How is rotor pitch best managed in helicopter autorotation? In a recent stack exchange question writers were comparing autorotation to an aircraft engine out rotation prop when something rather startling occured to me:

In an engine out the airflow will continue to rotate the prop on the same direction as with power.  When helicopter loses power, WRT to rotor, it falls "backwards", creating force AGAINST the powered direction of rotation.

The thought is to go negative pitch and allow the rotor to build up angular momentum in the same direction as powered rotation, then switch to positive pitch to use that energy to flare and land.

Is this how it is done?
No, that is not how it is done: minimal collective blade pitch is not negative. The procedure is to lower collective immediately to the full down stop to minimise blade drag, upon which the helicopter will start to descend. The air upflow tilts the local lift vector forwards. Indeed, just like in a glider.

The bit that is not intuitively clear for fixed wingers is the reference frame of the airflow, which is the local blade velocity.

The inner bit of the rotor blade has a lower rotational speed than the tip. The up flow has a relatively larger influence on the lift vector tilt here, and  upflow through the rotor drives the inner part of the rotor blade forward, while the outer part still experiences decelerating torques. From Leishman: