Nat,I assume you mean` in autorotation`,as opposed to `disabled`,but don`t worry; I can`t be specific,as it would depend on the aircraft weight,and altitude,and airspeed.However, as a `starter`,and guesswork it will probably be something like -, 20 kts/1200 ft/min; 60-80 kts /1000 ft/min; 100 kts/1600 ft/min;120kts /1800 ft/min.However,you may find that someone on the `Rotorheads `forum will be able to give you a much better and more accurate figures.Hope it works..