Checking that your engine and rotor needles will "split" is an important part of the pre-flight in a helicopter.
If they do not split you are not going anywhere and are calling the mechanic. The engine of the helicopter powers the rotor system which turns the rotors providing lift allowing the helicopter to take off. The rotor tachometer (top right of instrument panel) has 2 needles... one for engine RPM (E) and one for rotor RPM (R). These 2 needles are supposed to be "married" in flight as an increase in the engine RPM results in a speeding up of the rotor RPM.
|Startup - E and R needles at 0|
In pre-flight the pilot runs up the engine to check that the needles stay "married" and then "chops the power" quickly to see that they "split". This simulates a sudden loss of engine power. If the needles split this is an indication that the clutch has disengaged and the rotors are spinning freely allowing the pilot to land safely in an "autorotation".
|Needles are "split"|
And as Martha Stewart would say ..."That's a good thing". And so, I complete my first 25 hours of helicopter lessons. According to my husband 40 more to go before I am comfortable! (Or he is!!)