A little add-on note regarding NASA winglets: Experiments were conducted to determine the best angle for winglets - straight up and down, or some angle other than 90 degrees. The best angle was STRAIGHT OUT, in line with the wing. In other words, a little more wingspan works better to reduce induced drag than winglets can manage. I heard that Boeing considered increasing the wingspan of their 747 to reduce drag and thus save fuel, and went to winglets simply because the additional wingspan would cause space problems at the ramp.