Bruce wrote:

Derek Copeland wrote:
Well it definitely happened. Maybe the little lightweight Oly was more
affected by the lift than the Pawnee. The point is that once you get high
on a belly hook aerotow, you may get to a point of no return. I should
also mention that this was the only occasion when this has happened to me,
despite the fact that most of my gliders have been belly hook only.

Derek Copeland

At 13:44 10 September 2009, sisu1a wrote:
I once *almost* caused a tug upset flying an Olympia 463, also only
fitted
with a belly hook. Aerotowing towards the ridge at Talgarth, the
glider
was suddenly pushed up by either thermal or ridge lift. The glider
continued to go up relative to the tug even though by now I had the
stick
hard forward against the stop. This was after the accidents mentioned
below, so I realised what was happening and released immediately. As
it
happened, the piece of knotted twine that Talgarth used as a weak link
at
the time also broke at the same moment, so we lost a pair of Tost
rings.
If found, please return to the club!
How does that work, was the towplane not in the same thermal or ridge
lift?

-Paul

Glider has completely different response to vertical air mass movement.
The tug has much higher inertia compared to the glider and wing loading
is also much lower - that's why they thermal better than Pawnees.
Consequently when transiting thermals and down drafts the tug moves, but
typically less than a lightly loaded vintage - high wing loading glass
is less affected.

The tug also leaves the thermal before the glider.

I forgot to mention that in my upset event, the pitch down was so
rapid that the whole contents of the luggage space behind the rear
seat of the PA18 was dumped on my head. Sundry spare ropes etc.