What are flaps used for?

Flaps are high-lift devices mounted on the wings of an aircraft, and their primary purpose is to increase both lift and drag at slower speeds, particularly during critical phases of flight like takeoff and landing. When flaps are deployed, they modify the airfoil shape of the wing, allowing for a greater angle of attack without stalling. This enhanced lift allows an aircraft to fly safely at lower speeds, a crucial requirement when it is either departing from or approaching an airport.

Additionally, the increased drag that flaps generate helps to reduce the aircraft's speed as it descends and approaches the runway. This combination of increased lift and drag ensures that the aircraft can take off and land within shorter distances, making flaps an essential feature for safe and efficient operations during these phases.

The other options do not align with the primary function of flaps. While engine efficiency and speed are related to other design aspects of an aircraft, flaps specifically address lift and drag related to the wing's performance at slower speeds. Decreasing the weight of an aircraft involves different design considerations and materials, while the enhancement of speed in flight usually relies on other aerodynamic features and engine performance rather than the deployment of flaps.