On 21 Mar, 16:48, Martin Gregorie
wrote

Its no better than introductory texts showing packets of air dividing at
the LE of a ring and meeting up again at the TE, when a photo taken in a
wind tunnel shows clearly that doesn't happen. Far better to publish the
photo than a bogus diagram.

Oh, that one drives me mad. Not only does it not happen ... there is
no conceivable reason why it should happen. And yet many many websites
and books cite it as fact. Grrrrrrrrrrrrrrrrrr.

Incidentally, if you don't have a copy of "An Album of Fluid Motion"
by Milton Van Dyke, get it. You'll love it. Every gliding club should
have one.

Ian