Carbon Fiber / Aluminum corrosion insulation

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JMyers1

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I am on the verge of ordering a CH 750 kit, and I would like to make a few parts out of carbon fiber (most significantly the instrument panel). From what I have learned, simply priming is not enough to prevent galvanic corrosion. I am having a hard time finding information on how best to do this.

DarkAero uses a very thin perforated fiberglass to electrically isolate the panel. I can't tell if this is commercially available, or if they made it themselves. They also simply mention using paint on the carbon fiber. I'm a little nervous to simply paint both pieces.

Also, are there any special considerations in using titanium blind rivets? I'm probably biting off more than I should be as a first time builder, but I have 8 months to research.
 

12notes

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I think you're pretty much on your own to make a fiberglass lined carbon panel. DarkAero makes their own, as far as I could tell.

Titanium has a similar potential for galvanic corrosion with aluminum as stainless steel, a bit worse depending on alloy. Unless there's a really, really critical reason to use titanium, I would stick with the aluminum rivets Zenith recommends. Any additional strength gained won't have any advantages unless you re-engineer the plane to use less of the stronger rivets to save a bit of weight. The bond using aluminum rivets is more than strong enough. And I would imagine the titanium rivets would be much harder to install, and cost way more.
 

BoKu

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Bolting or riveting a cured carbon fiber assembly to aluminum is pretty safe. Avoid laminating carbon fiber wet directly onto alumimum or steel if you can. Where you can't avoid it, apply an insulating layer of at least 5oz fiberglass cloth.
 
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JMyers1

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I think you're pretty much on your own to make a fiberglass lined carbon panel. DarkAero makes their own, as far as I could tell.

Titanium has a similar potential for galvanic corrosion with aluminum as stainless steel, a bit worse depending on alloy. Unless there's a really, really critical reason to use titanium, I would stick with the aluminum rivets Zenith recommends. Any additional strength gained won't have any advantages unless you re-engineer the plane to use less of the stronger rivets to save a bit of weight. The bond using aluminum rivets is more than strong enough. And I would imagine the titanium rivets would be much harder to install, and cost way more.
If I insulate the carbon but them rivet it using an aluminum rivet would that not defeat the purpose? It seemed like titanium rivets exist primarily for this purpose, but I am definitely a neophyte here.

To be clear I was only talking about the rivets for the carbon fiber panel (the glareshield piece is I believe 6061) and any other carbon parts.
 

wsimpso1

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I am on the verge of ordering a CH 750 kit, and I would like to make a few parts out of carbon fiber (most significantly the instrument panel). From what I have learned, simply priming is not enough to prevent galvanic corrosion. I am having a hard time finding information on how best to do this.

DarkAero uses a very thin perforated fiberglass to electrically isolate the panel. I can't tell if this is commercially available, or if they made it themselves. They also simply mention using paint on the carbon fiber. I'm a little nervous to simply paint both pieces.

Also, are there any special considerations in using titanium blind rivets? I'm probably biting off more than I should be as a first time builder, but I have 8 months to research.
I have to question the reasoning behind a carbon instrument panel. Here is why it may not be a good idea in a tube airplane.

First thing to know is that in a forced landing, the occupants are very likely to make vigorous contact with the panel, so its design needs to include that event.

Second thing is that the instrument panel in the CH750 is secondary or tertiary in the structure involved in a forced landing. Primary is the tube fuselage - this ranking is based upon overall stiffness and strength of the structures. When the primary moves, there is not much the secondary and tertiary structures will do about it as they are much softer and weaker. When the tube structure gets to limits, it will deform, tubes will buckle and get out of shape, and absorb a lot of energy. When it all comes to a stop, the best result we can usually hope for is a fuselage truss that is bent and distorted, but keeps enough room in the cockpit for those within to live through it.

Third thing is that carbon fiber composites have a strain at failure of less than 2%, some closer to 1%. If tertiary carbon fiber structure is attached to the primary tube frame structure and the tube frame distorts more than the carbon composite can stand, the carbon composite will break and expose sharp, strong edges and points.

Combine these, and your carbon fiber instrument panel sounds like it could become one or more dangerous points or edges that your hands and arms and feet and legs and maybe even your head are likely to come in contact with during the crash pulse and during egress afterwards.

All of this is not to say that you can not use graphite-epoxy in the cockpit, you can. But you have to design the whole thing to stand some big crash pulse and stay in shape. Like F1 or Indy or LeMans cars. Beefy graphite tubs surround those cockpits. Ideally, that max crash pulse is up there around max human capability. You, know - "if it is any worse, you will not avoid dying anyway". But the CH750 is not in that league. The metal is likely to bend and break the graphite, sometimes into dangerous pieces. If those pieces are where you are, there are nasty hits.

Perhaps we can interest you in staying with the plans panel and do graphite fiber where its crash response matters less, like all the fairings, cowling, trim strips, etc? A nice aluminum panel will deform with the tubes, wrinkle and bend, but stay in a long continuous piece that will not impale you.

Billski
 

JMyers1

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The primary reasons are aesthetics/cool factor, stiffness (stock panel appears pretty flimsy), and learning how to do it. I had not considered crash worthiness, that is something I should think about. The panel itself is not directly attached to the tube structure at all, as far as I can tell.

It would seem in a crash lots of things could end up in your face that you do not want. Maybe I could create a carbon overlay and cut out the center of the aluminum factory panel to all but an inch of the edge, and fasten the CF to the aluminum lip. The rivets would then be aluminum to aluminum and I would screw the CF panel to the aluminum one (after priming/painting the aluminum and putting some fiberglass behind the edge of the CF), making it removable to troubleshoot avionics. The aluminum could then deform and tear off in theory before it would snap.

Some people have installed an aircraft specialty thicker aluminum panel this way. Any thoughts on this approach?
 
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Deuelly

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I could be wrong, but I believe the carbon fiber panels SteinAir does are just aluminum panels covered in graphite patterned vinyl.

Also, isn't the CH750 aluminum and not tube frame?

Brandon
 

JMyers1

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I could be wrong, but I believe the carbon fiber panels SteinAir does are just aluminum panels covered in graphite patterned vinyl.

Also, isn't the CH750 aluminum and not tube frame?

Brandon
3M carbon look vynil is common and pretty convincing from 5 feet away, but it does nothing for stiffness and you can tell up close it’s vynil. Zenith is semi monocoque with tube frame around the windshield.

I plan to do some FEA if I can figure it out (unlikely) and sort out a way to remove the two tubes from view (also unlikely).

DF62F4C7-320F-485F-9EF1-F0CAC29F92DC.jpeg
 

wsimpso1

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Maybe I could create a carbon overlay and cut out the center of the aluminum factory panel to all but an inch of the edge, and fasten the CF to the aluminum lip. The rivets would then be aluminum to aluminum and I would screw the CF panel to the aluminum one (after priming/painting the aluminum and putting some fiberglass behind the edge of the CF), making it removable to troubleshoot avionics. The aluminum could then deform and tear off in theory before it would snap.

Some people have installed an aircraft specialty thicker aluminum panel this way. Any thoughts on this approach?
We have had a couple of threads on the topic with Marc Zeitlen contributing big time. Funny thing, in composite structure airplanes, the instrument panel is one of the beams tying the fuselage wall together, and when fitting new panels, we usually apply an aluminum face sheet with all of the avionics mounted to it, then engrave labeling in the face.
 

Kiwi303

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Given the panel is not structural (to the best of my knowledge) and it's the tubing the panel fascia attaches to that is the structural part why use aluminum rivets on fiberglass or carbon fiber? You could run nylon or HDPE tape over the outer flange side to create your buffer, then use automotive plastic bumper and wheel well push clips. Those survive many years of abuse rattling down the roads, I don't see them failing between annual checks if you know to keep an eye on them.


 

Voidhawk9

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Could use a hybrid approach, carbon for the outer layer and a more fracture-resistant reinforcement behind that, like aramid or one of the newer types. Might get the best of both worlds - a stiffer panel and the fun of layups (hey, they're fun for some of us!). Cutting holes for instruments in it, however, could be frustrating.
 

BFE_Duke

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The primary reasons are aesthetics/cool factor, stiffness (stock panel appears pretty flimsy), and learning how to do it. I had not considered crash worthiness, that is something I should think about. The panel itself is not directly attached to the tube structure at all, as far as I can tell.

It would seem in a crash lots of things could end up in your face that you do not want. Maybe I could create a carbon overlay and cut out the center of the aluminum factory panel to all but an inch of the edge, and fasten the CF to the aluminum lip. The rivets would then be aluminum to aluminum and I would screw the CF panel to the aluminum one (after priming/painting the aluminum and putting some fiberglass behind the edge of the CF), making it removable to troubleshoot avionics. The aluminum could then deform and tear off in theory before it would snap.

Some people have installed an aircraft specialty thicker aluminum panel this way. Any thoughts on this approach?
If you're mostly after the aesthetics, then maybe basalt fiber might be a better choice? Otherwise if you top the carbon off with some thin fiberglass just to drill through and rivet, then maybe overdrilling and laminating a fiberglass tube/sleeve to protect the bare carbon might make sense?

Also keep in mind epoxy is quite soft, so if you rivet to carbon you'll need some fat washers to spread the load, as regular rivets might be problematic.
 

Wayne

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😅 I really need to update my CH750 build log - just registered it with the FAA and need to figure out how to get the inspection. Right or wrong my instrument panel is the supplied aluminum one with a layer of carbon cloth epoxied directly on to it. So far it has survived very nicely from a bending and cramming point of view. I also made a carbon fiber cuff for the wing roots which end up looking horrible and extends across the front top. I'll try to remember to grab some pictures tomorrow (beware, my memory is worse than @Victor Bravo) 😂🤣
 

geraldmorrissey

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Bondable Tedlar if you can find it in small quantities. Include it in the laminate schedule where the panel comes in contact with th AL.
Gerry
 

PiperCruisin

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I've seen some alternate materials used for the "cool" factor like the image below so you don't have to worry as much about corrosion or getting impaled.
1635351054107.png
 
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