Two out of three thermals (very unscientific study on my part) favor a
right turn. This is the result of the internal circulation of the
thermal. This adds yet another variable to the complexity of
thermalling. I'll leave it up to you to figure out how lift strength,
horizontal and vertical lift profile, vorticity, and turn direction
affect climb performance. Suffice to say in this short note that they
do.

There was a discussion in Soaring (maybe 15 years ago) on this
subject, with a nay sayer concluding, if thermals had spiral
circulation, you could look up and see clouds rotating. Well, I spent
an hour on my back the following weekend and found that they did, and
favored clockwise 2 to 1.

I use the right hand rule. By pointing my thumb up (lift) and curling
my fingers (as in induction fields), I can determine with about 66%
probability the direction of rotation of the thermal as a whole.

A friend of mine (no longer an active glider pilot) used to keep a
careful watch on his yaw string as he entered thermals. He felt that
you could briefly see the direction of rotation and planned his
centering turn in the same direction as its initial deflection. A
talented pilot, I took careful note, though I admit I've defaulted to
always using a right turn unless there are clear indications that I
should turn left (noticeable yaw string deflection, birds, other
gliders, visible shear beneath cloudbase, a dramatic surge up of the
right wing, etc.)

As a side note, I've found that reversing direction is a useful
technique for climbing through a shear. This may be a result of
reverasal of rotation at the top of the inversion layer, but that's
just a guess.

OC