Originally posted by sonhouse
You just don't get it. You always turn on your fantasy planet around the equator. You never have to turn on the real Earth. Do you even know what a tangent is? You go in a straight line starting on that circle, you go to the edge. Is that something esoteric to figure out?
Since you want to make an issue out of it, I will oblige.
On a spherical earth, the only way an airplane can follow a strictly easterly direction is to monitor the path by use of a compass.
Deviation from the intended direction, i.e., south or north, is constantly being corrected by minor alterations in the steering.
Doesn’t matter if the plane is on autopilot or is being controlled by the pilot: corrections are occurring for however long the plane remains in the air.
The same holds true for any direction taken; the momentum of the plane must be constantly corrected in order to avoid deviation.
However, on a spherical earth the pilot is also required to make constant corrections to the plane’s trajectory as it relates to elevation.
This means if the pilot wants to maintain an elevation of 35,000 feet for the bulk of the flight’s duration, they must take into account a ground level which is constantly curving down and away from their position as they travel.
This is not a concern for any pilot of any plane, ever.
There is no need to continually dip the nose of the craft downward to offset the ground curving down and away from them, because the ground
isn’t curving away from the trajectory of the plane: it is moving in its direction over a flat surface, not a curved surface.
What this phenomenon is revealing is the same thing which is revealed when we see distant objects which should otherwise be below the horizon of the observer: the reason for the observation is the same reason a pilot does not need to constantly guide the airplane in a downward slope.
The world is not a sphere.