At 23:52 15 July 2009, bildan wrote:

A misconception seems to be that a tension controlled winch goes
instantly from 0 to 100% tension at the beginning of the takeoff
roll. In fact, tension ramps up smoothly and only becomes constant
during the main climb. That's why it's called a "tension controlled
winch" rather than a constant tension winch.

The steady tension make it far easier for the pilot to maintain good
airspeed control. There is much less effect from thermals and gusts.
It's a quieter, smoother easier launch. Because the "area under the
curve" is greater with constant tension in the main climb, more net
energy gets transferred to the glider than in the case of varying
tension so launches are higher with no increase in maximum climb
angle.

How can you possibly know that without measuring the "tension" at the
release hook. You certainly cannot measure the increased tension caused by
a thermal at the winch as the inertia of the steel cable is the main cause
of the increase in tension experienced at the release hook. This
"tension spike" cannot be measured at the winch. From a point at which
the cable is at 45 degrees to the ground the "tension" imparted to the
glider, through the cable release, is increasingly provided by the weight
of the cable, and therefore measuring tension at the winch has no meaning
whatsoever, in fact the tension there should be almost 0.

Tension through the ground roll and rotation phase follows essentially
the same profile as with an excellent conventional winch launch.
There are limits set to preclude too rapid acceleration and the
tension cannot reach the weak link or rope breaking levels. The
automation make one launch pretty much like the next with little
variation due to the winch operator.

You may get good results by serendipidy but you certainly won't get them
through control of tension. What you are measuring at the winch bears
absolutely no direct relationship to what is experienced at the glider
end, and that is what counts.
With a good qualified winch driver you get consistent launches, sounds to
me you are worrying far too much about not being able to train your winch
drivers properly, and given some of the theories expounded that is perhaps
understandable.
What you are trying to achieve in a complicated way we solve by using
robust equipment and trained winch drivers who do understand what they are
doing.

By the way, tension control is nothing new. I recall an article in
Sailplane and Gliding from the 1960's on the subject. Soaring
Magazine had an article on an auto tow system using a tensiometer made
from a hydraulic master cylinder and a pressure gauge from about the
same time. Many of today's hang glider winches and auto tow systems
use tension control.