The Age Old Corrosion Question

[BigO]

OK, this specific question isn't strictly "age old". In fact, my Googling around the web hasn't turned up any answers or opinons that are relevant thus far. Here's hoping that one of you forum denizens can help me out.

Has anyone here used Por15 for corrosion protection? I've seen a lot of talk in automotive forums, but I can't find anyting relevant to the homebuilt corrosion discussion. It was reccommended by the guy at a Sherwin-Willams Automotive store, but I'd say it's safe to take his knowledge on aircraft construction with a grain of salt.

Any ideas, anyone? I'm building a Zenith 750 Cruzer, which uses 6061-T6 AL for most of its components.

[CarlOrton]

Hi, BigO;

I'm also in Ft Worth (KFWS); I'd say don't worry about it. I believe your Zenith uses the same 6061-T6 that's in my Sonex. According to the Sonex website, the 6061 corrodes extremely slowly; they don't recommend using anything.

I don't know how old you are, but I'd bet that unless you tie it down outside at the seawall in Galveston, that Zenith will outlast you.

That said, some folks have used zinc chromate primer where the longerons and channels rivet to the skin. Some have primered the entire inner skin. That adds weight. I used nothing on mine. Have never known of anyone using POR 15. Some Part 23 owners have misted their wings with ACF 50 corrosion treatment, but that stuff seeps out of every rivet hole or drain hole for about 2 years.

I had a 1967 C-172 with zero corrosion. Inside the fuselage and wings, the metal was shiny. Up here in North TX, it's just not a factor...

[champ driver]

Lets see if I have this right, your thinking about taking advice from an automotive guy at the auto store about aircraft construction. Come on, you should know better. What does this clown know about airplanes? I've used POR15 on my car and zinc chromate on my Champ and my guess is the POR will add a ton more weight than the zinc chromate. You decide.

[WLIU]

POR 15 is thick and heavy.

ACF 50 is accepted for corrosion protection of certificated aircraft, mists in really well, creates a lightweight film, and seems to last a long time. I understand that you should not use ACF on a structure that you intend to paint later. Easy to find, not expensive.

I will note that if you look up the properties of 6061 aluminum, you will find that it is a corrosion resistant alloy. So I will join the vote to leave it alone.

They were giving away samples of ACF-50 at Sun-N-Fun. If there is an aviation trade show near you, look around for a sample.

Best of luck,

Wes

[Downs]

If you go the Zinc Chromate route make damn sure you wear the proper PPE.

[Mike Switzer]

POR15 is great for steel. I primed & painted a truck frame with it back in 1994, then I lost my job & had to move, it is still sitting in dad's yard without a speck of rust on it. When I put my Fairlane in storage in 1997 I brushed their primer on to all the rusty spots & it is still just like when I parked it. But for aircraft aluminum I would use something more appropriate.

[BigO]

Thanks for the input, guys.

I'd already decided to limit any corrosion protection to mating surfaces. I too believe that protection on the entire internals is overkill with AL; however, if on the slight chance that the plane got left in the rain or someting (especially unforseen) and water seeped into some mating surfaces, then galvanic corrosion could become an issue. The small amount applied to the mating surfaces is a good middle ground, in my opinion.

That being said, I have now used POR15 on my rudder kit, and I agree that it is too heavy. My research has indicated that protection applied on mating surfaces should add ~7 to the aircraft's weight; This stuff added somewhere around .75 lbs just on the rudder; I con only imagine how much more it would add over the entire airframe. I'll use it for completing my rudder, but I'll be switching to something else for the remainder of the project.

On a side note, I checked out your kit log, CarlOrton. That looks like I very nice Sonex you've built there. I wouldn't mind meeting over a cup off coffee if you'd be willing to impart some knowledge to a local, novice homebuilder.

[RV8505]

Thanks for the input, guys.

I'd already decided to limit any corrosion protection to mating surfaces. I too believe that protection on the entire internals is overkill with AL; however, if on the slight chance that the plane got left in the rain or someting (especially unforseen) and water seeped into some mating surfaces, then galvanic corrosion could become an issue. The small amount applied to the mating surfaces is a good middle ground, in my opinion.

That being said, I have now used POR15 on my rudder kit, and I agree that it is too heavy. My research has indicated that protection applied on mating surfaces should add ~7 to the aircraft's weight; This stuff added somewhere around .75 lbs just on the rudder; I con only imagine how much more it would add over the entire airframe. I'll use it for completing my rudder, but I'll be switching to something else for the remainder of the project.

On a side note, I checked out your kit log, CarlOrton. That looks like I very nice Sonex you've built there. I wouldn't mind meeting over a cup off coffee if you'd be willing to impart some knowledge to a local, novice homebuilder.

I would look at balancing the rudder if not called out in the plans.

[CarlOrton]

I sent an email to the address you have on file. Give a call when you have the chance.

[BigO]

Carl,

Sorry for the delayed response, but I never did get that email. I've updated my profile since then, so if you get a chance to try again it should go through.