Shy wrote: "The problem with trying to maintain a level attitude in a rapidly rotating helicopter for more than a very brief period is (as SND wrote from personal experience) that cyclic inputs may not have the expected effect, even if the pilot was able to overcome the visual confusion caused by the rotation. "
In my first hand experience of two tail rotor events; one was a fenestron "stall" incident on a Gazelle where we probably span in excess of 15 revolutions before I got the yaw stopped. The other was a slipping tail rotor drive belt on an Exec where the onset of yaw was quite gentle but the rate of yaw built up until the world was a blur.
Is was lucky on both occasion because the wind was calm and had no difficulty keeping either aircraft level. However, had there been much of a breeze, the outcomes of both events would almost certainly have been very different.
JJ