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Old Jan 23, 2013, 12:46 PM
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sroge's Avatar
Germany
Joined Sep 2010
88 Posts
Question
Carbon wing joiner: diameter? How make outer tube?

Hi,

I am scratch building this 72" (10-11 lbs) aerobatic plane—like an Extra 300. At least in germany it doesn't seem very easy to get a tube wing joiner. There's one shop selling them, but they charge €40 (~$50) for a 40" tube of 1" diameter with an outer tube. I think this is quite expensive.

For a smaller plane I once took a standard aluminum tube from the hardware store and wrapped two sheets of paper around them, continuously applying wood glue. After drying and pushing it from the aluminum tube this was quite a good outer tube.

But now with my new and much bigger plane am thinking about using carbon this time.

2 questions:

—does anyone know a better way of making an outer tube, not using normal paper and wood glue?

—when building an aerobatic/3D plane, what dimension of a carbon wing joiner may be all right? Inner diameter, outer diameter, and how far should a joiner go into the wing (overall wingspan 72")? Half the way? And what dimensions for aluminum might necessary in comparison?

Stefan
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Last edited by sroge; Jan 23, 2013 at 01:11 PM.
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Old Jan 23, 2013, 01:20 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
Joined Jul 2011
4,316 Posts
This might be a good question for the guys in the composite forum http://www.rcgroups.com/composites-fabrication-210/

Ken
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Old Jan 23, 2013, 01:28 PM
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sroge's Avatar
Germany
Joined Sep 2010
88 Posts
OK, thought about that, too. But as my question is also about aluminum and making that outer tube I decided that this might be a better place.

Stefan
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Old Jan 23, 2013, 01:44 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,802 Posts
Do you have any fishing tackle shops in your area, they sometimes stock blanks or sections of carbon fishing rod.

Or maybe using carbon arrow shafts, I don't know what diameters they go to, but you could always use two or three.

Actually they probably don't even need to be carbon, just good quality fiberglass would probably do. (Or even hardwood dowel).

Considering we used to fly 6 footers with balsa spars and maybe some ply bracing, I sometimes wonder if we may go a bit overkill these days. I don't think carbon tubes were even available back then.
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Old Jan 24, 2013, 12:50 AM
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Leroy Gardner's Avatar
Coeur d' alene, Id.
Joined Jan 2010
785 Posts
Im building a bashed Tiger sport plane with slip tube mounted wings which could just as well be a tube joiner for a bolted on wing and my wing is also close, 74" to yours. The tube is 3/4" aluminum, was for a AT-6 90" wing so I know it's strong enough for ours. Outer sleeve is made on the tube of 1.5 oz. fibreglass and resin, there is a thread showing how it's done on my build.

See it here: www.rcgroups.com/forums/showthread.php?t=1786693 hope this helps, Leroy
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Old Jan 24, 2013, 01:13 PM
Bleriot's R Us
xairflyer's Avatar
Ireland, Donegal
Joined Nov 2003
1,201 Posts
Check out phenolic tubes you normally buy the tube with a matched alum tube for the inside.
I am sure you can get them in Germany, this is a UK supplier
Falcon Aviation
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Old Jan 24, 2013, 01:27 PM
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Joel K. Scholz's Avatar
Kingsland, Texas USA
Joined Aug 2000
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Find a kite material supplier like Peter Lynn international. They will have a variety of fiberglass and carbon spars.
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Old Jan 24, 2013, 01:40 PM
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sroge's Avatar
Germany
Joined Sep 2010
88 Posts
Hey,

thanks to all you guys! I will keep the carbon stuff in mind for my next project. This time I based my decision on budget an availability. I don't like it, but felt I had no other choice. I bought a tube of 3/4" with 1.5mm at a hardware store. This was 5, which is about 7. Here in germany I found several manufacturers and distributors and carbon tubes around 1"/1mm cost between $25-$45. Nevertheless the aluminum will give me two or three additional ounces :-/

As for the outer tube I will try several kinds of paper. Normal copy paper works quite well, but maybe brown packaging paper will be better..

Thanks,
Stefan
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Old Jan 24, 2013, 09:26 PM
Rob H
rph1225's Avatar
United States, MD, Rosedale
Joined Jul 2011
118 Posts
I just completed a profile that I did my own outer tube with fiberglass cloth and resin. At first I had thought it was going to be tough to do, but actually was very easy. I took the inner tube that I wanted to use and wrapped wax paper around it about 3 times, using masking tape to hold it in place.

Then I cut a piece of fiberglass cloth, so it would also wrap around the tube 2-3 times and soaked it with resin. After wrapping it around, I took another piece of wax paper and wrapped it around the fiberglass. Then starting at the center of the tube, start wrapping the tape to the end, overlapping at least half of the tape on every wrap. After, flip the tube over around and do the other half.

Once cured for about a day, the inner tube will just slip out and you can then pull out the wax paper.

Here is a site I used that kind of shows the way I did it. http://www.ofremmi.info/howto/Wingtu...%20sockets.htm
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Old Jan 25, 2013, 03:38 PM
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sroge's Avatar
Germany
Joined Sep 2010
88 Posts
Well, this is how I will finally do it: I experimented with several combinations of copy paper, packaging paper, wood glue and epoxy. I wanted to know what I could make out of the stuff I got in my workshop before buying something.

For my test I used am 0.6" aluminum tube and packaging paper. Using epoxy I only had to build up 0.7 mm of layers to give me even more stability as with 1.9 mm of wood glue. For a 5" outer tube the weights are 4g and 11g—quite a difference.

I think that the outer tube only has to stable enough to protect itself from being bent or otherwise broken during handling. Everything else is provided my the inner tube. The photo shows the epoxy tube, the inner aluminum tube and the wood glue tube. Sealed the ends with CA.

Stefan
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