On 14 Mar, 21:15, Derek Copeland wrote:
Most (sensible) people fly either above the tug's slipstream or below it.

That's the propellor wake. There is also a much larger region of
disturbed, but not turbulent, airflow caused by the action of the
wing. As a rough guide, there are significant effects in a cylinder
two wingspans in diameter (ie twice as wide as the wing) centred on
the tug's flight path and extending back to the point where lift
started being developed. In practice, of course, viscosity in the air
damps it out, but it will still be a significant effect at the other
end of the tow rope.

(The other end of the wing's wake is the starting vortex on the
runway. Nasty thing have happened to light aircraft which flew into a
starting vortex.)

In the first case the tug may be pulling the glider's nose down and in
the second case up. It doesn't seem to make a lot of difference to the
way the glider flies. There is a theory, mostly believed in by the good
folks of Oz, that low tow is slightly more stable.

It makes sense. In low tow, the pull of the towrope is upwards, so it
tends to pitch the glider nose up. If you sink a bit (with controls
held steady) the pitching up moment increases and the glider climbs
back to position. If you rise a bit the pitching up moment decreases
and the control forces you have been using to balance it pitch the
nose down and the glider falls back to position.

High tow is just the opposite: glider rises, pitching up moment
increases, glider rises, pitching up moment increases and so on until
either (a) the glider pilot does something about it or (b) the tug
pilot dies.

OK, it's not quite that simple, or impossible to control (clearly),
but a trimmed glider in low tow will generally be more stable than in
high tow.

I can't somehow
imagine that the downwash from the tug has that much effect on a glider on
the end of a 150ft rope!

See above. The downwash from the wing of a 757 has a considerable
effect several miles from the aircraft.

Ian