"Bertie the Bunyip" wrote in message
...
wrote in :

Tman x@x wrote:
OK, these are trivial, but nonetheless been bugging me and the guys
at the airport don't have a satisfying answer;

1. Why do wing tip vortices sink? They're not made out of lead.
2. 747 overflies at FL 310 (or whatever). Is the weight of the
airplane ultimately supported by the earth's crust? How?


FWIW, my opinions on these: #1: because of a general downwards
movement of air in the wake, induced by lift. I've also heard that
the turbulence causes locally increased pressure and thus density,
but I s'pose it was also create locally reduced pressure -- so I
don't believe that factor.

The tip vortices do have a different pressure/temperature which can
be seen on humid days when vapor condenses and they become visible.


Uh, no, that's not it. The vector as the air leaves th ewingtip is
generally downwards, that's why the travel is down. Also the reason they
travel out.

They travel outward because that's where the lower pressure is.
--
Regards, BobF.