Originally Posted by
Shackman
I personally cannot see any way a helicopter can have the rotors stop in flight or enter a tumbling descent without some parts of it falling off / being ejected / completely breaking up - but again there may be a way this could happen that someone could explain.
Once RRPM gets below a certain threshold and descent rate exceeds a certain value a fully developed blade stall will occur. In a low inertia rotor this will literally stop it in no time. (I Count everything below 50RPM as stopped). Parts falling off can't achieve nearly the same level of energy Dissipation that a fully developped stall can. Combine this with no engine power (for whatever reason) and you will have the blades completely stopped in about 5 - 10s.
In a flare after an autorotation the blades are operating in an area of drag significantly below the drag when fully stalled yet you will dissipate the energy in the rotor System within a few seconds.
So you stall the rotor and it will come to a halt very quickly. Parts breaking off or not.