For applying K&S Medium SGM Weight Silkspan to a GP PT-20 are the following steps correct?

Step 1: Apply a coat of straight nitrate dope to the framework.
Step 2: After light sanding place the wet silkspan onto the framework and pull taute.
Step 3: Brush a coat of 50/50 thinned nitrate dope to the outer edges of the frame.
Step 4: Lightly sand. Brush another coat of 50/50 thinned nitrate, this time over the entire frame to shrink the silkspan.
Step 5: Lightly sand yet again, and brush on a 2nd coating of 50/50 nitrate.
Step 6: Paint the model with your choice color of dope. At least two coats.
Step 7: Brush the painted airframe with two coats 50/50 thinned butyrate dope to fuelproof.

How close am I to the actual procedure?

At least three coats of clear after the covering is laid down. Mix clear dope with Talcum powder for a filler then sand. any low spots will be filled in. Now a coat of silver dope. this will show your mistakes and they will show up. Fill in mistakes with Talc Mix and sand. When done a coat of grey to act as a blocking coat. if satisfied you may now shoot the color

When is the dope/powder mixture applied?

I would skip the filler and silver steps for a PT-20, yes there are many, many steps to a proper dope 'showroom shine' finish but they are not needed for a trainer/utility model.

Are you planning to cover the wing with silkspan or just the fuselage and tail? I still finish many models with silkspan over sheeted fuselages and tails but it's not best choice for an open bay wing.

Consider sig koverall or some of the cheaper silks available for the wing. I've used silkspan on wings many times on smaller antique models but I accept that they must be handled carefully and holes/punctures are a distinct possibility.

I was planning on using the silkspan for the wing as well. I heard that koverall was harder to apply and get tight, and that it can't be applied with dope that it uses stixall and iron.

I agree somewhat with S Wallace on the fact that I don't believe that you want to use silkspan on the wings. You will forever be patching it. Silkspan is great for solid structures, but it punctures way toooooo easy. Darhma 5mm silk (if you want to do a traditional covering) would be a good route. You can forgo the silver on a trainer like was stated, but I would continue with the filler coat. Fills grain and weave faster than straight dope and sands easier. The filler coats would go after the 2 to 3 seal coats and when sanding a wing that has not been sheeted, use OOO Steelwool. Sandpaper will cut thru the covering at the ribs. You will need to run a strong magnet slowly over the covering after doing this. You will be suprised at the little pieces of metal you will pick up. Unless you truely are looking for that traditional look, I would just go with an iron on covering. Just my $.02 worth.

Good Luck,

John

Normally, I'd apply one very thinned coat of nitrate to the framework first. This will soak into the wood deeply and raise a bunch of fuzz when dry. Then I sand the fuzz off and apply somewhat thicker coat, repeating the fuzz sanding and nitrate application until the structure starts to show a slight sheen where the wood surface is fully encapsulated in nitrate dope. Now you've got a solid dope foundation to stick coverings to and you won't be struggling to have something stay put.

I reserve the one thin nitrate prep for very light things like stick/tissue rubber powered models where fractions of a gram matter.

Anything of decent size I do the multi-step "get a sheen" process.

I wouldn't worry too much about punctures on SGM. That's a fairly heavy grade of silkspan and somewhat puncture resistant. I've got one SGM covered plane with well over 100 flights on it last year and there were no punctures until I got stupid and dropped a glow igniter through a rib bay...patched that, then the next day I ditched/crashed the plane on purpose because someone had walked out into my space and my lizard brain instantly reacted and took the safest option. The wing survived the crash intact, without any tears or punctures, but the fuselage/tail were wasted. An SGM covered wing is pretty tough.

I haven't used silkspan in a long, long time, but continue to use dope on almost all my models. I transitioned to silk when I finally got a real job and could afford it, but in the late 70's, I started using dacron - either the Sig Koverall or the Stits Poly-Fiber. I think that if you will try either of those products, you will really like the way they apply. There are some good instructions on the Stits website if you have questions about attaching the fabric.

I agree with the comments about finish quality on a trainer. I usually just go with two coats of nitrate, two coats of color butyrate, and a coat of clear butyrate for a trainer. Keep 'em plain and light - Makes for a better flyer and an easier repair.

Koverall is actually very easy to use. It can be applied with Stix it, but I always adhere mine with dope and that works as well or better. It's adhered around the perimeter of your wing (dont wet the koverall!), then once the dope is fully dried it is shrunk with heat from an iron. Works wonderfully and almost impossible to get a wrinkle that wont pull right out.

The real beauty is it fills with just a few coats of dope and is ready for color trim or overall painting. Tough stuff, it will increase the torsional rigidity of your wing and is very difficult to puncture, unlike silkspan or silk.

Kudos to you for wanting use old school techniques but I think you would be happiest with silkspan on the fuselage and tail, koverall on the wing.

I completely agree with S. Wallace. I've used Koverall many times and always applied it with dope. On the edges, I iron it down because it's a little stiff and won't smooth down well without the heat. Dope is thermoplastic and works well with an iron after it dries.

And yes, get about three coats of nitrate down on the fuse before applying the silkspan. If you skimp at this stage you can have wrinkles later with changes in the weather. So make sure you have a good nitrate dope base for the silkspan.

Jim

Silkspan and dope look great! My black fused yellow winged Keith Rider R-5 'Jackrabbit' is over 15 years old and it still looks great with its silkspan and dope finish, (IMHO)! There's no mistaking a doped finish. Very light finishes can be had with it. But... it is fragile. That's why I use Koverall. One method can be just as difficult or easy as the next. This Fokker DrI middle wing was covered with one piece of Koverall. This Piper Super Cruiser fillet was formed by one piece of covering each side. This is much easier to obtain with Koverall (or similar polyester fabric methods: Nelson, Stits, PolyFab etc).

OK, so what are the proper steps for covering with koverall and dope?

Yeah, we gave it to you piecemeal, so let me make an attempt and others can modify/add...

1. dope all surfaces where you want it to stick (nitrate best, but butyrate works too); or use Stix-it or Balsarite
2. sand off fuzz after 1st coat, do about three total to get a slight sheen to the surface
3. if doped, use thinner or very thin dope to adhere the covering; pull out wrinkles; if using Stix-it or Balsarite, iron it on
4. when dry, trim and iron down any loose edges and wrinkles
5. apply dope to the entire surface of the Koverall; thin coats at first, try to avoid blobs forming in open frame areas
6. at a minimum, make sure the pores are sealed; to hide weave, add talc to dope
7. paint on the color

All you experts, please correct or add to this.

ARUP, your gallery is the BEST. But can you spell out for us your method of getting that nice fail fillet on the Cub? I've seen explanations before that just didn't work for me. Thanks.

Jim

To get the fabric fillet I start at the fillet area. I use Stix-It for this because it's a little more aggresive in its adhesive qualities. Use a cheap acid brush to apply one coat to framework. 'Tack' cloth to framework elsewhere just to keep it generally in place and out of way. I use Stix-It but you could tape it. At the fillet area 'push' Stix-It thru weave via brush and allow to dry. Stix-It isn't paint. Use just enough at the framework/ cloth contact points. 'Burnish' it thru the cloth with brush which helps it dry and stick. Once this is done start pulling fabric and putting Stix-It on cloth/ framewrok contact points opposite fillet. Pull up cloth that was previously tacked down and start pulling to taughten then re-tack. The iron has never come into play. Keep doing this. Make the fillet area as tight as possible by lifting and pulling then re-sticking fabric elsewhere. It will get done. I think it took me 2 hours to cover this 1/6 scale fuselage. Once the fabric is adherant to framework 'hover' (i.e., do not touch) the iron over the fabric to tighten. Don't tighten much because you still have the other side to cover. I like to shrink the fabric a little because it gives a sense of satisfaction that process is working. You could probably wait until other side is done. Other side a little more difficult. Use very sharp blades and be very patient. Once other side finished wrap a dowel with sandpaper to cut the fuzzies in fillet. Sand too much and you'll get more fuzzies! Flat sand paper elsewhere. Put on nitrate dope fullstrength at seams, let dry then sand fuzzies. Repeat as needed but if you put finishing tapes on it isn't neccessary. I hope this makes sense.
edit: P.S.- thanks for comment upon my Gallery. I've got more coming down the pipeline, too!

Thank you for that explanation. I copied it into a file to save. It sounds like you really have to play with it some, but I think I get the idea.

Jim