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UNI-Mechanics 2000
13.10 Auto-rotation
This term refers to a helicopter flying without motor power. The rotational speed of the main
rotor can be kept high by setting both blades to negative pitch, and the airflow through the rotor
as it descends then keeps the blades turning. The rotational energy stored in the rotor by this
means can be converted into upthrust when the helicopter is close to the ground, by the pilot
applying positive collective pitch. Of course, this can only be done once, and it has to be done at
the correct moment. Auto-rotation allows a model helicopter to land safely when the motor fails,
just like a full-size machine.
However, auto-rotation places considerable demands on the pilot's judgement and reflexes; you
can only halt the machine's descent once, and you must not „flare" too early or too late. Much
practice is required to get it right.
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