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Old Jul 09, 2010, 12:28 AM
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daboz's Avatar
HB cali
Joined Apr 2006
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my first JW build has a large steel rod in the wing and has flown over 200 more than one time, 219mph max and I think is the third fastest JW in the world weighs in at 117oz has crashed pretty bad at Mars and still flys and looks great.


Chris


who builds his planes thinking they may crash... and some of them have
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Old Jul 09, 2010, 10:08 AM
the occasional flyer
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Rexburg, ID
Joined Jul 2008
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Quote:
Originally Posted by Aerogance View Post
There is no question the rebar will fail before the joint to the foam does. Here is a photo of the bent rebar:
Wow. Now you'll have plenty of dihedral.

-David
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Old Jul 10, 2010, 12:29 AM
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I went ahead and tested the rebar joint to the foam. I put all my weight on the wing panel and then bent the rebar almost 180 degrees. The rebar pulled out of the foam in 2 places, but remained joined everywhere else. It was not easy to bend the rebar and any plane I have owned would have had some sort of failure at the level of force I was applying. I still think rebar could be the secret ingredient in a heavy and fast foam core wing, but a single spar design may have its limits.

I was at HD this evening and took a look at other common materials they stock. The stiffest material I could find was rigid conduit and these thin-wall steel handled carpet mops. If you wanted to save some weight, the carpet mop handle would be great. The rigid conduit was much heavier. Rebar was the heaviest since it is solid. The smallest diameter rebar I could find is 3/8". 1/4" would have been perfect for a double rod spar.
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Old Jul 10, 2010, 08:55 AM
Deniable plausibility
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Derbyshire, UK
Joined Aug 2008
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Get any odd looks from the store staff?
"Hey, there's a guy over there bending all the mop handles - SECURITY!"

Keep up the good work and the interesting posts,

S
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Old Jul 10, 2010, 10:10 AM
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Rexburg, ID
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Quote:
Originally Posted by Aerogance View Post
The smallest diameter rebar I could find is 3/8". 1/4" would have been perfect for a double rod spar.
You could still do a double spar near the root, and either drop one of them before you reach the tip, or overlap them near the tip (depending on how much weight you want). The sketch is a front view of the wing, with the top spar going all the way to the tip.

The advantage of doing the double spar near the root is that instead of loading the rebar in bending (not too strong), you're loading the rebar more like a truss. The top one will be in compression, and the bottom in tension. Truss loading is inherently more efficient than bending.

-David
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Old Jul 10, 2010, 11:15 AM
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United States, CA, Ventura County
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Quote:
Originally Posted by Shedofdread View Post
Get any odd looks from the store staff?
"Hey, there's a guy over there bending all the mop handles - SECURITY!"

Keep up the good work and the interesting posts,

S
Are you kidding, you can spend days in a HD without seeing a single employee
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Old Jul 10, 2010, 11:27 AM
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Quote:
Originally Posted by rothlisburger View Post
You could still do a double spar near the root, and either drop one of them before you reach the tip, or overlap them near the tip (depending on how much weight you want). The sketch is a front view of the wing, with the top spar going all the way to the tip.

The advantage of doing the double spar near the root is that instead of loading the rebar in bending (not too strong), you're loading the rebar more like a truss. The top one will be in compression, and the bottom in tension. Truss loading is inherently more efficient than bending.

-David
I will give that a try. It resembles the JW spar arrangement where the bottom one is shorter. Getting the bottom one in will be the trick since it is bent.
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Old Jul 10, 2010, 05:44 PM
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Rexburg, ID
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just cut a U channel, and fill it afterward.

-David
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Old Jul 10, 2010, 07:26 PM
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San Diego
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How about using square tubing, with a solid joiner for a two piece wing????
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Old Jul 10, 2010, 07:40 PM
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United States, CA, San Diego
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If you cut a U channel to install the spar assembly that rothlisburger suggested, that would allow you to potentially weld the two pieces of rebar together to at the outboard points make a stronger connection for a true truss design. Maybe add a vertical cross member in the center between the top and bottom members.
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Old Jul 10, 2010, 08:00 PM
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I was thinking about th welding option and it could be a cheap and quick way to add a ton of stiffness. Good idea.
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Old Jul 11, 2010, 12:15 PM
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United States, CA, San Diego
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Here's an illustration of what I'm talking about, with the red lines being welds. This is a front view of the spar.
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Old Jul 13, 2010, 09:46 AM
Deniable plausibility
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Derbyshire, UK
Joined Aug 2008
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May I suggest brazing the parts together? Welding does rather change the properties of the steel. You'd need to heat treat the assembly post welding to recover the properties.

Also, why not get hold of a press brake and bend either a [ section or a Z (but with the '/' part vertical). You could use a punch to take out material from the web region. Many fabrication shops would do work like this for quite small amounts. Some have CNC press brakes if you want to be really posh.

S
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Old Jul 25, 2010, 01:15 AM
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Near the Ocean in Hunt. Beach Calif.
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:/ oo';
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Last edited by flyboyjimi; Jul 25, 2010 at 01:43 AM. Reason: Not within the seriousness of the Thread
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Old Jul 25, 2010, 01:17 AM
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United States, CA, Ventura County
Joined Sep 2008
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Quote:
Originally Posted by Shedofdread View Post
May I suggest brazing the parts together? Welding does rather change the properties of the steel. You'd need to heat treat the assembly post welding to recover the properties.

Also, why not get hold of a press brake and bend either a [ section or a Z (but with the '/' part vertical). You could use a punch to take out material from the web region. Many fabrication shops would do work like this for quite small amounts. Some have CNC press brakes if you want to be really posh.

S
I imagine that it wouldn't be expensive to have some sheet metal formed on a brake. I also thought that using 2 C-channels interlocked female-to-female with a tapered plywood shear inside the crotches to follow wing thickness could be a quick and dirty way to get a heavy metal spar going.
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