"Rip" wrote ...

We all know it happens. I'm just one of those weirdos that wants to know
WHY it happens. As a result of this thread, it appears that nobody knows.
It's an unstudied regime of flight. I find THAT interesting!

Me too ;-)

I actually tried yesterday... with poor results for the connect ;(

But the GPS track provided an explanation. It showed my 360s were not proper
full circles, i.e. at the exit I crossed the previous flight path at an
angle (more than 45 degrees in fact) instead of actually flying in the same
circle track as the entry of the 360. Not so easy to explain, but the result
was that the airplane was only in the potential wake area for a fraction of
a second. I guess you need to fly so that the flightpath is well aligned
with the original circle, in order to catch the wake.

Back to the theory:
I read some interesting basic aerodynamics of drag. According to the book,
at low speeds the induced drag (which is a side effect of the lift force) is
larger than the parasite drag (caused by frontal area, landing gear etc).
But at higher speeds (above 70 mph in the example case, a light plane)
parasite drag becomes the dominant drag component. Now, the induced drag is
creating the tip vortices, which presumably descend, but parasite drag has
no vertical component, so in theory it should stay in place. So according to
this, the higher the airplane's relative speed, the slower the wake will
descend (if at all).

I look forward to the results of the group's experiments ;-)