To split, or not to split? that is the..

[advancing_blade]

Just a quickie

I have just started flying with a new instructor for some refresher training, and we are doing auto's with the thotle and govenor on (RH22), and so not splitting the needles. This is a change from all the others that I have done. The instructor is very experienced and obviously knows his stuff, but surely we aren't really autoing at all. If this is pretty standard in the UK then it's fine by me, just dont want be found lacking on the next check.

Any comments? pass your message

[ 01 March 2002: Message edited by: advancing_blade ]</p>

[Grainger]

Once you have lowered the lever fully the engine won't be supplying much power, even with the governor maintaining 100% rpm: just check the manifold pressure.

But you are right, for a proper auto, the throttle should be rolled off to split the needles. It's fairly normal these days to leave the governor on - but with the throttle closed so the engine rpm drops below 80% and the governor stops 'governing'.

In particular, you need to get a feel for controlling rotor rpm during the descent - raising the lever a little if rpm starts to increase, and flaring out to prevent rpm dropping below 100%.

Was taught this very well a few years ago by a good instructor who showed me how to 'feel' my weight through the seat as we descended. Loading the disc slightly would bring the rpm up, and unloading the disc cause the rpm to drop. Turns also load the disc and raise the rrpm, requiring a little input from the lever.

Leaving the throttle open will completely mess this up as the governor will keep intervening. And how would you do range autos (80kts, 90% rpm)?

If you ever get to practice auto all the way to the ground you'll definitely need the throttle in the detent before you raise the lever !

Finally, there is the 'fear factor'. I reckon it's quite important to get used to flying with the needles split to build your confidence and to reassure yourself that you are not going to die if the engine quits.

Plenty of carb heat for _at least_ 30 seconds before lowering the lever and there is no reason to be afraid of splitting the needles.

Discuss all this with your instructor and find out the reasons he/she prefers to do autos this way.

[ 01 March 2002: Message edited by: Grainger ]</p>

[RW-1]

Grainer's fairly spot on.

I learned to check the RPM needle with periferal vision while descending, and one can imagine it as a mini collective, if you note it rising, you may lift a little collective, if it descends, you can either lower slight collective, or if near the bottom, you could give a little aft cyclic to bring it up (as you would be about to flare anyway).

I actually asked my CFI about me practicing this way if solo, because solo students are not allowed to do autos without a CFI.

Mike's answer is that it would allow me to get the glideslope and feel of the descent, and flaring at the bottom, though I would not be controlling the RPM myself.

Personally, I'd rather start at 2-2.5K, and split in solo practice, and recover by 500Ft, that would give me time if something didn't go correctly to recover. But this fo me is more of a difference in training here in the state than anything else, liability and all that. One usually doesn't do afull down until going for CFI here.

I don't have an issue splitting the needles, having fun getting outside the bird and going by feel/sound so that I can pay more attention to where I'm descending to, etc. No need to have everyhing in the green and hit a tree ya know ...

And 180's are fun!

But why he wouldn't do splits with you is something you'll have to ask him.

[ 01 March 2002: Message edited by: RW-1 ]</p>

[Draco]

Most of it has been said. Splitting the needles concentrates the mind.

If you are going to do that on a detail, I would highly recommend a ground check to ensure that the engine does not stall itself when idling (it has been known). when you check the sprague clutch on the ground by splitting the needles, wait for the engine revs to decay completely until it stabilises at around 50% without stalling.

As an additional protection against stalling, keep the revs at 70-80% during the auto, too.

R

[advancing_blade]

Thanks all for the advice <img src="smile.gif" border="0">

[Buitenzorg]

advancig_blade,. .. .if you get the lever fully down in the auto and the needles still don't split that may be the problem and the reason why your instructor doesn't want to close the throttle. An R22 in autorotation, with two adult bods in the seats and half fuel or so, should have a rotor RPM of well over 104% (above green arc) with the lever fully down. Why? Well, imagine a smallish type flying solo, with only a few gallons left. Now he has an engine failure. How's he going to get adequate rotor RPM in the auto out of the same ship? The solution is simple, have your mechanic extend the pitch change links a turn each (IAW the maintenance manual of course).. .. .If you roll the throttle off completely (against the soft stop) you will notice how well you can tell rotor RPM by ear. You'll be able to keep your eyes outside far more, and this makes doing autos a lot easier.

[Helinut]

IMHO It ain't really an auto if you don't split the needles. One of the main points of dual auto training is to give the student a chance when the engine fails. If he has only seen a high rate descent with the governor still controlling RRPM, heaven only knows what will happen.. .. .Without the needle split all sorts of aspects of autorotation performance cannot be seen, demonstrated and practiced in dual training.. .. .Whether or not students are authorised to do solo autos - that's another question.

[Special 25]

All I can add to the good advice above, is to switch off the governor during an auto. . .. .When I was instructing, we allowed students to practice autos solo and the method was, first switch off the governor, which should have no effect other than to switch on the warning light ! Don't panic - It's not an emergency. Lower the lever slowly, roll off the throttle and enjoy the experience of autorotation with a high level of control even with the needles split.. .. .When it comes to the go around, throttle the engine progressively back up to 97ish% before switching the governor back on, to prevent a sudden surge on the engine as the governor kicks in at 80%, with accompanying yaw and general uncomfortable noises and aircraft movements ! Quick check of the T's & P's, then pull in power and go around as normal.. . . . <small>[ 07 March 2002, 07:21: Message edited by: Special 25 ]</small>

[Have a Chat]

As a matter of interest, do the pilots responding to this thread know how high the rpm goes during the flare? And if so what is the Max rpm for rotor? If you have the engine operating around 100% during the flare you are bound to exceed the rpm limits, as the governor won’t be able to hold the rpm. I would like to hear some opinions on the matter.

[Grainger]

That's right - have to add some collective during the flare to stop the rotor rpm increasing.. .. .Since the governor controls _engine_ rpm, it can't do anything to prevent a rotor overspeed - it can't slow the rotor down !

[Helinut]

I think we may be losing sight of the point of autorotation training here. It is mainly to train the student to cope with an engine failure. If you have an engine failure then you can forget the engine, the governor and any contribution from either in subsequently controlling rotor RPM, cos the engine has stopped and the governor is an engine RPM governor.. .. .It is not wise to let someone lose to do autos solo (at least initially) because there are hazards to occupants and aircraft in auto. But that is why we have instructors who are, or should be, very familiar with autos.. .. .I was doing R22 instruction when the then "new" governor was mandated. There were 2 schools of thought about how to maintain a needle split: switch off the governor or for the instructor to close the twist grip against the governor, sufficiently to overide the governor. In either case, the instructor would monitor engine RPM and normally keep it above "idle speed" but below 80% ERPM. The student got on with flying the rotor, as if the engine had failed.. .. .The RRPM at the end of the flare depends upon a number of factors, of course: the RRPM at the beginning of the flare, helicopter weight, how much you flare, entry airspeed and so on. However, if the RRPM was set in the green band before the flare, the increase would normally be contained within the upper limit.. .. .During training, where autos should be repeated many times, preservation of the whizzy bits forces instructors to ensure that the RRPM TRL is not exceeded. However, if one of my students had a real engine failure, I was not really worried if their technique did not ensure that the main rotor was not oversped during the flare. At that stage the important thing was for them to be able to walk away from the aircraft.. . . . <small>[ 07 March 2002, 09:55: Message edited by: Helinut ]</small>

[baranfin]

Admittedly I dont have much experience but if the governor is on and you are being forced to add collective at the flare to control rpm, I do not think this is the best thing to be doing. Considering in the full downs that I have performed it is necessary to reduce collective in the flare to avoid getting too high. My concern is that adding collective in the flare becoming instinct and thus causing one to come out too high when you level off. I would say governor on for intro to autos and beginning of training, but roll that throttle into the detent and flick off the governor for all other practice. imho

[the coyote]

A bit of food for thought:. .The ultimate objective in a real autorotation is to preserve Rotor RPM within acceptable limits right up until using rotor inertia to cushion the touchdown, as well as reducing an approximate 1800fpm rate of descent in the R22 to as close to zero as we can before touchdown. From a training perspective we need to simulate the real thing as much as possible. The throttle must be at idle, and stay there to the ground. A pilot must know INSTINCTIVELY that engine power is not in the equation.. .. .RRPM is directly proportional to ROD in auto, the higher the descent the higher the RRPM and vice versa. Pilots often think high RRPM is better, but that benefit is compromised by a higher ROD which we still have to lose before touchdown. Whether the aircraft is heavy or light, if the RRPM is the same the ROD will be the same all with all other things being equal.. .. .So the real key in my opinion lies in the pilots awareness and management of both RRPM and ROD. Get rid of the damn engine in training so they have no choice but to use aerodynamic resources.. .What will increase or decrease my rate of descent? What way can I increase or decrease RRPM if I need to? What effect will my actions have on RRPM and ROD (and range) in auto? These are the kind of things we all should be thinking about rather than what the engine is doing yes?. .. .By the way using collective during the flare to control a RRPM overspeed as we all know will make it float or balloon. A handy thing to have in the back of your mind if you need to clear a ditch or obstactle but maybe not ideal if you don't. Try using a small yet positive input of forward cyclic to bring the RRPM down if it gets high in the flare, the effect is almost immediate. Use coriolis effect to your advantage any way you can in auto I reckon...

[advancing_blade]

I have done a lot of autos in the past, all to power recovery, other than in the 206. My initial instructor didn't like students doing full on's because he beleived that people screw up the entry by being fixated on the ground contact, and IMHO the job is half done if you can stay ahead of the machine rather than reacting to it. All of these autos were with the govenor on, but the throtle held at idle until the flare. I really just want to get proficient at full on autos in the robbie as well as the easier 206.. .. .Thanks again for the input