What is the purpose of the primary stops in a control system?

The primary stops in a control system are designed to set the range of movement of the control surface. This ensures that the control surfaces, such as ailerons, elevators, and rudders, operate within safe and effective limits. By defining the maximum and minimum deflections, stops help prevent over-rotation or under-rotation, ensuring that the aircraft maintains its intended aerodynamic characteristics during flight.

In this context, the other choices do not accurately describe the function of primary stops. While controlling fuel flow, stabilizing the aircraft, and altering aerodynamic efficiency are important aspects of aircraft performance, they are not related to the specific function of primary stops, which is to limit the travel of control surfaces for proper handling and safety.