NR and N2 in Autorotation
I have been working on B206 for about 10 years, the governing range does not start till 70% and has absolutly no effect below that. You will not get a noticeable split in the needles in autorotation because the 'free turbine' is no longer loaded and the idle gas flow will keep the N2 at roughly the same sped as NR. The gas turbine engine is a very simple beast so never compare it with how a piston engine and clutch works. Piston engines mechanically drive the gearbox through the clutch. Turbine engines pass air over the free turbine which then drives the gearbox through the freewheel unit. In theory you could hold the blades of a free turbine while the engine is running, impossible on a piston engine. In practice anything above ground idle and the torque is too high and something would break.
Of course the terms ' ground idle' and 'flight idle' confuse lots of people depending on your country of origin. 'Ground idle' is when the engine is running at around 62% or so, 'flight idle' is when the engine is running at max goverened rpm, it means you can commit avaition, notice I sayed 'GOVERNED' rpm. The governor is there to control engine rpm as compared to rotor rpm, so if you pull collective lever the rotor rpm drops and the governor tells the fuel control to chuck in more fuel to maintain rotor rpm.
I am not trying to teach pilots or others how to suck eggs, but some people are not taught correctly or get on the wrong track at an early stage! I am not criticising any of the previous posts but there does seem to be some bad feeling about a subject that could potentially kill people, we are all professionals be we engineers or pilots and can all take advice and accept it without abuse. Wether you are right or wrong we are here to learn and no-one is ever too old to learn, if so, it is time to retire from the industry. Happy flying one of the safest and most reliable helicopters in the WORLD!!