Lots of good ideas, but some of the dynamics of a tug upset has been
missed. Chris Rollings mentioned the loads in the rope rapidly increasing
from c50lbs to over 700lbs as the glider assumes a winch launch attitude.
This load on the tug will RAPIDLY slow it down, thus losing flying speed.
So not only does the glider climb, the tug descends with rapidly falling
airspeed, and the elevator becoming ineffective. As the ug loses speed it
will pitch nose down anyway.

Chris also mentioned a very strong deceleration, and I can vouch for this
when a K6E kited behind me on a tow at Aboyne. The K6 pilot missed the
release toggle due to wearing gloves, and had already started his climbing
turn. He realised his mistake and releassed the rope, by which time I was
steeply nose down with little airspeed, albeit at 4000 feet! I was
effectively a passenger during the upset, but interestingly did not lose
sight of the glider in the tug mirror, showing the tail was NOT pulled up.
I have always been very wary of tugging gliders on belly hooks since!

Terry Slater

At 13:16 21 February 2014, kirk.stant wrote:
On Thursday, February 20, 2014 1:31:56 PM UTC-7, Martin Gregorie wrote:

Back to some sort of bridle from the wingtips so any pulling vector
is

through the CG (or close).



I'm sure that would work well in the air, but isn't there a potential

problem during the landing roll-out? With no tension on the tow rope it


seems to me that you've got a U-shaped loop of rope dragging on the

ground behind the tow plane which would provide considerable drag on a

grass field if it isn't recently mown. Would this also be a problem at

the start of the take-off roll?

Well, you could make the bridle in two pieces that connect at the
release,
and come apart when the glider is released; you would now have a long
towrope trailing one wingtip and a short one trailing the other.

Starting to get more complicated, of course...

Kirk