Skin modeling with foam sheets - Page 2 - RC Groups
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Dec 18, 2017, 09:46 PM
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osern's Avatar
Quote:
Originally Posted by 62pilot
Yup. Did this years ago. Good job.
I'm glad that you guys finally are interested!

If I make vid,I'll start with building the most needed parts like modern jets nose cone,
This should be practical and easy to build and repair for frequently damaged part without gaining dead weight from filler,although EPO could resonate from heating water,you may try that for a refresh one .

When you'v got that then you'v got that.
Last edited by osern; Dec 19, 2017 at 01:48 AM.
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Dec 18, 2017, 10:40 PM
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osern's Avatar
Quote:
Originally Posted by portablevcb
Yep, not very good finish and still not very durable unless covered with something very durable. Yes, the foam I have used is the "smooth" stuff you are referring to. It still needs a surface finish like fiberglass or paper covering to be suitable for what I would consider a good scale model.

Don't get me wrong, I do make foam planes, just not detailed scale planes. They are still scale, just not detailed. Such as the Pietenpol I am making now and the Citabria that I will make next. They will both need a little forming but not much. But...I do not expect them to last very long without getting dinged up. Kinda like the foamy ARFs that I have had. Good for a year or so. OTOH, my balsa scale models hold up for many years. I have one that is finally showing it's age after ten years of use (and several crashes).

https://www.youtube.com/watch?v=FOqkUmWkrmI

charlie
I'm glad to have you back on this surface finish issue that I'm pretty concern about,too.
It can go picky or easy on it for aspect of finish like prefabricated airframes with bead gap on it or finish like flawless glassing jets,that'll loop back to what power level you've got to load those extra weight of covering for flying models,that's bothering to me all the time.

Meticulous grind filler or fine putty will do for covering up those pores on surface with water thinning,no significant weight gaining and with capabilities to sand smooth if it bother me to.
I tried to use cement paint mix with acrylic as thick paint to cover up defects on surface and then sand out extra thickness for larger scale building which with plenty of power that thick paint covering counts for nothing,turning out with good result.

With miniature size building,weight matters for every added covering, in this case I'll try to make the joint seamless with trimming or sanding without filler,paint without any covering,with minor water thinning filler at most.
It's acceptable for me that molded foam airframe that you can buy would be done as far as this condition on surface finish.

You can do more approaches with alcohol thinning epoxy or fiberglass if you have good T/W ratio on result, but the glassing surface with thin epoxy that texture of clothe from fiberglass appears,too thick epoxy gains dead weight,all loop back to the power issue.


My philosophy is any thing cover on foam will tear off, even fiberglass will tear off due to air bubble gaps in between or misshape of inner wall,they'll crack with major crash after all for any covering,so the convenient way to fix and build would be the best solution to me.

It seems that Pietenpol kind of airplane need monokite covering to fit public impression,to make them shiny glow, to meet with or without light weight building needs would determine what covering should be taken,but uptodate micro light weight covering can't be ironed on foam for heat,the left options would be clear paint or hot glue gun with low temperature "ironing" on color tape,that's some ideas that I can only thick out,for senior modeler like you,sir,there must be things that I'v not learned yet.

regard and respect

Osern
Last edited by osern; Dec 25, 2017 at 12:38 AM. Reason: poor English texting
Dec 19, 2017, 02:38 AM
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osern's Avatar
Quote:
Originally Posted by portablevcb
The problem for most of the detail scale stuff is surface texture. To make a good surface for that any foam needs to be covered with something. Tape does not work for this. Too many edges and bumps. Shiny surface. Don't know if it can be painted with detail.

So, scale foam planes are usually covered with fiberglass or one of the paper coverings that can be sanded smooth for painting and detailing. The underlying shape still must be accurate, ie, no seam lines.

Most use fiberglass simple because of the damage issue. Once we have spent many hours detailing a plane we want it to last more than a few years. Bare or even taped foam will get dinged up badly in a short period of time and start to look bad.

But, for those cases where we aren't picky about surface finish the bare foam works ok. It is also used a LOT for the smaller scale stuff, especially the micro.

We can still get some depron from RCFoam but not sure how long that will last. Already hard to get 3mm. But, the cheap foam poster board is a decent substitute.

If the MPF stuff can be made in 3mm and 1mm then you will be filling a 'hole' in the supply chain. 6mm is a bit thick for the smaller planes but would do well for the larger ones, and, as mentioned, it is thick enough to allow sanding down the seams.

charlie
Thanks,Mike
I'm getting the picture now with your clarify.
It's my turn to worry about that depron supply would be short in Taiwan if they are mainly import from Europe,
by your judgement,are those depron I'd shown would be those?
I think maybe there should be some local manufacture can produce depron in Taiwan selling cheap without shipping,just not sure yet.

regads

Osern
Dec 19, 2017, 07:00 AM
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osern's Avatar
I suddenlly find that I opened this thread in wrong category again,should had put in Foamy Scratch class,just I hate the word foamy that skip them unintentionally ,that's some ofending to balsa fans,I owe you a huge apoligizing,this is truly embrrassing.
Last edited by osern; Dec 19, 2017 at 07:15 AM.
Dec 19, 2017, 07:36 AM
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portablevcb's Avatar
It is not in the wrong forum. It is for any scale building method.

But, yes, there is another one dedicated to foam.
Dec 19, 2017, 08:24 AM
An itch?. Scratch build.
eflightray's Avatar
osern, what's the largest model you have built using that technique ?, as your picture seem to show quite small ones going by the surrounding objects.

.
Dec 19, 2017, 09:32 AM
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osern's Avatar
Thanks for your understanding and forgiving,I'm relief now,
I just too attach to this forum that almost forget about the other one,they are more dedicate to big guys with 70MM up EDF,I thought my little guys would suffer with some bulling there,and there is a guru from Taiwan with talent to build a lot of cartoon fattie planes in that forum attracting lot of huge fans,don't want to be there like overshadowed.

For Ray,sir
The largest size I'd built into were 64mm EDF size,I use plastic corrugated board to against impact in between head part and fuselage as inner wall beneath thin skin,lately I use EVA(puzzle floor foam mat cutout) to make super indurable nose cones.
No match to your large beauties,they are awesome!

I tried to use 10MM thick depron boards to bend up the curve shape,that can be done with roughly smooth and need lots of surgery cuts for v-notches and butting out strength to squeeze them to bend,so I use 4mm thin depron for compound curve parts only,leave flat and square parts with 10mm depron boards.
The following pics are in early stage that I'd done with larger ones,due to short of fly field nearby, I determined to shift my route to build smaller ones to fly in more available open lot or parks around my living hood.

regards and respect
Last edited by osern; Jan 15, 2018 at 11:55 PM. Reason: poor English texting
Dec 19, 2017, 10:23 AM
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That last image: "experimental plastic corrugated board building with similar thinking way of shaping", is amazing! What thickness board did you use?
Dec 19, 2017, 10:58 AM
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osern's Avatar
Quote:
Originally Posted by benz11
That last image: "experimental plastic corrugated board building with similar thinking way of shaping", is amazing! What thickness board did you use?
Hi,benz

It's about 3.5mm thick as I measured.
They are about weight with depron one,striated bumps will pop out around any bent corner,it's not obvious on leading edge of main wing,but ugly in compound curve within head part that need plastic sheets to cover up,the disadvantage of this building is that vertical faces will twist horizontally as a result of that they are pretty difficult to secure the motor and keep control surface steady.
I stitched them with wire to joint parts on the back side hiding,there is nothing work for glue.
Just a experiment,very hard to fly due to unstable thrust angle and twisting surface.

regards
Last edited by osern; Dec 19, 2017 at 11:42 AM. Reason: poor English
Dec 19, 2017, 09:28 PM
Culper Junior
So you're saying you just take a piece of sheet foam and manipulate with your fingers until it looks like something?

I was thinking you are talking about something like DTF but that can't be right.
Dec 19, 2017, 10:20 PM
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osern's Avatar
Quote:
Originally Posted by aeronca52
So you're saying you just take a piece of sheet foam and manipulate with your fingers until it looks like something?

I was thinking you are talking about something like DTF but that can't be right.
eh,true that I finger them,with nail and finger tips without stick,rod or club stick rolling,
the most important idea about this building is geometry dividing simply from easy curve profile to shape round shape,
it's with more interesting to shape with one piece as possible and get rid of dust all around house with heavy sanding work.

Osern
Last edited by osern; Dec 20, 2017 at 10:26 PM. Reason: poor English texting
Dec 20, 2017, 02:12 AM
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osern's Avatar

Nose Cone Geometry


It took me long util I realize those geometry behind that I couldn't just bend and roll up a nose cone without curve edges.
Even you can roll depron like a piece of paper but you'll never roll cutout pieces with straight edges into roundly convex cone.

See the quick sketches below, the flatten draw (unfold draw) of cone template with straight edges which are commonly seen can only roll up a straight cone.

Template combined with profiles of 3-view with curve outlines, depron can bent them roundly in 3 spatial dimensions with the capabilities of shrink and bend easily in limited angle say less than 35degree.

Scribe lines or grooves on the back side would force depron bent toward the line going,faces formed with lines that piece by piece deflect into some angle,so these lines define faces and shape,if lines go straight then shape go straight,to form a round bullet shape you need to think of them like contour line of a geography map of a slop for a nose cone.
Last edited by osern; Dec 20, 2017 at 10:21 PM.
Dec 20, 2017, 11:18 AM
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Thomas Nelson's Avatar
Here are some ideas from a few years ago. The linked plan produces a very scale (silhouette) F-16 Falcon using the same approach you are using. The technique uses 'stressed skin' or 'monocoque' construction, with no formers, bulkheads or longerons, which is great for EDF.

tn
Dec 20, 2017, 11:28 AM
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osern's Avatar
Quote:
Originally Posted by Thomas Nelson
Here are some ideas from a few years ago. The linked plan produces a very scale (silhouette) F-16 Falcon using the same approach you are using. The technique uses 'stressed skin' or 'monocoque' construction, with no formers, bulkheads or longerons, which is great for EDF.

tn
Wow! this is incredibly smooth that I can't ever dream of!
Are you sure they are hand work?
What I'm pursuing is fast build without using mold and heat,the most difficult parts is the inward curve in back of the hatch,no way you can bend without creasing or plug mold,that is in the level of 'gods hands!
Have to do more research on him!

Regards

Osern
Last edited by osern; Dec 20, 2017 at 08:21 PM.
Dec 20, 2017, 11:37 AM
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osern's Avatar
Quote:
Originally Posted by osern
Wow! this is incredibly smooth that I can't dream of!
Are you sure they are hand work,
What I'm pursuing is fast build without using mold and heat,the most difficult parts is the inward curve behind the hatch,no way you can bend without creasing or plug mold,that is in the level of 'gods hands!
Have to do more research on him!

Regards

Osern
I checked the template,he did the same geometry dividing to form up the most difficult part that I'd mentioned, he is really with skills that is too perfect that I'm wondering how,the only two approaches I can thick out is rolled with tool or with some aid of hair dryer which I'd tried before.
Finally meet a expert work like my method,thanks for sharing!I'm overwhelmed!

Osern
Last edited by osern; Dec 20, 2017 at 12:19 PM.


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