How did Hargrave's vertical curtains improve the cellular kite design?

Lawrence Hargrave’s addition of vertical curtains between the wings was a pivotal innovation that transformed the cellular kite into the highly stable and efficient structure now known as the box kite.1

While the concept of multiplane wings existed previously, Hargrave was the first to successfully build and fly a design incorporating these vertical surfaces. This configuration provided significant structural advantages:1

• Increased Stability: The vertical curtains acted as stabilizing elements, helping the kite maintain its orientation in the air.12
• High Efficiency: The design proved exceptionally efficient at generating lift, allowing the kites to carry relatively heavy weights, such as meteorological instruments, to high altitudes.1
• Structural Foundation: By creating a rigid, stable cellular truss, Hargrave’s design became a critical precursor to the development of biplane aircraft structures, influencing pioneers like the Wright brothers and Alexander Graham Bell.12