In article ,
(Chris OCallaghan) wrote:

Point of interest: did you let the spin fully develop after the
coordinated turning stall? There is an aerodynamic tipping point --
that is the self-righting tendency of the tail that would typically
favor a spiral over a spin assuming that the only deflected control
surface was the elevator. Of course a wing drops when in a turning
stall, but without aileron deflection generating drag my guess would
be that designed yaw stability would prevent spin development.

Even with the string in the middle, the elevator will *not* be the only
deflected control surface.

The Blanik makes this very obvious. As you slow down in a shallow turn
(10 degrees, say) you need more and more out of turn aileron in order to
prevent the turn from steepening, and you need more and more into turn
rudder to keep the string in the middle. Both controls can get a
significant way towards their limits in what seems like a perfectly
normal turn. When the inner wing eventually stalls everything is
perfectly set up for a rapid departure and spin.

-- Bruce