What is the primary purpose of winglets on an aircraft?

The primary purpose of winglets on an aircraft is to decrease induced drag and control wingtip vortices. When an aircraft is in flight, the airflow over the wings creates a difference in pressure between the upper and lower surfaces, resulting in the formation of vortices at the wingtips. These wingtip vortices create additional drag known as induced drag, which reduces aerodynamic efficiency.

Winglets are designed to extend upward at the tips of the wings to minimize the strength of these vortices. By altering the airflow patterns, winglets effectively reduce the induced drag experienced by the aircraft. This reduction in drag not only enhances fuel efficiency but also improves overall lift-to-drag ratios, allowing the aircraft to operate more effectively.

The other options do not accurately capture the primary role of winglets. While increasing overall wingspan could theoretically reduce induced drag, winglets specifically target the vortices created at wingtips rather than simply lengthening the wings. Winglets do not enhance engine performance or improve cabin airflow; their main function is aerodynamic efficiency related to drag reduction.