Transform vectors in EOMs into ground-fixed axis (X and Y values)

Desired capability or behavior.

Currently, EOMs in Aviary do not use a consistent way to define forces and motion. A ground-fixed axis to define forces and motion could be helpful for several reasons: first, it gives a standardized interface to add in new EOMs. Separating out all the vectors into x- and y-components will make it much easier to bookkeep more complex couplings like aero-propulsion. Second, this allows for new capabilities that will work for any EOM, such as engine offset angle (or moveable engines like tiltrotors). Finally, it makes all of the different forces and moments extremely clear and harder to confuse. Replacing velocity with "true_airspeed" and separately defining "velocity_x", "velocity_y", along with all accelerations makes it near impossible to misinterpret what they are referring to.

To clarify, I am not proposing to remove variables like "thrust" or "drag", or even modify the existing EOMs at all, just adding a new component that transforms those vectors into the ground-fixed axis, which we can modify our dymos problem to work with instead.

Is your feature request related to a problem? Please describe.

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Associated Bug Report

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