Carbon fibre tube trusses

I don't know if this deserves a dedicated thread, but still..

I found a firm specialising in carbon structures, both engineered beams and tube trusses:

https://element6composites.com/carbon-fiber-applications/carbon-fiber-trusses-beams/

Some of their images look very like a traditional tube-frame fuselage, but black.
Square tubes with gussets too.

 

And they use metal fasteners to attach the CF gussets to the CF tubes. Hmmm.

 

I've always found the strength to weight ratio of carbon fiber to be very interesting.
But I'm going to show my ignorance of knowledge towards the material at this point.
I have always thought that carbon fiber was a poor material to use in a tube & gusset design due to it "fracturing" when drilled.
Excuse my poor terminology.

Kevin

 

Have you checked their prices? Hold on to your hat...

 

Kevin you can drill it just fine with the proper bit, no problem
Element 6 is dragon plate

 

It would be nice to put some real-world Cost to say a Plans Built Airframe like the Affordaplane Airframe. Cost + Weight. The Biggest Cost for some of these Airplanes is these overpriced Engines. Like, I believe an Aerolite 103 Airframe is around $13,500 complete with a Hirth 28hp $15,500+. With the Hirth F-33 (28hp) 235lbs - 45lbs for Engine = 190 lbs for Airframe, probably less than $6,500 in Material for Airframe.

Affordaplane
http://www.affordaplane.com/

 

A 2-part molded carbon gusset/connector, that gets glued across both sides of a tube joint, that is "cupped " to fit tightly against 2/3 or more around the tube circumference, could allow a carbon T & G structure to be fairly efficient.

The joint will take longer to make than the equivalent riveted gusset, but that is probably what this material "wants". There will have to be a bunch of 3D printed nylon or PE molds for all of the different gusset shapes for any given fuselage, but that would be an ideal use for a self-lubricating printed plastic.

You get a bunch of these little plastic molds printed, and lay up carbon BID into them, even vacuum them all down at one time, and after a few cycles you have a box full of carbon gussets that match the truss shapes.

The rest of the fuselage is just cutting the tubes, hot melt glue to "tack weld" the truss together, then you glue the gussets on, clothespin them in place, and come back the next morning.

I'm sure that the high end bicycle manufacturers have tried something like this already and have some sort of load test data.

 

Another idea that just popped into my foggy head is a universal molded carbon "tube end fitting" that the end of a tube gets glued in to, which terminates in a structural mounting tab. Kind of like an electrical spade terminal, but much larger and structurally glued onto the tube instead of crimped.

So your fuselage truss has 2-part taco shell shaped gussets that clamp and glue around the un-broken main longeron (in pairs) at certain points. The shorter tube sections (verticals, cross-members, diagonals) are cut and fitted with these molded terminals. The flat "spade" ends can be drilled and pop-riveted onto the flat gusset sections of the taco shells with glue. The glue is the structural attachment, the pop rivet allows you to hold it in place until the glue sets.

I can maybe take credit for bringing this strange idea up here on HBA discussing carbon, but several aircraft manufacturers have used a similar method using metal tubes and bolted end fittings years ago. If memory serves, the Hurricane (and previous Hawker biplanes) used this method to create an easily repairable structure.

 

The only serious attempt to use carbon fiber tubes to replace steel tubing in a truss fuselage that I know of is the Loudenslager Shark. It never flew. It can be seen at Oshkosh.




BJC

 

There are "off the shelf" square carbon fiber tubes that would allow flat plate gussets. I don't know much about them, other that they are commercially available. I recall another thread a month or two ago where a DIY version was discussed. Or was that this thread early on?

 

Aluminum thinking
You either think like a piece of thread or just stick to aluminum.

 

I'm reminded of the scene in "Blazing Saddles" where the mayor says to the town hall crowd "Not only was that authentic frontier gibberish..."

 

I saw it on the back wall at the EAA Museum.
The new German ultralight Corsair is carbon tube with wrapped end connections. I think it was $88k.

 

Carbon Cub?

 

Carbon Cub just has carbon panels like floors and wing tips. Structure is still Cub Cub.

 

I wonder why the Holy Grail of tube fuselages is hanging on a wall in a museum?
I suspect it's unairworthy.
I would sure like 2 see the reinforcement schedule

 

Loudenslager designed that airplane for himself. Only he was going to be good enough to do the crazy stuff it was going to be capable of for his airshow. I doubt there are ten people in the world that could fly it as intended. Maybe 5. That is why its a wall hanging. His staple airplane is in the Udvar Hazy. If he had not gotten smacked by a truck on his motorcycle, it would have been the bar, and airshows would either be way crazier or ban.

 

Because it is not the holy grail of tube fuselages.

That is a reasonable suspicion. The project was abandoned before first flight, circa 1997.

I suspect that there were some comprehensive engineering assessments of the structure.

What do you mean by "reinforcement schedule"?


BJC

 

The ply schedule

 

Anyone here who remembers seeing Loudenslager's airshow act in the Stevens Akro, can guarantee you that anything he designed (or had designed) to top that act would have to be pretty frickin' strong and durable !