Why is low rotor RPM dangerous?

Low rotor RPM is dangerous primarily because it leads to a condition where increased drag requires additional power to maintain rotor speed. When the rotor RPM drops too low, the efficiency of the rotor system decreases, and the rotor blades can encounter increased drag. This sensation of drag is exacerbated during maneuvers or when the helicopter is in motion, and if the pilot does not apply sufficient power to compensate for this drag, the rotor speed can continue to decrease.

This scenario can quickly lead to a situation where the rotor system is unable to generate enough lift to sustain flight. As rotor RPM decreases, there is not only a risk of falling below the minimum operating limits but also a potential for the helicopter to enter a state of controlled flight into terrain. Pilots must monitor rotor RPM closely and follow proper procedures to prevent it from dropping too low, especially during critical phases such as takeoff and landing.

Understanding this aspect of rotor dynamics is crucial for maintaining safe flight operations, emphasizing the importance of power management and responsiveness to changes in flight conditions.