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  #1  
Old 04-14-2011, 06:15 AM
Smilin' Jack Smilin' Jack is offline
 
Join Date: Jan 2011
Location: Cumming, Georgia
Posts: 873
Default Food for thought. Any engineers out there.

Zinc.

While I have been involved in aviation for my whole life. This build stuff is new and it presents an opportunity for a lot of questions and exploration.

I also have owned boats my whole life of various kinds. so my questions deals with corrosion.

If as several of my friends in Alaska have Halibut fishing boats made out of Aluminum that are protected with Zinc Anodes. Why can we not protect an aircraft with a zinc anode. We spend hours zinc cromating out skins and add a couple pounds of paint but could not an anode be used instead?

As noted on a lot of discussions and with Vans themselves they believe that the alclad coatin alone will provide sufficient protection and in fact most single engine Cessna's and Pipers never zinc coated the inside skins and many are still corrosion free 50 years after production.

I realize that the boats are immursed in the salt water. But on the 26 foot
twin 200 Yahamma Halibut boat that my buddy ownes in Alaska he only has about 4 lbs of zinc on it. when it wears down he replaces it. He has had this boat for 26 years and it looks as good as his aircraft does. I popped the question to him and he looked at me and said maybe no one ever thought of it. Probably be to simple

Well engineers...... fire away........... we got our helmets on.

Smilin' Jack
Empenage done.
Wings due in 5/16
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  #2  
Old 04-14-2011, 06:38 AM
Phlyan Pan Phlyan Pan is offline
 
Join Date: Aug 2010
Location: Rochester, NY
Posts: 174
Default

Quote:
Originally Posted by Smilin' Jack View Post
Zinc.

I popped the question to him and he looked at me ...


Smilin' Jack
Empenage done.
Wings due in 5/16
What does this have to do with zinc again?!

Anyway....I'm only half engineer so I could be way off base but my understanding is that the boat being immersed in the water actually causes a slight voltage differential between the dissimilar metals. Obviously when you have a voltage differential you have current flowing (very, very small amount obviously) and this is what allows the zinc anode to work. The current flows in such a direction as to break down the zinc, but not the aluminum.

In an aircraft, I don't believe you would have any voltage potential because there is no immersion. Thus, I don't think there would be any induced current and instead of being an anode, the zinc would just be a lump of zinc.
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  #3  
Old 04-14-2011, 06:43 AM
Mike D's Avatar
Mike D Mike D is offline
 
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Location: Houston, TX
Posts: 456
Default good food for thought

This seemed to be a good idea that I knew nothing about. So I did a search and found this statment on Wikipidia.

"For this to work there must be an electron pathway between the anode and the metal to be protected (e.g., a wire or direct contact) and an ion pathway between the anode and the metal to be protected (e.g., water or moist soil) to form a closed circuit; thus simply bolting a piece of active metal such as zinc to a less active metal, such as mild steel, in air will not furnish any protection."
http://en.wikipedia.org/wiki/Galvanic_anode

So, it seems the water is needed to make this work.

I suppose I will open a can of worms here, but I wonder if zink cromate is working on the same theory, and if so, does it ever wear out? Probally not in my lifetime, but it is some more food for thought.
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  #4  
Old 04-14-2011, 07:03 AM
Smilin' Jack Smilin' Jack is offline
 
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Well I guess the zinc anode being bolted directly to the aircraft ei counter balance weights, or on the belly would be a direct path to the aluminum. And since salt laden air is usually very high in mositure would that not be a medium?
All the zinc cromating in the world does not help acid rain.
so the only thing we are combating is salt laden air that we fly in that causes corrosion?
Jack
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  #5  
Old 04-14-2011, 07:19 AM
Phlyan Pan Phlyan Pan is offline
 
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Location: Rochester, NY
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Quote:
Originally Posted by Smilin' Jack View Post
Well I guess the zinc anode being bolted directly to the aircraft ei counter balance weights, or on the belly would be a direct path to the aluminum. And since salt laden air is usually very high in mositure would that not be a medium?
Take a good multimeter and measure the resistance between the probes in some salt water at a fixed distance.


Now hold those two probes up in "salty air" at the same distance and see what you get.
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  #6  
Old 04-14-2011, 08:04 AM
benbell4140 benbell4140 is offline
 
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Location: broussard louisiana
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There is a good article on this topic in the 27 years of the RVator book on page 44. I also read that zinc chromate does (wear out) eventually. It says that zinc chromate releases chromate ions which neutralize the corrosive salts and prevents electrolytic reaction. The protective elements in zinc chromate are exhausted eventually.
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  #7  
Old 04-14-2011, 12:42 PM
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Jerry Cochran Jerry Cochran is offline
 
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Location: Sherwood, Oregon
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Default Salty air??

I thought when water evaporated it left behind everything but an H2O molecule, hence the salt flats in Utah... Now if you are close to the ocean, you can sure get salt spray which will corrode things really well..

I hate to start something, I really do... Experts?
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RV-7a 707DD Bot from David Domeier 12/01/11
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RV6a 18XP 1st flite 03/21/07 sold to Dale Walter 10/22/2011
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Happily "autopaying" DR

"Suppose you were an idiot, and suppose you were a member of Congress; but I repeat myself."

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  #8  
Old 04-14-2011, 02:33 PM
instructor_bill instructor_bill is offline
 
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Location: Petaluma, CA
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Default Marine layer

some condensation nuclei is actually salt.

Salt-air that has been thrown about in this thread is a misnomer. When one is close enough to the ocean to smell "ocean air," we cannot say that what a person smells is salt. Rather, what we smell is ocean life-- and of course some of it rotting.

Anytime that you have fog or condensation formed near the coast in and around sea spray--salt will be present at the core of some of the fog as the particle that made condensation possible.

Anytime salt is not part of condensation (fog or clouds) it is fallout or dust.

There you have it. Sea spray, condensation nuclei, fallout, and dust.

And I'm a geek.
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  #9  
Old 04-14-2011, 02:43 PM
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pierre smith pierre smith is offline
 
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Location: Louisville, Ga
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Default Corrosion-X...

...the airplane every three years or so and forgetaboutit. This stuff is Mil-specked and will wick itself between the skin overlaps.....AFTER you paint it, not before!

Best,
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It's never skill or craftsmanship that completes airplanes, it's the will to do so,
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  #10  
Old 04-14-2011, 03:44 PM
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Flyfalcons Flyfalcons is offline
 
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I have 11 years experience flying seaplanes in and out of salt water. We use CorrosionX and the 50+ year old planes are in great shape.

Our water rudders do have Zinc attached to them, though.
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