The Murphy Builders Site

Hi All,
I'm seeking some anti-corrosion opinions and advice...

I have the Tail and Wing sub-kits for a Rebel, complete to pre-close inspection (Canadian style) that I bought from another builder. As I've worked my way through the build-logs and pieces, it's become apparent that the mating surfaces weren't epoxy primered, but the kits were Alodined. My eventual plan is an amphibious Rebel that will live on land but spend a significant amount of it's float time in salt water, so this is causing me some concern. The conclusion I've come to is that I should just bite the bullet and start drilling rivets so that I can epoxy primer the interior of all the bits and pieces and then reassemble them, but I'm curious to hear if anyone has another suggestion before I undo all this work.


Thanks,

Hi Sean,

I cannot answer to why a builder would not sufficiently protect their aircraft, after many hours of build time.

The Murphy Aircraft Mfg (MAM) build manual specifies the Standard Methods and Practices, right in Chapter 1.1 Metal Surface Preparation. (pdf attached)

You can search through CARs 549 (Part V - Airworthiness) Transport Canada website, also under Airworthiness Manual Advisory (AMA) Subject: Amateur-Built Aircraft: General, Section 5. Design and Construction (Ref. Chapter 549, section 549.5), para (e) Information and guidance concerning acceptable fabrication and assembly methods, techniques and practices are provided in the U.S. FAA Advisory Circular (AC) No. 43.13-1A, "Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair," and AC No. 43.13-2A, "Acceptable Methods, Techniques and Practices - Aircraft Alterations." These publications are accepted by the Minister.

My advice, prime between mating surfaces...... Salt will just turn the aluminum to powder.

Dale,
Thanks for the response and link - looks like a great resource. I thought I'd searched in all directions but hadn't considered our gov't...

So that's one strong vote to tear-down, epoxy, and rebuild - two counting my own.

Anyone else have any comments on salt-water specific build practices? I'm planning on using Super Koropon as an interior coating, now debating percentage of interior structures to cover.


Cheers,

Your welcome for the info Sean,

"My eventual plan is an amphibious Rebel that will live on land but spend a significant amount of it's float time in salt water, so this is causing me some concern."

Attached are a few more findings in AC43.13. I believe after reading you will do the teardown...... so here's the water, but I can't make you drink.

I wouldn't get too worked up. The Rebel is mostly made with 6061 aluminum, which is more corrosion resistant than 2024, which most certified airplanes are made from, and the FAA is talking about in ac43.13.
Have you ever seen the large aluminum ocean-going fishing boats? They are bare aluminum, constantly exposed to salt water. I believe these are 6061 like the Rebel.
I would consider a thorough treatment with Corrosion X or similar, but deconstruction seems a bit extreme.

I once did a tube fuselage in epoxy primer (Stits) immediately after sandblasting thinking it would last a long time. I saw the aircraft about ten years later sitting near Boundary Bay on wheels. I was very disappointed in the results. Even though that stuff sticks amazingly well it is not immune to corrosion and when it does give way it appears to me that it can do a pretty good job of hiding it. I used self etching etch primer but I wouldn't do that again either because when done properly I think it adds too much weight. I think now that they had it right all along and would use zinc chromate primer. Leaving an airplane in salt water pretty much guarantees you will have corrosion no matter what you do.

Jesse has a point but I have seen corrosion on some of the sheet that we received in our kit so 6061 may be better but still....

Bob.

i used everbrite on all interior surfaces, works great and should last forever
but also exoxy cromate between mating surfaces

cheers

mike#007

Here's my 2 cents worth on the subject of corrision and prevention in general. I've been around planes for 40+ years, but relatively new to building, so I will limit my info to corrision and salt water as it pertains to boats. I have had offshore boats in the Florida Keys for 38 yrs and experienced severe corrision UNTIL I started using Corrision X. It is fantastic stuff. I spray all exposed aluminum on the engine and boat fittings and have had NO corrision since. I usually reapply after a month of constant saltwater exposure. It adheres to the porous metal surface better than epoxy primer and will not let the saltwater thru. I use the Corrision X packaged for aviation use. I have heard that Corrision X is widely used in aviation on the inside of plane structures and works very well. Openings into all the plane's structures must be availabie for reapplication as required. It is usually applied via a spray system with a long wand. These are just my experiences with the stuff as it pertains to boats.

Lindall

Guess most of you saw that I didn't spell corrosion correctly. My apologies.

Well.... what it really comes down to is your MDRA Inspector; they have a mandate to follow. Those being build manual standards and if not available they will follow the standard industry practices.

BTW, Murphy did not always use 6061-T6 for thier parts. I have first hand knowledge that MAM did indeed use 2024-T3 to make parts (including skins). So that blows the theory that they exclusively used 6061-T6.

Get a MDRA inspector........ they are the person who will pass or fail your project.

Having built a kit that including lots of mistakes and drilling out rivets and taking things apart and having also taken said plane mostly apart again, I agree with Jesse that disassembly sounds very drastic. Almost like a prison sentence, actually. I'd think long and hard about that. On the positive, since you didn't build the plane, it'd give you some time to become familiar with it. Several years, most likely.

Corrosion X. Great stuff. Just don't use it if you plan on painting in the future. It will be everywhere. Guranteed. CW

Hey Craig and anyone with corrosion x experience, my rebel is painted and I'm just finishing up my floats and painting them with float lacquer over epoxy primer.
I plan on fogging everywhere with Corrosion X, i mean everywhere. Any reason not to?
Randy

Randy, when you say everywhere, do you mean outside of structures as well as inside? Like Craig and I mentioned, Corrosion X adheres really well and is hard to completely remove after application. Don't put on anything you will be repainting unless you can clean effectively before painting. As for applications, on my boat, I remove the engine cover and spray a heavy coat on everything, electrical and all. I use it on battery posts and anything that might corrode. Never had a problem. There is only one negative that I can think of and that is that it attracts dust and dirt because of its adhesion property. I wouldn't use it for lubrication in a dirty environment such as in the area of brakes or axles. But definitely good for the interior surfaces.

Lindall

Lindall, I plan on misting the interior structure wherever i can reach, outside every inch was alodined, epoxy primed and painted.
Randy

I found the best way to blow corrosion X or other sprays into hard to get place is use one of the high volume air nozzles and spray the product into the slot or hole of the nozzles. Creates a pretty good mist.