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“Precisely. I suggest going with a Seagull. Remember to line up the wing flaps for good balance. Set the dihedral angle flat or slightly up, the vertical stabilizers to approximately forty-five degrees to the plane of the wings...”

The two wings of a bird would constitute a monoplane, when they are in a horizontal position for soaring, or when the tips are uplifted and they form an angle like a broad V, called a dihedral angle.

At this point in Book VI it is customary to introduce the dihedral angle.

It is not necessary to dwell at length upon the dihedral angle, except to show the analogy between it and the plane angle.

The locus of a point equidistant from the faces of a dihedral angle is the plane bisecting the angle.