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Classic fuselage designe but in carbon fiber tubes?

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stanislavz

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Yes the method illustrated at the bottom was the first one I thought of.
But I believe, based on my little experience, that the Ʊ (omega) shape is difficult to obtain with carbon skins that do not willingly accept to be folded at excessive angles.
It could be made in glass or prefabricated in sections of sections to be previously inserted on the tubes, to then be glued on the tube and on the carbon handkerchief.
Now that I've understood the method, I actually think it's the best solution.
I do agree. But - even if omega shape is best at load/weight ratio. Square one are only 7% worse. If i do remember.

And as i have made on big post here, as asked by one person : https://www.homebuiltairplanes.com/forums/threads/tube-construction-alternatives-to-conventional-welding.27418/page-13#post-500148

Steel tubes are big yes. They are ready made, and have stable "performance" Caron tubes to mine afaik - are best if used as a tube - ie pushrod/tail tube etc.. Joining them is not that i would like to test with mine butt.

Dry fabric can be shaped as you want. So - why not to take our minimum number of layers, add to them reinforcements from saved truss weight. It is just easier. Truss made from tubes is need only then we do not need any skin. Like in space (Where they are used.. )

Ps. If someone will told me how easy is to made free formed composite - i doubt if they now how nice does it feel on your nose/skin this experience :) Will add new description to my avatar.
 

stanislavz

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I still do not believe in it.. Small contribution from my side :



From here: http://www.reaa.ru/cgi-bin/yabb/YaBB.pl?num=1495052195/all (in Russian, but images are international :) )

1 seater, empty ~ 70-80kg with motor. This fuselage as is is 15 kg i think.. Only tubes was 7 kg. One seater far 103 compliant. And no carbon.. Only fiberglass
 

Aviacs

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Wood, the original carbon fiber, went through this quickly during early years of aviation.
Stick framed trusses originally, but then the best/lightest/stiffest/streamlined constructions morphed into monocoque structures in the teens/war years, and arguably culminated in planes like the Lockheed Vega during the 20's. Of course the most efficient structures in terms of material and performance are not always cost-accessible to many small scale builders. So stick trusses are still common enough; & wooden monocoque rather more rare. Aluminum took over because it is easier, more reliably sourced, uniform, and less skill dependent at production scale manufacturing.

I wonder, given all the other options, what advantage really accrues to "stick-built" carbon fiber constructions?
Or is the intent to develop something universal, if possibly not optimally efficient, sort of like an aviation version of 8020 strut?

smt
 

Aviator168

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I still do not believe in it.. Small contribution from my side :



From here: Самолет PCHELKA (in Russian, but images are international :) )

1 seater, empty ~ 70-80kg with motor. This fuselage as is is 15 kg i think.. Only tubes was 7 kg. One seater far 103 compliant. And no carbon.. Only fiberglass
So the skin of that aircraft is fiber glass, not cloth? That's amazing.
 

Riggerrob

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An idea would be to reinforce the joints as is done in wooden buildings.
Simple sticked spruce blocks.
Forgive my first experiments with freecad.
Dear orsovolante,
A good concept to simplify gussets. Also a good first experiment drawing in freecad.
May I suggest that your second drawing include rounded out edges on those gusset blocks? Rounded edges will allow you to wrap carbon tape all around the outside of the joint. If you make outside edges the same radius as the outside diameter of tubing, then you eliminate tight bends and stress risers on carbon fiber tape.
If it is a complex joint joining 4 or more tubes, then you might need to assemble and tape it in 2 or 3 steps. Not a big deal with modern slow-curing epoxies.

P.S. Does you knick name mean "flying bear" in Italian?
 

Sockmonkey

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Wood, the original carbon fiber, went through this quickly during early years of aviation.
Stick framed trusses originally, but then the best/lightest/stiffest/streamlined constructions morphed into monocoque structures in the teens/war years, and arguably culminated in planes like the Lockheed Vega during the 20's. Of course the most efficient structures in terms of material and performance are not always cost-accessible to many small scale builders. So stick trusses are still common enough; & wooden monocoque rather more rare. Aluminum took over because it is easier, more reliably sourced, uniform, and less skill dependent at production scale manufacturing.

I wonder, given all the other options, what advantage really accrues to "stick-built" carbon fiber constructions?
Or is the intent to develop something universal, if possibly not optimally efficient, sort of like an aviation version of 8020 strut?

smt
Carbon fiber gives you the structural properties of wood while being less vulnerable to moisture.
I thought building a frame out of pieces that worked like Tinkertoys or K'NEX with straight members and specific multi-axis connectors was already a thing or I would have said something sooner.

You can make custom connectors for tubes just by taking some short sections of meltable or dissolvable material the same diameter of the tubes, sticking them together at the right angles, wrapping them in fiberglass, and removing the meltable material. Bam. You have a custom connector.
They would look like this when you're done.
 

Sockmonkey

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you might be overthinking it...

I didn't know you could cast CF like that. I thought it always had to be layered into a mold in sheets and stuff.
So if you had a kit that was all CF tubes and connectors that just needed to be plugged together and epoxied, you have a super-easy kit that can get in under the 51% rule.
Connection points for internal bracing wires could be molded right into the connectors too.
 

Hephaestus

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Well the graphite powder and short strand isn't as strong as woven, and I'm sure there are limitations - but throwing it out there that sometimes you can think a little outside the box (just test and verify before you risk your neck on it)

Assembly with say the biax carbon sleeves rather than flat wrapped would beef it up some too.
 

Bille Floyd

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Well the graphite powder and short strand isn't as strong as woven,
...

Assembly with say the biax carbon sleeves rather than flat wrapped would beef it up some too.
The engineer that introduced me to composites ; stated that ya loose
about 20-25% of tensile strength, the moment you weave a fabric ; a bit
more in the compressive value. So roll that mandrel for making the tube, with
Uni, and get better results ; add a bit of core material , and it gets even Better
results because now the local stiffness is much improved and more resistant
to column buckling at a small amount of added weight.

Generally a fabric is woven ; to make the fibers easier to work with.

Bille
 

Hephaestus

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The engineer that introduced me to composites ; stated that ya loose
about 20-25% of tensile strength, the moment you weave a fabric ; a bit
more in the compressive value. So roll that mandrel for making the tube, with
Uni, and get better results ; add a bit of core material , and it gets even Better
results because now the local stiffness is much improved and more resistant
to column buckling at a small amount of added weight.

Generally a fabric is woven ; to make the fibers easier to work with.

Bille
Yeah no argument, I was taking a known video distributed process and giving it as a baseline.

Just seemed like a reasonable connector for diy construction to me which does offer some possibilities for improvement if one wanted to go that method. Seemed better than random wrap with tape/cloth.

Fiberglast does list some uni carbon sleeves - probably should have known they exist but hadn't hunted much for them.
 

stanislavz

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Yeah no argument, I was taking a known video distributed process and giving it as a baseline.

Just seemed like a reasonable connector for diy construction to me which does offer some possibilities for improvement if one wanted to go that method. Seemed better than random wrap with tape/cloth.

Fiberglast does list some uni carbon sleeves - probably should have known they exist but hadn't hunted much for them.
But is all too unatural. I do like idea of BoKu in situ formed tubes much more and more useful and you have much less of secondary joints..
 

Geraldc

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you might be overthinking it...

The mold in the video could be used to cast the joint on the tubes.
You could 3d print joint molds with different joint angles and get a bit more strength with carbon tow as well as the stuff used in the video.
 

flyboy2160

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If you think about it a little or lay it out in 3D, you'll realize that you can't assemble one piece angled tubes into the structure if the end joints are a solid one piece that fully envelopes the tubes' outer diameters. If you break the angled tubes into 2 pieces, you can use one piece end joints.
 
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