Which flight control electromechanical trim system utilizes movement of the actual primary control surface?

The aileron trim system is the correct answer because it directly interacts with the primary control surface of the ailerons to maintain level flight or assist in turning without the need for constant input from the pilot. This system functions by adjusting the position of the ailerons, allowing for fine-tuning of roll stability and reducing pilot workload, especially during long flights or when dealing with crosswinds.

Each of the other options—rudder, elevator, and wing spoilers—does not utilize the movement of their respective primary control surfaces in the same manner. The rudder trim typically provides a secondary input to assist with yaw control but does not move the rudder continuously for control as an aileron trim system does. The elevator trim system assists with pitch, but similar to the rudder, it operates independently of the actual control surface for small adjustments. Wing spoilers primarily function to disrupt airflow and assist in roll control but do not serve as primary flight surfaces for maintaining level flight or turning. Therefore, the aileron trim system's reliance on direct control surface movement distinguishes it from the other systems listed.