Snowbird writes:

I guess Mxmanic uses the FAA AIM as his main source in his "research".

That is only one of many sources. They all say the same thing.

a) "Flight tests have shown that the vortices from larger (transport
category) aircraft sink at a rate of several hundred feet per minute,
slowing their descent and diminishing in strength with time and distance
behind the generating aircraft."

Note the explicit reference to large aircraft. In fact, it seems all actual
wake turbulence safety studies have involved large aircraft, i.e. B707 and
larger. This is in fact quite natural, as there was no real safety issue
before the large jetliners appeared.

The wakes of smaller aircraft descend as well.

b) "Test data have shown that vortices can rise with the air mass in which
they are embedded."

There you are, official proof to the statements of several of our
contributors.

Including myself.

c) "The greatest vortex strength occurs when the generating aircraft is
HEAVY, CLEAN, and SLOW."

Yes. Although the downwash itself should be strongest when the aircraft is
dirty and slow. The reason clean and slow produces stronger _vortices_ is
that it only produces one pair, whereas flaps and other control surfaces can
produce multiple vortices of smaller size that tend to interfere with each
other and reduce overall turbulence.

In contrast, a light aircraft doing a 360 is usually LIGHT, CLEAN and
(relatively speaking) FAST. Very different conditions, especially regarding
two major sources of wake: the AoA of the wing (which affects the tip
vortices) and the power setting (which affects the propwash strength).

Which makes it all the more difficult to understand how a pilot could feel his
own wake in a level 360-degree turn.

The interesting study question here, for the light airplane case, would be
the relation between the tip vortices (which presumably sink, as for large
aircraft) and the propwash (which is basically horizontal). I think glider
pilots can testify that the propwash is the dominant one, at least close
behind the tug airplane - any soarers out there who can comment?

You're neglecting the downwash, which is present in all aircraft. Downwash
tends to pull all turbulence behind the aircraft down with it.

But realistically, as the wake behind a light aircraft is no real safety
hazard, there is no compelling reason to study this case. So unless someone
can produce a reference, let's rely on the observational data from countless
pilots.

And ignore the factual data from countless resources? What makes pilots more
reliable? Most pilots barely understand how lift works to begin with.

--
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