Winglets are vertical extensions of wingtips that improve an aircraft's fuel efficiency and cruising range. Designed as small airfoils, winglets reduce the aerodynamic drag associated with vortices that develop at the wingtips as the airplane moves through the air.

Why do winglets reduce drag?

Winglets makes the passage of air from the bottom of the wing to the lower pressure top of the wing more difficult, thus reducing induced drag. The big manufacturers explored offering winglet retrofit kits to their customers but at the time, it wasn't economical since fuel was so cheap.

Why do 777 not have winglets?

For example, Boeing's hot-selling 777 wide-body airliner does not have winglets. According to Gregg, that's because the 777 operates from international terminals designed for larger jumbo jets. As a result, Boeing found the performance it was seeking without the need for vertical extensions. A Boeing 777.