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May 25, 2019, 05:11 AM
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Ampbomber's Avatar
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Question

Building with a 3 mm CF backbone tube


I've built a lot of CF framed planes in the last few years but I don't recall anyone talking about building one with the 3 mm CF tube for a backbone. All the planes I have built have 3 parts to the frame. Upper and lower vertical and the horizontal frames which make up the basic frame for a non-removable wing plane. I can see the tube would add a lot of stiffness but weighs more than a couple of .7 mm tubes.
The question is:

How is the 3.0 mm tube used for the build ?

Thanks
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May 25, 2019, 06:25 AM
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pmackenzie's Avatar
OldManY posted a link to some very detailed pictures of how to build with a backbone:

Direct link
https://www.starostov.com/%D0%A1%D0%...VIA-Composite/


Lots of detail in the images, study them carefully.

I do it a bit different, but basically I first put all the holes in the tube that the rods will go through.
Then build the side profile of the fuse.
Then stand it up though the "split" table and build the "shockie" ( flat profile), and wings and stab.


The part I find tricky is covering the fuse

Pat MacKenzie
May 25, 2019, 09:59 AM
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I had not seen anyone mention drilling holes. I can see it clearly now. I assume the tube with all the rods passing through both ways gives much more torsional strength to the tail feathers and that would be the reason to use the tube.

Thanks

George
May 25, 2019, 10:11 AM
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pmackenzie's Avatar
The final torsional stiffness still mainly comes from the diagonal bracing.
But the tube, and the fact that all the vertical and horizontal cross pieces are continuous through it, helps keep it all in alignment during the bracing process.
Jul 04, 2019, 02:52 PM
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Pat,

Thanks. I'm about to find out later this summer.

George
Jul 13, 2019, 04:16 PM
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[QUOTE=pmackenzie;41938325]OldManY posted a link to some very detailed pictures of how to build with a backbone:

Pat,


Well, the journey begins. Supplies arrived today. Took your advice and studied the pictures.

One question. Any dos or don'ts on drilling the holes?

Thanks,

George
Jul 14, 2019, 12:26 AM
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pmackenzie's Avatar
Hi,
I have a couple of small drill jigs I use, basically two identical blocks with a hole for the tube and two cross holes in them.
I think the blocks are 1/2" x 3/4" aluminum, about 1" long.
The tube hole is near one end, so the cross hole from the end does not have to be so long.
Put the tube through both blocks.
Line the edge of one block up with the first cross hole and drill it. Put a piece of carbon through it. This block stays in this position for the rest of the operation.
Slide the other block back lining up its edge with the next hole to be drilled. Repeat all the way back.
I work on the side view, with all the perpendicular positions also indicated.
This makes it quite easy to drill them all accurately.
A bit hard to describe, and I away from home for the next 10 days so I can't post any pictures.

Pat MacKenzie
Jul 16, 2019, 03:45 AM
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Pat,

You explained it well. It's done. Continuing the build. Thanks.
Jul 21, 2019, 03:48 PM
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The vertical frame turned out great. With rudder it weighs 3.8 covered. Surprised myself. 2 micron went on easily. I sprayed #M 77 with air brush. Easiest way ever!

Looking for best way to hinge rudder before painting the vertical frame. Any suggestions?

Thanks
Aug 05, 2019, 08:24 AM
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crossup's Avatar
What are you thinning the 77 with? I like the idea.

Quote:
Originally Posted by Ampbomber
The vertical frame turned out great. With rudder it weighs 3.8 covered. Surprised myself. 2 micron went on easily. I sprayed #M 77 with air brush. Easiest way ever!

Looking for best way to hinge rudder before painting the vertical frame. Any suggestions?

Thanks
Aug 05, 2019, 09:05 AM
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Did not thin the 3-M77. Just sprayed from can into a small paper cup (wear gloves) . Be careful when you pour it into the airbrush cup. Pour slowly and not to the top because it is carbonated coming out of the spray can and will foam over top of cup. Also backed up the frame with black paper so as to see where I was spraying. Used a #5 tip at 30 lbs.

BTW, everything is hinged and painted , will begin bracing tomorrow.
Last edited by Ampbomber; Aug 05, 2019 at 09:07 AM. Reason: Add picture


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