Ted Wagner wrote:
yaw string straight.

We've had this discussion on RAS before. I'm still
gonna say that yaw string straight doesn't prevent a spin
entry. Spins are when you're stalled and one wing is more
stalled than the other.

One wing is more stalled than the other if one wing
has less AOA/more airspeed than the other. With the yawstring
straight, this is still true in a steep bank, especially
with long wings. It's also true if you're in a slip and
then with a punchy foot coarsely correct it to
center.

The steeper the bank, the higher the stall speed AND
the greater the difference in wing speeds, even with a straight
yaw string.

When I teach rope breaks, I do them at 300 ft and 30-45
degrees of bank, and best L/D for that bank angle.
http://www.stolaf.edu/people/hansonr/soaring/spd2fly/
is a start. I also caution against super rapid roll rates
and coarse use of rudder.

I'm open to thoughts on this. I didn't do the math to
see how MUCH the factor affects spins (somebody else did and
came up with 3 degrees diff or so for 50 deg and 18m wings),
but it sure surprised me.

Now when I do spins in the L-13, I do them from string centered
flight, and sure enough it always spins in the direction of the
steep bank, and in a hurry too...

P.S. Of course this assumes the rigging is right. If
flaps are lower on one side than the other, hey man, there's
yet another factor...
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Mark Boyd
Avenal, California, USA