Final answer:
Maximum ground effect occurs at heights up to about 100 percent of the main rotor's diameter, which enhances lift and reduces power requirements during a hover close to the ground.
Step-by-step explanation:
Maximum ground effect occurs during a hover at heights of up to approximately 100 percent of the main rotor's diameter. Ground effect is a phenomenon that happens close to the ground, where the lift is enhanced and the power required for hovering is reduced due to the interference of the airflow patterns near the ground. For instance, if the helicopter has a main rotor diameter of 10 meters, the maximum ground effect can be utilized when the helicopter is hovering up to about 10 meters above the ground. Various factors such as wind, temperature, and the surface over which the helicopter is hovering can affect the exact altitude at which maximum ground effect is observed. However, as a general rule, pilots expect the ground effect to be significant up to a height equal to the rotor's diameter.