Blended winglets
One to ponder over morning coffee!
Whereas we hear that blended winglets on Boeings improve fuel efficiency by 2% to 5%, by reducing induced drag [Di] (although one can argue that a similar increase in AR would do the same), has anyone come up with a formula to translate Di into thrust/HP and thereby factor the 2% to 5% fuel saving [claimed] into a mathematical solution for varying alphas and air densities?