Are Ribs Alclad?

[RobinHou]

I decided not to prim Alclad (2024T3?) parts. But I am not sure if ribs are Alclad?

Vans tech support is not open till Monday and I am hoping to get an answer here soon so I can continue to work this weekend. Thanks in advance.

[frankh]

Nope...but they really don't need to be primed either unless you live on the coast. Priming the mating surfaces (between rib and skin) is perfectly adequate.

Zenairs are made entirely of 6061 and havebeen built this way for 30 years with perfectly acceptable results.

Frank

[msturgis]

Originally Posted by RobinHou

I decided not to prim Alclad (2024T3?) parts. But I am not sure if ribs are Alclad?

Vans tech support is not open till Monday and I am hoping to get an answer here soon so I can continue to work this weekend. Thanks in advance.

Hi Robin!

Hope your trip back home from TX and LA wwnt well...
Your plans will tell you what pieces are not Alclad, and there for need priming.

-Matt

[frankh]

My old Zodiac is now 10 years old and had no paint I it whatsover apart from mating surfaces. Not alclad parts, and no corrosion either. Van would have you believe the 6061 will corrode but it just ain't so

Frank

[RobinHou]

Thanks, Frank.

Hi Matt, the trip back was great. Christina and I made it back to KEMT from KNEW in one day and only one fuel stop. A little bumpy but very light head wind. The old Bonanza is no RV, but still a nice plane.

[paul330]

My understanding is that all sheet parts are Alclad. Anything you make from bar or angle has to be primed.

[rbibb]

While I am not positive I'm pretty certain the ribs are hydroformed from 2024 Alloy in a zero temper condition and then heat treated to the T3 condition. That's about the only way to form such parts. As such there is no ALCLAD on the ribs.

As for the comments about 6061 Aluminum not corroding that is incorrect. Whether it will corrode fast enough to be a problem is a matter of opinion but the white powder you will see form on 6061 (especially in the presence of moisture) is Aluminum Oxide. Corrosion is accelerated whenever you have dissimilar metals (say 6061 and 2024) being in close contact where, with the addition of an electrolyte (water) you have just made a small battery. Also keep in mind that the MS20246 and MS2040 rivets you use are 2117 allow and, even though they are alodined, are a dissimilar metal joint. Keep out the moisture and you eliminate the galvanic action.

2024 will corrode as well.

I am going with a variety of methods to deal with corrosion potential on my airplane but at a minimum I'm painting any non-alclad parts (basically anything but the skins) with a self-etch primer.

If a part doesn't come with Blue Plastic on it you can pretty much assume it isn't a CLAD part.

[flion]

Richard's last sentence is the key. There are some ribs that are formed from thin alclad and arrive covered in plastic. There are others that are formed from thicker non-clad sheet, and you can generally tell because they are not shiny and/or have no plastic covering. J stringers are clad, as is .025 angle; both come plastic covered. Other angle (.063, .125, etc.) and bar stock are not clad.

[chaskuss]

Originally Posted by RobinHou

I decided not to prim Alclad (2024T3?) parts. But I am not sure if ribs are Alclad?

Vans tech support is not open till Monday and I am hoping to get an answer here soon so I can continue to work this weekend. Thanks in advance.

Frank's comments regarding his Zenith do not apply to your RV6 project. RV sheet aluminum is made from 2024 alloy, not the 6061-T6 used in the Zenith series aircraft.
The ribs on my 8A project appear to have an Alclad covering on them. I say this because my wing main ribs were badly scratched. This was due to Vans packing them one inside the other, with no paper or other protection between them. My ribs did not come with a plastic coating [PVC] on them. To polish out some of the deeper scratches, required polishing through the Alclad layer. The layer was clearly visible to me. It reminded me of sanding through finish paint to the primer underneath when repainting a car.
I agree with Richard Bibb's comments regarding dissimilar alloy corrosion. His comments regarding the hydro forming process concern me. I would STRONGLY suggest you speak to someone at Vans to verify that YOUR ribs do or do not come with Alcadding on them.
Are you forgoing the priming due to weight concerns? Or are you trying to keep the labor to a minimum? If excess weight is your concern, I would suggest Alodining your 2024 parts. Even the Alclad items have areas where corrosion can start. Remember that all the edges and the rivet holes have no Alclad on them. They are pure 2024, which corrodes easily. Chromic acid conversion coating [the generic name for applying Alodine, Duradokote, Iridite, etc] adds no weight and GREATLY inhibits corrosion. Naturally, this process will add to the labor required.
Is added labor is the issue? You might consider Alodining JUST your wing parts. I say this because repairing corrosion inside a wing will require HUNDREDS of hours of labor to repair. This is because of the extremely restricted access to the interior of the wings, once they are closed up. You could simply build a new empennage part, if one became corroded in the future. The fuselage allows access to the interior. This will allow a relatively easy repair of most future corrosion on this sub kit.
Some builders prime only the faying [contact] surfaces, to reduce weight. Most corrosion occurs where two pieces meet, such as a skin and a rib flange. Just some things to consider.
Charlie Kuss
PS Richard's comments make me glad I Alodined and Mil Spec epoxy primed all my parts. I live near the Atlantic Ocean in SE Florida [corrosion capital of the world!].

[frankh]

As I wrote in my first post, I suggesting priming the mating surfaces..Thats what I did, put two coats of self etching primer on the mating surfaces between each part.

i would do that no matter what they are made of simply because of the galvaning potential.

but the open area of the ribs while yes WILL corrode, will only get a thin layer of aluminium oxide which is waterproof and the rib will not corrode any further.

Frank