Well....Owain, thanks for that detail and for looking into this..
perhaps my understanding of the terminology is at hand.
What I noticed with winglets is a movement of the turbulent air towards the wingtip. I understood this an an increased area of laminar flow, thus less drag.
There are a few things to keep in mind when looking at winglets.
First off, the radical differences in winglet designs, the particular models of aircraft they are installed on, and the outward flap configurations of those aircraft. Noting that there is little performance difference associated with the Airbus winglet vs sharklet, and the general differences between the Boeing and Airbus configurations.
If this was simply a span factor, then wouldnt there be significant differences in the winglets performances (Airbus vs Boeing)?
Secondary, but very important, is the winglet performance differences during phases of flight. There is a marked difference when the aircraft is at the beginning of a long haul (very heavy and the highest AoA) vs the performance when the aircraft is light, with a decreased AoA.
Boeing notes that the benefit from the winglet decreases with decreased AoA, and is negated by the friction drag of the winglet itself.
Finally, I must remind you that I only deal with the measurements from aircraft on final approach. There is significant influence from landing gear, AoA, and especially flap settings/flap configuration, and atmospheric conditions at this phase of flight...
Great conversation
