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Anodized Surface - Wing Spar

skelrad

Well Known Member
Friend
Just curious, does anodizing aluminum make the surface a little more brittle or something? I noticed tonight that just the pressure of a cleco against the front wing spar (9A) is enough to leave a ring indented in the anodized surface. At first I thought it was just grime or something, but nope, it's an actual indentation. It doesn't seem to matter how gentle I am with the cleco. The other thing I noticed is that the anodized surface shatters in a star burst pattern around the rivet. I only noticed this on rib rivets set on the single thickness portion of the spar (no doubler).

I'm not worried about it, but just got me curious as to why this occurs, when it doesn't seem to happen on non-anodized material.
 

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Yes, the anodizing is a hard layer of aluminum oxide grown out of the base material. This is why you don't anodize thin materials, it leaves them more prone to cracking / fatigue.
 
Just another data point.
I've got a 9G metal airplane with every piece of aluminum anodized in it. It has 1300+ hours of mostly acro on it, no cracks anywhere as of yet.
 
Not a black/white application

Both of you guys are mostly right IMO (for what that matters). Lots of anodized construction in aircraft including a whole lot of early RV spars including the thin webs. A lot of the Czech built Rockets utilized anodized sheet in various places. As long as it's considered in the engineering = no issues. That said, indiscriminately applying any passivation to primary structure is not wise.

Build safe.
 
I got the exact same thing and had the understanding it was perfectly normal and expected.
 
Both of you guys are mostly right IMO (for what that matters). Lots of anodized construction in aircraft including a whole lot of early RV spars including the thin webs. A lot of the Czech built Rockets utilized anodized sheet in various places. As long as it's considered in the engineering = no issues. That said, indiscriminately applying any passivation to primary structure is not wise.

Build safe.

Good point, depends a lot on the specific process as well. Not all anodizing is the same.
 
Just another data point.
I've got a 9G metal airplane with every piece of aluminum anodized in it. It has 1300+ hours of mostly acro on it, no cracks anywhere as of yet.

What that suggests is that any cracks which might exist are either too small to be seen or in a place that doesn't get examined. A more accurate interpretation of the portion in bold is that "no cracks have been found anywhere as yet." Still - as long as cracks get caught before they grow big enough to cause a failure, the plane is probably just fine.

Dave
 
Just another data point.
I've got a 9G metal airplane with every piece of aluminum anodized in it. It has 1300+ hours of mostly acro on it, no cracks anywhere as of yet.

You anodized every piece of aluminum? Or alodined? Two different processes..
 
That starburst pattern has been discussed here before, IIRC. A search might turn up something, but I seem to remember that it was determined (by Van's? by one of the members who is materials engineer?) that it's simply the layer of anodizing radiating fractures, not cracks in the underlying aluminum material.

I'll bet most builders have seen this, but many probably didn't think anything about it.

Here's one thread on it: https://vansairforce.net/community/showthread.php?t=29429

and another

https://vansairforce.net/community/showthread.php?t=100431

BTW, when, oh when, is the search feature on this forum going to be fixed? It *sucks* to have to use The Google every time you want to find stuff...
 
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