"Kev" wrote in message
ups.com...
On Apr 16, 9:41 am, Jose wrote:
I seem to recall recent magazine (web?) articles where the idea that
you can hit your own wake while actually holding altitude, should be
downplayed nowadays. You _have_ to descend a little bit to do so,

How tall is the wake?

Good point. Still, using the calculator at:

http://www.csgnetwork.com/aircraftturninfocalc.html

It's going to take about 30 seconds to fly a 360 steep turn at
100kts. My wake _should_ descend about 150' during that time (300
fpm). I can't imagine a C172 wake being tall enough to stay in my
way unless something else is ocurring (me descending, or the wake
staying up).

Would love to hear a decent explanation. Kev


I am certainly no expert on the subject, but I think most of the data on
wake turbulence comes from studies held at or very near the ground.
Certainly not all, because I recall an old FAA film on landing in wake
turbulence using a 182 to fly into the wake at altitude. But IIRC it was
part of an awareness film on wake turbulence on approach, just demonstrated
at altitude for safe demonstration of its actual effects.

Based on the numbers I recall, they did indeed teach that the wake from a
landing heavy would NORMALLY travel both down and away from the aircraft a 5
kts or so. But they were also quick to mention that a simple 5 kt or so
crosswind componet could leave the vortex in the middle of the runway for
quite some time.

The problem with trying to use this information at altitude is that you
don't have the ground to help stablize the vertical movement of the vortex.
And every pilot knows the air at altitude is very seldom static, especailly
in warm weather. As someone else mentioned, the vortex that started as a
very small column at the wing tip, can grow very large by the time you
complete a 360 turn at even 60 degrees of bank.

The point is, you are dealing with far to many variables to expect absolute
answers your question or even your own in flight results. Wake turbulence is
really only a problem at altitude if you don't avoid the flight path of
heaver aircraft, and understanding it's presence on take off and landing,
because it is much easier to intercept their flight path around runways.