BOAC
It was not my intention to ridicule anything, and I do not believe that I have done so. The simple fact is that the idea that two parcels of air, having been separated by the leading edge will meet again at the trailing edge is quite simply untrue.
We could if we wish put arguments about the effects of the inertia of the air resisting longitudinal acceleratrions, beven this would not cause the two particles to meet again.
dcoded
If the explanations so far have not cleared up the matter, you might like to try a simple demonstration.
Take a large carrot (or other generally cylindrical object).
Place the carrot on a worktop and cut vertically downwards across the carrot at 90 degrees close to one end.
About 1/3 of the way along the carrot, cut vertically downwards across it at an angle of about 30 degrees to represent 30 degree sweepback.
About 2/3 of the way along the carrot, cut vertically downwards cross it at an angle of about 60 degrees to represent 60 degree sweepback.
Now compare the cross-sections of the three cuts. These represent what air would experience if it were to flow over the carrot.
The 90 degree cut which represents straight winds will be approximately circular.
The 30 degree cut which represents 30 degree sweepback will appear to be elongated in one direction.
The 60 degree cut which represents 60 degree sweepback will appear to be even more elongated.
The greater the sweepback angle the greater will be the chord length compared to the thickness. This illustrates the way in which sweepback reduces the thickness to chord ratio of a wing.
This reduction in thickness to chord ratio reduce the accelerations experienced by the air flowing over and under the wing. This in turn increases Mcrit.