Why do some aircraft have upturned wing tips?
Normally the reason for winglets is to reduce induced drag (caused by vortices or whirling air mass over the outer wing). Reduce the drag you, increase spanwise lift. In most cases (it depends on the winglet type) the induced drag is reduced by increasing the vertical height of the lifting system (wing). With more vertical height more lift is created at the wingtips, reducing drag and making the wing more efficient. More efficiency…less thrust required, less thrust…more fuel savings. You mention the F4 Phantom II. Its upswept outer wing was to counteract severe unstable “dihedral” (upward angle of a wing) and lateral control problems at supersonic speeds. At twice the speed of sound you want a very stable airplane. The original wing had no dihedral at all. The horizontal tail of the F4 has “anhedral” (downward angle). Fuel savings wise the F4 was a fuel burning hog. The upsweep didn’t help its fuel efficiency. But when you’re in a go-fast machine like that shootin’ at stuff, who ca
