Which condition affects the rotor system's workload the most during a flight?

The condition that affects the rotor system's workload the most during a flight is high gross weight. When a helicopter is operating at a higher gross weight, the rotor system has to generate additional lift to overcome this increased weight. This requires more power from the engines and demands greater performance from the rotor blades. As the gross weight increases, the rotor blades need to work harder to maintain altitude and control, affecting fuel efficiency and overall flight performance.

While other factors like strong lateral winds or low humidity can impact flight dynamics and performance, their effects are not as directly related to the rotor system's workload in the same fundamental way that an increase in gross weight is. High gross weight directly increases the mechanical and aerodynamic demands placed on the rotor system, which is why it is the most significant factor in this context.