Winglet aerodynamic question.

[Squawk7777]

I am mulling over the statement that a winglet adds a small lift force that angles forwards the direction of flight. I found a good explanation on wikipedia:

The exact upward angle (called cant) of the winglet, and its inward angle (or toe) is critical for correct performance, and is determined for each aircraft application. The vortex which rotates around from below the wing strikes the angled surface of the winglet, generating a small lift force that angles forwards relative to the direction of flight - thus the energy in the vortex contributes to thrust rather than drag as it normally would. This is analogous to a sailing boat sailing very close to the wind. This small contribution can be very worthwhile on long-distance flights.

I am still not entirely getting it. Does somebody have a good vector diagram how a winglet adds the small lift force in a forward direction or how this can be compared with a sailing boat sailing close to the wind?

Thanks,

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[Mad (Flt) Scientist]

A previous discussion

Looks like the link which had the diagram is dead, though

[Squawk7777]

Thanks Mad (Flt) Scientist . If anyone stumbles over that diagram, would you mind sending me a pm?



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[Mad (Flt) Scientist]

here's a quite badly drawn version of the diagram!



typically winglets have a combination of toe-out, cant and twist to optimise the local AoA for the winglet airfoil to optimise their local L/D

[john_tullamarine]

.. is that so functionally different to autorotative forces in a helo ? .. with which we have been familiar for a long time.