Autorotation technique.
 

Can anyone here direct me to material that clearly states the importance of moving cyclic back in an autorotation entry.I seem to recall somewhere a document/book that mentions that the cyclic needs to move back ,in case of an engine failure,to "restore Rrpm".Can't find it.
Seems to me,over the years, this aspect of autorotation training and technique has been lost in transalation.There are references to "adjust cyclic to attain Vy " and so on and so forth,but no publication really highlights the fact that a raising of the attitude (i.e a mini flare, if you will) helps restore the Rrpm and will increase your chances of a successful auto.There is a lot of emphasis on collective lowering and rightly so. However,IMHO, the cyclic moving back is critical too.But that is not emphasized nearly as much by OEMs,training manuals and even the FAA handbook.
Any assistance in this would be appreciated.
Alt3.

Does this help?

As the advancing blade passes over the tailboom, it gets faster and produces more lift, which means that it climbs.

Because of the V2 part of the lift formula, the lift produced is way more than that of the retreating blade, and its maximum relative airspeed (and therefore lift) is gained at the front of the disc, because the climb starts 90° after it starts to increase its relative speed, and its maximum lift point is 90° after that, which is a shift of 180° overall. Thus there is a 90° difference between maximum flapping velocity (abeam) and displacement (at the front).

As well, there is more induced flow at the rear of the disc which increases the difference between the front and rear angles of attack (less at the rear)
.
Note: This is why the nose lifts when you apply collective pitch, or drops when you reduce it, so if the engine fails and you don’t apply rear cyclic to correct this tendency, you could get into an unrecoverable situation. The moral: don’t take your hand off the cyclic!

I know Shawn Coyle has his Little Red Book of Autorotations out now - perhaps he can help.

Phil

Thanks, Phil,
I am completely clear on the reasons for pulling back on the cyclic. I am just looking for some authoritative publishing on the subject.While the currrent crop of pilots might understand the need to lower collective and also bringing the cyclic back to counteract the tuck, I am not sure there is much understanding on how the action actually causes Rrpm to increase back into the green.That needs more emphasis and hence, more published material sayin that.That is what I am looking for.
I hope Shawn chimes in.
Alt3

Check out this thread also: http://www.pprune.org/rotorheads/435074-eols.html

I think it would be quite difficult for any publication to emphasise bringing the cyclic back on entry into autorotation because it depends very much on the airspeed at which the engine fails and rotor inertia. The amount and rate at which the cyclic is moved has to be judged by the pilot at that moment of entry.

TM

Also, by loading the disc the centre of gravity is moved inboard as the conning angle increases. This restores / increases the RRPM.

That's in Wagtendonk and just about every other book, shirley?

Increased rotor RPM because:

Collective is lowered as you try not to climb

Coriolis effect - increased TRT causes coning angles to increase and the C of G of all blades to move inwards

Increased load factor

The lift vector being more forward (because the RAF is shifted downwards) produces an autorotative force and reduces drag

Phil

Lowering collective prevents further Nr decay - flaring and/or rolling into a turn loads the disc and helps recover lost rpm. In an ideal world lower the lever and flare.

But, as hihover says, moving the cyclic aft if you are only at 30 kts will just take you further away from your normal autorotation speed and reduce the likelihood of you making a safe EOL.

Thanks, wont bother in future.

DFD - I see my answer ended up just after yours - I was responding to alouette3's post in case you think I was repeating what you said.

If you're below 30 kts you want a slight check back if you are going to attempt a vertical engine off.

Phil

it would be worth trying to get hold of Mr Sanfords quote which I can't recite as I heard it second hand, but I believe he was quoted saying that at cruise speed and collective pitch the R22 rpm has been demonstrated to remain within limitations following engine throttle-close for up to 7 seconds using solely aft-cyclic. Not a method I suggest teaching :} but it illustrates the benefit of using aft-cyclic on entry...

Edit - I still find this very hard to believe and if this is vastly misguided information I apologise and would like to be corrected as I didn't hear it first hand and wouldn't like to spread rumour (or try it :eek:)...

I'm becoming more convinced that regardless of the situation, the first thing should be to move the cyclic aft (at the same time as lowering the collective).
The few scenarios where this is not the best thing to do are pretty small - I can think of only a few - like at 40 knots or slower and less than 100 feet above the ground; (please feel free to add to the list).
Nearly anywhere else, it's a very good thing to do. There are way too many examples of helicopters hitting the ground with little or no rotor RPM, because the pilot tried to get airspeed but had no rotor RPM for control.
Remember that real engine failures have a huge element of surprise about them - way different than practice ones.

Ain't that the truth!

Early 80's southbound of out of the fomer RAF airfield Hethel in Norfolk flying at 900ft agl when the donkey quit in a Bell 206. First manifestation was that the aircraft yawed, then the sound of the donk winding-down, then the caution pips.

What I witnessed is that in a real-life scenario dumping the collective occurs with a reactionary efficiency which I believe is driven by the knowledge that this, ultimately, is what will preserve rrpm.

A 'stick back' initial response may well be a positive refinement to entering an auto but .. I do wonder whether drivers will give this precedence over dumping the lever in an actual emergency not least of all because, depending on the degree of aft cyclic, it may interfere with one's field of view and, in a single when the donkey's resting and you're still airborne, identifying where you will alight is something you feel with an impressive keenness.

Vertical EOL in a Robinson........no thanks:)

Better to pull the cyclic back than to shove it forward which reduces Nr and, on Robbie type helos, can lead to mast bumping or tail strike if combined with a rapid lowering of the lever.

Surely most crashes due to low Nr are due to the poor inertia characteristics of certain rotor systems and a lack of practise in PFLs - if you don't lower the lever you will never recover the Nr.

Sorry I cant see how any student cannot pull the cylic back after dumping the lever. In the types i teach on 300/500 if you dont pull the cylic back as the lever goes down you will be at about 40 degrees pitch down within a couple of seconds. So cant see how anyone can teach not to bring the cylic back, let alone a student not realising the ac is in an apparent vertical descent. Most low rrpm crashes I suspect are from people flaring way too high and pulling the lever up way to early. Most single engine machines ( unless 206 and R44) need to be flared at under 50 ft with a hard flare nice check and level followed by a cushion on to the ground

There was very good article written by a Pete Gilles in the Heli Ops mag a few years ago called Cyclic Back.
In the article he looked at 2 500 crashes where they both had engine failures in the climb out from Take off, so both where low and at high power settings.
He basically states that the only hope they had was to go aft on the cyclic.
He also states that when they do check rides at there company they put as much emphasis on pulling the cyclic back as they do on lowering the collective, if i knew how to post it on here i would, its well worth the read.
I agree with the cyclic back theory, especially in the hover such as longlineing etc, fwd cyclic will only lower the RRPM and the little bit of A/S that you build up will be of no use. It will also compound the nose dropping.
Someone tell me if i have got it wrong but in my opinion aft cyclic will help conserve RRPM and if you hit the ground going backwards a bit no big deal in fact better if over trees and as long as it hits the real estate skids/wheels first thats the main thing with hopefully a little bit more RRPM to cushion the impact than one would have had if he had gone fwd with the cyclic.

Assuming you get the lever down in time, I can't see ANY reason NOT to pull cyclic back other than wanting to go faster, because that's what she'll do if you do absolutely nothing with cyclic on entering auto:confused:

The topic raised by Alt3 here is the merit of advising pilots to pull back into a 'mini flare' when entering auto as distinct from merely applying enough aft cyclic to maintain the desired attitude/airspeed.

Certainly, I was taught the importance of maintaining Nr AND the effect of loading the disc.

I agree with hihover:

..and as Savoia points out:

I don't really see any merit in flaring the aircraft 'for the sake of restoring Rrpm' unless you've identified that Nr is low. In that case I would say fine get it back as a matter of priority by trading off some speed if necessary.

You've got my vote Oggers.

Sincerely speaking, in a real life scenario with a single, once you've implemented rrpm preservation (which is pretty much an instantaneous response), the only thing one is concerned with is identifying a suitable touchdown spot and lining-up for it.

In craft such as the Angry Bumble Bee (H500) rrpm would build rapidly and most D or F models I have flown would overspeed at the drop of a hat if one didn't re-introduce pitch on the way down.

I guess it depends on the make and model. In Recurrent Training at PHI when I was there, they taught a technique in which the *first* response to the engine-out was to come back on the cyclic. In an auto-entry from cruise airspeed in a 206, if you merely lower the lever without coming back on the cyclic the helicopter will immediately enter a descent. And if you're only at 500 feet to begin with, you've really screwed yourself if you subsequently have to turn into the wind. There's a lot of energy available as you decelerate from 120 mph to 60. Might as well not waste it.

Wot crab said.

It is all about loading the disc.

FH1100 in a 500 if cruising at 120 kts and you shut the throttle you darent bottom the lever as you will have the haed off the machine. I teach people to put the lever down about 2/3 and maintain quite a lot of progressive rear cylic maintaining until you get airspeed to 80 or 60 kts depending on what range you are after. You can then lower the lever gently to the bottom with more rear cylic as you get to 60 kts. This technique will give you an initial rate of descent of 500fpm for about 10 seconds rising up to 2000 ft a min at 60 kts lever fully down. From 1000 ft in 15 kts of wind you will get nearly a km range

Great discussion. Thank you all for the valuable inputs.A fine instructor once told me that the successful autorotation is determined by what you do at the entry to an auto.I am afraid that today in training, the emphasis on reflexive actions,to include aft cyclic, is just not there. The venerable AP3456, in it's extract for helicopter aerodynamics,talks about this and that was what I was taught as a baby pilot.In casual discussions with some of the younger blokes around me, I find the mindset is to lower collective and then look for a good spot to put the aircraft down.Blank stares when I ask how you would restore Rrpm in case it has edged into the lower part of the yellow arc.When I further explain what I am trying to get at then there is the shrug of the shoulders and the "Of course, the nose will pitch down and I will automatically bring the cyclic back" reponse.All answers are within the ball park.But, IMHO, not quite there.I am just hoping that someone someday does not run out of altitude,airspeed and a good idea(aerodynamics) at the same time,because the book did not at least add a note in passing.
Please keep the discussion going.
Alt3.

I suspect if you ever tucked a 269 you'd be hard pressed to do anything but draw the cyclic back instinctively as you dumped the collective.

alouette3:In a helicopter which does not cruise significantly faster than it autos (Bell 47 comes to mind), it's probably okay while dumping the lever to just maintain the current pitch attitude - which would probably be an instinctive response. "Did I input any aft cyclic? Uhh, I...guess so. The nose didn't drop so I must have."

But there's more to it than that.

In a helicopter that cruises substantially faster than it autos (e.g. Bell 206), lowering the collective lever while maintaining the same cruise flight pitch attitude WILL result in a descent, no question about it. If you're up at high altitude when this occurs, no big deal. But if you're down where helicopters fly, like at 500' agl or so it can be a very big deal.

So it's not merely a matter of making some automatic aft cyclic input to maintain attitude. The technique must be to consciously and deliberately raise the nose, get the disk up as you transition from powered flight to autorotative. And I think this technique is lost on a lot of pilots. Either that or they've never been taught it. I certainly had not until I'd been a professional pilot for a number of years.

It's not just a matter of maintaining pitch attitude.

FH1100:
Well put - the aim must be to have air flowing up through the disk. That's the thing that we should be emphasizing.

In addition to the reasons given by FH1100 and some others here for using aft cyclic, it would seem to me that another reason to do so in a helo that cruises faster than it autos (B407: 140kt cruise, ~70kt auto) is to trade airspeed for altitude (not to only maintain altitude), especially if low. Of course, all of this will depend on specific circumstances.

Some very simplistic answers to a complex issue - briefly and sorry about sucking eggs - practice autorotations are not merely a flying exercise but an essential tool to save your life in the event of an engine failure.
At the hover - freeze lever, counter drift/yaw - cushion landing,
air taxi - freeze lever - counter drift/yaw - cushion landing,
air transit say 50 feet/30 kts - lower lever - counter drift/yaw - flare how much depends on height/airspeed - level - cushion landing,
transition to forward flight - lower lever - flare as required depending on height/airspeed - counter drift/yaw - level - cushion landing,
in climb - lower lever - counter drift/yaw - flare as required depending on height/airspeed - cushion landing,
cruise - lower lever - maintain attitude/airspeed even lower nose to gain best range airspeed (where was that forced landing area I saw a moment ago?) - from point of engine failure to the forced landing area is the most important and generally least practiced part of autorotative/engine failure practice,
in descent - lower lever - counter drift/yaw - airspeed range? - forced landing area?,
on finals - lower lever - counter drift/yaw - maintain attitude/airspeed - flare dependent on height/ROD/airspeed - cushion landing.
Bear in mind the helicopter rotor system takes about 1000 feet of descent to aerodynamically establish autorotation.
You will not necessarily get an engine failure at the best time - I know a pilot who had an engine failure due to the addition of lead - he forced landed backwards into the LZ he had just departed from.
GAGS
E86

Pardon a question from a low timer but why anything like 1000feet?

Won't an autorotative region of the blade be providing some force just as soon as the underside of the disk of the rotor is presented to the airflow. Ie within a few seconds after pulling aft cyclic to get say from 10degs nose down disk in forward powered flight to 10deg nose up disk while slowing to best auto speed.

Oow

outofwhack:
Precisely!
It doesn't take 1,000' to re-establish autorotation. If it did, the HV curve would be a damn sight (dam site???) larger for every helicopter.

I am going to be shouted down over this.

Flying single-engined helicopters in Borneo in the sixties the choice of landing sites was somewhat limited if the engine packed it in. To reduce the percentage chance of arriving in 200 ft. high trees one went for the range autorotation. Should the engine stop than the Rrpm was allowed to decay to just above minimum controllable and the airspeed kept at the cruise. When (or if) you found a suitable landing area you flared at the appropriate time and took your chances with the undergrowth.

Otherwise you flared at the appropriate time and took your chances with the trees.

No Fareastdriver, I don't think anybody would shout you down for that; it was what worked for you guys in that environment and terrain. Plus, in the 1960's you guys probably were flying helicopters that weren't all that fast in the first place (S-58's?)

But as for this discussion, I think we're all operating under some general assumptions. First, I think we're talking about "plain vanilla" engine failures where it just stops with no warning and/or drama. I think we're talking about "normal" flying at between 300' and 1,000' agl over terrain which affords at least some decent forced-landing areas.

Higher than that and it really doesn't matter how you enter the auto as long as you do. Lower than 300' and it probably doesn't matter what you do as long as you put the pitch down, because you're most likely going to land/crash straight ahead regardless of the wind. (And if you're down below 300 feet you by God better be into the wind or have a damn good reason why not.)

"outofwhack" brings up an interesting point. If you're toodling along in your LongRanger in cruise with, say a 3 degree nose down cabin attitude (i.e. 8 degree nose-down disk), you will have to make a nose attitude change of 17 degrees to get the disk up ten degrees to the relative wind. That's a lot of pitch attitude change!

Which is why I sort of respectfully disagree with Eagle86 who, when talking about an engine failure in cruise says:Yeah well...maybe in a 47 or something. In cruise in a 206 you're already going faster than best-range-auto speed. And again, if you're down around 300-500 feet, you definitely don't want to descend any more, at least not until you've got a good landing site picked out, bearing in mind that it may be behind you and you have to turn around to find it again (assuming you remember flying over one a second or so ago).

I think that if the engine ever quits "for real" most pilots including myself will take a bit of time to recognize and react to it. During those few, hopefully brief seconds, the aircraft will have already started a descent. As you gather your wits and put the levers/pedals in the right places, you surely want to stop that descent to give yourself some time to start looking for a place to land.

Which is why "aft cyclic first" seems to me the proper technique in the event of an engine failure at any speed above 60.

I think Eagle 86's ancient fingers trembled a bit on the keyboard and he punched an extra 0 onto 100'.

Poor old bugga.:8

I meant 1000 feet for all the aerodynamics to line up - most helos stabilise a ROD in auto of about 1800 feet/min and this takes around 1000 feet for this stability to be achieved. Rest assured you are not in auto should an engine failure occur inside the HV envelope.
GAGS
E86
PS If I had a dollar for every practice auto/PFL I carried out up to the age of forty I could have retired long ago!

Just to clarify further in order to keep AC back in his box - can't remember what his autos were like but do remember his nav was cr@p - I am talking about an abrupt total loss of power or an absolutely unannounced practice by the QHI. The first thing that is going to happen is a WTF - RRPM will drop out of the bottom of the green - a couple of hundred feet will be lost while the pilot computes and gets the lever down - ROD will be in the order of 3000 ft/min at this stage. While ever RRPM are below the optimum ROD will remain high. Only when RRPM/IAS/balance etc are all stabilised will the helo be in a stable auto at around something like a loss of 1000 ft.
GAGS
E86
PS Try any fancy rear cyclic movement in any of Bell's underslung teetering heads with low rotor RPM and you stand a good chance of separating that rotor head.

Another thing to throw into the mix - a fixed wing in a fully developed spin is in autorotation - after the stall and subsequent prospin control inputs a considerable amount of height is lost until stable autorotation is established.
GAGS
E86

E86

What rubbish you speak, have you ever had the donkey stop ? Can assure you that it does not involve a height loss of 1000 ft If that was the case I wouldnt be here. If you had stuck with your 300 ft I would say yes thats about right. Regularly do throttle chops from 500 ft downwind to full touchdown with students, whom quite often are not expecting it. Yes you have to be quick to get the aircraft round into wind ( loose 300 ft in a 300 from 70kts to a 50 kt auto). Granted the reaction time to it happening for real is a bit quicker, but as I said at the start when it happened to me the lever was punched down without me having to think about it.

I will go with Hughes500 on this. My first engine failure was on a Whirlwind 10 (turbine powered S55) on my second solo on type 300ft downwind. I had the lever on the floor and was turning into wind whilst I was going through the fire drill. Everything worked out fine and I arrived, somewhat surprised, just over a line of trees and just short of some power lines. I had yet again been blessed, as before and subsequently, with an aircraft with a very high instinct of self preservation.

Fortunately from 1971 and to my retirement I could always rely on one of the two decibel levers in the roof.

I would like to see a source for this 1000ft hypothesis.

I used always say 300'. but an auto always has three components if you start early enough.
autorotational flight;- that's the same from 5,000' or 300',
termination area;- that's from when the first flare happens, a rule of thumb can be about one foot of altitude per every knot of airspeed and,
touchdown;- that's the same as a hovering auto or close enough.

In an R22, one can easily find that a nice tidy autorotational flight profile of at least 50 knots can be set up say at about 150' depending on DA, after a snap throttle closure from the hover at 300', well before the termination area with 2 up and 50 litres of fuel at least.

same in a '47.