What is the correct definition of "spanwise" and "chordwise" with a swept wing? For example, in the context of "spanwise airflow" and "chordwise airflow"?
a) spanwise is from root to tip, generally following the quarter-chord line, and chordwise is the direction that gives the shortest distance from leading edge to trailing edge, very roughly perpendicular to the quarter-chord line. I.e., roughly as illustrated in this related question (either diagram): Where is the spanwise flow? How does the span wise flow point the air towards the wingtip?
b) spanwise is perpendicular to the aircraft's longitudinal axis, and chordwise is parallel to the aircraft's longitudinal axis.
c) either of the above definitions could be considered to be correct, depending on the context
Not meant to be strictly multiple choice, those options are just offered as food for thought-- if one of the choices is almost right but needs some tweaking, please elaborate--
Among other things, the intent is to understand whether the diagrams linked in option a), exactly as drawn, really illustrate any net spanwise flow at all.