Why do older airplanes have the wing curved upward like a 787? I was just wondering one day about because the 787 uses a wing flex to reduce wing tip vortex, but back in World War 2 they didn't know about wing tip vortex, so then why would it be curved upwards?



You can see in the middle picture the wing is curved upwards. I see this on a lot of commercial airplanes too like the Boeing 737
You are confusing 2 concepts here, dihedral and winglets. What you are showing in the picture is dihedral, which is not a curvature but an angle positive from the horizontal. This angle helps improve lateral (roll) stability in flight. This is nothing new, almost all commercial jets have dihedral. Winglets improve efficiency. A Boeing 787 has both.