On Friday, March 11, 2016 at 6:31:54 PM UTC-8, C2 wrote:
I asked Dr.
Mark Maugham about how much slip angle the winglets on my discus would tolerate before they stall. This was his response.

"In our flight tests, it wasn't possible to stall the winglet at any sideslips we could generate. There is a misconception that a winglet behaves as a vertical tail, but in reality, it operates in a "bubble" of induced velocities generated by the wing. So, when the glider is at some yaw angle, the flowfield around the winglet does not "experience" nearly as much."

I hope this helps.

Unless I missed something here, all of you misinterpreted the argument Johnson was making. Basically, he stated (I was there when he said it) that the geometry of a coordinated sailplane in a turn placed the yaw string slightly ahead of the airflow passing over the wings. Thus the yaw string would be displaced slightly to the outside of the turn (again, assuming the sailplane is in coordinated flight). At no time did he advocate flying uncoordinated in a turn.

I worked out the geometry involved and found that this displacement would be less than the width of the yaw string. I told Dick so, but he could be pretty stubborn at times :-)

Tom