Primer - Corrosion Protection

[ynkster]

We used a product called "Never-Dull" on our show tractors and trailers. It looks like cotton- pull a piece out of the can and rub till it shines the way you want it to. the last time I bought it it was about $10 a can. Two cans would come close to doing a Panther. Most Truckstops have it in their store.

[BobJacoby]

Paul,

Which route did you go with the priming? Acid Etch from NAPA, Epoxy Primer, Zinc Chromate, Alodine? And, what were the process steps?

Also, Dan mentioned an aluminum cleaner used to clean the aluminum on tractor-trailer trucks that was inexpensive and worked well. I can't remember the name, but am looking for any hints on how I might add some corrosion protection - especially in the tight seams.

Related, what type of primer will you put underneath the paint on the outside?

Lastly, none if this is intended to take away from the key message, that "6061 is very corrosion resistant".

Let us know.

Thanks,

Bob Jacoby
Panther SN018

[Tony Spicer]

Mike,

Track down some Alabama Sonex folks and pick their brains. Same construction materials as the Panther.

Plug Alabama in here: http://builder.sonexaircraft.com/cgi-bin/search.pl

Tony

[MikeS.]

Paul,

Thanks for spending the time to post your thoughts and knowledge on this topic. My Panther will be hangared in several locations but two in particular do not provide much protection from the extreme humidity that we get here on occasion. I also plan to attend plenty of fly-in’s and there is always the chance of dealing with rain. Guess I’ll have to beat the dead horse a little longer ….

Mike

[psalter]

If you would like an engineers perspective on corrosion control, I will off this.

I am an structural engineer with the US Navy, and work with corrosion repair and protection all of the time.

Most of your commerical and Military aircraft use 7000 series aluminum as the primary structure, and must be protected against corrosion. The only 7075 on the Panther is the landing gear legs, that should be primed and painted.

2000 series aluminum is much better against corrosion that 7000 series aluminum, and the Navy alodines and primes all of their 2024 parts also.

6000 series aluminum is the best against corrosion and is not really necessary to prime. The Panther uses this for all aluminum structure with the exception of the landing gear legs.

Having said all of that, all corrosion requires an electrolyte and a tight space. Water typically serves as that electrolyte. If you plan on keeping your aircraft in the hangar and mainly flying in sunny weather (typical Panther flying) then priming and painting 6061 is not as necessary.

When it comes to what to use as the protection, Alodine and Zinc Chromate is still the best, and everything is compared to that about protection. Adam is correct that Military and Commericial aircraft uses epoxy primer, but that is mainly because of Hazmat concerns of Chromates, not because epoxy is better. The Navy uses alodine then 2 thin coats of epoxy primer for all of their parts.

All aluminum requires some type of etching for the primer to adhere, if you use alodine, part of it's process is to etch, and while the part is still wet, alodine it. Then dry and prime it. Some primers are self-etching, and if you use that, I would probably not alodine the part, as the etching would probably damage the thin alodine coating. I believe AKZO from Aircraft Spruce is self-etching, and in at least one letter, they recommended not to use alodine. There are many versions of AKZO primers listed on their website, and I had problems figuring out what ACS sells compared to the AKZO website. AKZO is a large supplier of paints and primers to Commercial Airliners and Military aircraft.

Etchants and Alodines contain acids, and they have to be rinsed off well. If you use them, it is recommended to do it before assembly where they can be rinsed well. If done, after assembly use a lot of water to get the acid out of all of joints, or you might be worse off than not doing anything on 6061 aluminum.

Water can destroy everything including rocks, so keeping aluminum dry is the best corrosion protection. Even with all we do on Navy aircraft, we have signifcant corrosion problems with the 7075. But that is in the worst possible environment, constant salt water baths, and very little fresh water to clean the planes with. You can never eliminate corrosion, just slow it down.

As you will probably see in some pictures for the builders manual and on the website later, I am priming the interior components. But mainly that is because I expect my plane to be sitting on wet flight lines at a lot at airshows and other airports. And I will certainly admit to a bias towards protection because of the damage I see at work on Navy aircraft, which is certainly worse than most homebuilts will ever see.

Most important thing, get the airplane finished. As Dan said once, all the corrosion protection in the world doesn't help, if you never get it flying. Don't let alodines, primers and paint be the reason to not finish a Panther.

[MikeS.]

Adam, I have the tail kit in hand and plan to start playing with some aluminum in a week or so. Thanks for the primer suggestions.

Tony, Thanks for the information. I wondered why your parts did not have primer on them and now I understand. This will save time, money, and weight. All good things.

Mike

[Tony Spicer]

Adam,

Go to the ACS catalog and compare the price of 2024 to 6061. The 2024 is about 30% stronger and considerably more expensive. All the 6061 is T6. Makes for a slightly heavier, but much less expensive airframe. You won't break it.

http://www.youtube.com/watch?v=5-ne17wH ... e=youtu.be


Tony

[Adam Wright]

Tony,
That is interesting that the Panther uses 6061 I just assumed it was 1024T-3 like my RV. Any particular reason why they went with that vs 1024 ? The specs seem comparable but the 1024, it seems, is a more accepted alloy for aircraft building and supposedly has better fatigue resistance vs 6061. Do you know what thickness and temper(t-?) of the wing and tail skins used in the Panther?

Adam

[Tony Spicer]

Hi Mike,

There's not even one square inch of alclad aluminum in the Panther. 2024 is clad, but not the 6061 used in the Panther construction. 6061 is very corrosion resistant. Use primer if it lets you sleep better. Can't find the link talking about the C-47/DC-3. It was built with unprimed 6061. Plenty of them still flying in some pretty nasty environments. I'm 10 miles from the coast in NC. Didn't prime my Sonex (6061) RV-3 (2024), nor will I prime my Panther. Give this a read:

http://www.vansairforce.com/community/f ... ysprune=-1

Tony

[Adam Wright]

Mike,
Most of the big boys(airliners and military) use a epoxy primer. It does not require any top coat(extra weight) to seal, can be applied fairly thin and is very durable. Might I suggest the mil spec AKZO primer. I have had great results with it and it dries really fast. Drawbacks are paint gun usage, having to mix it every time and ventilation and respirator concerns. That being said it is really easy to mix and apply. If you use small mixing cups(test make sure they dont melt first;) its not too hard or too messy to do small batches. For prep I use a product developed for Boeing called Prekote, you first wet it down with prekote and then scrub the areas to be primed with a scotchbrite pad and then you wash if off and wait for it to dry, thats it! This replaces your traditional clean, etch and alodine steps. Both AKZO and Prekote are available at Aircraft Spruce. The AKZO primer is pricey but you could easily do the entire plane with the 2 gal kit(1 gal primer / 1 gal catalyst) Hope this helps with your decision!

Another note, good to see another Alabama guy here. Do you have any of the Panther kits in hand yet? Best of luck.

Adam