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musket
02-01-2010, 01:29 PM
I was recently advised to not use stainless AN hardware when fastening aluminum parts because the dissimilar metals will cause galvanic (?) corrosion to the aluminum. Have any of y'all noticed this, enough so that you agree with the advice above?

Are there specific applications in / on which you would NOT use stainless hardware?

I'm finding that the education acquired in building an airplane can be an expensive endeavor !

NimpoCub
02-01-2010, 01:38 PM
Well, I'm thinking that since there is no such thing as aluminum AN hardware, you HAFT'A use something dissimilar. :)

behindpropellers
02-01-2010, 01:39 PM
Well, I'm thinking that since there is no such thing as aluminum AN hardware, you HAFT'A use something dissimilar. :)

There actually is aluminum AN hardware....


I would not use stainless just for the fact that it is heavier. I like the idea of stainless on the tailbrace wires and other areas that are often exposed to the elements.

DW
02-01-2010, 01:45 PM
Stainless and Aluminum do have a dissimilar metal electralasis reaction to each other but it is used in some aircraft without any problem, Cub Crafters uses it in there sport cub wing to attach the ribs to the spar, and skin to the ribs. I wouldn't use it on any wing or gear attach bolts as stainless is a softer metal.

Logan
Shouldn't you be out working on your wings? I know I sould be.

DW

spinner2
02-01-2010, 03:53 PM
I would not use stainless just for the fact that it is heavier. I like the idea of stainless on the tailbrace wires and other areas that are often exposed to the elements.

The specific gravity of different alloy steels is very close to the same - meaning the weight for a given size AN bolt is the same whether its steel or stainless steel.

We use two tyes of steel in the product we manufacture; 416 stainless and 4140 and the 4140 is actually very slightly heavier.

skywagon8a
02-01-2010, 04:10 PM
I was recently advised to not use stainless AN hardware when fastening aluminum parts because the dissimilar metals will cause galvanic (?) corrosion to the aluminum. Have any of y'all noticed this, enough so that you agree with the advice above?

Are there specific applications in / on which you would NOT use stainless hardware?

I'm finding that the education acquired in building an airplane can be an expensive endeavor !

Stainless on aluminum does cause galvanic reaction. The stainless needs to be separated from the aluminum. The aluminum will corrode possibly requiring replacement of the aluminum part. This won't happen with regular steel. A good insulator such as a nylon/ plastic washer will do. Or a good paint which will not allow the two to make contact.

Stainless is not used in structural applications as a rule. Also if you keep regular steel painted or otherwise protected, it will work fine. Stainless is more expensive.

marcusofcotton
02-01-2010, 06:10 PM
When I was building my first aircraft, an A&P, IA suggested I use regular AN hardware with AN aluminum flat washers. Made good sense to me and so far so good.

Mark Johnston

JayH
02-01-2010, 09:55 PM
HHHmmmm, what about an entire stainless steel firewall riveted tight to an aluminum boot cowl. Just one example that comes to mind. I'm sure there are other smaller non-structural aluminum plates and such I have used stainless screws on. Stainless sheet metal screws on interior panels. Are the PK screws on the leading edge skins stainless or, in some aircraft, PK screws attaching fabric??????? Just some questions here, learning is always good.

J

NimpoCub
02-01-2010, 11:16 PM
There actually is aluminum AN hardware....

:oops: Oh. :oops:
Does that mean I'm STILL a rookie?
Acknowledgement: I'll always be a rookie.

Dennis, leave me alone 'eh?
Just waiting for a friend to bring me some Tremclad from the 200mi away hardware store. I thought I should hit the ferrous metal parts before I start pulling fabric.
No real rush, now that I've decided to not bother with the skiis this winter. Now I'm thinking I have time to take my engine for a visit to Uncle Bart!! :)

courierguy
02-02-2010, 11:26 AM
I took a 60's era Airstream trailer apart once, it had been crushed by snow sliding off a high roof. I got it for free and wanted the undamaged running gear. The fabled "aircraft construction" of the trailer was bolted at the bottom plate/longeron to the steel trailer frame with common steel bolts, and corrosion was evident, I couldn't believe the factory built them that way! I got 300 bucks for the scrap for a half days work plus the running gear.
I and lots of others in the renewable energy business have used stainless hardware in attaching PV modules (anodized aluminum framed), it is the industry standard, or so I believe. Taking apart arrays I had set up years ago showed NO problems, no corrosion of the hardware or the aluminum frames, possibly the anodizing made the difference.??

skywagon8a
02-02-2010, 07:03 PM
When I was building my first aircraft, an A&P, IA suggested I use regular AN hardware with AN aluminum flat washers. Made good sense to me and so far so good.

Mark Johnston

EDO uses a sacrificial thin aluminum washer under stainless screws to hold down the inspection covers on their larger floats. Seems to work.

musket
03-03-2010, 01:56 PM
Many thanks, folks. It’s a good thing (as Martha S. would say) that I have your sage advice and guidance to keep me on the straight and narrow.

I thought it might be helpful for future readers to reiterate the advice above; if I got some of it wrong, please correct me:

1) Stainless is good on many places that are often exposed to the elements;

2) Cadmium-plated steel hardware is a better choice for structural applications, i.e., wing and gear attach bolts;

3) Stainless needs to be separated from aluminum – this can be by paint, nylon washers, or possibly a sacrificial aluminum washer.

4) Stainless hardware is more expensive – but cosmetically, it is purty!

Nothing was said about it, but it probably wouldn’t hurt to use zinc chromate (or whatever passes for it these days) to coat the various fasteners to delay the onset of corrosion.