"Dallas"

Why would a horizontal wing create "more effective lift" than a banked
wing?

Let's think of a set of wings with a dihedral angle of 10 degrees up from
horizontal, on both wings.

Now, think of the shadow the wings would make, if the sun were straight
overhead, while the plane is banked at 10 degrees. The wing that is up
would make a smaller shadow than if the plane were flying level. The wing
that is down would be making the largest shadow that is possible.

The size of the shadow is the only size that is important, because the lift
that is straight up (towards the sun, in our example) is the only lift that
will be important to the plane, as that is what is counteracting the force
of gravity. The fact that the down wing's shadow is larger, will make have
more effective area than the up wing, and will tend to bring that wing back
up.

While you are in level flight, the same thing will constantly be at work,
automatically trying to keep the plane level.
--
Jim in NC