To summarise lets take the simplistic R22 Beta model.
Empty weight say 861lbs.(FROM MY pfm)
Minimum allowable Gross weight to drive the rotor system is 920 lbs.
Think for one second, when will the aircraft enter the EOL phase says inventor Frank. Right the aircraft is full of oil, with a pilot and a dumb ass pilot at that who has used all of the fuel, so calculate as follows;
empty weight plus minimum allowable pilot weight with doors off, 135lbs. = 996lbs.
Min AUW for safe EOL is 920lbs, hey presto we are safe.
Mother nature, that's good ol gravity, will therefore turn the rotors fast enough to have a happy downward flight and successful termination.
Franks' engineers will have also provided that at the minimum ROD that is possible, as long as the aircraft is not overloaded. At this point we say 'Thank you Frank'
.
I have only said thank you Frank three times, although that may have been mixed with blasphemy about his bloody drive belts or upper bearings, but there are many times I have said Thank you to Arthur. He was a top dude.
Now when checking auto RRPM always have the collective
on the bottom,
it says so in the book but no one has said it here yet.
You will find that there will be a straight line variation pretty much between
- RRPM at minimum Power off RRPM limit (90%) at that minimum weight, and
- RRPM at top of RRPM limit power off (110%) at max AUW. You can look at the Maintenance Manual chart or work it out on the back of an envelope.
The engineer will adjust as necessary.
What no one else has said here so far is that by following the book as above you will be blessed with the full collective lever available to apply at the bottom to slow things down, isn't that great?
Because if you were a damm fool or a know it all and had the auto RRPM set too high for a reason known only to yourself you would have the collective some ways up at high weight to maintain it in the green, or at a low weight you might have had it right down with RRPM right up at the top of the green.
In each event you will have given yourself a higher ROD than necessary and certainly a lot less collective to pull at the bottom.
Dumb eh?
I could put my final edit in here and say that the higher the ROD that you have the more collectiove you will need and also the harder it will be to learn the basics. REAL, REAL DUMB EH?
Besides every thing else that is said here and I will argue with anyone, high ROD regardless of the RRPM at the time, is what kills, maims and hurts, work and study at getting it low.
That is not to say that during EOL flight you may occasionally encounter slightly high RRPM, turning for example especially towards the gyroscopic precession direction, or during a tight flare. Trees a bit close you know, that sort of thing.
No, as others have said don't worry about that too much but report it each time to the engineers. I had the dubious luxury of owning an aircraft once (R22) that had the spindle bearings replaced after 300 hours of instruction including autos. They were close to failing be jeeesus, so don't do it if it can be avoided the MM book knows best.
That's pretty much it.
But I will finish with a quote from a previous and famous Chief Pilot of ours from many moons ago, who sent a scathing Teletype message to a renowned and famous Bell pilot based in Cairns many years ago after being real p**ssed off with the auto RRPM set up on a machine that he tested upon delivery to us.
The message? "it would have real good RRPM upon impact". Go figure.
Learn the basics from the book and worry about the complexities later.
cheers tet