P.S. any concerns about none anodized wing spars? maybe i should have asked before i bought but the argument i heard against the idea sounded good what is the other side/opinion, thanks for any input
Back in the day, Van did not build the spar for you, nor was any part anodized, unless you took an option and had the spar built-up by a company called Phlogiston. It is not an option any more with the new RV7/8/9 kits. All spars come anodized and pre-assembled standard with the kit. You really have no choice. For 20 years anodized spars have been used and not been an issue. However this came up when Van started to offer this the Phlogiston spar option on the RV4 and RV6.
For the RV4 and RV6 I assume you still have the option to buy a pre-assembled anodized spar or a do it your self spar with bare?
If I had a choice of a pre-fabricated anodized spar or getting bare parts to rivet together, I would have to think about it. On one hand not having to trim straps, cut lightning holes, etch/alodine/prime all parts and drive the 3/16 rivets is nice but no big deal. On the other hand, I would rather have an etched/alodine/epoxy primed surface than just anodized, my preference. Anodized is NOT a problem, just my thinking, it is not really the ultimate corrosion protection treatment for this application. Anodizing is a surface finish that tends to be done to make a surface harder and more wear resistant or pretty.
(PS driving the big spar rivets is a easy with a big pneumatic squeezer and large "C" jaw. Beg or borrow one by all means. It takes about 20 to 30 minutes to squeeze all the spar rivets once you get going.)
There are things about anodized parts that make people concerned, mostly with out cause to be concerned. The thinking is a harder coating than the parent material is a crack starter? Well it's unlikely with the materials we have in the environment we fly in.
From a metallurgy stand point IF anodization is NOT done properly, it may cause the metal to be susceptible to hydrogen embrittlement. Baking eliminates the likely hood the anodizing process will leave behind chemicals that cause hydrogen embrittlement. I'm sure Van or the vendor is using the proper process. Hyd-embrittlement is a corrosion problem of greatest concern on machined blocks and forgings, where end grain is exposed, in a high stress and high hydrogen environment. Metal like wood has grain orientation. With sheet metal and bar, grain is not exposed. Also for hydrogen embrittlement to happen, an elevated hydrogen environment is needed. We don't operate in elevated hydrogen corrosive environment, like in some industrial applications. My point is anodizing the spar is not a typical application but it's not a problem. Why anodize? The normal corrosion resistant process (etch/alodine/prime) is good to excellent. Priming is good enough. Anodize does look pretty, but that's not really a factor with a spar is it?
The anodized surface is harder than bare or clad aluminum. (I think Van uses a "softer" chromate anodized process.) Is that harder anodized surface brittle and a crack starter? Well even if there where cracks in the anodized coating (there are lots of them), there is nothing that will telegraph that into the metal. The metal is taking the load not the anodized surface which has zero strength. Again sheet metal and bar does not have exposed end grain.
However this is my argument to prime or that primer is a tad better than just anodizing in this application. Anodized surfaces can break down if flexed enough. It's just an oxide layer like rust on steel. Rust can flake off. Primer coatings have one job in life, that is to protect against corrosion. Primer is made to flex and stay on for life. Anodizing parts is usually done to make the part more durable to physical wear and tear from rubbing and for appearance. This is not an issue with the spar. Anodized is hands down better looking. I suspect anodizing is more automated than than the etch/alodine/prime method.
What is better, anodized only or prime only? Using a good process and good primer product, priming is better to me. I have no proof of that, just my opinion based on the ramblings above.
It would be nice to hear RV owners with the early anodized pre-made phlogiston spars. Some are over 20 years old.
If Van offers the anodized pre-made spars only, be happy. If Van also offers a build your own spar with bare metal than you have to decide. If you are lazy than one option is easier. If anodizing bothers you, than the choice is made for you. When Van first offered the pre-fab anodized spar option, it was a few $100 extra. Money may be a small factor if there is a charge for it. Most RV'ers with new kits have no choice, it's standard. The big draw back (no proof just opinion) is the anodized surface is not as flexable as primer. Will this cause corrosion? May be in 100 years in a severe environment. Primer does not last forever either.
Looked at the kit yesterday and decided to "take the plunge" so to speak. tail kit is complete, Most of the control surfaces are complete the wings are clecoed together. I am leaving this wednesday on a ski trip to MI so i will be picking the kits up near the end of the month. I wanted a side-by-side for the benefit of training others in the future but decided that the 4 will better meet my needs/wants
