Many years ago when I was being taught to thermal,
ALL of my instructors here in the UK taught me to sense
which wing pitched up and to turn in that direction
in order to find and centre the thermal (subject to
no other glider already being established in the thermal
of course).

I would imagine that any benefit achieved by turning
against any airmass rotation in the thermal would be
greatly outweighed by turning into the thermal towards
the core in the initial turn and then sticking with
that direction (subject to the first turn being in
the correct direction).

My instructors also used to watch for any bias students
might show in their turns in order to ensure that they
are comfortably able to turn in either direction (and
therefore centre thermals as fast as possible).

I would imagine that any pilot who has a 'preferred'
turning direction (either becasue they like turning
in that direction or because they believe they will
benefit from some rotational effect) is going to be
slower to cente a thermal compared to a pilot of similar
ability who has no such preference.

Happy New Year





At 15:24 01 January 2004, Bill Daniels wrote:
KK

If there is a uniform lift distribution, and the thermal
large enough, there
would be little advantage to one direction of turn
over another. However,
if there is a small, strong core then turning against
the rotation would
reduce the turn radius and make it easier to stay in
the core. At least
that's how it seems to work for me.

Bill Daniels

'Ken Kochanski' wrote in message
. com...
Bill,

The Weatherwise article also supports the view that
thermals (if you
consider them weaker cousins of dust devils) have
equal probability of
left or right spin.

'To summarize, the Coriolis force has little bearing
on the sense of
rotation in dust devils--about half of them spin one
way and half the
other. By contrast, the large-scale rotation in the
vicinity of
tornadoes and the storms that spawn them is usually
cyclonic,
influenced by the Coriolis force.'

But, how much advantage will you get choosing the
correct thermalling
direction ? Let's assume the thermal is 500' in diameter
with a
uniform lift of 5 knots and the rotation speed at
the 250' radius is
10 MPH.

KK


'Bill Daniels' wrote in message
news:...
'Ken Kochanski' wrote in message
om...
This article from Weatherwise looks at the mechanisms
that cause spin
in storms, dust devils, etc. The thermals we fly
in typically form in
the high following a frontal passage ... the flow
in a high is
clockwise ... could it cause most thermals to have
a clockwise
rotations ?

http://www.weatherwise.org/qr/qry.02coriolistorn.html


Alas, there have been studies that have found an
almost even population
of
left and right hand rotation with, perhaps, a small
edge to the left
hand
rotation in the northern hemisphere. Coriolis effects
are more likely
to be
seen on large scales - much larger than dust devils.

On one occasion I observed a very large dust devil
over a dry lake in
California. The central thermal was rotating counter-clockwise
but
ringed
by a dozen or more dust devils rotating clockwise
in the shear layer at
the
edge of the large one - somewhat like planet gears
around a sun gear.
The
smaller dust devils were more obvious than the large
central one so a
casual
ground observer would think that the majority of
dust devils that day
were
clockwise. You had to be airborne to see the larger
pattern. It pays
to be
careful with observations.

When you can determine the direction of rotation
from airborne trash or
dust, it pays to turn against it.

Bill Daniels