At the field you may have heard helicopter guys talking about “Autos”, and seen some of the guys practising them. Autorotation is what the full size machines do if they have an engine out or other mechanical failure, and it is a major part of the pilot’s licence. A critical skill to have when flying a helicopter with a glide ration of almost 1 to 1. You get one shot it at!!
In model helicopters it is exactly the same principle. The guys you see practicing these are doing so not only to improve their skills, but also making sure that they can do an auto if something goes wrong. I have saved my heli a few times by auto-ing down, as have others.
The full size information on the technique can be found here
And for model helicopters have a look here
A great video of a full size can be viewed here