Comment by kqr
Paper airplanes do not have barndoor wings, though. Most of them have stepped camber through the way they are folded.
It's not finished but I started writing this to clarify: https://entropicthoughts.com/paper-airplane-aerodynamic-stab...
Scroll down to "trim and angle of attack".
(I hope there's nothing embarrassing in there. It's an old, early draft.)