What are spring tabs used for?

Spring tabs are used to aid in moving a primary control surface, such as an elevator or aileron. They work by creating a force that assists the pilot in moving the control surface, reducing the amount of effort required. This is particularly beneficial in larger aircraft where control surfaces may be heavier or require more force to actuate. The spring tab is essentially a small mechanical device that provides an advantage in control surface movement without completely replacing conventional actuation mechanisms.

The other options do not accurately represent the function of spring tabs. For instance, spring tabs do not replace hydraulic actuators, nor do they directly increase aerodynamic drag or stabilize the aircraft. Their primary purpose is to assist in the movement of control surfaces, making flying more efficient and manageable for the pilot.