I have a quick question regarding the wing center sheeting. Is the fillet on the center sheeting really important? What is its purpose?

Thanks.

Ryan

The fillet reduces the stress concentration at the corner. In general it's bad to have sharp inside corners - this is why the lightening holes are round, or have rounded ends. If you forgot to include the fillets when cutting the centre sheeting, you can glue a triangular piece of sheet material in there. The curve will distribute the stress a bit more evenly, but a 45° fillet will be almost as good.

If something bad happens, it would be cracks radiating from the sharp corner.