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.