Peter Scholz wrote:
Don Johnstone wrote:
...
If you were to say that measuring the tension at the glider release and
using telemetry to pass this information to the winch then that might
indeed work, however if you were going to the trouble of doing that you
might as well send useful information, like the airspeed of the
glider, so
the winch driver could maintain a constant speed.
Cable tension during a winch launch has sod all to do with anything
except
as an indicator to the winch driver of possible over or underspeed. It is
the speed which is of relevance and importance.


We have recently tested the Launch Assistent that is sold by Skylaunch,
http://www.skylaunchuk.com/index.htm
and have found that is can be (as the name indicates) an *assistant* to
the winch driver to help him/her judge the speed of the plane. It helps
escpecially unexperienced winch drivers, or in adverse conditions like
shearing winds within the launch.

After 20 years of experience as a winch driver and winch instructor
(Tost winch) I still believe a well instructed and experienced winch
driver (and all winch drivers should have a certain minimum of launches
per year) is able to judge and control the launch as good (or even
better) than any automated (tension-controlled) system, that in the end
also relies on the correct behavior of the pilot instead of the winch
driver.

--
Peter Scholz
ASW 24 JEB

There has been some interesting scientific research beeing done on this
topic by the Akaflieg group of the University of Karlsruhe (Germany)
some years ago. It would go to far describing it in detail, but one
diagram where they measured a winch launch is quite interesting:

http://www.akaflieg.uni-karlsruhe.de...%20Schlepp.pdf

The parameters measured we
Height (blue)
Airspeed (magenta)
Torque at winch drum axle (dark blue)
elevator position (green)
Acceleration in x-direction (brown)
Acceleration in z-direction (yellow)

It shows that what appears to be a relative smooth winch launch, looking
at airspeed and height, has a quite significant variation in torque,
elevator position and acceleration.

The findings of this sientific work in one simple sentence: A simple
"constant tension" cannot cope with all the parameters that influence a
winch launch and that are dependent on eacht other.

So the (also economically) best approach would be to aid the winch
driver doing his job right instead of inventing a highly sophisticated
fuzzy logic system that may take into account all parameters to act as
well as a winch driver.

The goal is not to have winch launches that are all perfect and one as
optimal as the other, but the goal has to be to have safe winch launches
with an acceptable performance. And safety lies within a quite large
corridor.

--
Peter Scholz
ASW 24 JEB