On Sunday, December 13, 2015 at 6:29:14 PM UTC+3, Martin Gregorie wrote:
As to "Auto rotate" in "conventional choppers, you need height and/or
forward speed for it to work (as far as I know), if your're hovering
low, you're sorta "along for the ride" straight down. :-0

I don't know enough about choppers to comment. I'd be interested to see
what anybody who flies them has to say about this: there must be some
inertia in those blades.

They vary.

The common and cheap R22 has very little rotor inertia. If you're hovering higher than maybe five feet then you're going to have a hard landing if the engine stops. Unless you're above 400 ft, in which case you can dive to 55-ish knots, level off, and do a nice flare. If you're doing at least 55 knots then you're ok from any height. It only takes maybe 30 knots to make 200 ft safe.

Other choppers with heavier rotor systems can be ok from below 20 or 30 ft zero speed, or above 300 ft, or maybe even less.

Things such as the Huey or Enstrom can be cut to zero throttle on the ground, picked up and hover-taxi'd a few meters (or turned around 180º) and set back down softly, all on rotor inertia.

I even once saw John "Prickles" de Ridder lift off a Hughes 300 and move it from one side of a fence to the other (turning 180º at the same time) after he'd chopped the throttle.