more speculations
Pardon my lack of formal education in this matter but I seem to recall that vortex comes from the need for lift.
Hence:
- the heavier, the more vortex
- the shorter the wings, the more vortex (with less air mass/sec to swirl, it has to swirl harder)
- the slower, the more vortex (same reason as above)
Could the landing/takoff speed difference between A320 and B757 account for the above observations? Is B757 approach slower?
(Just curious and trying to make sense of aerodynamic questions in general.)