On Tue, 17 Apr 2007 00:19:02 +0200, Mxsmanic
wrote:

Tom L. writes:

It doesn't have to continue to sink forever. It can stabilize its
position at some point.

It will sink indefinitely unless some other force acts to stop it. In theory,
it will sink until it reaches the ground.

This is not happening in vacuum, the force that acts to stop it is
encountered as soon as the disturbance is created. The questions is
how long does it take for that force to stop disturbed air. That would
be related to how much energy is in the vortices (in their rotation).
Smaller aircraft probably creates vortices with less energy.


E.g. if the vertex radius is 15 feet and sink rate 20 fpm, we hit the
wake after a 30 second turn.

Twenty feet per minute is too slow. The downwash will move at at least a few
knots, and even three knots is 300 fpm.

I've seen numbers from flight tests indicating several hundreds feet
per minute for big aircraft, but I've never seen any numbers for small
aircraft nor I've ever seen a theory that could explain or calculate
everything measured in the flight tests.

Can you point to such test results or a complete theory? It seems that
you have access to at least one of them. Thx

- Tom