@@KylesAviationChannel me too ! My first travel in a helicopter was is a bell 47 what a beautiful machine with his piston engine ! (Franklin or lycoming)
Thanks for sharing a great video of a classic Heli ! I am sure that there is a simple explanation but I would be grateful if you could explain why the throttle RPM remains within the green range and matches the Rotor needle but the Rotor RPM needle sits below the green range of the inner ring markings on the dial . This almost suggests that the main rotor blades are over pitched but this would normally drag the engine RPM down?
Been a good many years since I instructed in a Bell 47 but the Rotor RPM is in sync with the engine thru the transmission by way of a sprag clutch that allows the rotor to freewheel in the event of a sudden stoppage of either component to provide autorotative capability. That RPM is critical for Deceleration and stop on touchdown. I am guessing that Green arc is the safety arc. If you'll notice they check the clutch to be sure the needles split on run up.