In ground mode, the idle setting is approximately how many percent N1?

In ground mode, the idle setting for many turbofan engines is typically around 60-70% N1. This value reflects the engine's operational parameters while on the ground, where the engine needs to maintain enough thrust to support various operations, such as taxiing and staying stable on the runway. The percentage of N1 represents the rotational speed of the engine's fan relative to its maximum capability.

The reason that 60-70% is the most appropriate range relates to the behavior of the engine under different power settings. At idle, the engine does not require the full thrust needed for takeoff, and operating in this range allows for sufficient thrust without overspeeding or causing undue wear on the engine components. The other options extend the range too far upwards, which may indicate higher N1 values than necessary for ground operations. Therefore, 60-70% is the balance that ensures operational safety and efficiency in ground mode.