom to the most compund of curves. It's really amazing.
From there, apply two or three more coats of clear dope. If you want to get a smooth finish that eliminates all grain and covering weave, we now get into the area that can add a lot of weight. Make up a filler out of talcum powder and dope. I've never measured, just added the talc till I got a good looking, runny, pasty filler/primer. From there you add two or three coats of this primer. Leave it for a week to dry. Then, take, fine sandpaper, 400 grit and wet sand. Sand down to the fabric. Let dry and apply two more coats of filler. Sand again, but avoid getting down to the weave, or fabric. It's a lot easier to apply too much filler and sand till just smooth. You get a thick coat of primer and a lot of weight. It's harder to get exactly only as much of a filler coat needed to just cover the grain.
The preceding is for silk and tissue. For silkspan, you wet the covering, apply it to the framework while wet so that you can form it over compound curves, stretch out all the wrinkles etc. Apply dope, heavily, with a brush directly on the s/span on the outer framework. Work it in with your thumb, all the while keeping it stretched and smooth and wrinkle free. Not to worry, the dope will work despite the wet covering. It will now REALLY look like a mess. Again, a few coats of dope will fix that. Fill with primer as above.
The problem with the "silk and dope" method is that dope keeps drying and shrinking, seemingly forever. If you let one coat dry for a week and sand, and if you come back to it a month later, grain that you thought you filled may now start to re-appear.
The silk, dope, talcum method is one that requires years to master and a lot of patience to apply.
Much easier is to use 3/4 ounce glass cloth and epoxy. Epoxy cures solid and once cured, undergoes no shrinkage. Then, you can apply an epoxy type primer that also undergoes no shrinkage.
Epoxy finishes are harder to find these days due to safety concerns. Newer, water reducible finishes that promise to be as fuel proof as epoxy are available. These are urethane finishes with a cross link additive that is raw fuel proof to 10%. I've tested these with raw 25% fuel and they held up . I've still to cover a plane with one of these but I'm hopeful.
See the add for Nelson Hobby Specialties for more info.
Hope that's at least a start.
First, you apply two coats of dope to your airframe, everywhere that the covering material touches. Then you lay the covering down over the part and apply dope directly to the covering, with a brush. Then, with your thumb, you rub down the dope, into and through the covering so that the fresh dope and it's solvents, re-activates the dope on the frame work. Keep rubbing out till the applied patch of dope is dry or nearly so. Keep doing this in patches till the entire airframe is stuck down. It WILL look like a mess. But not to worry, the next coat of dope will smooth all out.
On compund curves, you need to apply the tissue in patches. Silk will confrom to the most compund of curves. It's really amazing.
From there, apply two or three more coats of clear dope. If you want to get a smooth finish that eliminates all grain and covering weave, we now get into the area that can add a lot of weight. Make up a filler out of talcum powder and dope. I've never measured, just added the talc till I got a good looking, runny, pasty filler/primer. From there you add two or three coats of this primer. Leave it for a week to dry. Then, take, fine sandpaper, 400 grit and wet sand. Sand down to the fabric. Let dry and apply two more coats of filler. Sand again, but avoid getting down to the weave, or fabric. It's a lot easier to apply too much filler and sand till just smooth. You get a thick coat of primer and a lot of weight. It's harder to get exactly only as much of a filler coat needed to just cover the grain.
The preceding is for silk and tissue. For silkspan, you wet the covering, apply it to the framework while wet so that you can form it over compound curves, stretch out all the wrinkles etc. Apply dope, heavily, with a brush directly on the s/span on the outer framework. Work it in with your thumb, all the while keeping it stretched and smooth and wrinkle free. Not to worry, the dope will work despite the wet covering. It will now REALLY look like a mess. Again, a few coats of dope will fix that. Fill with primer as above.
The problem with the "silk and dope" method is that dope keeps drying and shrinking, seemingly forever. If you let one coat dry for a week and sand, and if you come back to it a month later, grain that you thought you filled may now start to re-appear.
The silk, dope, talcum method is one that requires years to master and a lot of patience to apply.
Much easier is to use 3/4 ounce glass cloth and epoxy. Epoxy cures solid and once cured, undergoes no shrinkage. Then, you can apply an epoxy type primer that also undergoes no shrinkage.
Epoxy finishes are harder to find these days due to safety concerns. Newer, water reducible finishes that promise to be as fuel proof as epoxy are available. These are urethane finishes with a cross link additive that is raw fuel proof to 10%. I've tested these with raw 25% fuel and they held up . I've still to cover a plane with one of these but I'm hopeful.
See the add for Nelson Hobby Specialties for more info.
Hope that's at least a start.
03-11-2003, 06:23 AM
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Covering advice
Better still..........water based uarathane and 3/4 ounce glass cloth. Quick, easy, light, no smell, clean everything up with water.
Lay down cloth and brush into place with a dry brush, then apply a very light coat of paint. Too much and the cloth will float to the surface. Remove excess liquid with toilet paper. Let dry a few hours. Apply one more coat, let dry and remove overlaps with a light sanding. Sand lightly and apply one more coat and you are ready for color. Will accept dope.
Lay down cloth and brush into place with a dry brush, then apply a very light coat of paint. Too much and the cloth will float to the surface. Remove excess liquid with toilet paper. Let dry a few hours. Apply one more coat, let dry and remove overlaps with a light sanding. Sand lightly and apply one more coat and you are ready for color. Will accept dope.
03-11-2003, 03:41 PM
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Covering advice
Frank,
That's an interesting technique. I like the idea of no fumes and smell. Do you use store bought urethane, or some sort of hobby type? Do you thin it out some or use it straight?
That's an interesting technique. I like the idea of no fumes and smell. Do you use store bought urethane, or some sort of hobby type? Do you thin it out some or use it straight?
03-11-2003, 05:36 PM
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its cheaper too.
get it a walmart or any hardware store. it doesnt have to be anything fancy. i have used both polyurethane and polycryllic. i personally like the polyurethane better for planes. i have used it over fiberglass and ripstop nylon with decent results. i just tried the ripstop the other day. the ripstop can be bought at any fabric store, but try to get the untreated kind.
i just noticed my plane in my avitar was covered with fiberglass and WBPU.
i just noticed my plane in my avitar was covered with fiberglass and WBPU.
03-11-2003, 06:35 PM
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Covering advice
Any brand, straight from the can. Try it on a test piece and you will be amazed how easy it is. The process is very light, as most liquids evapotate.
I covered a three foot pair of floats in one afternoon, outside on a sunny summer day. I put on four coats, lightly sanding between the last two. Ran to Crappy Tire and got a can of their rust paint, Armour Cote, sprayed on one coat and let dry over night. Mounted them the next day and was float flying that afternoon.
Thay was three years and they still look great.
By the way, the dry brush thing is that you create static electricity and it sticks the cloth down where you want it.
Ah...........sunny summer days, remember those Andy
I covered a three foot pair of floats in one afternoon, outside on a sunny summer day. I put on four coats, lightly sanding between the last two. Ran to Crappy Tire and got a can of their rust paint, Armour Cote, sprayed on one coat and let dry over night. Mounted them the next day and was float flying that afternoon.
Thay was three years and they still look great.
By the way, the dry brush thing is that you create static electricity and it sticks the cloth down where you want it.
Ah...........sunny summer days, remember those Andy
03-11-2003, 09:34 PM
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Frank,
I've used their Armor Coat in the past and had found that it's truly fuel proof. By that I mean that it's not just exhaust proof,,, that you can pour 25% raw fuel on it and it is totally unaffected as though it were a true epoxy paint.
HOWEVER, I've run into a few cans/colours that weren't truly fuel proof. Have you found this to be the case? I will admit that sometimes I have to spray in rather cool conditions,,, like at just above freezing (in winter) and leave the piece overnight to dry. I then bring it in to "cure". It may be these that did not maintain their fuel proof qualities but at the time, I didn't realize the cold spray technique might be a problem. Any comments?
I've used their Armor Coat in the past and had found that it's truly fuel proof. By that I mean that it's not just exhaust proof,,, that you can pour 25% raw fuel on it and it is totally unaffected as though it were a true epoxy paint.
HOWEVER, I've run into a few cans/colours that weren't truly fuel proof. Have you found this to be the case? I will admit that sometimes I have to spray in rather cool conditions,,, like at just above freezing (in winter) and leave the piece overnight to dry. I then bring it in to "cure". It may be these that did not maintain their fuel proof qualities but at the time, I didn't realize the cold spray technique might be a problem. Any comments?
03-12-2003, 05:52 PM
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Andy:
I've only ever used the white AC paint and yes it really is fuel proof.
The ambent temperature may cause a problem. I've had problems with other paints, spraying out in the garage, then bringing it inside.
I've only ever used the white AC paint and yes it really is fuel proof.
The ambent temperature may cause a problem. I've had problems with other paints, spraying out in the garage, then bringing it inside.
03-12-2003, 08:40 PM
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Frank,
Just got back from Canadian Tire. I didn't notice this before but they have two brands of rust paint, Armor Coat and Tremclad. This might be a factor as well. Tremclad might not be so fuel proof as the other.
Just got back from Canadian Tire. I didn't notice this before but they have two brands of rust paint, Armor Coat and Tremclad. This might be a factor as well. Tremclad might not be so fuel proof as the other.
