Scale Soaring UK

I am building a DFS Habicht and have finally got to the stage of spraying it. I have never actually sprayed, or really painted a balsa model before and after 2 coats of rattle can acrylic grey undercoat it shows the grain and the tiny slots in it.

I did a very light rub down with 400 wet/dry used wet but the surface is still pitted with the grain 'slots'. Would it be a better idea to paint it with cellulose sanding sealer before the spraying?

I actually work with wood a lot as I am retired and my hobby/passion, besides RC gliders, is wood turning and I have the sanding sealer for that. I realise that there shouldn't be too much paint or sealer applied because of the weight it adds, but any ideas would be gratefully received.

John, this is a subject that would take a novel the size of War & Peace to cover...! First, you need to cover the fuselage with something, either an iron on fabric or glass cloth and resin before painting. Then you have to decide what to cover the wings with: fabric or film. A lot depends on where you intend to fly it; slope or aerotow?

I tried War & Peace once and gave up on it after a quite short time, but I did read A Brief History of Time by Stephen Hawking !

Seriously though. The open works are covered with Ceconite 104 and fixed with Balsalok so it would make it difficult to cover it with any other type of film or glass on the non Ceconite parts. Plus, I have already sprayed the tailplane with acrylic undercoat. That's when I realised that balsa doesn't give the same sort of finish as the wood that I turn on my lathe!

Would the old fashioned cellulose dope be better than sanding sealer I wonder? It's one of your early plans with the Frise ailerons and the fuz is 1/32" ply covered with 1/8" planked from the back of the cockpit forward.

I will be slope soaring almost all of the time on the hills around the Stroud area with the South Cotswold Soaring Association, so a nice tough finish will be better. I haven't ever done any aerotowing. I think it would terrify me!

John,
As Chris W has said, the fuselage needs to be covered in something such as fabric or glass cloth to suit the full size surface/landing environment. The fabric needs the weave sealing with dope or similar before painting, whereas the glassed surface will take paint directly.
For Ceconite covered wings (as for the old Solartex covering), just seal the weave with dope & that can be painted also.
Just make sure that your paint is compatible with the covering sealant.

These techniques have worked on the various builds over the past few years, including all of the 1/3 scale prototypes built for Cliff Evans including the T21 & ASK13 to name the 2 latest ones.
Peter

Thank you Peter, I will see if I can get some dope?

What would you recommend? I am looking at Eze Dope on Amazon at the moment. It's a non celulose dope?

Hi John,
I’ve never used the Eze dope but I guess it should work - just a water based alternative? This is certainly less smelly & probably compatible with most paints.
I normally get cellulose dope in larger (0.5L tins) & thin it a little for application with a 3/4” or so brush.
The cellulose dope comes in shrinking (as used with tissue etc. which slackens when wetted) or non-shrinking variety. With Ceconite, I use the non-shrinking type as the Ceconite can be taughtened if necessary with gentle heat from an iron afterwards.
Peter

The Eze Dope I was looking at is a shrinking dope and the Ceconite has already been done with my film iron so I don't want that or it will either pull it off of the frame or distort it!

I will see if I can find some non shrink cellulose dope tomorrow? In fact as far as I can recall the job of the dope is to fill the grain on the wood and the weave on material coverings. Is that correct? Because if it is then my cellulose sanding sealer would do the job perfectly?

Off subject for a moment I am not getting emails letting me know that I have replies even although I have the box ticked. Any ideas please?

John,
My take on sanding sealer is that it is basically a cellulose dope, loaded with particles to improve its filling ability.

Can’t help on the notifications issue, but maybe Cliff will be along to advise.
Peter

I have got some non shrink cellulose dope from Leeds Model Shop and the smell of pair drops takes me back a lot of decades! I was surprised to see on the tin to thin it with cellulose thinners as I had read that these dopes should have all sorts of expensive thinners chucked in them.

I bit the bullet and tried it out on an elevator then as it looked good I have now done most of the control surfaces just the stbd ones to do. Then on to the port wing.

For the fuz I may well cover it with doped tissue?

John,
You will probably need to go over coated wood areas with fine sandpaper to smooth off as the dope with raise the grain - but I’m sure you are well aware of that from other woodwork jobs.
The edges of the Ceconite will also benefit from similar treatment. I usually tidy up edges using a fine sanding block, reseal the edges & then go over the edges with a hot iron to smooth everything off.
Peter

Hi John.
I have been following this thread for a while now and have resisted replying till now. Like Peter and Chris I come from a dope and tissue age and have seen and tried most finishes. If you go down the bare balsa and dope/sanding sealer route I guarantee that you will soon regret your decision. After a few slope landings the nicely finished balsa sheeting will be splitting among the grain as the structure flexes. It will also be covered in deep scrapes and scratches.
Balsa surfaces need something to toughen the surface, be it tissue, nylon, tex or glass cloth. No ifs, no buts! It would be best to bite the bullet and choose the most suitable option. Looking at your structure which is mixed open and sheeted construction I would have covered the whole model in tex or diocov. Alternatively cover the sheeted surfaces in 25gm/m glass cloth then cover the open sections with tex or diacov. It will be more satisfactory in the long run.
Best of luck.
Brian

I was going the 'feather' the edges of the Ceconite Peter, but ta for the reminder. Knowing my memory I would have probably forgotten

Brian, thank you for your input. It's too late now to cover the open areas with tex or the like as they are already
covered with the Ceconite, but the idea of tissue on all of the other surfaces, fuz included is what I think I will do. It should be a good and light solution, i hope!

My 5th scale Grunau Baby was originally covered completely in tissue/dope, but as you know, slope soaring isn't friendly to it so the open sections are covered with Ceconite, glued down with Balsalok, and dope. That was about 30 years back. My Minimoa also has Ceconite/dope for the open sections of the wings and tail feathers. the solid bit, sanding seal/paint. The fuz is balsa planked/sanding seal and painted white, again about 28 yeas old. They are both only ever flown on Selsey Common,Stroud and it's a very scale friendly site, so no problems there.

This is the Minimoa wing. I included spoilers as well, not on the plan, because the write up said that if you wanted to get it back down in lift they were a good idea. Rudder/elevator and I love flying it.

The Habicht will almost certainly only be flown there too