I had all three from the very start, hour 0 my CFI "rode" them with me.
We had briefed control scenarios and for the most part if I felt I was losing the hover battle, I would call for control transfer on occasion before he would take it. sometimes he would let me wrestle with it for a moment longer, however we never got into an unsafe situation, as I never tried to make radical hard control movements.
For your research the true danger of a new student on the controls of any heli is that they will overcontrol, not knowing how sensitive the controls are, even fixed wingers transitioning.
(however a funny story, some fixed wingers make a mistake of raising or lowering the robbie cyclic grip to initiate a turn, a practice that they lose after trying it twice
)
I had enough exposure to heli's before to appreciate the dangers involved in overcontrolling that giving me all three to start was not an issue. It did take me 2-3 hours to get my hovering down (in calm winds) and to be able to manage a basic hover in any direction in a good wind was reached after about 10- 12 hours (and is still ongoing, like anything else).
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Marc
[This message has been edited by RW-1 (edited 18 March 2001).]