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Oct 19, 2019, 06:33 PM
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FlyingW's Avatar
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Discussion

Large Foamboard Wing


I want to make a 90 inch wingspan airplane out of foamboard insulation. I was thinking of making a Jedelsky style airfoil that should be stronger and stiffer than a simple flat plate wing. I do not want to make a KFM type of airfoil.

To test the idea I made a wing section using 1 inch thick foamboard. I cut three pieces and beveled the long edges. Used white Gorilla glue to fasten them together. In the final design I would make the wing from three panels each 30 inches long for total of 90 inches. The chord is about 16 inches.

The result was a very stiff and strong panel. I think that 3/4" thick foamboard would suffice. However, I have no experience with the Jedelsky airfoil performance.

What experiences or opinions about this type of wing design can you offer?

Thanks,

Paul
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Oct 19, 2019, 08:33 PM
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AleRRon's Avatar
A “folded” airfoil should be pretty strong and have a lot of lift but I would still use a wooden or carbon spar at least for the inner third or so
Oct 19, 2019, 10:34 PM
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Quote:
Originally Posted by FlyingW
I want to make a 90 inch wingspan airplane out of foamboard insulation. I was thinking of making a Jedelsky style airfoil that should be stronger and stiffer than a simple flat plate wing. I do not want to make a KFM type of airfoil.

To test the idea I made a wing section using 1 inch thick foamboard. I cut three pieces and beveled the long edges. Used white Gorilla glue to fasten them together. In the final design I would make the wing from three panels each 30 inches long for total of 90 inches. The chord is about 16 inches.

The result was a very stiff and strong panel. I think that 3/4" thick foamboard would suffice. However, I have no experience with the Jedelsky airfoil performance.

What experiences or opinions about this type of wing design can you offer?

Thanks,

Paul
I used that type of wing on a 60" wingspan Old Fogey , it is strong enough that it doesn't have a spar ( except for a length of packing tape underneath ) ...... I wouldn't try to do a loop with it , though .




FT Old Fogey-ish with 60" wingspan (1 min 56 sec)
Oct 20, 2019, 06:13 AM
Registered User
As soon as you mistakenly pull a high G turn it will snap.
I would put in two carbon fiber tubes (8 mm diameter, 750 mm length), joined by a short steel rod inside. Relatively light addition for peace of mind.
Oct 20, 2019, 08:58 AM
treefinder
springer's Avatar
If I was going to that much effort on that large a plane, i would cut kerfs in the bottom surface , then form a real undercambered airfoil over some ribs using gorilla glue in the kerfs to set the shape. The ribs could be permanent or temporary. You could fill one or more kerfs with 1/8x34" spars while you do it. The resulting wing will look better (smooth curve) and possibly fly better. Though i have no experience in comparing Jedelsky to smooth undercamber airfoil, it "seems" right that smoother surfaces will perform better in larger scale wings.
Oct 20, 2019, 09:25 AM
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Thanks all for the ideas.

Is a "kerf" a slot cut into the foam?
Oct 20, 2019, 09:59 AM
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Please show us the result , with video if possible !
Oct 20, 2019, 10:08 AM
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BTW , here's an under-cambered flying wing design based on a toy " Sky Surfer " glider , I believe . Could possibly be scaled up , he has plans on his website .

Slowly Indoor Glider (4 min 51 sec)
Oct 20, 2019, 10:42 AM
Registered User
FlyingW
The problem with using a solid board as a wing is that 80% of the foam is doing very little towards strength or stiffness.
A hollow structure using say 6 mm board as a 'skin' would have very similar strength yet be 1/4 the weight. In addition a thin board is likely to be flexible enough to be 'bent' into a true air foil section with plenty of internal space for a spar.
Not so simple to do but a wing that is 'built up' like this can be thicker at the root than the tip to better follow the actual bending forces imposed on it.
Oct 20, 2019, 12:22 PM
treefinder
springer's Avatar
Quote:
Originally Posted by FlyingW
Thanks all for the ideas.

Is a "kerf" a slot cut into the foam?
Yup, there is a lot of hints and tips on kerf bending foalular board here: http://tnttt.com/viewtopic.php?f=55&t=44081

Gpw, one of the original foamie builders has built a foamie camper. Some of his and other guys techniques in that t&ttt thread have great application to large foamie planes!
Oct 21, 2019, 07:29 AM
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Ok thanks all again for the information. I binned the idea for the 3/4" thick, 90-inch, solid wing because of the excess weight.

Instead I put together a 40-inch Old Fogey wing using white Gorilla glue to see how stiff it was. It was surprisingly lightweight and stiff and I'm not surprised many have had great success with it.

I have another sheet of the same Model Plane Foam 6mm foamboard that is about four feet long so I will make a four foot wing. I'll likely make a simple balsa boom fuselage to hold a tail behind and to mount a motor up front to fly.
Oct 21, 2019, 10:23 AM
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Your wing looks good !
Oct 21, 2019, 10:34 AM
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Quote:
Originally Posted by FlyingW
Ok thanks all again for the information. I binned the idea for the 3/4" thick, 90-inch, solid wing because of the excess weight.

Instead I put together a 40-inch Old Fogey wing using white Gorilla glue to see how stiff it was. It was surprisingly lightweight and stiff and I'm not surprised many have had great success with it.

I have another sheet of the same Model Plane Foam 6mm foamboard that is about four feet long so I will make a four foot wing. I'll likely make a simple balsa boom fuselage to hold a tail behind and to mount a motor up front to fly.
Change the balsa boom to a square carbon tube and you've got yourself a Slow Stick. Perhaps you can use some of their components:

https://alofthobbies.com/slow-stick.html
Oct 21, 2019, 11:46 AM
treefinder
springer's Avatar
FlyingW, both the 3/4" thick foamular wing and thinner, or built up wings are acceptable flyers. Each has it's advantages and disadvantages. It is sometimes fun to play with different techniques than we are used to so we can learn and appreciate other builds. While I tend to use KFM5a airfoil for most of my builds (relatively easy to build and looks "mostly" realistic) when I decided to experiment with a big wing without plans (2 diversions from my typical building) I tried a built up 7' wing. It would have been 8' but I got confused when trimming tips parallel to root! Doing plans would have avoided that, but I probably wouldn't have hit on the spar technique I finally used or how I inadvertently added exactly the right amount of washout to the tips. Fun and rewarding to tinker!
Oct 21, 2019, 02:51 PM
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Ok, I'm psyched. Here is a basic fuse having the rough moments of the Old Fogey. I lengthened the nose by two inches because the motor I have planned for it is only 1/2 ounce and I'll likely need a forward place so the battery can help with the CG.

This thing should weigh no more than eight or nine ounces and fly incredibly slow - can't wait to put it in the air. Calm conditions will be required.

Springer - Your wing looks beautiful. I made my own measuring and cutting mistakes while building a large wing many years ago. It kept getting smaller until i got the tips right. I remember gluing the last "wedge" back on and trimming it that so that I didn't lose any more span.
Last edited by FlyingW; Oct 21, 2019 at 02:56 PM.


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