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For you Alclad Guys and Gals

sloengineer

Active Member
Seems like folks that don't prime the Alclad parts get shamed into hiding, but I thought I'd see if I could bring a few out of the hangar..... :D


We aren't priming Alclad parts, but I know there are some non-Alclad parts in the RV-14 kit. In particular, the 6061-T6 rudder horn. Those of you that went the no-prime route, did you prime the non-Alclad parts in any way? If so, did you conversion coat, rattle can, epoxy, etc?
 
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Yep. The steel weldments and all of the 6061 extrusions (basically anything that say's "must be primed" in the plans). Used two coats of SEM self-etch from a rattle can.

For corrosion prone areas like the aft bulkhead/tailspring mount, I followed up with Eastwood rattlecan expoxy primer. It is a true 2-part that you mix by pushing part B into the can, from an integral tube, then shake well to mix.
 
In the empennage, I primed only mating surfaces. Wings and fuselage are getting a fancier treatment. Only time will tell if it's wasted of effort. The tail feathers were in decent storage for 10 years and they still look spotless.
 
Plus 1 for SEM rattle can

Non Alclad Aluminum and steel obviously benefit from etch/wash primer. But when that gets scratched between mating surfaces during fabrication and assembly, How will you keep the aircraft from falling out of the sky ?

My plan is to treat the longeron/skin interface type areas with Boeshield after paint. Other opinions/comments are appreciated.
 
But when that gets scratched between mating surfaces during fabrication and assembly, How will you keep the aircraft from falling out of the sky ?

I know there's a reason this entire topic is in the never ending debate section, but I completely agree with this sentiment. No matter how carefully you prime, paint, alodine, etc, you will scratch through it at contact points during assembly. There are many items in the build for which GEMO is not acceptable.
But this is one where I think people obsess and over do it, adding hundreds of hours to the build and fatiguing themselves needlessly.
 
Prime it all..

Alclad is just a non-structural layer of pure aluminum (very corrosion resistant), and great for unpainted skins, ect. There are no Alclad extrusions unless they are roll-form extrusions like a gutter on your house and made from Alclad sheet (none on an RV). BUT, Alclad sheet is in Layman's terms like a sheet of plywood..the edges and holes expose the structural alloy sheet, and open the path to corrosion. 99% of corrosion starts at an edge, fastener hole or scratch. I'm all about 100% prime, with detail focus on edges and holes. I'm a bit over the top, but most of my career day job has dealt with corrosion control and prevention on heavy jets. All extrusions should be primed without exception, although Vans uses 6061-T6 in lieu of 2024-T3 which is less susceptible to corrosion. No Primer Wars here, just factual data.
 
No 2024 extrusion on the -4

-4 has zero 2024 extrusion, its all 6061 for the extruded raw stock supplied in the kit. I cant speak for other kits, but suspect VANs didn't change much in his material choices. The spar strips for wing and empennage are 2024 plate, which is not extruded, but its not Alclad either, hence, priming is recommended. My point is, all extrusion and non-clad aluminum benefits greatly from priming.
 
In an effort to offset the extra equipment in my RV-10, I decided not to prime most of the alclad. Not trying to fuel the primer wars, because my RV-6A was fully primed. However, there are some exceptions. The battery box, which I modified for a larger 24V battery, is powder coated. This was prompted by the condition of the battery holder in my 1965 Chevy pickup; it looks like the battery was a magnet for grime and corrosion. I went ahead and powder coated the mount for the O2 tank and other mounting pieces of thicker alclad material. And I also powder coated the brake reservoir bright yellow, the better to see brake fluid. I'm lucky to have a good coater nearby who serves the local automotive and aviation industries. He also did my engine mount after I had the reinforcement SB done and my steps, too.

On the other hand, I had the control stick mounts machined per the plan recommendations and decided not to paint or prime. Nor did I prime the F-1065 pushrod as those parts are easily to inspect and are well protected inside the fuselage. The tube pushrods are primed and the other extruded pushrods will be powder coated. I also do not prime fluid tubes; it's too easy to disrupt the paint/coating/whatever during installation anyway, especially if you need to flare an end after the tube is in place.

My point is that, even if you prime 'everything', there is no single mindless approach, as people who have inadvertently primed the inside of their fuel tanks have come to realize. You should consider the part's application and environment.
 
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