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Sandable Filler Material

Post  Sig Skyray on Wed May 06, 2015 7:29 am

What's the best material to fill gaps like around triangular engine blocks that flank the fuse so you get a nice, smooth surface?  Epoxy doesn't seem so sandable.  Wood filler?  What type? I used some very light drywall spackle on my wings to fill the grain for a nice paint finish.

If I did use wood filler, would there be any adverse effects of the materials reacting if I put a thin coat of epoxy over it like was suggested to me to fuel-proof the nose area?  New modeler here Smile
Greg


Last edited by Sig Skyray on Wed May 06, 2015 7:56 am; edited 1 time in total (Reason for editing : Clarification)
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Re: Sandable Filler Material

Post  pkrankow on Wed May 06, 2015 8:10 am

I am using lightweight spackeling compound. DO NOT use vinyl types below dope as it is a guaranteed blistered mess. I am using Dap Fast and Final under Rustoleum with good success. I am filling grain to save paint and effort, as well as shallow imperfections. I have not done heavy fillets or similar bulk buildup with this product.

http://www.amazon.com/12141-FastN-Spackling-Interior-Exterior/dp/B0006MXS10/ref=sr_1_1?ie=UTF8&qid=1430917686&sr=8-1&keywords=dap+fast+n+final

Buy it locally, since it seems everybody has it, and use the smallest container you can. I've only used an inch out of my 1/2 pint on 3 models, and some wall repair.

When it starts to dry out toss it. Also don't return any to the container.

Phil
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Re: Sandable Filler Material

Post  KariFS on Wed May 06, 2015 10:53 am

"Traditionally", before paint, you first sand the balsa as smooth as you can, with 240 or even 400 grit, then apply a coat of 30-50% thinned dope or clearcoat (compatible with the paint you are going to use), sand, apply another coat, sand and repeat until you are happy with the surface. After maybe two coats of clear you can use filler to fill dents and such. The filler I have used is not water soluble, it is meant for outdoors and can be painted with almost anything.

Long time ago I heard some oldtimers talk about adding something to dope to make it fill the grain better, not sure if it was talcum powder or something... Never seen or done it myself, but I may look into that after I get to the skill level where my planes may last longer structurally than finish-wise Smile

For airplane use I would recommend that you make the basic shapes out of balsa and just finish the surface with spackel or filler. Thick layers of filler are heavy and phone to cracking.
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Re: Sandable Filler Material

Post  TDbandit on Wed May 06, 2015 11:23 am

MicroBalloons, Dave Brown products used to make it other companies make it too Alumilite is one which can be gotten at hobby town and ther like. It's very light and all you do is mix it with what ever resin or material you are using by volume. You can use balsa dust too as well. (Bandit)
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Re: Sandable Filler Material

Post  Sig Skyray on Wed May 06, 2015 11:44 am

KariFS wrote:"Traditionally", before paint, you first sand the balsa as smooth as you can, with 240 or even 400 grit, then apply a coat of 30-50% thinned dope or clearcoat (compatible with the paint you are going to use), sand, apply another coat, sand and repeat until you are happy with the surface. After maybe two coats of clear you can use filler to fill dents and such. The filler I have used is not water soluble, it is meant for outdoors and can be painted with almost anything.

I'm planning on using Rustoleum gloss over Rustoleum gray Pro primer and avoiding dope. No plan on clear either since I'll have a nice gloss.

The gaps I need filled on the nose blocks is not a lot. Just need something light and sandable but it seems to me spackle is not the right product. Greg
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Re: Sandable Filler Material

Post  Sig Skyray on Wed May 06, 2015 11:52 am

TDbandit wrote:MicroBalloons, Dave Brown products used to make it other companies make it too Alumilite is one which can be gotten at hobby town and ther like. It's very light and all you do is mix it with what ever resin or material you are using by volume. You can use balsa dust too as well. (Bandit)
Looks like what I need. Hope I can find locally.
Thanks Bandit. Greg
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Re: Sandable Filler Material

Post  RknRusty on Wed May 06, 2015 3:00 pm

I got a big jar of it from Sig, but I see now my LHS has it in small bottles with a nozzle dispenser too. I don't follow the instructions any more, just spoon it into my freshly mixed puddle of epoxy. It soaks up a surprising amount to get the consistency you want. I don't know about sanding it, I just try to smooth and shape it and pull the masking off before the glue kicks.
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Re: Sandable Filler Material

Post  GallopingGhostler on Wed May 06, 2015 4:31 pm

I've found the synthetic spackling compound Smart Non-Shrink Wall Fix

works really well, spreads smoothly, adheres well, flexes (unlike traditional spackling which is somewhat brittle) and is easy to sand. Seems stable as I painted it with Coverite Balsarite, which is dope like in nature.
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Re: Sandable Filler Material

Post  pkrankow on Wed May 06, 2015 7:22 pm

Dope + corn starch works pretty good. The dope needs thinned, and the correct thinner must be used, which is a pain.

The Hobbyco lightweight filler is spackle, according to what Stunthanger says.

When the grain and small gaps are filled with spackle, most is sanded off so only what remains trapped in the gap is left. After paint is applied the paint is bonding the filler in place as well.

Rustoleum is much more forgiving. Using grey automotive primer, then sanding down to the wood, reapplying primer, sanding, reapplying, ad nauseam...the results are excellent and seem lightweight since the vast majority of primer is removed...as dust.

Using the lightweight spackle instead of primer provides excellent results with a lot less ad nauseam.

Phil
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Re: Sandable Filler Material

Post  dinsdale on Wed May 06, 2015 8:03 pm

... Sig Skyray wrote:Epoxy doesn't seem so sandable.
Firstly, every surfboard or windsurfer maker or repairer, amateur or pro would disagree entirely with that sentiment, as would I. However, not withstanding that, dope with cornstarch works a-treat and is quite light and easy to come by. I use the cornstarch alternative to talcum powder.
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Re: Sandable Filler Material

Post  Sig Skyray on Wed May 06, 2015 8:13 pm

Just bought some micro balloons at Hobby Town.  Running a test to compare how sandable it will be with straight epoxy and 2 different concentrations of microballoons.  I know it will sand easier with more MB's, but how much is really needed is the test.  I made some nice looking wing fillets using balsa wood dust with 30 minute epoxy and wetting my finger with alcohol as Rusty suggested.

I covered the tops of my balsa plank wings lightly with this DAP product that looks almost the same as yours, Phil.  Yes I'm planning on one coat of gray primer and expect after sanding and finish coat to have a very nice gloss finish.  

Gee, after all this input and research, hope I don't nose dive the Skyray to splinters the first day out. Learning a lot and plan to build more so it's all good.

Greg

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Re: Sandable Filler Material

Post  RknRusty on Wed May 06, 2015 8:36 pm

Sig Skyray wrote:...
Gee, after all this input and research, hope I don't nose dive the Skyray to splinters the first day out.  Learning a lot and plan to build more so it's all good.

Greg
just don't forget tp take a picture of it with your son holding it out on the circle before you launch it the first time. If you know what I mean Lol
Rusty

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Re: Sandable Filler Material

Post  Sig Skyray on Thu May 07, 2015 6:38 am

lol yep, I'll be sure to get pics of the lad with my plane, and his Lil' Wizard before our first flights :-)
Our builds are not progressing quickly... we're working on them betwixt football practice, cub scouts, etc.

On dope... I'm such a green builder.  Guillow's/Midwest has Aerogloss clear gloss, clear flat, balsa fillercoat primer, sanding sealer, etc.
What is the basic dope of choice for mixing with corn starch for light filling of crevices, like around nose blocks?
Thin dope with lacquer thinner?

Greg


Last edited by Sig Skyray on Thu May 07, 2015 6:40 am; edited 1 time in total
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Re: Sandable Filler Material

Post  ian1954 on Thu May 07, 2015 6:38 am

http://www.stitspolyfiber.com/superfil.html


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Re: Sandable Filler Material

Post  Sig Skyray on Thu May 07, 2015 7:00 am

Thanks Ian.  Rusty mentioned this was popular stuff over at Stunthanger.com (What's with the "er" in Hangar anyway?)

Brodak has their labeled superfil also: http://brodak.com/aeropoxy-lite-super-fil.html
Quick research indicates aeropoxy lite is very different from super fil.  Described for use for the same purposes, users indicate is doesn't stand up to the authentic super fil.  Now, to find where to purchase a smaller quantity of superfil rather than a quart or gallon.

Greg
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Re: Sandable Filler Material

Post  pkrankow on Thu May 07, 2015 7:32 am

A hangar is a building and a hanger is a person who hangs something, or a hook which is used to hang something... I am baffled by it too.

With dope USE THE CORRECT THINNER!

USE THE CORRECT THINNER!

If I was unclear THE CORRECT THINNER SHOULD BE THE ONLY THINNER USED!

Adding lacquer thinner to dope will most likely curdle the paint.

Blending thinner to suit using chemical named thinners after research is a choice. I had poor results which involved excess shrinking and coating failure leading me to swear off dope.

Test fillers under the paint, especially dope.

Also be careful with layering different types of paint. I learned the hard way that dope under enamel (Rustoleum) under Balsarite causes the enamel to blister and fall off. What appears to have happened is the balsarite softened the dope through the enamel. Balsarite goes over enamel on wood or dope on wood without problems.

Phil
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Re: Sandable Filler Material

Post  Ken Cook on Thu May 07, 2015 3:24 pm

In the event that most aren't aware, the Skyray is tail heavy. It requires about 3-4 nose breaks before it flies correctly when glued back on with CA. I wouldn't be overly concerned with a fillet at the cheek block. The block already is making a stress riser right at that intersection and it will snap the nose off with the engine directly behind the cheek block. The solution to fixing that is to provide a piece of 1/64" ply with the grain running the same direction as the fuse and notch it out to slide back onto the wing about 1 1/4" then apply the cheek blocks over it. For added strength and reinforcement a strip of 1/2 oz glass cloth can be laid over that joint with slo cure epoxy or finishing resin. This is structural and not cosmetic like a filler.
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Re: Sandable Filler Material

Post  Sig Skyray on Thu May 07, 2015 3:56 pm

Ken Cook wrote:        In the event that most aren't aware, the Skyray is tail heavy. It requires about 3-4 nose breaks before it flies correctly when glued back on with CA. I wouldn't be overly concerned with a fillet at the cheek block. The block already is making a stress riser right at that intersection and it will snap the nose off with the engine directly behind the cheek block. The solution to fixing that is to provide a piece of 1/64" ply with the grain running the same direction as the fuse and notch it out to slide back onto the wing about 1 1/4" then apply the cheek blocks over it. For added strength and reinforcement a strip of 1/2 oz glass cloth can be laid over that joint with slo cure epoxy or finishing resin. This is structural and not cosmetic like a filler.

I'm building a 1/2A. Those are tail heavy?

I just glued on my nose blocks... too late for fuse doublers, but I'll note that on the plans for next time.  Note, the cheek just touches the wing.  That's probably not good.  Next time I would finish up the nose blocks before installing the wing.
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Re: Sandable Filler Material

Post  Ken Cook on Thu May 07, 2015 4:48 pm

This is in regards to the 1/2A even with a Black Widow on the nose. They generally come out tail heavy. Not to the point of uncontrollable but twitchy. As I mentioned, a couple of repairs tames it spot on. The plywood I mentioned does the same thing in terms of weight but from a structural standpoint it typically doesn't break. The Skyray nose is weak and generally it can take about 3-4 ground poundings before it snaps off. It breaks like I mentioned directly at the back of the cheek block. What I found works quite well on this model and many others that use a plank wing is to split the wing in the center. I use a piece of 1/8" x 3/8" bass as a spar and glue the wing sections back onto it. The Skyray tends to flex it's wings through hard maneuvers and this strengthens it up. This can really bleed off speed and maneuverability. To keep the weight down on these, I usually put two coats of dope and all color and trim is done with jap tissue. Ken
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Re: Sandable Filler Material

Post  RknRusty on Thu May 07, 2015 4:59 pm

It'll be fine.
And yeah, they do come out tail heavy, so use some wood glue and thin paint or Monokote for the empennage. I think I mentioned that on the phone before we got started on this bird. When you glue the nose back on, or better yet, make a new nose, your learning curve will have been kick started by these threads, and your creative sludges of building expertise will result in a stronger, better, more stable Skyray. You have the technology... and the tech support.
Rusty


Last edited by RknRusty on Thu May 07, 2015 9:29 pm; edited 1 time in total (Reason for editing : Fixed a mistake)

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Re: Sandable Filler Material

Post  Sig Skyray on Thu May 07, 2015 5:33 pm

Didn't you mean to say tail-heavy Rusty? And now I do remember you mentioning that. I failed to jot that in my notes.

Thoughts... Why not find and adjust the CG before the first flight? I will investigate how to do this but can't it be found fairly close by trying to balance the fuse (with engine attached of course?) on a pencil or something round?

We could use a wiki so you experts don't have to keep typing the same advice to us newbies. I find the search function built into the site many times gives me zero results for what I know is there. Tried both buttons, search inside this site and search this site by Google.

So next investigation topic is how to trim a plane. As always, many thanks to all. Greg
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Re: Sandable Filler Material

Post  RknRusty on Thu May 07, 2015 9:43 pm

Sig Skyray wrote:Didn't you mean to say tail-heavy Rusty?  And now I do remember you mentioning that.  I failed to jot that in my notes.

Thoughts... Why not find and adjust the CG before the first flight?  I will investigate how to do this but can't it be found fairly close by trying to balance the fuse (with engine attached of course?) on a pencil or something round?

We could use a wiki so you experts don't have to keep typing the same advice to us newbies.  I find the search function built into the site many times gives me zero results for what I know is there.  Tried both buttons, search inside this site and search this site by Google.

So next investigation topic is how to trim a plane.  As always, many thanks to all.  Greg
I did mean Tail Heavy. I edited it so it's right now. You can build with the CG in mind. Of my last three planes, the Yak-9, Osprey(Skyray35-Flite Streak bash), and ARF Oriental, two have needed no weight anywhere to balance, and the Osprey took some lead in the nose, though my flying buddy didn't think so. But his hand is much steadier than mine. On 1/2A I put round head sewing pins in the wingtip where the CG, measured at the root, should be. I can pick it up by the pins as I adjust. But it'll never be true until all the finish is on it and dry.
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Re: Sandable Filler Material

Post  Ken Cook on Fri May 08, 2015 4:29 am

Not all engines weigh the same. I mean this in regards to Cox engines . I have many Black Widow engines from different years that all weigh slightly different from one another. It certainly wouldn't hurt to put about 4-5 grams of nose weight in the plane. If you know a golfer, they use a lead tape for their golf clubs. I keep this in my pitbox and this can easily be trimmed and formed around a leading edge or nose block. It can later be fitted into the plane. It will fly fine just the way you have it, it just might hunt up or down while flying. This plane is certainly a good flying plane and capable of doing pretty much everything. One thing I would pay close attention to is the single screw control horn provided with the kit. A poor design which can result in a crash if not closely inspected. The horn will just rotate on the screw vs moving the elevator. There's no footprint on that horn so tightening it usually crushes the wood not to mention pull through the wood. I dislike that horn due to it's size and I use a medium Dubro horn . A small drop of epoxy on the mating side of the horn to elevator can prevent it from turning.
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Re: Sandable Filler Material

Post  Sig Skyray on Fri May 08, 2015 6:51 am

RknRusty wrote:I did mean Tail Heavy. I edited it so it's right now. You can build with the CG in mind. Of my last three planes, the Yak-9, Osprey(Skyray35-Flite Streak bash), and ARF Oriental, two have needed no weight anywhere to balance, and the Osprey took some lead in the nose, though my flying buddy didn't think so. But his hand is much steadier than mine. On 1/2A I put round head sewing pins in the wingtip where the CG, measured at the root, should be. I can pick it up by the pins as I adjust. But it'll never be true until all the finish is on it and dry.
Rusty

I was able to find *Lots* of good info on CEF about finding and adjusting the CG, so with lots of good notes extracted, I'm good to go now. And I assume trimming the plane really applies just to adjustment of the CG as to how it handles.
Greg
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Re: Sandable Filler Material

Post  Sig Skyray on Fri May 08, 2015 6:55 am

Ken Cook wrote: One thing I would pay close attention to is the single screw control horn provided with the kit. A poor design which can result in a crash if not closely inspected. The horn will just rotate on the screw vs moving the elevator. There's no footprint on that horn so tightening it usually crushes the wood not to mention pull through the wood. I dislike that horn due to it's size and I use a medium Dubro horn . A small drop of epoxy on the mating side of the horn to elevator can prevent it from turning.
Great, thanks for pointing that out Ken. I'll beef that control horn mount up.
It's also been mentioned that the bellcrank screw is a bit wimpy as self-threaded into a small piece of ply on one side of the wing and I'd be better off bolting it thru the wing with ply on both sides to sturdy it up.
Greg
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