Guillow's Model Builders Forum

[fychan]

So I'm approaching the point at which I'm going to cover the plane - which I've done on gliders and things before, but none with any plastic parts. I'm not sure what to do now...

Do I glue the parts in place and then tissue over them (nose cowelling) and cut areas out (engine exhausts etc)? Or do I attach the nose cowel after I've tissued & doped? Another reason I'm asking is because of the way I cover the planes I usually dope the wood twice, and then wet cover, and paint over the tissue with the dope thinner that I rinsed the brushes in when painting the plane... Which gives me about a 1-5 ratio of dope to thinner. I find that it's useful in that it then disolves some of the dope out of the wood and increases the adherence of the tissue to the wood. I then dope another coat or two on top of this as per usual (saving the thinner I use for the brushes for my next plane ).

My only concern is that will the thinner "dissolve" the thin plastic? Or will it make it too pliable? Do I need to have tissue on top of the nose cowel to make the paint look consistent from the wood onto the plastic? Do I need to coat the plastic in a clear acrylic first to stop any problems with the dope (and / or thinner)?

Sorry to be a pain - I just don't want to make a mistake at this late stage

[David Duckett]

Relative to the cowling...if you want it to blend in smoothly glue it to the former and sand it to match the former. You might need to add some extra pieces of wood, or remove some, and then I fill any remaining gaps with lightweight filler and when that's all dry a final light sanding should suffice. On some planes, a Piper Cub for example, the cowling is not at all smooth where it meets the rest of the fuselage. But on the Spitfire one doesn't see a transition because the real plane isn't built that way. I will always attach the cowling if possible before covering. It also gives a lot bigger area to attach tissue to that just the edge of a former.

Maybe I can make the prepping and covering a bit easier for you and save the thinner to be used as thinner. Realizing lots of builders might read this and have questions about the entire process, with your indulgence I'll try to make it sensible.

The frames need to be prepped with either dope or the "white glue mixture" before covering to strengthen them and to fill the rather porous balsa so that the adhesive used to attach the tissue will have something to adhere to. For the first 50, or so, years I always used dope but once this last year while building one of the eleven, I decided to try the white glue mixture since Guillow's advocates it so strongly. And guess what? It works! So now that's what I use to fill the balsa before any covering starts. I found that a precise ratio isn't necessary and rather thin works much better than slightly thick.

So, ready? Using a large brush, whatever's comfortable, paint the mixture on ALL the balsa liberally, hopefully over a drop cloth of some sort, and let it dry thoroughly. Here in very dry Arizona that requires about 30 minutes but if you have any kind of humidity it will take longer. I try to have all the frames ready for this process so one can de painted while others are drying. The thin mixture will soak into the balsa and as it dries it will make the balsa harder. (Dope will do the same thing but the glue is actually harder) When it's dry use your best tools, your fingers, to feel the surface and you'll see that the glue has raised some of the fibers of the balsa and even though you had sanded it smooth prior it is now rough. This is good.

Using 220 sandpaper IN YOUR FINGERS lightly sand all the balsa and it will get smooth again. Then add another coat, let it dry, and sand smooth. The balsa will start taking on a sheen and if the process is continued it will shine but two coats is enough. Sanding with your fingers as opposed to using a sanding block will make you a bit more gentle.

Covering wet is the only way I ever learned to cover and the thought of doing it dry just doesn't seem a comfortable way to do it. Many people swear by the process but since you're also covering wet with dope this will basically apply to that process.

When wet the fibers of the tissue "relax" and become much more pliable. With the lightweight silkspan supplied in the Guillow's kits one really doesn't have much latitude because the lightweight does not allow it to manipulated. If stretched too much it will tear whereas the heavy grade I use can be man-handled and stretched to conform to curves that dry simply can not do. I covered one side of the front section of the B 29 with one piece and to get it to conform I had to tug and pull a bit more than normal. On the other side I covered the part with the most curvature first and in a smaller section. Even as much as the stuff will stretch I don't suggest you try it unless you have some experience. It's far easier to cover in sections. More on this later.

Covering the wing is usually the easiest because it can be done in one section but that's not the rule. It's always best to just put the tissue down on the frame and see just how it will fit before making any rash decisions. With a wing the easiest way to cover is to attach the tissue at the wing tip and root rib as this will allow the tissue to be in place as the rest of the covering continues. And here's where the thinner comes in. You want to thin the dope to a slightly less than normal consistency to allow it to flow onto the frame more easily and not clog up in any one spot. You do NOT want to use just the thinner.

I put the silkspan/tissue (it's silkspan as far as I know but tissue is easier to write) in a bowl of water to thoroughly wet it and then on a towel to absord the excess. Then some dope on the wingtip and root rib and lay the wet tissue on the frame. Add more dope on top of the tissue at those points and the dope will soak through and meet the dope just beneath the tissue and the adhesion has started. With the tissue now anchored in place dope the leading edge, roll the tissue onto it and dope from above and start using your fingers to stretch it taut. Once that's relatively secure dope the trailing edge and repeat the process. You'll find that having the tissue anchored in the first place will allow the rest to be done much easier. It's exactly like stretching canvas onto a frame for a painting and even if you've never done it you probably get the idea.

As the tissue starts to dry you'll have to go back at least once with the small brush you're using for this and give the edges another coat just to make sure it's all doped down. While it's still moist you can pull and tug it all gently into place and as it starts drying you'll see it become so taut you can drum on it, at least with your fingers. When everything is dry the extra tissue will have shrunk to conform to the outline of the frame and can be trimmed off with sandpaper or a sharp knife (I use both).

When dry the covered surface needs to be filled just as the balsa was before being covered. The glue mixture can be used for this but after trying it I prefer to use dope. The glue mixture will sag the tissue and it will become taut again after it dries but each additional coat will also sag it. One coat of dope and the sag is stopped. The one coat of dope is also slightly thinned to insure an even coverage and also cause it's much easier to use. Using the large brush again apply one coat of dope to everything and let it dry. When it dries use your fingers and you'll see that it's rough again. This is also good. Using a finer grade of sandpaper lightly sand the entire structure. Yes, sand it. LIGHTLY. It's relative to how thick the tissue is. The heavy grade is fairly durable.

At this point one could start painting but...an additional coat of dope will fill the tissue even more and after another light sanding the surface will be ready for paint.

A note about dope. One of the reasons it's so effective at this is that it actually shrinks and that action definitely helps in getting the tissue taut. There's a difference in types, nitrate and butyrate, and there's even a "lite" which shrinks less. To make matters worse they are not totally compatible and there's a definite rule about using one over the other. I use only butyrate cause that's what most hobby shops carry as the Testors or Pactra brand in the colors and while I rarely use them they are what I'm familiar with.

And finally to the last part. Assuming you are now using a thinned dope and not thinner it will not affect the plastic in any way except to make it shinier and will in fact make it stronger. The paint will not be noticeable where it changes from a wood to a plastic surface but any difference in height will. But then there will be several areas like that and the plastic pieces will never be perfect. It should also be remembered that real airplanes are covered with many different panels. If you'll look at the latest pic posted on the aerodrome of the B 29 you might notice how shiny the nacelles are and that's because everything has two coats of clear dope applied so it's ready to go to the paint shop.

And finally, if you'll send me your email address in a PM I have some pictures of a Spitfire built in 1/5 scale of metal and in incredible detail.

David

[David Duckett]

After seeing CDWheatley's triplane and reading his description of using thinner for covering, I read the original post about it here again and must say that even though I have never heard of it it does certainly make sense. I suppose my reaction is partially because I can handle dope all day but the smell of thinner is too much for me and when I do use it I will do so outside.

So use the method that works for you. We all have our way of doing things and there's usually another way even then. When I was learning to build these kits back in the late 50's I was using Testors wood glue to attach the tissue and that made for some fairly horrific results. I can still remember that it dried white under the red tissue. At the time the instructions all said to use dope but I just didn't believe that would work. Dumb ass!

[fychan]

Well, I've already put my two coats of watered PVA glue on & sanded - so I'm all ready for the tissue covering... I thought it'd be worth trying somethinng new - especially as it meant I could prepare the wood in the house with the kids in it still.

I will however still be doping the tissue rather than using glue on it... I'm not that brave

As you might be able to tell, the amount of time I can put towards the plane each week is somewhat limited - so it'll take me a while... No holding your breath please