Carbon Fiber Tube Fuselage

[Synergy]

One reasonable path to the OP, a tube-based warren truss, is to use a foam core as the shear web between a top tube and a bottom one. Sculpt the core to the tubes, then wrap the whole thing with the required number of layers of fabric. Done well there would be no advantage to partial removal of the solid shear web.

 

[wsimpso1]

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?

I encourage anyone thinking this is a hot ticket to:

Find the combined loading of all structural elements of such a truss, including flight loads, emergency landing loads, aero loads of the skin, and fabric tension;
Compute total stress states at worst cases;
Iterate design until all elements have adequate FOS;
Determine weight, estimate cost and man hours to build.
Compare this carbon tube scheme to competing schemes - molded graphite-epoxy shell being the usual bench mark. If you are willing to look at space frames, a titanium tube structure may be suitable as well.

You may be surprised...

Billski

 

[TLAR]

I will address the comments shortly

 

[delta]

Delta
Are you lashing the Tow or are you cutting and placing?

Lashing.
There have been some very intelligent discussions about truss construction using cf and one thing that hasn't been brought up about protruded shafts would be the sharp broken ends coming at you in a crash.

 

[Victor Bravo]

You mean that the name of the design engineer would be Vlad the Impaler?

 

[TLAR]

One reasonable path to the OP, a tube-based warren truss, is to use a foam core as the shear web between a top tube and a bottom one. Sculpt the core to the tubes, then wrap the whole thing with the required number of layers of fabric. Done well there would be no advantage to partial removal of the solid shear web.

Synergy
Thank you for your comments.
All of the points well taken.

A lot of comments on HBA about this topic, but none get down to the actual fiber path in the Node.
If I could message you directly about this matter that would be helpful.

A lot of comments here are not helpful, and they seem to discourage experimentation.
I try to post on the forum so as to be helpful to others

 

[TLAR]

I encourage anyone thinking this is a hot ticket to:

Find the combined loading of all structural elements of such a truss, including flight loads, emergency landing loads, aero loads of the skin, and fabric tension;
Compute total stress states at worst cases;
Iterate design until all elements have adequate FOS;
Determine weight, estimate cost and man hours to build.
Compare this carbon tube scheme to competing schemes - molded graphite-epoxy shell being the usual bench mark. If you are willing to look at space frames, a titanium tube structure may be suitable as well.

You may be surprised...

Billski

This topic is a thought on fiber placement.
Disregard weight, labor, cost and anything else other than constructing a carbon fiber Node.

 

[TLAR]

Lashing.
There have been some very intelligent discussions about truss construction using cf and one thing that hasn't been brought up about protruded shafts would be the sharp broken ends coming at you in a crash.

That is a very real concern, and I don’t have an answer.

 

[TLAR]

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?

Dana
I am looking at fiber path first.
Composite is my first choice of materials and efficiency is secondary, although it seems when one constructs a part, the second or third try is always an improvement so time will tell

 

[TLAR]

You mean that the name of the design engineer would be Vlad the Impaler?

IGNORE

 

[BBerson]

I wouldn't use carbon tube alone for cockpit structure.

 

[Synergy]

Synergy
...
If I could message you directly about this matter that would be helpful.

I might not see your message or be able to get back to you quickly, but you may certainly try. I am not hard to find if you'd like to call, it's more efficient.

 

[sigrana]

The best thing is to ask Jim Marske for advice. He has decades of experience with carbon composites. https://marskeaircraft.com/contact-marske-aircraft

 

[stanislavz]

Op. Do you have loads determined ? If you could give me, i would design it in two variants - only shell and only tube. For tail section only.

As mine numbers shown already - it is safer and faster to make a shell and add only local reinforcements against buckling of large panels.

Tubes are nice and sound (done using pultrusion or other high fiber epoxy ratio), but joints are not..

One of example :

 

[wsimpso1]

Lashing.
There have been some very intelligent discussions about truss construction using cf and one thing that hasn't been brought up about protruded shafts would be the sharp broken ends coming at you in a crash.

This is the best reasons for designing the entire cockpit to the FAR Part 23 crash loads (23g and 19g), and maybe higher. That way the cockpit will stay in one piece at least up to the point where the seat belt system begins to fail. Making the cockpit sturdier than the seatbelts doesn't help you much, but might make the coroner's job easier.

Crash safety is one of the reasons classic welded tube fuselages have a great reputation. Everything is sized to yield, and then when crash loads happen, it stays welded in one big piece but absorbs big energy.

Billski

 

[BJC]

Making the cockpit sturdier than the seatbelts doesn't help you much, but might make the coroner's job easier.

That is one of the things that I like about you, Bill; you are always thinking of others.

FWIW, I gave lots of thought to the CF tube truss fuselage concept many years ago, circa Leo’s Shark development. There are many reasons to reject it. Too bad that Leo was killed before his was finished and flown.


BJC

 

[TLAR]

I am looking at constructing a Baby Ace.
Snowmobile engine or motorcycle engine for power.
Carbon tube for the spar.
Aluminum streamlined struts.
Carbon wheels.

If and it’s a big if, I will document the procedure, a “how to” as it were, and publish.
I there will be enough interest, because once the procedure is finalized, it could be used to build any number of rag and tube small HP aircraft.
Having received some awesome advice, I will move forward.
I would like to be able to build from Raw materials, ie carbon reinforcement fabric and foam that can be machined with woodworking tools.

 

[TLAR]

Continuing, no molds, Hotwire only.
So the fuselage is foam core, round and square in section, reduced in areas where a thicker wall is necessary.
Four frames are built and taped together, actually the longerons are wrapped, and you quickly have the basic structure. The easy part if you will.

 

[TLAR]

Op. Do you have loads determined ? If you could give me, i would design it in two variants - only shell and only tube. For tail section only.

As mine numbers shown already - it is safer and faster to make a shell and add only local reinforcements against buckling of large panels.

Tubes are nice and sound (done using pultrusion or other high fiber epoxy ratio), but joints are not..

One of example :

View attachment 103616

A very nice offer sir. I don’t have the education to determine the loads.
I will just go by the tube size and wall call outs, and if necessary add some more.
I not gonna wring out every ounce because I don’t have the education and also I want some wing loading.
Light is right— to a point, weight can be your best friend when the wind is blowing

 

[TLAR]

One of the many attractions for me to carbon fiber is the extremely rigid and stiff connection between parts obtained without rivets or welding, which may be of interest to many potential builders.
Carbon tow can be used to make many hard to fabricate shapes that would be very difficult in steel or aluminum.
For me it’s a very nice material to build an aircraft