What is the maximum glide speed for a helicopter to maintain optimal rotor RPM?

The maximum glide speed for a helicopter to maintain optimal rotor RPM is essential for ensuring effective control and performance during an autorotation or any descent. Approximately 75 KIAS (Knots Indicated Airspeed) is often cited as the optimal speed for maximizing glide distance while maintaining appropriate rotor RPM, a crucial factor in preventing an underspeed condition that can severely affect the helicopter's ability to safely land.

At this speed, the helicopter can achieve the best lift-to-drag ratio, enabling it to cover the maximum distance while in a glide. Additionally, maintaining this airspeed ensures that the rotor system remains within its operational parameters, which is critical during any engine-out scenario or emergency descent.

While the other speeds presented might seem feasible, they either exceed or fall short of this optimal threshold. If a helicopter glides at speeds significantly above or below 75 KIAS, it could lead to reduced rotor efficiency, instability, and an increased risk of uncontrolled descent, highlighting the importance of this specific glide speed. Mastery of this concept is crucial for informed decision-making during flight, especially in emergencies.