On Jul 20, 11:28*am, brian whatcott wrote:
Don Johnstone wrote:
At 11:50 20 July 2009, brian whatcott wrote:
Don Johnstone wrote:
... *a "tension controlled" winch is about the craziest idea I have
ever
heard, not least because, thankfully, it would never work.
Why not?

Brian W

Because there is no direct relationship between the tension experienced at
the winch and that experienced at the glider release using wire rope.
Even with plastic rope the relationship is tenuous at best, the rope does
have some mass and in addition has an elastic quality as well. The
tensions experienced at each end of the cable can be vastly different and
are different more often than they are equal, so measuring at the winch
end tells you very little about what is happening at the glider, it may
indicate what has happened but even this is not likely to be very
accurate.

That sounds like an interesting reply: in a comparable situation, a kite
can only carry so much line aloft, and the tension at the kite is
certainly at a different angle to that oseen by the kite flyer.

These days, a wireless sensor could be provided to measure and relay the
tension at the sailplane - but I think I am hearing that a constant
tension is not in fact wanted???

Brian W

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.