On Sunday, February 7, 2016 at 5:09:42 PM UTC-5, wrote:
I know this is a silly question, but I was reading an article by Dick Johnson that talked about holding a slight slip while thermally. This article was written before winglets and I was wondering if the same idea applied to gliders with winglets. Also, as for slipping to lose altitude for landing in a glider with winglets, does this place a lot of side load on the winglets. Should you not slip in landing with winglets?

Sorry for the questions, but would appreciate any help in this.
Karl is more forthright, than I was going to be!
When I installed homebuilt winglets ( Maugner airfoil) on my 20E,
I set them at the recommended -ve angle to the horizontal axis
of 3 deg from the zero lift setting. Upon tufting these winglets,
it was quickly apparent that keeping them both unstalled was
almost impossible ( Note , the flow at the wingtip is not
along the axis) I added 2 deg extra negative AoI and the problem
became manageable, but I still now pay a lot more attention to
slip ( or not).

Slipping turns ( without winglets) are useful.
Years ago, flying a rented Libelle std I found climbing against the
Std Cirrus discouraging. After ballasting to aft CG and circling
with a fair amount of slip, I could climb with the best Cirrus
drivers. But they left me on the glide!

John firth; an old no longer bold pilot.