split needle

split needle

The indication on a helicopter tachometer that shows the rotor-clutch is not fully engaged. When the engine is started and the rotor is coming up to speed, the engine RPM needle is higher than the rotor RPM needle. When the engine is throttled back, and the rotor freewheels, the rotor needle is higher than the engine needle. In either case, the needles are said to be split. See also married needles.