Silkspan and Dope Question

Ken Cook or Kim probably uses dope more anyone on this forum. You may want to PM them if they don’t see this thread.

Also you could do a search as there have been many questions asked about silkspan/dope. Can’t wait to see it finished.

Ron


Here, I found the thread I posted a few years back.

https://www.coxengineforum.com/t5828-dope-for-dummies?highlight=How+to+dope

Sorry for being late to check in on this, and this is ONLY my way of doing it. I use Brodak buteryrate all the way through, but figure the rules are close to nitrate also.

Like Tico says, full strength clear around the perimeter of the frame on top and bottom. It's easier for me to do the wingtips first, and let them dry well before doing the main frame.

I have the silkspan pieces cut to size and ready to go for both sides of the wing. Then I lay the dampened sheet of silkspan onto the frame and go around it's edges with 50/50 clear to attach it, then flip it over for the same on the other side.





I then set it aside to fully dry, hopefully getting a smooth tightness across the span. Then I start clear coats with a day's wait and REALLY in between, 'till it gets a gloss.

When sticking down the covering ,do you dope the ribs also?

Like Kim, I use butyrate only. My first coat on the perimeter is thinned ~ 65/35 i.e., 35% thinner. I do this to get good penetration into the open grain; following coats are full strength. BTW, when finishing stocks on muzzleloaders, I use linseed oil thinned with turpentine for the same reason - good initial penetration.

Following base coats are full strength non-tautening butyrate with light sanding in between to knock down any grain that rises. I continue with base coats until the grain appears filled and the finish is slightly glossy. Apply the silkspan damp, pulling out wrinkles as well as possible and keeping it taut. Stick it down with 50/50 - because the dope is cellulose based, the following coats will soften underlying coats and literally melt together. The thinner helps with adhesion (my opinion only) and the doped edges of silkspan sometimes needs a little finger rubbing to soak through.

Use tautening dope on open areas only.

I don't dope the ribs when initially sticking down the covering since it needs to be able to move as it drys. You can apply a sealer coat initially to ribs, but I don't over paint when applying either silk or silkspan until it has dried and tightened.

Lots of ways to do this stuff; this is just my approach.

OhBee wrote:When sticking down the covering ,do you dope the ribs also?

No, the silkspan needs to be able to slide across the ribs as it contracts.  This is another reason for fine-sanding everything to get the lumps out.

Once the covering is drawn tight, I dope everything with clear, and this sticks the silkspan down to the ribs.

Awesome, that’s guys

[quote="Cribbs74"] Ken Cook or Kim probably uses dope more anyone on this forum. You may want to PM them if they don’t see this thread.

Gee, that's quite a resume builder there.

ticomareado wrote:

Cribbs74 wrote:   Ken Cook or Kim probably uses dope more anyone on this forum. You may want to PM them if they don’t see this thread.

Gee, that's quite a resume builder there.

You’re funny. I just know that they build and fly a lot.

I always wondered why my mother never complained about the dope fumes permeating the house when I was a kid!...🤪

OhBee wrote:I always wondered why my mother never  complained about the dope fumes permeating the house when I was a kid!...🤪

Well, I got evicted a few times! I could get away with doping small parts, but when I started up on wings with the Aerogloss, all that extra drying surface apparently became too much! This was also when I discovered the winter time finishing phenomenon of "Blushing"!!!

Kim wrote:
..............
No, the silkspan needs to be able to slide across the ribs as it contracts.  This is another reason for fine-sanding everything to get the lumps out.
..............

Can't emphasize Kim's fine-sanding advice enough.  Every tiny bump ends up looking like a mountain under the covering.

Meant to post the following pics last evening, but my phone crapped out.  This is a stab built from a simple design of mine and the set of plans I drew back in the early 70's, maybe '71 or '72.  The span is 20.5" and it weighs 2.75 oz.  While it's not silkspan, this is covered in yellow silk filled with clear butyrate and trimmed in black butyrate.  The thing to note is that the silk is as taut today as it was nearly 50 years ago, not to mention 4 moves and hanger rash. I love silk and, for me, a silked plane is a real thing of beauty.  

I like silk for it's strength, beauty. I have had it crush many wings. That's the drawback. It goes around compound curves like nothing else though. I was just recently working on a old combat wing that's starting to go through the boa constrictor phase and the trailing edge is beginning to buckle.

andrew wrote:

Kim wrote:
..............
No, the silkspan needs to be able to slide across the ribs as it contracts.  This is another reason for fine-sanding everything to get the lumps out.
..............

Can't emphasize Kim's fine-sanding advice enough.  Every tiny bump ends up looking like a mountain under the covering.

Meant to post the following pics last evening, but my phone crapped out.  This is a stab built from a simple design of mine and the set of plans I drew back in the early 70's, maybe '71 or '72.  The span is 20.5" and it weighs 2.75 oz.  While it's not silkspan, this is covered in yellow silk filled with clear butyrate and trimmed in black butyrate.  The thing to note is that the silk is as taut today as it was nearly 50 years ago, not to mention 4 moves and hanger rash. I love silk and, for me, a silked plane is a real thing of beauty.  

That Does Look Really good

Also, which you may already know, when you're paintng the tailfeathers, it's a good idea to flip the piece back and forth as you paint the dope across it, so both sides get their paint fairly close to the same time. This can help prevent it from warping.

All right...time for my nap !!!

Kim wrote:Also, which you may already know, when you're paintng the tailfeathers, it's a good idea to flip the piece back and forth as you paint the dope across it, so both sides get their paint fairly close to the same time.  This can help prevent it from warping.

All right...time for my nap !!!

thanks , That’s one of them things I might used to know but forgot.

Hello Akjgardner
                         I used to use pactra dope in the old days. Later on I used SIG Lite coat dope to avoid the excessive shrinking that happens with time when using dope. Some people Use a plasticiser  to reduce shrinking of the dope called Flexall that was sold by Dave Brown products. Also there is a non tautening dope made by randolph paints.
Juan



http://www.ohio-superstar.com/dave-brown-product-line/flexall-paint-plasticizer
https://www.aircraftspruce.com/menus/cs/randolphcoatings.html