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Old Apr 03, 2009, 04:01 PM
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Wing cardboard? Can that fly?

I was studying what makes a wing flies and learning about airfoil. Then I had the crazy idea of building an airfoil with light cardboard and try to get this thing airborne. Obiously, if I am posting this here, the maiden flight did not go well. Do you see anything on the attached pic that I did wrong? Can a rectangle wing with an airfoil, and ailerons really fly? Any input would be greatly appreciate it. Thank you. Andre
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Old Apr 03, 2009, 04:38 PM
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Staffs, UK
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Plank wings on their own without any stabilisation don't fly very well.

And that's not a very good airfoil. Way too much camber, too sharp on the edges and the high point is too far back.

I have made wings of cardboard (for conventional looking planes) and they can fly. But cardboard is quite weak and quite heavy. Far better to use corrugated plastic as in the thousands of SPADs that have been built. See http://www.spadtothebone.com/

Steve
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Old Apr 03, 2009, 05:38 PM
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Thank you

Steve, thanks for your input. I'll be careful when I build my next wing made of corrugated platic. So if I make a better shaped airfoil wing, add stabilizer on each side, can that actually flies without a fuselage? Sorry I am sooo beginner at building if you would see my first plane I attempted to build you'd get a good laugh at it!
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Old Apr 04, 2009, 03:26 AM
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Joined Oct 2002
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There's a way to produce an airfoil that will work better if you insist on making this a plank style flying wing. Here's a sketch of how to do this. Note how the red camber line S curves up and then back down to the center line then dips below and back up. This S curve will provide the stability you need. It's also important for a plank wing that the high point of the first part of the curve of this camber line occurs up near the leading edge or the reflex in the rear portion won't have enough leverage to counter the pitching moment.

And it's this pitching moment and the lack of control over it that caused your cardboard special shown in the pictures to fail to fly well........OK, to fail to fly at all except long enough to find new places to crash. If the truth be told your airfoil would likely fly best upside down where the shape would actually be stable. But flown with the arch upwards it is just completely the wrong shape for stability with a plank style flying wing.

To control the shape more closely you'll need to use some ribs. A simple arch form may work OK for the SPAD's that use normal tails but with a flying wing you need to control the airfoil's shape far more closely.

In this sketch you'd place the hinge line just at or very slightly behind the point where the upper surface part joins the lower surface part.

Another option would be a simple and totally symetrical airfoil. To get the pitching stability you need just add a bit of reflext by adjusting both elevons so they point up 2 to 4 degrees.

A trick for corrugated plastic or cardboard is that in areas you need a lot of curvature such as the leading edge and the first portion of the upper surface you slice through the inner layer between the corrugation webs. This makes it far easier to curve the material more sharply. For example at the leading edge you would slit every corrugation line. And for the first portion of the upper leading edge you'd slit every one as well for the first 1/10 of the wing. Then slit ever second or third one up to the highest point of the airfoil. Behind this highest point maybe every 4th or 5th for a couple of cuts. On the lower surface you may not need to add any slices at all.

Best of luck with the next one.
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Old Apr 04, 2009, 06:08 AM
An itch?. Scratch build.
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Here's some very simple shapes you could try. (Picture below)

They are sometimes referred to a Kline-Fogelman type sections, if you look in the Flying Wings forum you should find more information.

Straight wing planks as they are called, are quite difficult to get the CG in the right place, (usually well forward, 15 to 20% of wing chord), also the section needs some 'reflex', as BMatthews pointed out.

If you want to use cardboard for experimenting, I would suggest a fairly conventionally looking model with a fuselage and tail so that you have a good stable base to work with.

If you do an Advanced Search here on RCGroups, enter cardboard as the search word, then set the box just underneath to Search Titles Only, you should find plenty of threads where people have used it.

Good luck with your projects.
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Last edited by eflightray; Apr 04, 2009 at 01:09 PM. Reason: Corrected Cline-Fogalman to Kline-Fogelman, (Oh dear)
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Old Apr 04, 2009, 08:43 AM
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Google cardboard models and you will find some amazing scale models made from card the construction tips will help you http://home.earthlink.net/~charlesfelton/index.html here's a start.
Find your section, build it as a Jedelsky then cover the underside in plastic,cloth or another layer of card.........its an idea I saw applied to a German glider wing the results were very good according to the owner.
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Old Apr 18, 2009, 10:35 AM
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Hi, Chuck Felton here and that's my website mentioned above. I hope you will take a look at it to see that corrugated cardboard can be used for both RC & CL models. My latest design, a 60" wingspan CL model of the Piper Pawnee crop duster, is shown in the photos and a good example of the scale-like appearance which can be achieved. It has a weight of 55 oz and a wing loading of 15 oz/sq ft. Cardboard is inexpensive, easy to cut and can be scored and folded to make large sections in one piece. Give it a look and maybe you'll be tempted to try one. Good Luck!
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Old Apr 18, 2009, 05:15 PM
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Chuck, that plane rocks...Jim H
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Old Apr 19, 2009, 07:15 AM
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Chuck you do some wonderfull things with Card trully you are a grandfather of SPAD design ........... a CAD seems a slightly unfortunate abreviation but like your planes it puts a big smile on peoples faces
Ive just recieved plans for a Mudduck Agriduck sport so seeing the agmaster CL has me grinning like a Loon

Andre I can put up a 6ft Plank flying wing section if you wish.........some reflex is advisable for F,wings and deltas like the Mugi/Flick designs
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Old Apr 19, 2009, 08:04 AM
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Don't worry about the shape. A brick WILL fly if you add enough thrust.
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Old Apr 23, 2009, 03:43 PM
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A long time ago, I seem to remember a couple of kit reviews in one of the magazines for models made of cardboard. I don't remember the manufacturer, perhaps it was "Craftsman Models" or somesuch. I do remember the reviewer finishing the model in the style of a weetabix cereal box though.

You could do something simple with cardboard though, maybe like this sketchy plan I just drew up. Its probably rubbish, but it looks "do-able"

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Old Apr 24, 2009, 01:05 PM
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Andre747 are you watching?
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Old Apr 27, 2009, 10:00 PM
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haha! nope I think you guys are talking to yourself here.
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Old Apr 28, 2009, 03:36 PM
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I am back!

Thank you all for this great info. Next time I decide to build something out of cardboard, this will help me a lot. I got sidetracked a little: I mounted a rocket under a Stryker 27. Did a fly by, pitched up and fire the rocket. Spectacular! Everything was going super great for my "airshow" until I did a fly-by inverted and the battery was not secured properly. My lipo still MIA.
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Old May 05, 2009, 05:10 PM
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OOOOpps!
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