About Pete's post:
Mostly for the benefit of our fixed wing friends, (Hi Chris!
)
I recall from being trained in five different models of helicopter (all military) that the first step if one loses power (single or twin) is "control Nr" which means do just that. Whatever you are doing, keep the Nr in the desired range. (Also true if you lose a single engine on a twin). Collective pitch and cyclic both have influence on that, depending on your mode of flight.
Fly it first.
Whatever the criticisms of Pete's post, if one is in cruise then one is probably at a speed higher than best range, or best RoD, autorotational airspeed, so a part of the transition from cruise when the drive quits would (generally) be controlling Nr (reducing pitch on the blades to stop Nr decay) and some aft cyclic to slow down to your desired speed range. The aft cyclic will load the rotor head a bit, which that tends to make Nr go up, or at least preserve it.
TC's point about choosing an airspeed that gives you better range may be better understood in that light.
HC makes a point that I had forgotten about, and I am glad he raised it.
If you floor the collective without moving the cyclic, everything flies up to the roof as the g falls below zero. Zero or negative g means no significant autorotational effect and the Nr plummets whilst IAS increase
While various aircraft may have subtly different responses, his point about "don't unload the head if you lose the engines" is a basic helicopter flying matter that our fixed wing brethren may not instinctually have a feel for. (For that matter, unloading the head in a Huey raises the prospect of mast bumping .. but that's going off topic)
The feature in rotor blade / rotary wing design that makes for good autorotative characteristics from air flow up and through the rotor system are on a loaded airfoil, which is "biting" the air, be that airflow be "from top down through the rotor head" in powered flight, or "bottom up" in autorotational descent.
The points of technique, sweet spots, and the varying autorotation cases for a helicopter with high inertia or low inertia heads would (I believe) be covered in the type training so that pilots flying that model know what the machine is likely to do if things go wrong with the power plant.
Chris:
1. Cyclic back and pitch down, simultaneously or in that order.
In cruise, as others have noted, one would typically lead with lowering the collective and then aft cyclic, but in a stick and rudder sense, those two inputs would probably go together and be closer to "simultaneous" than not. A previous poster pointed out "control attitude!" which goes hand in hand with the two inputs going together.
"Control Nr, fly the bird."
I'll defer to the current instructors here on what they teach.
There are multiple cases for when and how one enters an auto, as you can see from some of the previous posts, "control Nr" and fly the bird will have some subtle differences depending on the case you encounter.
Does he mean "pitch-down" in the sense of the a/c attitude, or is he referring to the collective lever?
As I read it, he's referring to pitch on the blades, which is controlled by the collective.
(BTW, not planning on trying to fly a heli any time soon!)
Chris, if you like flying, you'll love flying a helicopter. All of my friends who flew fixed wing and got to try flying a helicopter loved it. It's stick and rudder flying.
If you get the chance, take it. You won't regret it.
For G0ULI:
You are missing a real treat. Take your rotary wing friends up on their offer the soonest chance you get. You'll enjoy the flying.
(That last encouragement was an unpaid political announcement on behalf of rotary wing pilots everywhere!
)
G0ULI:
It would seem from the answers in this forum and information elsewhere that something such as a vortex ring formation could in theory put a helicopter in such an attitude that the engines would stop from fuel starvation
no, that's not what's been said.
and in that event, the pilot would have very little time to recover the aircraft.
Well, if you lose the engines and enter VRS, you are in deep sheep dip.
It might be more accurate to summarize some of the discussion as "if the Nr decays below a certain amount, and you stall the rotary wings / main rotor blades, you are truly screwed." That is a risk of happening after you lose the engine drive to the rotor system, not before.
The issue of VRS in powered flight is a different problem of losing lift on the rotating wings while under power, which won't cause you to lose the engine but can cause you to fall / plummet to earth rather than to land as gently as you had intended.
I'll let TC explain VRS to you, as he's passionate on that topic. (See the recent crash near Shetland which lost four lives, long thread on that in this sub forum.
A discussion about VRS and IVRS begins here. )
I never knew that the main rotor rpm had to be constrained to within such tight limits or fully appreciated that a full main rotor stall would be unrecoverable irrespective of altitude.
I hadn't grasped the full gravity of stalling the head in unpowered flight before henra brought it up a few pages back, so don't feel bad. I flew helicopters for a number of years and was more concerned about retreating blade stall than Nr low enough to stall the air foils. You learn something new every day.
This may add some weight to the basics at the top of my post for our FW brethren: The prime directive is .. control Nr, fly the aircraft.