If you were me...Priming and CG

[SilverEagle2]

I searched the archives and was not able to get a satisfactory amount of information from the annals. I am truly l open to your opinions, knowing full well there are many.

As a reformed RC plane builder, I strove to build all my planes with the idea of NOT having to bolt on weights to achieve the correct CG. This has got me thinking as I progress through the Tail of my 7.

Knowing that any extra weight in the tail is far more costly than weight in the nose and that the 7 can come out tail heavy anyway, I have been having an argument with myself over my priming choice.

I primed the inside of the HS and VS skins already, but as I am now onto the rudder and contemplating its' location relative to the CG, I am asking....if you were me, would you prime the inside of the rudder beyond what I have done here?

Rudder Log Entry

My choice to prime had much to do with my close proximity to the Great Salt Lake and the associated WX.

I have had good luck with the Duplicolor Self Etching from a rattle can.

I still intend to scuff and prime where parts interface, but what about the field of the skins?

[Danny7]

i'd skip the field of alclad surfaces, but i don't really know how much salt you get in your area. Do you get a salt craze on your car after certain storms? we did in hawaii and al would definitely corrode very quickly there.

[wrongway john]

Some time back, I did more research into various two-part primers, which I was told tend to be heavier than others. But some popular brands recommended as little as .5 mil coverage, and when I did the weight per s.f. at .5 mil coverage that helped alleviate my concerns when I found out it was only going to add about 3-5 lbs to the entire inside of the airframe if I did it correctly, and not put it on too heavy.

Not a bad insurance policy which is also going to give your plane a higher resale value too. Just a bit more of a pain to go through the process though. For priming the entire inside of the empennage, I’m thinking you’re adding about one pound here for the .5 mil epoxy primers.

[RV6_flyer]

As for weight and primer:
In A&P school, we had a project to prep and prime a piece of 0.032 aluminum. Pass / Fail was Pass equal less than 1% weight gain. Fail = more than 1% weight gain. Pass was a translucent coat of primer.

One option that is not on your poll that I would pick is prime only the extrusions that are not alclad.

A Hartzell constant speed prop takes care of most to the aft CG issues that one can have with an RV.

[Kyle Boatright]

I'd use a light coat of zinc chromate on anything non-alclad AND the faying surfaces. You'll get far more corrosion protection that way than with most other rattle can primers, which are mostly designed to make paint stick rather than to protect against corrosion. In fact, a translucent coat of ZC throughout the empennage wouldn't add much weight and would add a lot of corrosion protection to what are essentially sealed structures.

[chaskuss]

Jason,
You could simply Alodine the interior parts of your elevators and rudder. That would add corrosion protection, but would add no weight. A second option would be to Alodine and prime only the "faying" [contact point] areas. All that said, remember that the empennage parts are cheap and easy to build.
If in the future, you discovered a prohibitive amount of corrosion in these parts, you could simply build replacement parts. Once you finish your RV, your skill level will allow you to build a second set in about 1/3 the time you will take to build the originals.
Empennage parts are easily replaced [and replacing them means minimal down time, compared to rebuilding]. Fuselage interior areas are generally accessible. This allows relatively easy access for corrosion repairs. The wings, on the other hand, would be a "bitch" to access, if corrosion is found in the future. Best to focus maximum corrosion protection to your wings.
Charlie
PS Corrosion X works. However, it adds considerably more weight than primer. Over time, Corrosion X's weight will go up, as dirt and debris cling to it.