US Patent 10173787 Rotor speed indication systems for rotorcraft

A rotor speed indication system configured to communicate a rotor speed operating range for a twin engine rotorcraft having a rotor during one engine inoperable conditions. The rotor speed indication system includes a governing reference indicator located on a display and configured to communicate an upper operating range threshold. A droop reference indicator located on the display and configured to communicate a lower operating range threshold. A sensor configured to measure a current rotor speed of the rotor. A dynamic rotor speed indicator located on the display and configured to communicate the current rotor speed of the rotor such that when the dynamic rotor speed indicator is positioned between the governing reference indicator and the droop reference indicator on the display, the current rotor speed of the rotor is within the rotor speed operating range.