Which two rotor systems are involved with the main rotor blade?

The best answer is the pitch change mechanism, as it directly affects the performance and control of the main rotor blades. The pitch change mechanism is an essential component of a helicopter’s rotor system that alters the angle of attack of the rotor blades during flight. This change in pitch allows the pilot to control lift and thrust effectively, enabling maneuverability and stability. As the pilot adjusts the collective and cyclic inputs, the pitch change mechanism responds accordingly to facilitate these changes.

The other options do not have the same direct interaction with the main rotor blades. For instance, the tail rotor assembly primarily provides anti-torque and directional control, but it is not directly involved with the main rotor blades’ functioning. Flight control surfaces are typically associated with fixed-wing aircraft and do not apply to rotor systems in the same manner. Additionally, the control rod system might be part of the overall control mechanism but does not specifically alter the rotational characteristics of the main rotor blades themselves. Thus, the pitch change mechanism's role is crucial to understanding how the main rotor blades operate in flight.