Charlie Longley
MEMBER
Anchorage, AK
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Sometimes they just crack on the ends. That does look like damage, but there ought to be other evidence. I would look it up - some cracks may be acceptable - that one looks like new spar city to me. In the olden days it would get spliced - an ugly affair on a beautiful wing.
Looks more like a deep check to me. They'll do that if they don't get to dry slowly enough.
John
I'd say the wood grain was compromised (for any number of naturally occurring reasons, or while being dried) and over time the compression of the attach fitting caused it to pop. Basically just rotten luck.
You might be onto something but I think your scenario would cause it to crack at the strut attach point. A cursory "look" at the geometry and load paths in my mind makes me think the strut fitting would be the more vulnerable location for a fracture. In my opinion, over-zealous jacking while replacing a strut seems a more likely candidate.Something pushed up on the end of the wing. The lift struts were the fulcrum. The top bolt on the root fitting provided resistance to the downward force on the root until the spar cracked. (IMHO)
I am thinking this might be the answer. The spar is quarter sawn a bit don’t know if that made a huge difference.
View attachment 46347
It’s definitely not a deep check. Take a closer look at the pictures. It’s cracked through both sides. You can open the crack by hand...
The spar is quarter sawn a bit don’t know if that made a huge difference.
A check is a longitudinal crack in the radial direction of the wood and usually on one end of a board or the other. It can go all the way through. It's usually caused by uneven shrinkage when drying. IF there were some evidence of damage or rough handling, I'd say it wasn't a check.
John
That's on a plain sawn board....but it doesn't matter....you're replacing the spar, which is the proper fix. The only reason I specified that, is that it ties in with wanting to know why it did it. I'll be interested to see if you find any evidence of damage when the spar is completely out so you can examine it. I'm not trying to argue.“ Checks are longitudinal cracks extending, in general, across the annual rings. .”
How do you slide the new spar in there with the ribs still attached to the rear spar? Gonna add the plywood plates after sliding it in?
That's what I did on a 7GCB without even uncovering the wing. Just a slice in the fabric over the spar area.How do you slide the new spar in there with the ribs still attached to the rear spar? Gonna add the plywood plates after sliding it in?
Steel fittings are bolted over the spar.I wonder if that split happened during installation. Bolt through the front fitting and then the wing slipped, dropping the trailing edge and twisting the front spar. I would think such a twist would bend the attach fitting. Maybe it did and the fitting replaced but the crack or start of it was overlooked.
How do you slide the new spar in there with the ribs still attached to the rear spar? Gonna add the plywood plates after sliding it in?
That's what I did on a 7GCB without even uncovering the wing. Just a slice in the fabric over the spar area.