Flight Instructor for Rotorcraft Category Helicopter Rating › XI. Emergency Operations › Task G. Low Rotor Revolutions Per Minute (RPM) Recognition and Recovery

HI.XI.G.K6

Knowledge

Difference between low rotor rpm and blade stall.

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Get a short, cited explanation of this element written from the FAA handbooks: the core idea, the numbers that matter, common test traps, and a quick self-check.

From the FAA library

Helicopter Flying Handbook p. 11-10
Chapter 11: Helicopter Emergencies and Hazards › Retreating Blade Stall
some point as the forward speed increases, the low blade speed on the retreating blade, and its high AOA cause a stall and loss of lift. Retreating blade stall is a factor in limiting a helicopter’s never-exceed speed ... development can be felt by a low frequency vibration, pitching up of the nose, and a roll in the direction of the retreating blade. High weight, low rotor rpm, high density altitude, turbulence and/or steep, abrupt turns are all conducive…
Helicopter Flying Handbook p. 11-16
Chapter 11: Helicopter Emergencies and Hazards › Low Rotor RPM and Rotor Stall
Other causes of a power-on low rotor rpm condition include the pilot rolling the throttle the wrong way in helicopters not equipped with a governor or a governor failure in helicopters so equipped. As the rpm decreases, the amount ... horsepower the engine can produce also decreases. Engine horsepower is directly proportional to its rpm, so a 10 percent loss in rpm due to overpitching, or one of the other scenarios above, will result in a 10 percent loss…
Helicopter Flying Handbook p. 11-15
Chapter 11: Helicopter Emergencies and Hazards › Low-G Conditions and Mast Bumping
Recover from a low-G situation by first gently applying aft cyclic to restore normal G before attempting to correct any roll. If turbulence is expected or encountered, reduce power and use a slower than normal cruise speed. Turbulence (where ... high rotor flapping angles are already present), and higher airspeeds (where the controls are more sensitive) both increase susceptibility to low-G conditions. • Use a flight simulator to learn to recognize and experience low G conditions that result in mast…
Helicopter Flying Handbook p. 4-11
Chapter 4: Helicopter Components, Sections, and Systems › Transmission System › Dual Tachometers
Main Rotor Transmission The primary purpose of the main rotor transmission is to reduce engine output rpm to optimum rotor rpm. This reduction is different for the various helicopters. As an example, suppose the engine rpm of a specific helicopter ... rotor speed of 450 rpm would require a 6:1 reduction. A 9:1 reduction would mean the rotor would turn at 300 rpm. Dual Tachometers Most helicopters use a dual-needle tachometer or a vertical scale instrument to show…