cuwaert

Hi, I'm a scratch builder of 2.2m span 50cc modern and vintage aerobatic aeroplanes.
Normally I go for balsa sheeted structure with Oracover (Ultracote in US) covering.
But, I must say I'm not the most skillful Oracoverer but when the shapes are not that complicated, I can live (just) with the result.
Now however I 've finally turned to the construction of a Katana T30 design, one that I've postponed for some years because
of the difficulties involved with it such as ,amongst others, the all round forms which for sure I will not be able to cover decently.
So the idea rose to cover the balsa sheeting with a 47gr glass cloth and to paint it.
To save weight, I decreased the balsa from 3mm (I usually apply) to 2.5mm which saves me 60gr/m².
The Oracover costs me 87gr/m² so I have 147gr/m² to spend on glass/epoxy and paint.
Normally the weight of glass/epoxy is 2 times the weight of the glass, in this case say 100gr/m².
Now has anybody an idea of how much weight the painting of this covering will contribute?

All Day Dan

My Feedback: (5)

Here's what I do. The entire finish weighed 1.7 pounds. The model weighs 20 pounds. Dan.

Brush on a full strength coat of Valspar Lacquer Sanding Sealer NAS1420. A well-stocked paint store that caters to the professionals will carry this. It is usually used for furniture finishing. One of those two-inch inexpensive disposable brushes is ideal for this application. Sand lightly with 220-grit sandpaper. Apply ¾ fiberglass cloth over the surfaces brushing through it with the sealer thinned 100% with lacquer thinner. Sand lightly with 220-grit sandpaper. Brush on another thinned coat of the sealer. Sand with 220-grit sandpaper being careful not to cut into the cloth. Brush on two more coats of the thinned sealer. Try to fill the weave of the cloth as much as possible. Sand with 150-grit sandpaper to keep the surface flat and smooth.
Spray on three coats of Pacific Coast Lacquer’s PCL 913 lacquer based primer thinned 125% with medium lacquer thinner. Sand the first coat with 100-grit sandpaper, the second coat with 150-grit sandpaper and the last coat with 320-grit sandpaper. You should now have a pretty good surface for your color coats.
Apply a coat of Kilz that is thinned to two parts Kilz to one part naphtha. This will improve the adhesion of the final color coat
The model was painted with Benjamin Moore’s oil based paints. It took two coats of paint, each thinned to a mixture of three parts paint and one part naphtha.

LesUyeda

I would suggest that the weight of the paint will be insignifigant related to the weight of the glass/expoxy.

Les

kenh3497

Back in the hey day of 1/4 Midget pylon I built an all wood Caudren. Glassed it with 3/4 oz. cloth and epoxy and of course it was painted using automotive lacquer paint. Minimum weight was 2 1/2 pounds. IIRC it was about 3 oz shy of the minimum weight, so I stuffed a 500 MA battery in when everybody else was using 250 packs. Most everybody else was flying a glass fuse with wood wings that were monokoted. Done correctly, a painted surface need to be no heavier than your favorite plastic film covering.

saramos

47g fiberglass is a bit heavy. I would suggest something around 15g - 20g. This will give an even textured surface that you can fill either with primer or more epoxy. I prefer primer because it's easier to sand.

I like to spread the cloth over the surface, then starting in the middle, adding the epoxy working outward in all directions. That will help avoid wrinkles. Then squeegie off the excess epoxy and let dry. Then I spray with high build primer, let dry and sand back to just starting to expose the tops of the weaves. I repeat as needed to get a smooth finish. Then it's time to add a final coat of regular primer and when dry, it's ready to paint.

Scott

BMatthews

The guys suggesting the lighter grade of cloth are telling you the way to go. I've used 2oz (roughly the same as your 47gm) cloth before but only on sailplanes where I'm looking to actually go for an actual load bearing skin. In your case you are looking more for a stable base for the following painting. For that you only need very light cloth.

Because you've gone thinner with the planking I'd suggest you put patches of this same cloth and epoxy on the inner sides of the planking between the formers in those areas where you'll be handling the model a lot when picking it up and where folks will hold the model during runups. By going thinner than usual you also made it a bit weaker and more prone to splitting inwards. The curved shape will do much to resist this but a few well placed patches that turn the planking of those areas into a core between two stressed skins will do much to avoid any embarrasements.

cutaway

Nitrate dope and silkspan makes a nice base for subsequent painting and adds almost nothing. Sanding dope/silkspan is a lot easier than epoxy.

BMatthews

True, and I've certainly used dope and silkspan before with great results. But nitrate dope will also shrink more over time and possibly cause the sheeting to shrink inwards and develop a bit of the old "starved dog" look. Much depends on the thickness and density of the sheeting or planking and how wide spaced the supporting formers are located. There's also the issue of bonding compatibility with subsequent paints if the use of dope isn't carried on for the whole finish.


For a really big model such as this sounds like it may be the light veil like fiberglass along with a finishing resin of some sort provides a stable "film" that will also accept a wider variety of primers or paints with no possible adhesion issues. And at this size it's more easily able to carry the greater weight compared to a dope and tissue base.

cutaway

Almost every finishing system sticks to nitrate dope...epoxys, polyurethanes, automotive paints, etc.

Butyrate is a completely different animal though. Almost nothing but butyrate or acetate based glues like Ambroid or Sigment stick to butyrate very well.

If you were having shrinkage issues with nitrate, you may have had a tautening version of it. Randolph and Certified PRoducts make both tautening and non-tuatening flavors of nitrate.

Bundubasher

Be careful with epoxy/glass, whilst it will give strength and a good fnsh, you may find it is not as easy as it seemed at first, also, you can end up much heavier. Not a good idea to cut on wood thickness for a number of reasons - you're reducing strength, and longivity of the plane - when handling the plane i.e picking it up you can press right thru the wing etc or crack it - been there, done it, got the T shirt.

My material of choice is Solartex (nutral orange one that can be spray painted) or Oratex (it is thicker and slight more more difficult around corners). Both have a nice stretch advantage, especially around corners. This option makes very strong planes, but can also be a little heavy if you are not careful.

Lately I'm having good results with Oracover - cut it slightly longer so you have something to hold on to stretch it around corners while ironing it. Use a cooler iron to get it on and sealed. Then go over with a hotter iron, leave a couple of hours and give it another once over shrink. It will also spray paint ( automotive K2) very well. Start with the base colour Oracover you want, then spray the other trimming colours on. This saves weight.