On Sun, 07 Feb 2016 14:09:35 -0800, ucanemailmoi 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.

Doesn't this follow from the fact that the yaw string is a fair distance
in front of the wing?

Think about it: if the tipwise axis of the wing is exactly aligned with
the radius of the turn, which it should be for maximum climb efficiency,
the yaw string should also be at right angles to the turn radius but,
being a good 2m/6ft or thereabouts in front of the wing, the turn radius
it is on is angled forward of the turn radius the wing is on, which
therefore makes it point out slightly out. This looks like a slight slip
to the pilot.

Draw this situation on a piece of paper, but exaggerate the situation by
drawing the circle diameter and about twice the wingspan and you'll see
what I described.

If you redraw the diagram with correctly scaled turn radius and wingspan,
the angular difference between the wing radius line and the yaw string
radius line will be very small, but this needs to be adjusted because the
curved shape of the canopy will amplify the angle of yaw string in a
slip. Now Dick Johnson's advice makes perfect sense.

Practically, if the yaw string is central or pointing slightly out in a
thermal you're doing it right. If its pointing a long way out or to the
inside of the turn you're sideslipping while turning and this is hurting
your climb rate by generating excessive drag.


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martin@ | Martin Gregorie
gregorie. | Essex, UK
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