Another Moded Super Cub, was How Do I Deal With the Details - Paper Covered Foam Wing - Page 2 - RC Groups
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Feb 12, 2018, 01:49 AM
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mpikas's Avatar
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Originally Posted by psychedvike
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.
Are you saying that you've gotten away with cutting the ailerons off and then covering their front edges with paper/glue and not warping them? If yes then I'm sold, I can have everything sealed and reinforced on all sides...
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Feb 12, 2018, 02:51 AM
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mpikas's Avatar
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Originally Posted by tspeer
We're watching! Experience is a wonderful teacher, but it's a lot less trouble to learn from someone else's experience.
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Originally Posted by benz11
Great info, thank you!
Quote:
Originally Posted by psychedvike
Your work to this point looks great.
LOL, although I do appreciate the vote of confidence, I have to admit, I find it frustrating, and I've been in the same position before, where I'm posting something "how do I do this," and after a while of no real responses I go "Hey, is anyone out there?" and get a bunch of "your work looks great, we're just watching and learning..."

From my end "Hey, nervous newbie over here, I've never done anything like this before, I don't know what to do, can you help? To put this in concrete terms, I've never built or even had a foamie of any sort before, and the last time I built an RC plane it was stick built when I was 10y/o in the early 80's, I literally have not stinking clue what I'm doing, I'm not kidding."

If I knew what I was doing I would spend more than 30min a day working on this and not most of my time thinking about how I'm going to do it....
Last edited by mpikas; Feb 12, 2018 at 03:01 AM.
Feb 12, 2018, 02:59 AM
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mpikas's Avatar
Quote:
Originally Posted by tspeer
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?
You could get a good part of the way there by just cutting perpendicular to the top surface as opposed to the bottom surface and then beveling the back edge of the wing instead of the front edge of the aileron.

That said, I'm not sure I see the point, the problem with adverse yaw is one of less drag with the aileron going upward (in the airstream above the wing), but if you hinge it on the top and the way most people mount control horns your hinge pivot point is at the top surface of the wing so you're not only getting the tip of the aileron deflecting upward more than downward but you'll actually get some diferential upwards also, all of which should counter any tendency to adverse yaw. Worst case, mount the servo arm pivoted slightly forward when centered to make that more pronounced.
Feb 12, 2018, 12:05 PM
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Bare's Avatar
Small points;
Watered white glue Alone is what has worked well for me since '95.
Do prime the foam First (white glue mix) or applied paper will sooner or later delaminate
Miniwax IMO is Low grade product . there are better wpus out there... 'nuff said.

Dr Drela has stated that the typ v slot for ailerons should point up into the top of an airfoil. Ailerons should be bottom hinged and fully sealed (tape? or glass skin?)
Heresy ! except that he is THE source on toy aeroplane hi performance airfoils
His claim is that there is mainly separation turbulence back where ailerons live.
Not so on an airfoils underside where flows are critical.
Feb 12, 2018, 12:31 PM
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psychedvike's Avatar
Quote:
Originally Posted by mpikas
Are you saying that you've gotten away with cutting the ailerons off and then covering their front edges with paper/glue and not warping them? If yes then I'm sold, I can have everything sealed and reinforced on all sides...
Yes you can cut a strip of paper the length of the aileron and it only needs to over lap a small amount on the top and bottom. You will need to have an angle sanded along the front edge to give the aileron clearance to move downward without binding.
Feb 12, 2018, 05:41 PM
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mpikas's Avatar
Quote:
Originally Posted by Bare
Small points;
Watered white glue Alone is what has worked well for me since '95.
Do prime the foam First (white glue mix) or applied paper will sooner or later delaminate
Miniwax IMO is Low grade product . there are better wpus out there... 'nuff said.
Yea, that's pretty much the consensus with the woodworkers that have tried the "better" products but there are plenty that have gotten great results with minwax. In my case like I said, I've done some children's furniture with it and I was thrilled with the results, but I did spray them with a gun. To be honest I'll likely pick up some "real" WBPU when my can of polycrylic runs out, but I'm really trying not to before then (I have that tendency to "this one should be a little better so maybe I'll get some..." and ending up with a dozen different types of everything sitting around).

I may try some plain elmer's white glue this time, the kids have some sitting around...

Quote:
Originally Posted by psychedvike
Yes you can cut a strip of paper the length of the aileron and it only needs to over lap a small amount on the top and bottom. You will need to have an angle sanded along the front edge to give the aileron clearance to move downward without binding.
I decided that I was going to sit on it for a day and decide if no one posted and I didn't find anything concrete one way or another, and I've decided that I'm going to cut them off and try to cover them. On that we're on the same page.

The thing is that I've been thinking about the warping potential and decided that the 3/4 that is already covered will add some resistance to that but I was thinking that I was going to cut a strip that will cover most of them anyway so there would be tension on all sides from the shrinking, in other words, my ailerons/flaps are 2" wide and over 1/2" tall at the front edge so I was going to cut a strip of paper 4" wide, center the front of aileron/flap on it and then wrap it almost to the trailing edge with the new strip (yea, it will add some weight but it's a small part and some extra stiffenss in a control surface never hurt).

It sounds like you've gotten away with just covering that edge (like if I cut a 1 to 1-1/2" wide strip) without warping them... and I'm not sure what I'm going to try now. I'm betting the reason why that worked is that you had the rest of the aileron already covered and didn't wet it so that tried to hold it straight.

Argh.... now what???
Last edited by mpikas; Feb 12, 2018 at 05:48 PM.
Feb 13, 2018, 01:38 AM
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tspeer's Avatar
Quote:
Originally Posted by Bare
...Do prime the foam First (white glue mix) or applied paper will sooner or later delaminate...
I plan to use Titebond II because I'm making a seaplane, and I don't think white glue would tolerate the water. I'm concerned that thinned water-based glues will bead up on the foam, so even Titebond II may have problems. What do you think of using 3M 77 spray adhesive as a primer before applying the paper with Titebond II?

Quote:
Dr Drela has stated that the typ v slot for ailerons should point up into the top of an airfoil. Ailerons should be bottom hinged and fully sealed (tape? or glass skin?)
Heresy ! except that he is THE source on toy aeroplane hi performance airfoils
His claim is that there is mainly separation turbulence back where ailerons live.
Not so on an airfoils underside where flows are critical.
Separation and turbulence are two different things. It's true that a modern sailplane airfoil can have laminar flow along the entire bottom surface, even at moderate to low lift coefficients. There would be a drag penalty for giving up some of that laminar flow. You actually want the transition on the upper surface to move forward as the angle of attack increases so the boundary layer is turbulent when it encounters the strong increase in pressure leading to the trailing edge. So the transition to a turbulent boundary layer probably occurs ahead of the gap, and if it doesn't, it may actually be valuable for the gap to act as a turbulator so as to prevent having a long laminar separation bubble. But we're still talking about attached flows not separated flow.

It's also true that modern sailplane airfoils are a lot thinner than the kind of flat-bottomed foam skinned wings we're talking about in this context. The gap on a thinner airfoil is smaller than on a thick airfoil. This can shift the drag tradeoff. I would also like to know, especially for the thicker sections, whether the wing stalls sooner with the aileron deflected down with the gap on top vs on the bottom. Unfortunately, XFOIL may not be all that reliable when predicting maximum lift.
Feb 13, 2018, 11:11 AM
You know nothing....
Stuart A's Avatar
Bottom hinging seems to be pretty standard on flying wings,for the reasons Dr Drela cites.
If you have more foam cut another set using the MH45 airfoil,very popular for swept flying wings.A comparison would be very interesting.
Feb 14, 2018, 03:08 PM
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psychedvike's Avatar
[QUOTE=tspeer;39165102]I plan to use Titebond II because I'm making a seaplane, and I don't think white glue would tolerate the water. I'm concerned that thinned water-based glues will bead up on the foam, so even Titebond II may have problems. What do you think of using 3M 77 spray adhesive as a primer before applying the paper with Titebond II?

I wouldn't use the spray adhesive. I think it will just cause difficulties. I've used the Titebond for years. Never had a problem with beading.
I use the thinned Titebond on the foam only and wet the paper. When you squeegee off the excess it draws the glue through the paper. Very light weight and very strong.
Here is a a video I did about the process. The video is 8 and a half minutes long. Hope it helps you with your plane.
How to cover foam wing cores with water/wood glue and news print (8 min 30 sec)
Feb 14, 2018, 08:17 PM
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mpikas's Avatar
Well, to be honest with you, after trying it I'm not sure what all this stress about them warping is. All these pics are completely unsanded and untrimmed, and they didn't warp at all as far as I can tell.

I ended up doing them in 2parts because when I cut the paper to cover them I somehow miscalculated and cut the pieces too short to cover the ends completely, and instead of stopping everything and cutting new ones I decided it would be less work to come back later and cover the ends in a second pass.

This is after the first pass, with the ends of the ailerons and flaps not completely covered:
Feb 14, 2018, 08:39 PM
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mpikas's Avatar
Oh, FWIW, between the first and the second pass on of my ailerons ended up sitting in a puddle of water (it was on the surface that I was spraying down the new pieces and the water ran and I didn't notice), probably soaked in it for 30min before I noticed. if anything was going to warp that was the one, the bottom surface was soaked and the top was dry. Obviously, it didn't and I can't tell which one is which.
Feb 14, 2018, 08:58 PM
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mpikas's Avatar
Quote:
Originally Posted by Stuart A
Bottom hinging seems to be pretty standard on flying wings,for the reasons Dr Drela cites.
If you have more foam cut another set using the MH45 airfoil,very popular for swept flying wings.A comparison would be very interesting.
Was this directed at me? Isn't an MH45 something with some reflex in it designed for flying wings? Why would it be an interesting comparison? I'm not opposed to doing this, my whole point is to make easily interchangable wings for this thing, but I'm not sure why I would go there specifically?

[QUOTE=psychedvike;39174463]
Quote:
Originally Posted by tspeer
I plan to use Titebond II because I'm making a seaplane, and I don't think white glue would tolerate the water. I'm concerned that thinned water-based glues will bead up on the foam, so even Titebond II may have problems. What do you think of using 3M 77 spray adhesive as a primer before applying the paper with Titebond II?

I wouldn't use the spray adhesive. I think it will just cause difficulties. I've used the Titebond for years. Never had a problem with beading.
I use the thinned Titebond on the foam only and wet the paper. When you squeegee off the excess it draws the glue through the paper. Very light weight and very strong.
Here is a a video I did about the process. The video is 8 and a half minutes long. Hope it helps you with your plane.
I saw your video when I was looking for instructions on the process, It was helpful.

I agree that spray adhesive would couter the shrinkage that makes this process work, and I'm not sure it would help at all with a wet surface.

As far as what to use, at this point I've tried PolyCrylic, Titebond II, some regular wood glue (whatever was in the glue bottle, I believe it was a mixture of some Titebond I and mostly plain old wood glue), Elmers white glue and various mixtures. My inflated $.03:
  • If you want water resistant I would go with anything mixed with Polycrylic (I'm assuming that a better quality water based poly would be similar). It does't really seem to matter when it dries if it's just straight poly or poly mixed with a glue, even white glue. What does seem to make a difference in water resistance is sanding after it drys makes it less so.
  • I'm not sure about all the talk about watering the stuff down. I sprayed down my paper with some water, applied the glue to the surface I was sticking to and kind of pressed it in/spread it/whiped it. If anything I wanted my mixture thicker, not thinner.
  • If you want thicker and better sanding add talc. It makes the stuff nicer to work with and much nicer to sand. With enough talc in it sanding it the dust is like rubbing talc around on everything, paper doesn't clog and it all cleans off nicely and your hands feel nice, not dusty.
  • For me I think something poly based is the way to go. Plain old glue is a nice consistency but too sticky to work with, poly can be a bit slippery so I've been happiest with poly with talc or poly with glue in it- basically take some poly, add some talc in it till you have the thickness you want and if it feels like it needs to be stickier then put a squirt or 2 of glue in it. I'm not sure that there is a difference between wood glue and white glue, though I wonder if the white glue won't sand as well (I'll likely know in the next day or so). Poly and wood glue mixed got lumpy but didn't affect the end result.
Feb 15, 2018, 08:39 AM
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psychedvike's Avatar
I looks like you are getting good results. Keep us posted on your project.
Feb 16, 2018, 03:54 AM
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mpikas's Avatar
Yea, I guess this has turned into a bit of a build log, so I changed the title to reflect that.

I went and sanded all the wing pieces/control surfaces and was about to mix up a little more thick poly/talc to give it all a coat and completely level it and then realized, "what are you doing you big dummy? You're probably going to wreck this thing on the first flight, and it's not like its scale anything, it doesn't have to be glass smooth..."

So I thought about the servo mounting, wiring (I want to add some lighting to the wing also) and decided that that needs to hold until I figure out hinges for the flaps. Again, anyone has any recommendations?

Since I plan on using a DX6i transmitter I'm likely to try to run a y-harness on the flap and aileron servos, which will probably mean that one of the flap servos will need to be mounted flipped around. That is unless I'm missing something, I'm still thinking very much in the same way as the last time I built something in the early 80's + whatever works out in my head. I know that I can reverse the servos in the Tx programming but not if they're not on separate channels, I don't have enough channels to run them separately.

So in the meantime, I stripped the decals on the fuselage. Any recommendations on color scheme? I hear this foam is a pain to paint and mask, any thoughts there? I'm not excited about paper covering the fuselage also just so I can paint it easily.


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