Building Tips and technical articles. > Paint and finishing
Hello, my name is Steve, and I'm a procrastinator
Mike Alimov:
Here are my thoughts, based on recent experience helping my boys build their Nats airplanes (electrics, profile):
- Sheeted foam wings have enough strength in the wood sheeting alone, IF (IF!) joined together properly. I would expect that Tom has provided an internal slot in the foam for the customary lite-ply spar. Join the two halves over the spar (glue applied to the spar, of course, and bellcrank/pushrod installed inside). This should be done in the cradles/schucks to maintain alignment. When dry, run a 2" wide strip of fiberglass tape over the entire center seam using laminating epoxy. When cured, this assembly by itself should be strong enough to withstand flight loads and not fold. Any type of covering will further reinforce that.
- From here on, I would go with a heat shrink covering on wing+flaps and stab+elevators, while doing a Rustoleum finish on the fuselage. Here's why. Fuselage typically has some compound curves, hard-to-reach places, and areas with plywood (nose doublers, for example). It is much, much harder to do a decent Mono(Ultra)cote finish on the fuselage than it is on wings and tail.
- For heat shrink covering, I would pick Monokote over Ultrakote any day. Yes, I've used both. The best written and illustrated source for high quality Monokote covering is a book by a Toledo-winning master Faye Stilley called "Covering R/C Airplanes". Available from Amazon and possibly elsewhere. Worth its weight in gold.
- Fuselage: sand everything going from ~220 grit down to 600. Spray two coats of Rustoleum primer. Next day wet sand with 600. Spray Rustoleum (see a recent thread with my comments). Let dry for 2 days. Done.
- Mark fuselage/wing joints on the Monokote, and melt 1/2" diameter circles spaced out by 1/4" in Monokote using low-power soldering iron. This should provide enough glue area to join wing and fuselage.
- Glue wing/tail to fuselage, using prepared alignment jigs, using epoxy. Remove excess with Q-tips. When cured, mix epoxy with microballoons and make fillets.
Hope this helps.
Brett Buck:
--- Quote from: Steve Berry on April 28, 2021, 08:27:05 PM ---This is all really good info, but still hasn't really answered my question.
--- End quote ---
Since this is sheeted foam, you can do what I did -
Carbon mat adhered with nitrate dope
Klasskote White primer
spot-fill any pinholes with polyester filler (Bondo, etc) - in TINY amounts, you should see barely-visible red dots
Klass Kote color of choice
2-part automotive clear
An alternative is to replace the KlassKote color with automotive base coat color; do that, and you are in the Phil Granderson/Jim Aron territory. Klass Kote is nice, and Jim used the primer on his airplane, but the automotive colors are a lot easier to deal with, cover better, and a lot easier to clean/safer for the gun. The downside is it isn't remotely fuelproof, so if some fuel gets underneath the clear, you are in trouble. That should not be a problem with electric, and I will probably use House of Kolor base coat next time on my electric.
Brett
Steve Berry:
--- Quote from: Mike Alimov on April 30, 2021, 03:56:40 PM ---Here are my thoughts, based on recent experience helping my boys build their Nats airplanes (electrics, profile):
- Sheeted foam wings have enough strength in the wood sheeting alone, IF (IF!) joined together properly. I would expect that Tom has provided an internal slot in the foam for the customary lite-ply spar. Join the two halves over the spar (glue applied to the spar, of course, and bellcrank/pushrod installed inside). This should be done in the cradles/schucks to maintain alignment. When dry, run a 2" wide strip of fiberglass tape over the entire center seam using laminating epoxy. When cured, this assembly by itself should be strong enough to withstand flight loads and not fold. Any type of covering will further reinforce that.
- From here on, I would go with a heat shrink covering on wing+flaps and stab+elevators, while doing a Rustoleum finish on the fuselage. Here's why. Fuselage typically has some compound curves, hard-to-reach places, and areas with plywood (nose doublers, for example). It is much, much harder to do a decent Mono(Ultra)cote finish on the fuselage than it is on wings and tail.
- For heat shrink covering, I would pick Monokote over Ultrakote any day. Yes, I've used both. The best written and illustrated source for high quality Monokote covering is a book by a Toledo-winning master Faye Stilley called "Covering R/C Airplanes". Available from Amazon and possibly elsewhere. Worth its weight in gold.
- Fuselage: sand everything going from ~220 grit down to 600. Spray two coats of Rustoleum primer. Next day wet sand with 600. Spray Rustoleum (see a recent thread with my comments). Let dry for 2 days. Done.
- Mark fuselage/wing joints on the Monokote, and melt 1/2" diameter circles spaced out by 1/4" in Monokote using low-power soldering iron. This should provide enough glue area to join wing and fuselage.
- Glue wing/tail to fuselage, using prepared alignment jigs, using epoxy. Remove excess with Q-tips. When cured, mix epoxy with microballoons and make fillets.
Hope this helps.
--- End quote ---
This helps, tremendously. Exactly the type of info I was looking for. Thanks.
--- Quote from: Brett Buck on April 30, 2021, 04:06:06 PM --- Since this is sheeted foam, you can do what I did -
Carbon mat adhered with nitrate dope
Klasskote White primer
spot-fill any pinholes with polyester filler (Bondo, etc) - in TINY amounts, you should see barely-visible red dots
Klass Kote color of choice
2-part automotive clear
An alternative is to replace the KlassKote color with automotive base coat color; do that, and you are in the Phil Granderson/Jim Aron territory. Klass Kote is nice, and Jim used the primer on his airplane, but the automotive colors are a lot easier to deal with, cover better, and a lot easier to clean/safer for the gun. The downside is it isn't remotely fuelproof, so if some fuel gets underneath the clear, you are in trouble. That should not be a problem with electric, and I will probably use House of Kolor base coat next time on my electric.
Brett
--- End quote ---
I may do this exact thing on my next one. I just need to get set up for spraying paint first. Unless....I use polycrylic instead of nitrate dope, and use the spray cans of auto paint. Minimize the smell so the wife is happy, and minimize the wallet impact. Thanks for the info and a workable process.
Steve
Brett Buck:
--- Quote from: Steve Berry on April 30, 2021, 07:30:17 PM ---This helps, tremendously. Exactly the type of info I was looking for. Thanks.
I may do this exact thing on my next one. I just need to get set up for spraying paint first. Unless....I use polycrylic instead of nitrate dope, and use the spray cans of auto paint. Minimize the smell so the wife is happy, and minimize the wallet impact. Thanks for the info and a workable process.
Steve
--- End quote ---
You are welcome. I would note that if you are going to use film over your sheeted foam wing, *there is nothing else required*, just put it straight on the wood. It takes good technique and nerves of steel (because on mistake and you might have to start over), but otherwise it is very satisfactory, the point that one of Bill Fitzgerald's airplanes (David's dad, unfortunately no longer with us) looked like the very best dope job ever, and several of us have gotten 15 points at the NATs with a just Monokote over balsa.
The technique is critical and very demanding (I posted the technique I use, which is very similar to that used by Bill F and Gary McClellan back in the day), but done correctly it looks like it was made of molded plastic. I *would not* recommend trying to put film over a fuselage - just paint it - but for the wings and the tail it is perfectly acceptable and admirably light.
Brett
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