(Ian Johnston) wrote in message . com...

In my experience, yes, but only during the initial rotation, and it
only happens at a reasonable speed. In the climb it's fine. And a very
gentle initial acceleration avoids the earlier problems, mostly.

Sorry to follow up to myself but ...

The reson, I think, is that the Pirat has quite a high-set wing and a
belly hook as low as it can get. As a result, the lever arm, and
therefore upwards pitching moment from the winch cable about the wing
is relatively high compared to the typical glass glider with mid-set
wing and belly hook offset and up a bit. So with a good fast winch
launch, yes, this moment can overcome anything the elevator is trying
to do.

However, this is an intrinsically stable situation. As the cable angle
relative to the glider's longitudinal axis increases, the lever arm
reduces (by approximately 50% when the glider is 30 degree nose up and
the cable is 30 degrees down). So as the glider pitches up the effect
of the cable reduces, the effect of the elevator (all other things
being equal) stays the same and a point of equilibrium is reached. To
put it simply:

Nose down: winch pulls it up again.

Nose up: elevator pushes it down again

That, I think, is why a good winch launch - "it's like going up on
rails" is so easy and comfortable: the glider is much more stable in
pitch than it is in free flight. I'd expect this to be more marked as
the hook-wing distance increases.

I know, by the way, that I have omitted things like the effect of the
changing AoA on the lift and drag (secondary effects in this case, I
think) and the slingshot effect of a short rope and the relatively low
tow forces behind a tug.

Ian