What is the most common example of effective translational lift?

Effective translational lift refers to the increase in lift that a rotorcraft experiences when it transitions from a hover to forward flight. This phenomenon occurs because, in forward motion, the rotor system encounters more relative airflow, which enhances the efficiency of the rotor blades.

In the context of the provided options, performing a running takeoff is a prime example of effective translational lift. In this scenario, the helicopter begins moving forward while still gaining lift, utilizing translational lift to assist in becoming airborne. As the rotor blades move through clean, undisturbed air above the helicopter, the increased airflow over the blades enhances lift more efficiently than in a stationary hover.

The other options, while they may involve aspects of flight, do not exemplify effective translational lift as directly as a running takeoff. For instance, flying in a straight line under heavy load doesn't emphasize the transition into forward flight and the benefits of increased airflow. Achieving lift in ground effect pertains to the effect when close to the ground but doesn't necessarily highlight the benefits seen in translational lift when moving forward. Hovering indefinitely, on the other hand, relies on the helicopter being stationary and does not take advantage of the benefits that come with forward motion and increased rotor efficiency.