Wit a composite structure you cant just look at the internals and say "its good".

You have to look at the entire structure including the skin.

What is the layup schedule of the skin?
What thickness airex?
What version airex, c70.75, c70.55, etc?
Where is the placement if the reinforcements and what weight, style, etc?

From what i see in the photos, it looks pretty good.

Some personal things i dont like:

1. No full length root rib to support the shaft along the full chord line (this could be a piece of airex, i just cant tell)
2. No full length rib at the outboard end of the pivot shaft, again to give full support.
3. Two short bolts for anti-rotation. I much prefer one long pin sandwhiched between a three part rib for antirotation.
4. A full span spar that interlocks with the outer pivot shaft rib, or even better yet, one shaped so the pivot shaft goes through the spar and the spar continues to the root rib.