Swap fabric with carbon?

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Cc__

Filing Flight Plan
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Cc__
I’ve been quite interested in the bearhawk 5, but I’m really not a fan of fabric on control surfaces, I was wondering if it would be safe to do carbon fiber instead? If so, how many layers?
 
You'd do well to ask that question on a Bearhawk or Homebuilt specific forum. The general answer is that adding weight to control surfaces is a bad idea due to flutter risks. Also, you don't just cover an aluminum structure with carbon fiber. That's a no-go due to material compatibility issues including corrosion... You'd need to completely redesign the surface.
 
If the control surfaces are fabric then going to carbon fiber is probably going to change their weight. This will have an impact on the control surface balance. If it were me, I would check with the factory.
 
Cc__ said:
but I’m really not a fan of fabric on control surfaces,
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Interesting. Do you have a specific reason why not a fan? Regardless, keep in mind carbon fiber is not necessarily the best product for all applications. Would definitely discuss with the kit OEM as you could open a whole slew of issues by simply swapping it out on your own. From a historical point the last part to be metalized on newer aircraft designs was the control surfaces.
 
I think its definitely worth investigating, not just for control surfaces but for any fabric surface. You would want to be sure that you arent adding too much weight or creating more problems than you hope to solve.
 
moparrob66 said:
I think its definitely worth investigating, not just for control surfaces but for any fabric surface.
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But why?

It's not going to be lighter, it's not going to be cheaper, and it's not going to be easier to work with. What's the benefit of a retrofit to an airplane that's not designed to take advantage of it?

Nauga,
itchy
 
It could be lighter, depending on how thin you can get the fabric. Probably stronger, maybe last longer in the sun. Dont get me wrong, traditional fabric is entirely adequate, but would the flapping and fluttering create drag more than a rigid surface?
 
moparrob66 said:
It could be lighter, depending on how thin you can get the fabric. Probably stronger, maybe last longer in the sun. Dont get me wrong, traditional fabric is entirely adequate, but would the flapping and fluttering create drag more than a rigid surface?
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You know the fabric has to be filled, right? Stronger? Probably. Does it need to be? If so then I probably wouldn't be considering that airplane in the first place. Traditional fabric does not "flap and flutter" if applied properly, and the matrix to make the CF rigid is not weightless.

Carbon fiber is an excellent material in applications that are designed to take advantage of it. When it's used like "black aluminum" or in this case "black ceconite" it loses much of its advantage.

Nauga,
and a box full of dull rotary knives
 
moparrob66 said:
It could be lighter, depending on how thin you can get the fabric. Probably stronger, maybe last longer in the sun. Dont get me wrong, traditional fabric is entirely adequate, but would the flapping and fluttering create drag more than a rigid surface?
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Flapping and fluttering? No, not really. I've got around 1220 + hours in airplanes with fabric covered control surfaces (and only about 230+ in metal planes), and I've never seen my fabric "flapping and fluttering". I was trueing out at about 205 mph in the photo below. No flapping and fluttering here.

BTW, the fabric and paint job are 36 years old on this plane.

3936ca6eea62b48a3d8a2e5a7958c7e9.jpg
 
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Great shot! I have seen videos of other wings with obvious movement of the fabric surface. I dont thing they were doing 200+ either. Not flapping like a flag, but definitely a distinct, fluttering that I found to be slightly off-putting.
 
moparrob66 said:
It could be lighter, depending on how thin you can get the fabric. Probably stronger, maybe last longer in the sun. Dont get me wrong, traditional fabric is entirely adequate, but would the flapping and fluttering create drag more than a rigid surface?
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Doubtful it would be lighter unless you made the entire control item out of CF. But simply replacing the fabric with CF no. As to the "flapping and fluttering" it depends on a number of things if it is actually an issue. In my experience fabric control surfaces are more than adequate for most applications until you get going faster like 250+ mph. Really don't see any advantage replacing fabric, but in replacing metal skins I could see a possible advantage provided you could attach the CF to the existing structure.
 
That would probably require or at least permit you to redesign the inner structure. As for it being a direct replacement for fabric, I agree that it would have little to no benefit.
 
Keeping the same rib structure? How would you attach it? Sounds like a solution looking for a problem. I’m a fan of fabric and rib stitching.
 
moparrob66 said:
It could be lighter, depending on how thin you can get the fabric. Probably stronger, maybe last longer in the sun. Dont get me wrong, traditional fabric is entirely adequate, but would the flapping and fluttering create drag more than a rigid surface?
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Flapping and fluttering? Naah. They used fabric on the rudder and elevators of the P-51, much of the Corsair's wing, and a ton of other places on WWII aircraft. Properly done fabric on a 125 knot airplane isn't gonna be an issue. Even better, you won't have to redesign the ailerons as composite surfaces.
 
Cc__ said:
Nope, was just curious what people think. My idea may have been a little more out there than I thought.
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Not out there at all. Boeing does it. Raytheon does it. Your application is what doesn’t make sense to me. How much experience do you have with fabric covering? Why would control surfaces concern you? Piper used metal-skinned flaps and ailerons on the late model Supercubs, but for production reasons. My own Cub has fancy double slotted (Fowler) flaps that are metal-skinned, but they’re produced in a shop on a jig. Everything else is fabric.
 
Using carbon as the fabric to cover a control surface designed for regular fabrics is not the same thing as designing a composite control surface.

Creating a carbon fiber control surface might be a good idea. Using carbon as fabric on a classically designed control surface is probably not a good idea. Boeing and Raytheon are doing the former, not the later.
 
You would have to completely redesign the structure of the surface as a drop in replacement for what’s provided in the kit.

Covering the original with carbon is not an option. The end result would not perform any better than the original. It would cost more and take a lot longer to build.
 
It probably could be adapted similar to Razorback which was a fiberglass covering system that never caught on for many reasons, mostly because it was very heavy. And it would crack and was hard to remove.

But the reason nobody's done carbon it is because it would be heavier, more costly, more difficult, harder to repair/recover. No advantage, all disadvantage.

Not sure why would you would not like the idea of fabric control surfaces on a tube and fabric airplane. It's about the simplest most well-proven aircraft construction method there is. You can build a Glastar or Murphy Rebel if you don't like fabric.
 
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Mike Patey covered his Super Cub derived "Scrappy" with carbon fiber over the wing and fuselage to add strength. I watch his Youtube videos and the plane was apparently successful enough to get to Oshkosh but havent seen any videos on it since.
 
If you are worried about fabric being "tough enough" take a look at Oratex. That stuff is ridiculously tough and has the advantage that it doesn't need painted.
 
moparrob66 said:
Mike Patey covered his Super Cub derived "Scrappy" with carbon fiber over the wing and fuselage to add strength. I watch his Youtube videos and the plane was apparently successful enough to get to Oshkosh but havent seen any videos on it since.
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Lots of fabric covered Cubs make it to Oshkosh too. :)
Patey's FKA Super Cub is modified to meet a very different mission from the average Super Cub. If there were requirements other than "I’m really not a fan of fabric on control surfaces" it wasn't clear from the OP.

Did Patey skin the control surfaces with CF?

Nauga,
tubeless
 
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