On 16 Apr 2007 06:37:13 -0700, "Kev" wrote:

On Apr 14, 4:27 pm, "george" wrote:
I always maintained altitude and rate of turn in steep turns with the
end result being hitting my own slipstream.

As have we all on nice days, and students like to brag about it. Yet
Mx is correct, in theory we should not be able to do this.

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,
which means that, while you might be within the +/- 100' test
scenario, you are NOT holding the same exact altitude.

Hmm. Or else it means that the wake doesn't necessarily descend as
we're taught. On a warm clear day (which is when I've hit my own
wake), I betcha that the wake is being held upward a tiny bit by the
heat from the ground.

Cheers, Kev



The big question is "why does the wake turbulence descend?"
Is the air volume inside the vortices denser than surrounding air?
Probably not. So the descent is probably not due to gravitational
force.

I am no expert on fluid dynamics and have no access to texts that
answer the question (if there are any), but figure 7-3-5 in AIM is
interesting - it shows a wake sinking at several hundred fpm
immediately after an aircraft, but than stabilizing at several hunderd
feet below the flightpath, i.e. no further sink. This might indicate
that the sink is due to wing downwash.

If that is the case, than
1. Wake turbulence in steep turns will not move just downward, but
down and out, that is: opposite lift.
2. The speed at which it moves will depend on downwash - it's speed,
intensity, strength (?) I don't know which term would be appropriate
here. Whatever it is, it might be much smaller for GA aircraft than
for large aircraft.

It would be interesting to do the following flight test:
On a nice day (meaning: perfectly still air) fly turns at different
bank angles and speeds and note when you do and don't experience the
bump at the end of the turn. Do this in different aircraft - low/high
wing, small/large/...

Does anyone know whether big aircraft experience the bump at the
conclusion of their steep 360s?

- Tom