Regarding induced drag, I understand where it comes from-the horizontal element of the resultant lifting force due to the rear facing lift vector.
But what is this 'horizontal' element in relation to? The ground, mean chord line or the direction of travel?
What is the correct term for this plane?
Is it possible to have a 3D lifting aero shape (not something symmetrical) in which all the lift is perpendicular to the 'horizontal' plane, so that there is no induced drag?