SAFE Winch Launching

At 18:15 20 July 2009, bildan wrote:

Constant tension during the climb phase is exactly what you want.
Read George Moore's article in this month's Soaring Magazine. Tension
telemetry is a great idea - someone please build it.

A kite string or a winch rope forms a catenary arc due to it's weight
and air drag. The tension on each end of a catenary arc is the same
except for the rope/string weight difference if the ends are at
different heights. If 2000 feet of Plasma rope were hanging
vertically the tension due to its weight is zero at the bottom and
only 20 pounds at the top - that difference doesn't matter much.


I think we have established two facts, firstly that you have absolutely no
first hand knowledge of the operation of a Skylaunch winch so I think your
opinions on that subject can be safely ignored. I have driven many types
of winch, for many hours, including the Skylaunch and I know that it works
extremely well with none of the "faults" that you imagine it has. It is
not the best winch I have ever driven but it is very close and the MVG is
not an affordable option for most UK clubs. The MVG is also too
complicated for use at most clubs, too many advance features.

Now consider the following case. A glider at the top of the launch, the
cable is exerting a force on the release hook of x pounds which you deem
to be tension. This force is due almost entirely to the weight of the
steel cable and is considerable. At the winch end the cable is being
retrieved very slowly or not at all, the measurable tension at that end is
close to or maybe even equal to 0. The force exerted at either end of the
cable is totally different, that is the extreme case of course but, as a
glider climbs the "tension" or force exerted on the release will
increase as the glider takes more of the weight of the cable. Please
explain how this increase can be measured or taken into account at the
winch end.

Please do not evade the question by discussing plastic rope.

All the winches I have ever driven or observed have had something which
takes care of the changing circumstances very well, we call that something
a driver and a skilled driver does not need gizzmos to give a good launch.
I am fast coming to the conclusion that the real problem here is that you
are actually afraid of winch launching and if that is the case, don't do
it.