Ventus C rigging

It's unlikely to be built in unless there has been
damage and a poor repair.

Are you using 17.6 extensions, these have a spring
to set a 'neutral position' is it still present on
both wings and is the neutral position the same.

Have you set up the flaps for equal displacement, eg,
does the same deflection happen from both full left
and right stick, normal check here in UK for CofA.

If you set the flaps to equal positions is the stick
still in the centre.

Its quite a complicated setup and could well have gone
adrift over the years or you might be seeing damage
or impending problems. If you have actually started
to notice it then it must be fairly dramatic by now.
Do a control movements check to see if anything is
out and work back from there.

John

PS reading between the lines, I presume that it is
only evident at neg flap positions, 86 being the change
over to -1. If so ten you need to check control movements
at all flap settings