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Classic fuselage designe but in carbon fiber tubes?

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Orsovolante

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Good morning.
I think the idea came to many but I didn't find any discussion on the forum.
Build a classic fuselage, in tubes and canvas, but instead of using steel tubes use carbon fiber tubes.
The joints would probably be too weak to stick. But they could easily be reinforced with pieces of fabric and resin.
all of this should make it possible to obtain light and robust structures. Good sizing would allow the use of tubes for industrial uses that are very common in the automation world.
Believe something similar has already been done but with processes unsuitable for amateur construction. this would be a technique closer to wooden constructions, or welded steel, than to lamination on foam blocks.
 

Bille Floyd

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Sep 26, 2019
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Good morning.
...
... but instead of using steel tubes use carbon fiber tubes.
The joints would probably be too weak to stick. But they could easily be reinforced with pieces of fabric and resin.
...
If it was a Kit plane ; all those joints, could be pre-made
with the angles already set , so all the builder had to do
is stick them together with a real slow epoxy ; with a pot-life
long enough to place the frame in a pre-made jig before it
went off.
The wing could be made the same way ; the pre-made spar
has rib mount attachment points already set in place, and
the builder just plugs everything together , in a home-made
jig.
Even the jig parts , could be prefabbed ; all the builder
needs is a self leveling rotary laser level, to ensure it's all
at the correct angles with the horizon.


Bille

dino posted this on another Thread ; the pre-made joints
could look like this :
 

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Orsovolante

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Apr 17, 2016
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If it was a Kit plane ; all those joints, could be pre-made
with the angles already set , so all the builder had to do
is stick them together with a real slow epoxy ; with a pot-life
long enough to place the frame in a pre-made jig before it
went off.
:
Yes, I thought about it, but in a fuselage every joint would have different angles.
It would be easy to get the shape of the joints to the CAD but their production would be a little different. The zepelin system is very nice but I think it is expensive to produce those pieces in limited series. It is easier to imagine aluminum semi-shells, or internal joints to be glued. But in the end, temporarily gluing the tubes in place and then reinforcing the joint by wrapping the resin-impregnated roving, should not be a difficult operation.
 
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Aesquire

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This is much like "black aluminum" thinking, translating carbon fiber for metal. Early bicycle composite thinking, with aluminum head tube, seat tube joint, and bottom bracket connected by carbon fiber tubing in a brazed/welder steel tubing shape.

There are multiple ways to do this. Internal plug into tube lug joints, glued in place. External wrap around gussets, like aluminium tube & gusset. Hand wound wrapped roving composite joints. ( There's a bamboo bicycle frame using this technique ) and others.

Factors to be considered include:
how much you want it to look like a welded steel frame. ( not a big consideration here, I think, but important for bicycle marketing )

One off or kit production.

Hand labor vs. Faster CNC fabrication ( labor or cash )

Hand lay up vs. Pre made parts.

And Since the main idea is using presumably commercially available tubing, you need to figure weight vs. Molded & Moldless composite construction, and the same calculation for labor time.

And just to tweak the idea completely out of control... ;)
Aluminum tube construction, tack welded together, wrapped in carbon fiber, cured, then the aluminum dissolved away with pool chemical ( muriatic acid ) leaving a light composite frame behind. ( as used in the Gossamer Albatross, human powered cross Channel aircraft )

It's not a terrible idea to use carbon tubing to replace steel tubing but it's not optimum use of the material. You have to perceive an advantage in time or money over other methods.
 

wanttobuild

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Aesquire
Wow!
Now that is thinking OUTSIDE the box man!
This topic is consuming all my spare time, and I don't have much. People don't really like it when my freight liner swerves over into their lane while I am busy driving and drawing.
I am thinking Baby Ace with an aeromomentum AM10.
I have been reading a lot of archived posts on the matter, and I am drawn to building on a caul plate for the bottom, top is flat. Billski full credit.
My solution for now is to offset the vertical members from the horizontal members it allow a full uni wraparound the longeron.
 

Orsovolante

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It's not a terrible idea to use carbon tubing to replace steel tubing but it's not optimum use of the material. You have to perceive an advantage in time or money over other methods.
Proper consideration.
I believe that a monocoque fuselage made in an autoclave would be on top of everything.
however, compared to the classic techniques for self-builders, foam and glass or carbon sandwiches, it would be simpler.
Small amounts of resin or glue at a time. no large surface to be treated. No large surface to finish.
Of course it's good for a J3 repplica or a romantic high wing, not for a quick canard.
Compared to riveted aluminum tubes, I think you would have greater strength in exchange for a little more complication.
 

stanislavz

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There is one much easier solution - hat/omega profile reinforcement. Just make skin as thin as possible, and add reinforcement in a standard rag and tube placement.
 

Orsovolante

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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.
 

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wanttobuild

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Could you execute the fuselage frame in Rohacell, then wrap? I believe the gussets, maybe some attachment points could be prepared before wrapping. The foam could be reduced in size in places for extra reinforcement like landing gear, firewall etc...
 

wanttobuild

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There is one much easier solution - hat/omega profile reinforcement. Just make skin as thin as possible, and add reinforcement in a standard rag and tube placement.
I don't fully understand what you mean, I am a truck driver not an aviation professional so I believe I don't understand your terminology. Mold skin first. then hat shape reinforce?
 

Orsovolante

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Hi,

Such a design has been built by Thierry Pujole in France a few years ago, called the Agrion :
http://www.ulminimalist.sitew.com/#Projet_minimaliste.B

The carbon fibre tubes are bonded/tied together using a carbon fibre wrapping:
The problem, which I have already experienced, is that carbon fiber skins do not easily mold, as can also be seen from the photo.
If it were possible to design a cell with angles of the same joints in several points, then it would be possible to make connecting shells prefabricated in molds.
 

wanttobuild

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Maybe another approach
Construct 4 frames top bottom and the two sides and then tape together.
Unless I am convinced otherwise, I plan to use foam as a core, carbon both sides, then tape them together.
Not optimized I know, but pretty high speed for a truck driver
 

Aesquire

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Miyata ( Bicycle maker, Japan ) used cast aluminum lugs that plugged into aluminum tubing for the 3 main joints on a bicycle. ( fewer joins than a plane, but similar complexity. ) This allowed the use of hardened aluminum tubing, No post assembly heat treat, with no angle cuts or coping, just flat ends. Interference fit & epoxy to hold it all together. I could show you a picture, but it looks just like a normal welded bicycle frame when painted. ( with nice clean fillets )

https://www.ragandbone.ca/PDFs/Miyata Catalogue PDFs/Miyata Catalogue 87 Alumitech.pdf

You can do the same with composite joints and tubing. No wrap, just glue & plug in.

If you are doing a kit, all the hard work can be in the molded joints, which can have stainless or aluminum reinforcement for bolts and other fasteners built right it. Yes, that means a lot of custom molded parts, but assembly in the workshop is very fast & simple. Just cut tube to length, glue, and plug in. It should even be self jigging to a degree, so all you'd need is a flat table and a few spacer blocks. You should be able to do an entire fuselage side in an evening, and as long as you pay attention to assembly order, be able to walk away & get back to it later at many, but not all, stages of assembly.

The opposite approach calls for coping cuts to join the tubes like a steel frame, then wrapping the joints by hand. A lot more labor during the build, but far less expense for the kit or plans maker.

And you may consider the detail esthetics as a plug in design should be externally smoother, like a welded steel frame, but a wrapped joint frame is a bit lumpy, like a tube & gusset frame. How important that detail is, I'd call an artistic choice. How important is it to see a dead straight line down a longeron?
 

Orsovolante

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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.
 
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