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Carbon Fiber Tube Fuselage

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TLAR

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Joined
Sep 29, 2020
Messages
56
Are there any folks out there building/designing a fuselage using a Warren Truss type frame?
 

sming

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Joined
Apr 10, 2019
Messages
92
Sorry, in french but flying ;)
400lbs empty
 

TLAR

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Joined
Sep 29, 2020
Messages
56
Sming
Thank you for the link!
Incredible design!
Wish it was in English. I need a set of plans!!!!
Can you get plans for the ultralight?
 
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TLAR

Well-Known Member
Joined
Sep 29, 2020
Messages
56
Why a Warren Truss vs a single CF mono tube? Weight?
Cheers
Good Question
I guess the short answer would be penetrations thru the main tube.
Aerodynamics, ease of fairing everything.
I am not a designer so just copying an existing, flying aircraft
 

delta

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Joined
May 26, 2011
Messages
2,273
Location
Brookside Utah
So, in your area, was there sudden rise is CF golf club thefts!😂 . Just wondering, CF golf clubs are not cheap, not better to source raw cf rods? Cheers
I was using cf arrows to build rc and they were more expensive than some cf golf shafts I found on Ebay., I bought some to experiment with and later was contacted by the guy with I an offer to buy the remaining 1000 he had left. I don't think they fell off the truck, but rather a manufacturer that decided to give up.
This is a representation of the frame I have built but couldn't locate a picture of. It's 160"L 25"W 14.5"H/. The figure in the frame represents a six footer.frame 160 -25-14.5.JPG
Most of the designs I come up with are based on this frame and the 45" length of the shafts.
 

TLAR

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Joined
Sep 29, 2020
Messages
56
Delta
Are you lashing the Tow or are you cutting and placing?
 

slociviccoupe

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Joined
Apr 1, 2011
Messages
306
Location
Palm Bay Fl.
There is a plane hanging in eaa air museum that is carbon tube nonded to anodized aluminum tube clusters. Not sure of anything other than seing it.
 

dana62448

Active Member
HBA Supporter
Joined
Jul 29, 2008
Messages
31
My question is whether carbon tube trusses is another example of “black aluminum “
Is it more efficient to replicate a truss designed for steel. How does this compare to a carbon shell?
 

Synergy

Well-Known Member
Joined
Jun 10, 2010
Messages
332
Location
Kalispell, MT USA
A few things to say in the interest of safety:

Composite frames and structures are best envisioned and constructed as a single assembly of load-carrying members, consolidated and cured together at one time, for example, by skinning a core of the required shape. There is false economy and possibly serious danger in approaches that create or allow stress concentrations.

Joining extremely strong, stiff structural members (such as precured carbon fiber tubes) via a secondary bonding process requires great care and attention to joint design, load path, combinatorial loads, reinforcement, flexibility, adhesive selection, and bonding preparation. It may be wiser to intentionally take strength and stiffness away from the connections than to allow it or increase it.

If we're not yet nodding along in total agreement, please take that as your clue to consider the whole thing a very bad idea. It isn't a bad idea, just a very dangerous one because rigid frame construction 'looks great and works great'...right up until it suddenly doesn't.

The kinds of failures that can be expected are too often 'catastrophic surprises' unless the designer has knowledge of the principles and issues of moment frame construction, plus ability to test the structures under all required loading scenarios, including 'easily tolerated' vibrations at various frequencies (which can heat things up enough to challenge many resins.)

Here's why it's such a challenge to get it right: whatever load the tubes can carry, they can concentrate somewhere. They will carry that load right to their end, delivering all of it to the joint, which may be getting other loads as well due to the combination of forces and resulting deflections/rotations.

Since carbon tubes can transmit extreme tension and compression loads and usually a lot of torsion too, there can suddenly be a lot more load than might need to be absorbed by a less rigid system. On the bright side, the more 'thunderous explosions of carbon shrapnel' one has witnessed, the more informed one can become if still alive to learn from it.

Joint design: Either make it strong enough to carry all the forces and moments the tube can deliver (and free of abrupt thickness changes such as the step that results from the cut end of a tube that hasn't been tapered)... OR, design a connection with selected degrees of freedom, perhaps taking a page from the flexible bolted connection designs and semi-flexible, welded 'moment frame' connections common to structural steel building design. A safe joint will NOT be a mitered tube glued to another one. If the joint is of the 'strong' variety it will probably have to grow in size and thickness quite dramatically, perhaps as seen in the mount pictured below.

Bonding preparation: Commercially available precured tubes will usually have a VERY effective release agent still on them, especially those built on a mandrel. Solvent wipe, grinding, sanding, and solvent scrubbing may not do much more than move it from the inside to the outside. It's important to be extremely conservative in calculating the areas and allowable stresses you will accept for the bondlines.

Adhesive selection: secondary bonding is a crapshoot, even when testing has validated the basics of what we want to try doing. How much do we actually know about the tube, its resin system, processing, and resultant properties? How much of our bond will be electrochemical, rather than mechanical? What have we done to enhance the mechanical advantage and minimize force transmission through the bondline, and what is the nature of the predicted (and hopefully tested) mode of failure? Have we designed to accept or mitigate the weakest mode of adhesive failure, such as peel?

As someone who collects carbon tubes, I fully understand the appeal of this idea. As someone who would advocate a stressed skin, continuously curving monocoque shell with gently increasing thicknesses at load points, I can tell you with credibilty: the latter is lighter, stronger, and much faster/easier to build. Especially when you include the required number of failures along the path to a decent carbon spaceframe.

I'm sorry I won't have time to weigh in on anything I'm working on or answer specific questions. This post is to help keep people alive and on a productive path. There are still many awesome ways to use carbon tubes, and plenty of reasons to keep inventing for them. Please be careful.
 

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