Carbon fiber skin

[TFF]

I know most of the properties. I have covered planes and know enough about composites that it would be a total mess if covering was done traditionally with carbon. All aircraft use to be sewn. Glue use to not be good enough.

Glueing it. Would you pick a classic fabric contact type or would you epoxy? Traditional stuff oozing through would probably be more successful. Epoxy would have to be clamped. You could get a couple of panels done where you can access the whole tube. You would probably have to do one tube and wait, and work your way around as each cures. Spanning between like the belly would cause new issues. No way to clamp. Super glue corners?

Just the unraveling when fingering the raw carbon is a mess. Rows of the weave will unravel. I guess one could treat it somehow.

After it’s attached you have to fill the weave with epoxy. I imagine one coat to imbed. And at least another to level it. Do you choose thin and very fast or slow and thick?

Endless questions to answer just to figure out the process. Then you can have the conundrum of if it looks good.

 

[arj1]

Then you can have the conundrum of if it looks good.

) yes, that one as well...

 

[Richard Roller]

Synthetic, yes, but totally different use. Fabric on an airplane is literally clothing. Carbon or fiberglass are usually not clothing. I have always wanted to see raw Razorback fiberglass covering unused. I don’t know if it was woven or a fine mat. I’m thinking it was mat.

To cover a traditional airplane, one has to shrink the fabric. At least to make it look right. Cotton and linen is water and shrinking dope. Dacron heat. The Razorback used shrinking dope. Carbon gets longer with heat but in reality it’s just stable. How do you get the wrinkles out around curves if it doesn’t shrink? What would you glue it to the airframe with? You could sew it, but it’s slippery and will want to unravel without a glue. There are lots of issues to overcome. While not impossible, it’s a one on one experiment. You would probably have to do it two or three times to get acceptable results and be very flexible in thinking out the issues.

Razorback is woven.

 

[TFF]

It must be woven special so it can pull in some. I remember thinking about driving over to the company to check it out because I wasn’t too far from the business. I never did. To me it’s the perfect fuselage covering for non wood structures.

 

[Fiberglassworker]

Synthetic, yes, but totally different use. Fabric on an airplane is literally clothing. Carbon or fiberglass are usually not clothing. I have always wanted to see raw Razorback fiberglass covering unused. I don’t know if it was woven or a fine mat. I’m thinking it was mat.

To cover a traditional airplane, one has to shrink the fabric. At least to make it look right. Cotton and linen is water and shrinking dope. Dacron heat. The Razorback used shrinking dope. Carbon gets longer with heat but in reality it’s just stable. How do you get the wrinkles out around curves if it doesn’t shrink? What would you glue it to the airframe with? You could sew it, but it’s slippery and will want to unravel without a glue. There are lots of issues to overcome. While not impossible, it’s a one on one experiment. You would probably have to do it two or three times to get acceptable results and be very flexible in thinking out the issues.

Razorback is a fine woven fiberglass fabric it does not shrink; it is applied as tightly as possible and glued on with fabric cement.
Then nitrate dope is applied, the nitrate dope shrinks causing the razorback to pucker between the threads. Successive coats are applied until the fabric has tautened sufficiently. Or as an alternative the fabric is pulled almost tight then Butyrate dope is applied to finish before Silver.

 

[Tiger Tim]

You have to admit, if carbon cloth could be laid on using the Razorback system and finished with a UV-resistant varnish it would look awfully cool on the right plane.

 

[Pops]

Razorback is woven.

I have taken Razorback off a Piper Tri-Pacer and was surprised at the high weight. Did some tube repair and recovered with Poly-Fiber. Don't remember the weight change.

 

[TFF]

I still use Nitrate and Butyrate on my RC planes when painting. I will be sad when it’s gone. Cotton can be heavy too. Especially if going for extra smooth.

 

[AOG]

Considering CF sucks you down the rabbit hole. Descending... why not carbon/aramid fiber top coat blend? Then, why not make it structural? Why not integrate a carbon fiber sandwich skin structure to eliminate traditional front a rear spar structures? Why not integrate the fuel in that structure to reduce weight further? Why not integrate existing graphene resources to further reduce the carbon fiber "volume."

I am sure many of you have seen the DarkAero Project kids on YouTube. They are doing amazing things with Carbon Fiber. This is a link to there 100 lb wing for a long distance, high speed home build kit. I wish I was younger and richer.

 

[AOG]

yes. I would like to know if it's possible to use carbon fiber instead of fabric on metal and if that have already been made on sonerai.

CF is weird, though not a metal it is conductive. CF will cause galvanic corrosion on any metal with which it contacts. It is one of the unique challenges of CF. You would most likely need to layer either an aramid or fiberglass layer between the fastening points of choice.

 

[BBerson]

Might want to cover the frame with Dacron first and shrink tight. Then contact cement thin carbon fabric.

 

[addaon]

CF will cause galvanic corrosion on any metal with which it contacts

Not any metal, electronegativity of titanium is close enough that it (and all alloys I'm aware of) are fully compatible with carbon fiber with no galvanic isolation.

 

[Boscovius]

I followed Mike Patey for a bit before he got off into palace building and scuba pool construction. When Patey was building his Carbon Cub he used a sacrificial piece of aluminum to cover his main fuselage, coated that with PVA or whatever for a release agent, then covered that with several layers of pre-preg carbon fiber sheets. Once it had set he removed the carbon fiber and aluminum from the frame and after trimming the carbon fiber he had essentially what the OP is looking for. A carbon fiber skin.

 

[rv7charlie]

Since this thread is in the Sonerai section, that should be the answer. For the OP: the GlaStar basically does that (in fiberglass) around the steel fuselage cage. (The tailcone is obviously structural, however.) Something similar is done on a some unlimited acro a/c, as well. Makes maintenance/inspection a lot simpler, at some sacrifice in weight.

 

[wsimpso1]

Tube structure of the Sonerai is complete by itself. It does not need any additional strength or stiffness.

Add anything heavier than the various coverings, and you have added weight without a purpose.

Usual polyester fabrics are around 2 oz/square yard, tightly woven, compliant around curves, glues easily, and shrinks tight. These raw polyester cloth have had characteristics adjusted to covering aero structures.

The usual graphite is 6 oz/square yard, unravels easily along cut edges, resists wrapping around stuff, is a pain to get glued down, and actually gets shorter along the length of the fibers as temperature goes up but is not tautenable by itself. These woven graphite cloth have been adapted to making parts in molds with vacuum bags holding them on the molds.

Graphite fiber cloth for covering will be awful to work with, tough to get on well, flutter in the breeze, heavy, and look terrible. Experiment if you must, but you have been warned...

Billski

 

[AOG]

Not any metal, electronegativity of titanium is close enough that it (and all alloys I'm aware of) are fully compatible with carbon fiber with no galvanic isolation.

Thank you, I always lose the argument of absolutes. Titanium is about $14 per 5/16" x 3" bolt. Even sleeves would cost a ton. I think the accepted practices include layering aramid or fiberglass into the boundary layers.

Tube structure of the Sonerai is complete by itself. It does not need any additional strength or stiffness.

Add anything heavier than the various coverings, and you have added weight without a purpose.

Usual polyester fabrics are around 2 oz/square yard, tightly woven, compliant around curves, glues easily, and shrinks tight. These raw polyester cloth have had characteristics adjusted to covering aero structures.

The usual graphite is 6 oz/square yard, unravels easily along cut edges, resists wrapping around stuff, is a pain to get glued down, and actually gets shorter along the length of the fibers as temperature goes up but is not tautenable by itself. These woven graphite cloth have been adapted to making parts in molds with vacuum bags holding them on the molds.

Graphite fiber cloth for covering will be awful to work with, tough to get on well, flutter in the breeze, heavy, and look terrible. Experiment if you must, but you have been warned...

Billski

I don't think people would consider using raw CF cloth for a fabric covering. The cloth would come apart, it is porous. It must be in a matrix. BTW, CF is not conductive without resin.

 

[addaon]

Titanium is about $14 per 5/16" x 3" bolt

Depends on where you're buying, and in what quantity, of course. My rule of thumb (which might need to be inflation adjusted, but order of magnitude) is that aluminum sheet and plate goods (2024) are around $5/lb, and titanium (6AL-4V) is around $30/lb. So yeah, it's definitely more expensive, but it's not prohibitive in some applications, where the advantages pay off. Fittings in CF to handle point loads is one of those applications where sometimes it checks out.

(Edit: Also, purely for curiosity, and not to disagree with the basic point -- titaniumjoe.com has 6AL-4V bolts at about half the price you mentioned. Super limited selection since that's the way their business works... but they're good people, and when they have what you want it's at a competitive price or better.)

 

[wsimpso1]

I don't think people would consider using raw CF cloth for a fabric covering. The cloth would come apart, it is porous. It must be in a matrix. BTW, CF is not conductive without resin.

Agreed that applying it as cloth is impractical and inappropriate, but going back to the original post of this thread and the OP's followup posts, that indeed does seem to be what he is asking about.

 

[rv7charlie]

Agreed that applying it as cloth is impractical and inappropriate, but going back to the original post of this thread and the OP's followup posts, that indeed does seem to be what he is asking about.

I wish the OP would clarify. I didn't interpret his original post that way; he asked:
"does someone consider carbon fiber instead of fabric for fuselage skin ?"

Carbon cloth is fabric, too. I interpreted 'instead of fabric' to mean a carbon fiber shell (which would need the resin matrix), as seen on multiple existing tube fuselage designs.

Only the OP knows for sure....

 

[fifidibosco]

My question was just to use carbon fiber as a fabric without any idea to increase the strength. just a "Dacron remplacement"