What do flaps primarily increase during takeoff and landing?

Flaps are movable surfaces on an aircraft's wings that play a critical role during the phases of takeoff and landing. Their primary function is to increase both lift and drag. When deployed, flaps change the aerodynamic properties of the wing. They increase the camber, which allows the wing to produce more lift at slower speeds, making it easier for the aircraft to take off and land safely.

During takeoff, the additional lift provided by the flaps allows the aircraft to become airborne at a lower speed. Similarly, during landing, the increased drag slows the aircraft down and helps maintain a controllable descent rate. This enhanced lift and drag also allows the aircraft to maintain stable flight characteristics at slower velocities, which is essential for safe operations during these critical phases.

With regard to the other options, roll stability relates to how well the aircraft resists rolling motions, thrust refers to the forward force produced by the engines, and yaw control pertains to the aircraft's ability to rotate around its vertical axis. While these factors are important in different contexts, they are not the primary functions of flaps during takeoff and landing.