Nyal Williams wrote:

I notice from the back seat in a left turn that the yaw string for the
front cockpit is slightly more to the right than the one in the back; I
believe this to be because the front one is farther from the center of
lift -- or the tangent of the turning radius.


I suspect not. Assuming the following: 1. on a 2 seater, the front yaw
string is about 6 ft (2m) ahead of the center of lift. 2. According to
the American Soaring handbook, a 45 degree banked turn at 60 mph (52
kts) has a radius of 240 feet (73m).

High school level geometry and trigonometry (I've been out of high
school for a looong time :-) ) shows that this results in an error of
only 1.4 degrees - small enough to be ignored for all practical purposes.

I suspect that a yaw string, typically taped to the canopy, may have
errors because the string is in the boundary layer.

Tony V.