Where Primer Won't Go

[XOverZero]

Soliciting suggestions from more experienced builders. The very first statement in Section 5 of Van?s build manual says unclad aluminum must be protected from corrosion. No problem in most cases, but for the inside surfaces of tubing and the threaded bore of the tail tiedown AEX I?ve chosen Alodine rather than primer since it?s easy to apply, covers completely and doesn?t clog the threads.

Now I?ve come to the tiedowns for the wings. Those extrusions come anodized and already riveted to the main spars, and the only thing I?ve thought of for protecting their bores is to mask off that entire part of the spar, stand the spar up edge-wise, plug the lower end of the tiedown bore and fill it with solution. That seems beyond awkward even for Alodine, what with the acid etch, water rinse, and chromate steps involved.

I?m thinking there?s got to be a more elegant process, and I?d love to hear ideas from builders who know what they?re doing.

[roee]

My general recommendation is that you use the alodine process only on individual parts. Don't use it on parts or structures that are already riveted together. If you do, you risk trapping acid in nooks and crannies between parts where you won't be able to fully rinse it out. If that happens, you will get accelerated corrosion, and you will have done far more harm than good.

About the parts you're asking about, you said they came anodized? If they're anodized, there's nothing you need to do. An anodized surface is highly corrosion resistant.

Or are you saying the bores or threads were cut after the anodize process, so they're not protected?

[David Z]

If it's 6061, then it's naturally a lot less prone to corrosion.

[XOverZero]

Originally Posted by roee

...alodine...you risk trapping acid in nooks and crannies...

Or are you saying the bores or threads were cut after the anodize process, so they're not protected?

OK, alodine bad idea. Understood and thanks for that, Roee. And Yup, drilled and tapped in situ, by me, after anodize.

Is this a question for Van's? Wonder what they do on -12s...

[smiller]

Good question. I didn't prime or treat the bores in my tie-downs and am especially concerned about dissimilar metals corrosion given that the tie-down rings are made of some sort of steel. Pending a better solution, I decided to coat the tie-down ring threads with that copper-colored antiseize you can get at auto parts stores. But I really don't know what my "best" action should be at this point.

[Bill_H]

Spray every once in a while with Corrosion-X?

[XOverZero]

Is Corrosion-X the stuff that remains wet? If so, I'd guess that the tiedowns would be especially prone to gathering dust and dirt and turning to muck inside the hole...assuming one would not leave the tiedown rings installed during flight.

I sent an email to Van's support address this morning, asking them what they do.