I recall a discussion some time back about carbon fiber accelerating corrosion of steel parts it's attached to. Is that a correct memory? My new project has carbon fiber floors and interior panels. Do I need to isolate/insulate between the carbon fiber and the powder coated airframe? I'm to that point so if I need to add rubber tape it's now or never.
Where's Dave Calkins? Randy Appling? I need some or your experience-based wisdom..
Thanks.
SB
You have a good memory.
I remember asking about it after my local FAA guy told me to be careful of corrosion if installing CF in my plane. I was flying lots of salt water, and CF, salt water and metal is what makes a battery- lots of electrolysis.
The cure seemed to be some sort of insulator. Powder coat was one suggestion I remember, but using 3m tape on the tubes where the CF would be touching was also a simple way to prevent the issues. Screws, bolts and such will still have issues though.
Now, if you are not flying salt, it did not seem to be such a big deal.
That is what I recall. I had decided to go CF and 3m tape after all the discussion
I don't know where you've been me lad, but I see you won first Prize!
There's lots of info on the web about carbon fiber and metal corrosion but most of it is worst case in a deicer or salt environment. All of my screw attachments will be to tinnerman plates so corrosion will be easy to see and parts easy to replace. I don't guess taping the tubes will be important with the tubes being coated. It's interesting what this article says about carbon surface area and corrosion of screws. And also about stainless steel being fairly unaffected. I guess that warrants SS screws.
https://www.corrosionpedia.com/2/155...orced-polymers
I'm still hoping for a pirep from somebody with a few years of carbon fiber in a Cub.
Last edited by stewartb; 05-31-2016 at 10:01 AM.
Not a cub but the Pilatus PC12 has all carbon fiber honey comb floor panels. It also has carbon fiber cowling, wing tips and belly fairing panels. The one i work on has about 4,000 hours of Alaska charter, village, heavy haul dirty work. Lots of parking lot salt and other crud gets tracked in the plane. Pilatus uses a mix of hardware but the floor panels are installed with regular cad plated steel camlock/ c-spec studs and the side panels with stainless screws. I have not seen any corrosion on the hardware, or aluminum seat rails the panels sit on, that i would attribute to the CF.
I've seen guys tape all tubes that touch the cf, and I would as well. Carbon fiber is extremely abrasive, and if there's any relative motion between it and the tube, it will remove your coating in a hurry, and then you're guaranteed corrosion, not to mention it will eat the tube too. Seems like very little effort and weight penalty to head off a potentially ugly problem.
I have had CF boards in my cub since 1998 and have not had any corrosion issues at all. seven years of that was spent on floats in fresh water. I have had the baggage floor and rear seat lid out yearly to shop vac all the silt and crap and not one sign of corrosion. my frame is epoxy primed not powder coated.
Could also have something to do with the amount of time you fly that cub. Cubs that sit get water pooled. Airflow is a good thing!Originally Posted by 8856Charlie
I don't know where you've been me lad, but I see you won first Prize!
instead of tape, run a bead of pro seal or the right stuff between the CF and the metal. No wear and much quieter.
How thick is the carbon fiber in your floors. .054 ? .062 ?
I completed my Carbon Cub EX build in 2011 with this being the sixth flying season for it. The floor boards and interior side panels get looked at closely when I do condition inspections. I've not seen any evidence of corrosion or fretting where the fuselage tubes and CF touch.
My my plane is hangared so I'm sure that helps but it isn't babied.
"Fast is fine, but accuracy is everything." Wyatt Earp
How thick is your carbon fiber on the floor ?
It is a variable thickness depending on the location. Thickest might be .1" and thinnest half of that maybe. And there are some ribs molded into it too.
"Fast is fine, but accuracy is everything." Wyatt Earp
Sorry. Been flying out West and only slightly in tue sc.org loop
isolate from relative motion for sure. This will Insulate from relative potential (corrosion?) at the same time
Rallyer pretty much sums up the empirical knowledge on this issue. It is a NON issue.
Still some people I know and like poohpooh carbon for this reason.
Use a layer of glass on your carbon layups to insulate them. Aluminum and carbon are on opposite ends of the galvanic scale and have the most problem with galvanic corrision. If you put screws through the carbon, build in a glass filler for the screw to penetrate and you wont have any corrosion issues. 1 layer of glass wont even be noticed on a floor board...and it protects the brittle carbon fibers from abrasion. Tim
Last edited by astjp2; 02-16-2017 at 02:19 AM.
Airhutch liked this post
After talking to friends who've had CF panels for several years I've dismissed all concerns about corrosion. The panels are abrasive on the powder coat but the purpose of all the screws is to prevent any motion. My side panels are very thin but the floors are CF sandwiched on a foam core so bushings are necessary where screws require torque, like under the AP servos. Big truss head screws spread out the bite elsewhere so no bushings at typical screw locations. All screws on sides and floor go into nut plates. Lots and lots of nut plates. Maybe not the ideal application but its what I did.
Last edited by stewartb; 02-16-2017 at 08:06 AM.
I believe the corrosion associated with carbon panels,etc is an old wives tale.
To alleviate crushing concerns to cored composite floors a simple bushing scheme is to:
1 use a bent nail in a screw gun inserted into each hole and spun,
2 then vacuum out the broken up core remains,
3 followed by filling the voids with epoxy putty,
4 then redrilling the holes after putty cures.
Voila!!! Permanent bushing between the skins reinforcing and sealing any penetrations.
Is a pretty universal method in the composites world.
Actually Ken Weiand used to demonstrate the corrosion at the UAA composites class as part of A&P program back in the 90's, not as prevalent on steel but catastrophic on Aluminum. All it takes is some moisture and the two different materials, a few months and Viola! holes in the aluminum.
I practice isolatation of the carbon composite. Maybe that os why I have not seen it. Nor have I seen it on others' work
Hi guys, do you know anything about galvanic corrosion issues between aluminum and Chrome Molybdenum steel?
Regards
Dave Calkins thanked for this post
Thanks for your answer. I was thinking use for the floor nomex with inferior and superior aluminum 2024 T3 fixed in 4130 fuselage.
Interesting. See post #15 and my aluminum anti-crush spacers inserted into carbon fiber. I’ll have to check those next year to see what if any corrosion is occurring there.
Corrosion/oxidation occurs with an electrolytic potential difference between two metals in the presence of an electrolyte. Greater potential differences produce higher corrosion rates. Of course, salt water exposure will accelerate corrosion over fresh water. Therefore, if you remove any intimate contact or the electrolyte, no corrosion. The 2024 is an al-cu alloy and has poor corrosion resistance. So,it will have an increase potential for corrosion if in contact with bare 4130; unless its alclad, usually an 1100 or 1200 aluminum alloy clad on both sides,. The alclad will decrease corrosion potential, not necessarily eliminate it. As stated previously, if the materials are insulated against any contact between the surfaces and kept dry, then the corrosion potential is decreased or eliminated. Paint or powder coat on the 4130 would certainly be a good idea.
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