What is the main purpose of flaps on an aircraft?

The main purpose of flaps on an aircraft is to increase lift at slower airspeeds. When deployed, flaps alter the wing's shape and increase its camber, which enhances the wing's capacity to generate lift. This is particularly useful during take-off and landing phases of flight when the aircraft is operating at lower speeds. By increasing lift, flaps allow the aircraft to maintain smoother flight characteristics and control at these critical operational speeds.

While some may consider the other choices, it's important to recognize that flaps are not primarily designed to reduce drag during cruising; in fact, their deployment usually increases drag. They also do not fundamentally enhance stability during flight, as stability relates more to the aircraft design and control surfaces. Finally, while flaps can assist in facilitating steep descents, their primary role is still related to enhancing lift rather than controlling descent rates without speed gain. Thus, the function of increasing lift is essential for safe and efficient aircraft operation during low-speed flight regimes.