In this video, Nick discusses Induced Drag.
Why winglets work in the first place is because of induced drag. Induced drag is one term of the drag equation. I’ll explain it to you here. “CD,” is your drag, and that is comprised of your form drag “CDo,” plus induced drug “CDi.” There are other forms of drag, but these are the two main terms. Induced drag is CL squared, over π, multiplied by “e,” times “A,” the aspect ratio. The higher “A,” the aspect ratio: the lower “CDi,” the induced drag. At high altitudes, when “CDo” and “CDi” are pretty close to the same - that’s when your best endurance is. So: the higher the aspect ratio, lower induced drag.