The Westwind II is the upgrade from the original Westwind Jet.
https://centraljetcharter.com/westwind-2.html "WESTWIND 2 Private Jet, Information!" The ten-passenger Westwind I was produced in 1972 with a stretched fuselage. In 1980, IAI announced a second go-around, the Westwind II, with redesigned wings and the addition of winglets. The Westwind II’s winglets are its most notable improvement. Positioned atop the tiptanks (while most aircraft substitute one for the other). The usual winglet design was proven to be more effective and improved the lift-to-drag ratio. Another improvement the Westwind II has over its predecessor is what IAI refers to as its Sigma wing, a recontoured wing that holds 1.5 more fuel. This allows for a higher takeoff weight (500 additional pounds to 23,500 lbs); reaches a 2,000 feet higher initial cruise range; and increases range by five percent. Due to these modifications, the Westwind II enjoys greater operating weights and improved hot-and-high performance evidenced by the aforementioned...