Chris OCallaghan wrote:
Eric,

Point of interest: did you let the spin fully develop after the
coordinated turning stall?

No, but there didn't seem to be any need to, as the inner wing dropped
and rotation began.

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.


As Mark points out, the ailerons on the Blanik are significantly
deflected with "down" aileron on the inner wing, which is part of the
reason the inner wing stalls first. They are also deflected this way on
other gliders, but perhaps not as much.

There is a significant difference in the assymetric drag profile with
and without aileron deflection. Remember that most modern aircraft
begin their stall at the root.

At least, for a straight ahead stall. I don't think this is true for
many gliders in a turn.

That means less torque and less
disposition to overpower yaw stability and enter a spin. Slapping an
aileron down to pick up the low wing adds significat drag at the tip.
Add some rudder (cross-controls), and now you have a greater
disposition to get the aircraft spinning rather than spiralling.

I'll give this a try over the weekend -- that is, making no recovery
to a coordinated turning stall to see how it develops. My Ventus spins
happily if aggrevated. It should prove a good test bed.

We await your report with interest!