Originally Posted by
TruBlu351
A wing with infinite length has ZERO spanwise flow as there is no pressure differential along its span. No vortices are then created and therefore no drag as a result of the vorticies. So you are right, a longer wingspan, or ASPECT RATIO, is good.
However, the longer the wingspan, the more bending (fatigue) it creates at the wing root where it connect so the fueselage (longer moment arm). With more bending comes the requirement of more strength and it's associated weight penalty with a beefed up airframe, which cancels out the original bennefit.
Also, a bigger wingspan has issues when getting into the passenger terminal area for parking.
So winglets do increase the SPAN of the wing but just in a vertical direction, the result is the same. Less spanwise flow, less wingroot bending and the weaker vorticies are actually moved up and away from the main airflow over the wing.
Most books/texts don't tend to actually explain HOW the vorticies increase drag - which is nice to know (INDUCED drag from lift).
Does it mean that instead of adding winglets to a wing, you could retrofit an existing wing by sawing off some of the wing and installing a winglet instead? The wing, having shortened wingspan and less wing root bending moment, would still provide as much or more lift?