Interesting stuff on the stepped airfoil. It is of course difficult judging something without looking at wind tunnel data and something that indicates the accuracy of the wind tunnel test. It is certainly not something that would give you an immediate "whow that looks like the way it should be done" based on the birds in the backyard.

Certainly there is no advantage in structural weight. For a given load the structure would need to be heavier as the structure in the cutout near the centerline of the airfoil isn't as good at load carrying as the same material at the surface of the airfoil.

Tatoo - and I thought I was being mean, it is a wonder the airplane doesn't bite you at the field. Those prop kick backs are not an accident perhaps!