Another Moded Super Cub, was How Do I Deal With the Details - Paper Covered Foam Wing - RC Groups
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Feb 09, 2018, 09:06 AM
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Another Moded Super Cub, was How Do I Deal With the Details - Paper Covered Foam Wing


Short version:

I just hot wire cut my first foam wing and gave it a quick coat of paper (hardware store masking paper in 9" width, so it took 3 strips to do a wing with a little over a 9" chord). Right now it's pink 250 weight foam, a single coat of paper (except where it overlaps) and only the minwax polycrylic it took to glue down the paper, no spar with 2 24" wing sections which will be joined with a little bit of dihedral.
  1. Do I put additional coats of Minwax on it now or do I do it when it's finished? Over the color or under it? If I add a little talc to it to make it sand smoother will it add too much weight?
  2. How do I hinge the ailerons? Right now I'm considering cutting them like the typical foam board deal (v-cut on the bottom, then taping the paper with clear packing tape as a hinge. I'm sure that this masking paper isn't strong enough to be a hinge on it's own.
  3. I'm considering just cutting the flaps clear thought and then desgning/3d printing hinges that work somewhat like the tundra/timber flap hinges (sort of drop-down sort of fouler) unless someone knows of where I could just buy a set of those hinges? Do I try to wrap the cut edges of the flaps with paper or am I just asking for trouble (I'm worried about warping them when I wet things down to get the paper on them) on something that thin? If I don't cover the exposed foam with paper I'll likely try to tape it, not sure how that will look.
  4. Suggestions on joining the center? I have the dihedral angle cut and was originally thinking of drilling a hole at that angle for a fair length spar, but honestly, these wing sections are STIFF, I'm not sure that I need it and/or the extra weight. Right now I'm leaning towards gluing the 2 halves together (hot glue, gorilla glue, goop???) and then just wrapping the joint in a layer or 2 of paper and leaving it

Longer version and pics of what I have so far coming up
Last edited by mpikas; Feb 16, 2018 at 03:39 AM.
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Feb 09, 2018, 09:29 AM
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Longer version:

I haven't built or flown anything for a long time (the last time seriously foamies and even electric weren't really a thing, my old stuff is stick built monokote covered glow powered), so I decided that I needed to build something and fly.

Long story but I have most of an HZ Super Cub LP sitting around so I decided that would be what I'm starting with, but feature creep/while-I'm-at-it-itis being what it is "making this brushless and re-learning all this" turned into "I'm making this brushless and turning it into a bush plane style with flaps and ailerons. I probably need more wing area to keep speed down (my wing is already damaged) and seeing some longer wingspan ones out there (need to find another wing) or with ailerons/flaps added behind the stock wing (ugly) turned into hey, I'll build a foam cutter and cut a wing with a 2" bigger chord, that whole 2" could be flaps/ailerons. More chord and airfoil thickness will slow it down faster than more wingspan. Might as well put horner wing tips on it, possibly get rid of the struts and a dozen crazy little ideas...

Yea, I deserve the lecture that someone out there wants to give me... Oh well, at least I'm keeping some dihedral in it so I have some chance of not destroing it on the first flight ;-)

I grabbed some 2" pink foam, made a nice cutting bow and some fat clark y airfoil templates:
Last edited by mpikas; Feb 09, 2018 at 09:55 AM.
Feb 09, 2018, 09:35 AM
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Setting my power supply to 4A gave me a reasonably hot wire that cut fast (maybe 20 seconds/ side for a 25" section). My first try was OK, it had a bit of a scallop on the leading edge but otherwise, it could almost be used the way I cut it out.
Feb 09, 2018, 09:39 AM
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My second and 3rd try came out almost perfect.

I did feed them through my tablesaw to make sure the leading edge was 100% straight, but it only took about 1/16" cut to do that, no warp, about 5-10min worth of sanding and I have some really nice wing sections.
Feb 09, 2018, 09:50 AM
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I wrapped the 2 sections in masking paper using Minwax Polycrylic as an adhesive. Honestly it was too thin and didn't stick the paper down well, but when it dried it looked good and appears to be stuck on well enough. The only wrinkles I got were where the minwax coated wing got too slippery in my gloved hand and shot out and landed on my shirt. I figured I'll leave it and sand it out/fix it when it's dry. You can barely tell after I sanded them.

These wings were easily 2x as stiff as the stock wing before covering, after covering they feel as stiff as if they were made of wood (they actually look a lot like wood wrapped in the brown paper).

The tips got coated last night, I'll try to get pics later today. This time I mixed the minwax with wood glue to make things stickier/thicker. That was a mistake, it got kind of lumpy, we'll see what it looks like when it dries.
Feb 09, 2018, 01:14 PM
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I cut the ailerons out first and face everything them with balsa. Then cover.

https://www.rcgroups.com/forums/show...7&postcount=47
Feb 09, 2018, 04:43 PM
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I just got my first chance to go and look at how the wingtips dried. I was really worried about them.

Since just the straight polycrylic seemed too thin I mixed in some woodglue and when I started brushing it on it had what almost looked like cottage cheese curds in it. I figured they'll be squishy but when I put the paper on them the paper had that texture over the top of them and it wouldn't squeeze out. Looks like for the most part, they went away when it dried. I'm thrilled with the way it turned out, even the bits that are wrinkly towards the leading edge are mostly smooth to the touch, this should sand out fine.
Last edited by mpikas; Feb 09, 2018 at 05:01 PM.
Feb 09, 2018, 04:55 PM
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Quote:
Originally Posted by pmullen503
I cut the ailerons out first and face everything them with balsa. Then cover.

https://www.rcgroups.com/forums/show...7&postcount=47
Did you use glue or poly or what to glue it down? Was it diluted?

I'll look at your thread to get a sense of scale, but I'm getting a little cocky with this stuff and wondering if I could cut the ailerons and flaps off and cover their front edges with paper without warping them. At this point, they should be fairly stiff- last night I kept stepping on one fo the pieces that I cut off the wingtips (it landed on the floor and I had my hands covered in sticky mess so I didn't go after it till later) and it seemed pretty rigid for being only foam about 1/3 or so covered in paper.

I'm worried about getting a clean cut. I'm thinking these things will be pretty big, probably 2 or 2.5" wide and something like 12 and 8" long.

Any thoughts on the rest of my questions?
Feb 09, 2018, 06:33 PM
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I used WBPU undiluted. I've given up trying to use the foam ailerons. Even with a balsa LE they would often warp. Now I just build them up from balsa.
Feb 11, 2018, 04:34 PM
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Anyone else out there?

I gave them another coat of Minwax mixed with some talc to smooth things out, that sanded really nicely, the sanding dust is just like talc, but I'm a little concerned that some of the paper wrinkled when I put the stuff on and then flattened when it dried again. It's like this stuff is not sealing correctly (which is weird because I've used it on furniture for my kids that is constantly covered in stuff like I made them stools for brushing their teeth on which are always wet and covered in toothpaste and they seem to be sealed up well).
Feb 11, 2018, 07:14 PM
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Well, I could really use some advice at this point.

I marked off the ailerons and flaps and cut them out using a ruler, box cutter and my pocket knife (I'm one of those knife sharpening weirdos, my pocket knives are typically sharper than a razor blade).

I cut the flaps all the way off and I'm fairly certain I'm going to add paper to the open area when I join the center of the wing. I don't know if I'm going to try to wrap the front of the flap (do I dare? Will they warp?), or if I'm just going to paint them and then put some packing tape across the front to keep the paper from pealing. They're PLENTY stiff right now even if I intended for it to fly 2x as fast as I do.

The Ailerons are my debate. I want to hinge them at the top surface of the wing. Right now I have them cut within about 1/16" of an inch of the top (they are surprisingly still rigid like that without "breaking" the joint). there is part of me that says "finish the wing, paint it, "break" the hinge line and then put some packing tape on it and call it good. The other side of me says "the flaps came out nicely, maybe I should cut them out, wrap the back of the wing, paint everything and then hinge them entirely with tape when the whole thing is done.

Thoughts?
Feb 11, 2018, 07:21 PM
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Quote:
Originally Posted by mpikas
Anyone else out there?...
We're watching! Experience is a wonderful teacher, but it's a lot less trouble to learn from someone else's experience.
Feb 11, 2018, 07:33 PM
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Great info, thank you!
Feb 11, 2018, 07:58 PM
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Frise Ailerons


Speaking of ailerons, the top figure shows how the ailerons are typically cut out, hinged at the top and leaving a gap on the bottom surface to allow for movement of the aileron. This kind of aileron needs differential deflection (more up than down) to minimize the adverse yaw.

Does anyone cut their ailerons as shown in the lower figure? This is a bit more complicated, but not that much more. The aileron cut itself has the opposite slant from the conventional approach. The wing needs to be cut out kind of like a bird's mouth to allow the aileron to deflect downward. But other than that, the hinging and actuation would be the same.

The advantage of this approach is the leading edge of the aileron dips down into the airstream when it is deflected up, which causes some drag and an offsetting yawing moment to compensate for adverse yaw. When the aileron is not deflected, there's hardly any gap at all, which should reduce the drag somewhat. I know this isn't important for models, but there is also a reduction in the hinge moment, which reduces the load on the servo.

Has anyone tried this approach?
Feb 11, 2018, 09:43 PM
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Your work to this point looks great. Your method of using packing tape will work just fine. I like to cut my alerons out and then cut a 45 degree angle on the top and bottom of the aleron. Cut a slot in the center of the wing and aleron and use CA hinges. I glue them in with gorilla glue not CA. The raw foam I will cover with a strip of paper and thinned wood glue. I will some times use balsa for the aleron and toss the foam piece. The CA hinges will work well with both materials. I like CA hinges because they last as long as the air frame will. The tape hinge may need to be placed some day, but they are quicker to make.


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