You know, a forward swept wing could kill off all of the induced drag simply becuase the induced flow would be going inwards instead of outwards, the vortex has NO interaction with the wing, if anything it will enhance the lift features by sucking down the back of the fuselage. You can cut the drag by up to 29%! The difficulty comes from its loading, most happens at the tips and not the roots.
With winglets, to be perfectly honest (and I will get slamed for this) I see them all as functionally the same. Their names and shapes almost don't matter to me. But some people/customers are asthetically obcessive apart from justifying the costs/weight.
From what I can tell, there are currently two different kinds, one decreases the rotation of the induced vortex itself and the other is actually a micro delta surface that spins its own vortex as it trys to produce lift and the main induced flow gets caught up in it reducing the size of the whole.
The first is either vertical or curved up and might be for allowing closer separation of large planes. The latter is usually parallel with the wing and may reduce the impact of the vortex on the plane's wing downstream, as QantasA332
stated, the " they diffuse the vortices and reduce vortex interaction with the departing airstream
I think another can be designed within the next few decades, one where it severely disturbs the rotation of a vortex, killing it's effect on anything. The only way I can think of is to mix the rotating flow in one direction with the other direction; it should cancel out. I guess this would be curved down or going in an inverted ringlet arraingment...just an idea...that I thought of a long time ago but since subsonics weren't my thing then, well...
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