What RPM range should be maintained to establish a cruise airspeed of 90 KIAS?

To maintain a cruise airspeed of 90 KIAS (Knots Indicated Airspeed), the appropriate RPM range must provide sufficient power while ensuring that the aircraft operates efficiently at that speed.

The RPM range of 2100-2300 is optimal for achieving this cruise speed in many light aircraft configurations. This range typically allows the engine to produce the necessary thrust while keeping fuel consumption reasonable and ensuring that the aircraft is operating within its power band.

Operating within this RPM range also helps to maintain engine performance and prevent excessive wear, contributing to the overall safety and operational effectiveness of the flight. Additionally, this RPM setting aids in maintaining better controllability and stability during cruise, which is important for both performance and safety.

In contrast, the other ranges provided are either too low or too high, which could result in inadequate thrust or introduce unnecessary drag or engine strain. Maintaining the engine RPM within the specified range not only ensures that the aircraft can effectively sustain cruise airspeed, it also optimizes performance and fuel efficiency, making it the correct answer for achieving 90 KIAS.