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Jan 03, 2012, 02:51 AM
Ego varius quis.
Cheesehead's Avatar
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Discussion

Square vs. round carbon tubes? Also, how much does brand matter?


As a highly lazy individual, I generally prefer "stick" models to those which require any real fabrication ability. Most models I've seen use round carbon tubes, but a few use the (slightly more expensive) square ones available. Is there a benefit in strength?

Also, how much does strength vary between brands? I'm quite fond of the Hobbyking variety's low prices, but the stuff at the hobby store seems stronger. Then again, it may be thicker-walled.
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Jan 03, 2012, 09:00 AM
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talonxracer's Avatar
What size tubes are you referring to? What are the tubes function in the airframe?
Jan 03, 2012, 10:38 AM
closed due to popular demand
...
Last edited by ibuild; Oct 19, 2013 at 01:11 PM.
Jan 03, 2012, 01:55 PM
Ego varius quis.
Cheesehead's Avatar
Thread OP
Quote:
Originally Posted by talonxracer
What size tubes are you referring to? What are the tubes function in the airframe?
Fuselage tube on a sort of mini-sized SlowStick.
Jan 03, 2012, 02:41 PM
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Ward Hagaman's Avatar
Technically speaking, square tubes are slightly less efficient material-wise. However, if you consider mounting considerations, the square tube makes up for it in that application to me.
Jan 03, 2012, 07:27 PM
Just fly it!
wyowindworks's Avatar
It would be fun to do some testing between the two. I always thoughy that a round one was less efficient. With a square tube you have more material farther apart that is under tension and compression when bending. With a round object you have the least amount of material in the area that is under the greatest tension and compression when bending.

I've always wanted to test this in respect to bending strength and stiffness.

I think is really depends on how the loads are applied. Bending, tension, compression, point loaded, etc.

I say use what you got.
Last edited by wyowindworks; Jan 03, 2012 at 07:37 PM.
Jan 03, 2012, 07:36 PM
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Ward Hagaman's Avatar
Interesting....there is strength for a given weight, and then strength for a given size.

I think that for a given weight that round has the edge. They don't use square tubing for hang gliders or kites, for example. But if you are making a flat plat foamie, or if you need to mount servos off the tube, then the extra weight would be worth it.
Jan 03, 2012, 07:39 PM
Just fly it!
wyowindworks's Avatar
Quote:
Originally Posted by Ward Hagaman
Interesting....there is strength for a given weight, and then strength for a given size.

I think that for a given weight that round has the edge. They don't use square tubing for hang gliders or kites, for example. But if you are making a flat plat foamie, or if you need to mount servos off the tube, then the extra weight would be worth it.
Here is another thread for full sized builders. It has some good info.

"http://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/3372-round-vs-square-tube-strength.html"

For some reason a hyper-link doesn't work with this site.
Last edited by wyowindworks; Jan 03, 2012 at 07:52 PM.
Jan 04, 2012, 03:50 PM
Entropy is happening!
Jim.Thompson's Avatar

Round/square?


Quote:
Originally Posted by wyowindworks
............ I always thoughy that a round one was less efficient. With a square tube you have more material farther apart that is under tension and compression when bending. With a round object you have the least amount of material in the area that is under the greatest tension and compression when bending.

.............
I also have assumed this to be the case. However, Ward's reference to hang glider and kite application of round tubes is indicative of the complexity of the comparison.
I would think that stress in the two vectors (O deg. / 90 deg) of the square tube would be superior, but for stress's in random vectors, the round tube would be best.
This subject is relevant to choosing wing joiners. I have recently been deciding on square or round, and have gone for the square. The bending force is aligned with the sides of the tube.
I'll see if I can open the link Adam provided for further reading later.

Jim.

Jim.


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