NR HI mode is used during hover flight, single engine operations, and other demanding low speed maneuvers as it provides a greater margin for NR droop as well as which benefit?

• A. Increased Engine Performance
• B. Increased Tail Rotor Authority
• C. Increased Torque Margin
• D. Significantly Greater Lift Capability

Answer: (B)

NR HI mode keeps the rotor speed more stable and provides a larger margin before rotor RPM droop occurs. In hover, single-engine, and other demanding low-speed maneuvers, the anti-torque (tail rotor) capacity depends on how much engine power remains available after meeting the main rotor demand. When rotor speed is allowed to droop, the engine tends to devote more power to sustaining the main rotor, leaving less for the tail rotor and reducing yaw control. By maintaining a higher rotor speed and reducing droop, NR HI mode preserves more engine power for the tail rotor, increasing its thrust capability and overall yaw authority. This is the most direct benefit in those slow, precise flight regimes. The other options don’t directly reflect the practical advantage of NR HI mode in these situations: it doesn’t inherently boost engine performance or lift, and the primary, tangible improvement is the increased tail rotor authority.