bildan
July 20th 09, 05:25 PM
On Jul 20, 8:15*am, 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.
Lets see, you pull on a rope but the force is "vastly different" at
each end? I can hear millions of teenage science students laughing at
that.
The weight of steel cable does have an effect but not it's
elasticity. Plasma rope has neither a lot of weight nor elasticity.
The tension at the winch and glider are the same to several
significant digits.
> 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.
Lets see, you pull on a rope but the force is "vastly different" at
each end? I can hear millions of teenage science students laughing at
that.
The weight of steel cable does have an effect but not it's
elasticity. Plasma rope has neither a lot of weight nor elasticity.
The tension at the winch and glider are the same to several
significant digits.