Originally Posted by
tdracer
If you measured the rate of descent of a chopper with a fixed rotor, you'd find it initially would descend slower than one performing an auto-rotation maneuver. With a fixed rotor and a vertical descent, the air will be hitting the rotor blade nearly perpendicular - making the rotor basically just a big flat plate to the air (the drag coefficient of a flat plate perpendicular to the airflow is nearly 1.0 - which is roughly the same as a parachute. In short fixed rotor blades become a huge drag source during a vertical descent. In contrast, the blade pitch during an auto-rotation is controlled to specifically prevent it from stalling - using the resultant rotational lift component to accelerate the rotors to a high speed so that the kinetic energy an be used to create lift and slow the descent in the last second before impact. There is some induced drag associated with creating the lift that provides the rotational acceleration, but it's much less than the drag created by a fully stalled rotor blade.
No. There is so much wrong with that paragraph that I am led to the conclusion you have virtually no understanding of rotary wing principles of flight. Debunking the misconceptions contained is worth a thread in itself so I will just debunk the first line: as soon as there is a rate of descent airflow, even with the blade at zero pitch, combined with with the rotational airflow from any reasonable Nr, the relative airflow will result in the blade producing lift (aka rotor thrust in rotary parlance). The total rotor thrust of the disc will be orders of magnitude higher than any 'drag' from non-rotating blades subject to the rate of descent airflow only. There is absolutely no way that a helo will descend slower with the blades stationary, neither initially nor in a steady state auto.