Knife edge! My red US 40/OS .55AX will do consecutive knife edge loops. They're large and oval shaped, but this isn't pattern.

I am using a strong, digital servo with pull-pull on rudder. I have 3 degrees of anhedral on each wing panel to cancel out the roll with rudder. I have also mixed in nearly 1" of down elevator with full rudder to stop the pull to the top of the plane with rudder.