Hi Renegade,

If I could toss my $.02 in here, I had a similar situation with an LT-25 I'm currently completing. Someone with good intentions and bad skills got to it first but I've just about fixed all the issues.

FYI, when I use my Slot Cutter, even with the thicker blades, sometimes the slot is still a very snug fit on a CA hinge. I think that these 'caverns' (well said) are going to be a problem. I don't think that thick CA is the answer and the loss of all that wood will create a weak spot in the spar. One of those is going to get you someday when it buckles in flight.

IMHO, and for what it's worth, I would cut some filler pieces (called a Dutchman) for each of those slots and insert them. Carve them for a snug fit but DON'T glue them in yet (more in a second). Between the slots, you could cut fresh holes for Robart pin hinges. Once these holes are properly located, you could then glue in your filler pieces in with THIN CA. The Thin CA will wick in nicely and strengthen that weak spot.

If you should glue the Dutchmen in before you drill holes for those Robart pin hinges, the thin CA could migrate through the surrounding wood and make it as hard as a rock, and difficult to drill for those Robart hinges.

As I said earlier, just my $.02

Bob