50% of it was worn away, or it was 50% of its original diameer? Big difference there. If it is worn to 50% of its original diameter it means only 25% of the original material is left meaning it is 25% as strong as it was when new.
1947 North American Navion N8747H. It isn't the fastest, doesn't have the biggest payload, burns gas almost as fast as I can pour it in the tank and requires lots of TLC, but it's cool as hell and that's why we play the game.