SPS:

Agreed, you wouldn't ever see the tail rotor in an autorotative state itself for the reasons you gave.

I have to admit though I haven't heard of friction effect on the fuse as the reason for left thrust, I always associated it with the tranny drag.
(Quoting from the basic heli manual: "The capability for tail rotors to produce thrust to the left (negative pitch angle) is necessary because, during autorotation, the drag of the transmission tends to yaw the nose to the left in the same direction that the main rotor is turning.")

Can you elaborate further?

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Marc

When the helo is in auto, there is no torque applied to the main rotor! Therefore the airframe cannot yaw in the opposite direction to the applied torque. In the event of a total tail rotor failure, (a) the tail rotor will either have gone! or (b)have stopped, TR auto doesn't exist! There is consequently no friction effect.
When selecting auto after a tail rotor drive failure the a/c will recover some of the yaw induced by the malfunction(i.e. the yaw in the opp direction to the rotation of the MR). Then, when the engine(s) is/are stopped, this corrective yaw will increase (in your favour), though probably not sufficiently to allow you to be pointing in the direction you wish to go!. At the bottom of the engine off manouevre, when you flare like ****, the corrective yaw will again increase, substantially this time as the rotors speed up and the airframe (thru friction effect) yaws in the SAME direction as the main rotors. It is this rapidly developing change in yaw that one should strive to take advantage of to offset as much yaw as possible prior to cushioning the touchdown.. In reality because of lack of experience/judgement, 99% of all helo drivers will be unable to align the a/c fore and aft, and must therefore attempt to wash off ALL fwd speed (zero spd landing)prior to touchdown. Otherwise you will cart-wheel!!

http://www.gograph.com/Images-7298/A...if/redstar.gif

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Thermal runaway.

Whirly,

I had the same concern when I got my PPL and a very good instructor showed me how much I didn't know.

The plain fact is (now I've seen it all from the other side) is that 45 hrs is barely (and often not) enough to get basic competence in most of the exercises (don't forget that bloggs may also have to learn all the other subjects from scratch at the same time)and it is almost dictated that this sort of 'extra curricla' subject remains just that. It is not in the PPL H syllabus JAR (or NZ) and there is not enough time for what is.

It is only the same as getting a basic drivers licence in many ways, no one teaches you skid recovery or similar unless you specifically ask fo it and even then they'll say 'Lets get the licence first' because they want you to succeed in that without too much blurring your focus.

Happily, more and more PPL's have a good, healthy attitude towards their flying and future training (like you have) and they
are doing what the rules don't. But let's not blame the rules either, we would complain like crazy if the PPL time where doubled (as it should be IMHO)and remember the govt, state or whatever cannot wrap us in cotton wool.

If it did we'd likely suffocate anyway!

To all PPL's I firmly recommend you go and do TR problem prcedures after gaining the licence, together with regular autos, EOL hover, etc. etc. and get to the stage where YOU have confidence in your ability.

If you want to know where you can get the best possible training for TR problems then mail me (NO financial interests in UK)

Fly safely all!

Sorry Thomas, beg to differ.

I agree that there isn't any torque applied to (or exterted on) the MR in auto. There isn't any in powered flight come to that. Torque is only applied to the fuselage in powered flight, the rotor is moved by power. Torque is a reaction to power.

When in auto friction effect does indeed make the nose yaw left and that is why we have to use far more right pedal than is required only to remove the left pedal input that was necessary to provide anti torque thrust to the right (at the tail) before power was lost.

You may prove this easily using one of those
model helis that are launched from a hand held spindle, spun up by pulling a string.
It has no TR and it will 'fly' with its fuselage yawing in the same direction as its MR blades. This is 'friction effect', a term I use as you cannot keep using the same ones. It causes unneccesary confusion (eg 'Friction torque'is a common and in MHO bad term) So, the above model has no TR but still has friction effect otherwise its fuselage would not yaw in the same direction as MR rotation.

The same is demonstrated by a model gyroscope (I still have mine and treasure it!) As it 'runs down' in rotor RPM the RPM of the outer gimbal will increase to almost parity as this happens, and it does so in sympathy with the rotor's rotation (if that's English!)

It is the same with full size helis in that friction in the drivetrain attempts to stop the MR and in so doing exerts a force upon the fuselage sympathetic to MR rotation. The desire is for them to get to equilibruim.
They will if allowed to.

So the TR has to make thrust to the RIGHT to stop this....and it is only driven by the MR through the gearbox.

Notice also that I said yest. that the TR does not enter auto 'in forward flight.'
(Just for interest). It CAN enter auto but to do it you must fly with 90 of starboard (or port) roll on and then descend almost vertically to get an upward incoming airflow going through its disc. I hope this is going to remain just theory and don't try this at home!

It brings up some interesting thoughts on addtion to TR induced flow though....


AH! and by the way....

French helis.... throttle same orientation,
more torque makes nose go LEFT, (right pedal being 'power' pedal'), close throttle little finger goes LEFT, nose goes right....NO!
LF rule is no good for the french. Sorry Jaques!

SPS

Never beleive what is in a box until it is open.

For the French it could literally be a 'rule of thumb'... :)

Hi guys,

Just reading the last few threads and I thought that I should probably clarify my question (point) on T/R auto. My last post was in response to a tail rotor drive failure, ie: no drive at all. Sure, if there is any pitch on the tail rotor itself then there is no chance for an autorotative force. BUT - what if you could boot in some right peddal and zero the pitch ........ I have always been under the impression that there has been flapback on the tailrotor in forward flight, most of which is cancelled by the delta hinge but there is always a slight angle of incidence compared to the relative airflow. Nut over that one!!

As to the friction effect, (I always use transmission drag to explain it) You must use a little bit of engine power in the descent and landing when confronted with T/R drive failure. Firstly, in the descent not only do you have trany drag but most 'American' heli's, bar the B47, have a vertical stabilizer that produces lift to starboard (nose to port) in forward flight that must be accounted for with a little power. As the speed washes off when we flare we have to lose a little bit of power but still account for trany drag.

Lest to say - throttle control will still play a pivotal role in the successfull outcome of a tail rotor drive failure.

Here's a little side line. If any of you fly a B47, you probably found yourself using the throttle to keep you nice and straight when landing in gusty conditions without even noticing it. Hopefully the same will happen if/when the back end plays silly buggers.

Hey, don't worry - just don't forget.

cheers

Agree on the TR flapback - It does happen and thus it has translational lift too. It is also subject to a constant 'flare' effect which helps to reduce TR power requirment in forward flight (one reason we put in more right pedal as speed increases).

But it all means nothing if the thing does not rotate or its blades fell off!

And you are right, a little throttle tweak here and there helped the old girl to stay stable.....

To ALL

With regard to"throttle steering", I know this sounds stupid but what happens when "throttle" is not on the collective (109, Gazelle, etc)????
Having not flown this type of machine (yet) the question has been in my head.
I guess you run out of hands!!!!!!!!But seriously what is the answer(please forgive my ignorance)

To RW 1

I like the rain in Florida(its the only place I'd like to live other than UK),but when I was in Phoenix at MD they had more rain in 24 hours than I've seen in the UK for a month, but it felt just like home!!!!!!!!!!(they say the sun always shines on the righteous,guess thats why I'm always wet!!)

Regards
hoverbover

To: Rotorque and SPS

You stated,” I have always been under the impression that there has been flapback on the tailrotor in forward flight, most of which is cancelled by the delta hinge but there is always a slight angle of incidence compared to the relative airflow. Nut over that one!!”.

If you are addressing a two blade tail rotor such as that used on the Bell or the Robinson you can use the term “flapback” if you wish but what is happening is that the advancing blade has a greater degree of lift than the retreating blade. The advancing blade will flap inward and in doing so the delta hinge removes pitch and at the same time the retreating blade because it is mechanically attached will flap outward and the delta hinge will add pitch. In performing this flapping the delta hinge effect will equalize the lift across the tail rotor disc and this keeps the tail rotor from flying off due to the fatigue on the tail rotor gear box quill shaft. You get the same effect on a two-blade main rotor. If the advancing blade is caused to lift then the retreating blade will drop. The delta hinge effect will remove pitch from the advancing blade and increase the pitch in the retreating blade thus restoring the symmetry of lift across the disc. If the perturbing force continues “blowback”(flap back) will result.

On a multi blade tail rotor where the blades a free to individually flap only the advancing blade will flap and the delta hinge effect will reduce the pitch on that blade. The remaining blades will maintain their position in the disc track and only move when those blades become the advancing blade. On very large tail rotors where the individual blades are free to flap those blades are attached to the tail rotor head by a composite hinge that allows leading and lagging as well as flapping.



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The Cat

LZ,

I do use flapback as my chosen label and it is similar enough to yours to be reliable.

I agree on the effects of the Delta three hinge and encapsulate it by saying that
"the Delta three hinge reduces flapping amplitude". But it still does flap whether two blade (which is where we were) or multi
blade for that matter. Thanks for the input, it looks like this thread will run and run until we have done all that could be done on the TR and that is actually no bad thing as it is too often ignored in P of F.

What about TR vortex next? Any takers?

And the Gazzelle/109 question - NO practical knowledge at all but I assume that the Pilot
would set the collective for correct (desired) ROD and move that hand to the stick and operate the throttle with the right or just operate the throttle with the left depending on position of the throttle.
But as I say, NO knowledge and I am just guessing.

This has certainly turned out to be a very informative discussion. Four pages and everyones heads seem to be intact!

Thanks to all who have contributed, keep it coming but please let's keep it on topic and not too technical, it makes my brain hurt!

I know there is a temptation to get down to the last nut or bolt but if you can't affect it from the cockpit, then don't bother with it.

There's nothing wrong with having an in depth knowledge of all systems, in fact your engineers will love you if you do, but what I was after here were your thoughts on dealing with various tail rotor problems.

Cheers, OffshoreIgor http://www.pprune.org/ubb/NonCGI/eek.gif

To: SPS

You Stated,"the Delta three hinge reduces flapping amplitude". In fact, the delta hinge allows the tail rotor to, using another UK term, “flap to equality”. It is the positioning of the pitch links relative to the movement allowed by the Delta Hinge that either increase or decrease the pitch on the blades as they rotate. The amount of flap is a result of the aerodynamic forces acting on the advancing blade and the centrifugal forces acting on the blade system. A combination of these two forces will determine the degree or amplitude of the flapping. The Delta Hinge allows the flapping but it does not limit the flapping. Under extreme conditions the Delta hinge will allow the blades to hit their mechanical stops



------------------
The Cat

to Thomas Coupling:

regarding your post on page 3, I don't follow your reasoning for the nose to continue yawing opposite the MR blade rotation in an auto once the engine has been removed from the equation. In an auto, once throttle is reduced, there is an immediate requirement for right pedal (american helo) which would lead me to believe that if the TR had failed, the nose would be yawing in the direction of MR blade rotation (left in american helos). Perhaps you could clarify your post, or correct mine... thanks

LZ

OK, let's look at it another way.

If a TR were produced and fitted without Delta 3 hinges (of course, the pitch links would still have to have control over blade pitch) would you expect it to flap more (its amplitude increased) than its Delta 3 equipped relative on another Heli.?

I think you would.

It could still flap to equality as does any MR, but would do so more slowly than if D3 equipped.

I accept that a TR with Delta 3 is still capable of hitting its stops but it would do so LESS readily (if at all) than a similar TR
without D3.

Flapping is indeed caused by dissymetry of lift which is countered by flapping to equality but the difference with D3 is that the process begins 45 degrees or so EARLIER
in the cycle and thus -

"The Delta 3 hinge reduces flapping amplitude."

Now let's not have a blood and guts, OK?

A timely reminder here chaps! Some of this advice is becoming very type specific and needs to be heeded with great caution. It must be borne in mind that each aircraft has its own foibles and characteristics. In particular, the throttle response from a piston engine is very different from a turbine, mainly in the response and lag departments. Similarly, some aircraft are more directionally stable in yaw than others.

ALL the single rotor turbine powered helicopters I can think of require an engine off landing for a tail rotor DRIVE failure (possible exception is where the throttle/s is/are on the collective, not too many of these types about nowadays and I can't comment as I'm not type qualified on any of them). There is a very great danger involved in removing hand from collective in this situation to attempt to adjust power on a remote throttle /ECL except to shut down the engine/s, with the collective lever already on its bottom stop. Trying to adjust power to keep straight with a remote throttle in powered flight is highly likely to result in disaster, especially on a twin where you are manipulating two ECLs. Some turbine aircraft do not even have a "manual" facility anyway. Exceeding the upper or lower Nr limits is one easily possible result. Also, if you get it wrong, once the aircraft begins rotating you are very likely to have lost it completely. In my experience it is far better to accept that an engine off is the final outcome because you can be more sure of the aircraft handling. Some are forgetting that the aircraft's "weathercock" effect can be used to great advantage in autorotation, using what would normally be quite extreme sideslip angles to fly the aircraft towards a landing area.

Having experimented, practised and taught tail rotor drive failures many times, albeit in simulators, thank goodness (in both directions of main rotor travel) I think the most important advice anyone can receive is that of the manufacturer of the aircraft.

Read the Flight Manual, guys.

Shytorque: (my response assumes you have alluded to my post on the 1st page) I'm suprised you feel that way about the power manipulation ..... I agree if poorly or excitedly used then you could very easily end up using too much or too litle power and have a resultant limit bust on the NR - max or min values. (if it's transient - who really cares - you have a bigger fish to fry)

IT IS IMPORTANT to STRESS that any manipulation of the POWER may only be necessary if you have a TR CONTROL problem or a TR FAILURE (in FWD FLT - and need to power on position to avoid the conurb or oggin below). In addition to this it is also important to ensure that either your crew or yourself as a single pilot fully appreciate the problem by EXECUTING A THOROUGH BRIEFING (if possible exercising some Throttle manipulation - in order to gauge it's effect prior to making the approach and using the NR variation in anger)

Hey - the problem is SEVERE and it requires skill, discipline and sound judgement, ALL within the capabilities of most HELI pilots (otherwise most of us wouldn't be playing the game).

It is essential that every opportunity is given for junior and senior pilots to practice such problems - it highlights the difficulties but more IMPORTANTLY - if considerately and sensibly practiced will give everybody more confidence in understanding that it might not be the end of the world.

By way of qualfication: I too have taught the TR problems in the SIM and in twin and Single engine MIL & CIV helos. I must agree to differ with you about avoiding using the aircrafts performance envelope.

But - support your concern if it points towards those that might hastily respond to the problem without considering their actions or those who try to use the techniques without proper and prior instruction.

Hoverbover: Interested what you were getting at in your throttle steering query ....could you expand on what you're not quite sure about?

eden

Imlanphere: In normal fwd flight, the airframe will try and rotate in the opp direction to the MRB, correct? If one increased collective(power), this reaction would try to increase(obviously we prevent it from doing so by applying corrective yaw pedal input). If one was to reduce the collective to almost a min pitch setting (auto) then the opposite would occur, correct?
Now, when the TR lets rip (!), then the airframe will immediately yaw in the opp direction to the MRB, correct? If you lower the lever fully (auto) then this dramatic yaw swing will be reduced (but not fully), correct? BUT, because your engine(s) are still switched on! the drive train will continue to transmit some power (torque) thru to the head thus the residual yaw will STILL be in the OPP direction to the rotation of the MRB. Now, when you switch the engines off....there is no REACTION thru to the MRB from the running engines, other, now than plain old friction, and it is this force which causes the airframe to attempt to yaw in the direction of the MRB's. This results in a further reduction of your yaw problem but will not completely remove it unless you are travelling with sufficient fwd speed to act as a wind vane also!!!

TR failure (fwd flight)will always provide you with a fighting chance if the engines are switched off. Leave them on (singles or twins) and you are dicing with death, literally!!

Throttle manipulation in modern helos (post twist grip) is NOT an option...

http://www.gograph.com/Images-7298/A...if/redstar.gif

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Thermal runaway.

Tail Rotor failures,
There must be some of you Pro/Mil types out there who have actually hador suffered a T/R failure, it would help low hour jocks like me to read what your reactions and cures were at the time of impending doom, please tell!
My Regards 180Hr R22/R44/B206


------------------
Peter B

thomas coupling: in the example above, are you stating that the nose will be yawing toward the advancing side, or toward the retreating side after engine(s) are switched off? (assuming some weathervane from normal autorotation airspeed)

To all,

Please note: I was & still am talking ONLY about the tail DRIVE failure here. The actions for tail rotor CONTROL failure are quite different.

Eden,

No, I was not specifically alluding to your post but I am becoming concerned that general advice on this thread is apparently heading towards favouring experimenting with power on, rather than entering autorotaion in what is probably the most critical emergency a rotary pilot will ever have to deal with, i.e. tail rotor DRIVE failure. Hopefully most of us will never have to deal with it for real. Get it wrong on the day and in many (if not all) aircraft you're possibly in a loss of control situation. I have seen many an occasion (in simulators only - agreed and thank goodness! - but in at least three different ones, two American and one French) where a pilot has elected not shut down the engines following a tail rotor DRIVE failure and has completely lost control well before hitting the ground. I lost control myself on a number of occasions before I had got my own skills up to scratch.

There is an infamous piece of film where a Bell 47 (throttle on collective, please note) on a photographic sortie over Sydney harbour, back in the 1960s, lost its tail rotor drive. The (relatively highly experienced) pilot tried to fly out of it under power and completely lost control. For its finale the aircraft descended in a very rapid flat spiral, finally tumbling over. The aircraft crashed hard onto a factory, killing all on board. I was first shown the film back in the 70s by a military QHI, himself now long since retired, who was a personal friend of, and an ex-colleague of, the pilot involved. The mainstream thinking even back then on the '47 was that the correct action in the event of tail drive failure was to autorotate and shut down the engine, which puts the aircraft in a more controllable and predictable flight regime. If he had done that he might have got wet but still been enjoying his retirement today. Whatever, this unfortunate pilot didn't survive to debrief it.

The yaw from transmission drag in autorotation is much less than from the torque reaction in normal powered flight and is quite controllable by use of opposite cylic, in other words cross-controlled. Many tail rotors have considerably less "negative pitch" range than "positive pitch" for this reason.

I cannot see how varying engine power on throttle will do much else more than cause Nr variations and further problems, especially bearing in mind that on something like the R-22, for example, that Nr can be absolutely critical. The main transmission power to keep the aircraft in balance following loss of tail rotor drive would only be that required to offset transmission drag plus any aerodynamic yawing effects from the tail and insufficient to sustain more than a descent.

I accept that it MAY be possible in a controlled situation for an experienced, well trained and pre-briefed crew to do something different and make a safe landing in some cases (hence my comment on reading the flight manual) BUT often, tail rotor drives fail at critical moments, at low speeds close to the ground and sometimes without much warning. A delay of a second or two before pilot action can make a big difference to the outcome. We used to get pilots to realise this in the sim by feeding in vibration as a pre-warning that something was amiss, then fail the tail drive. After a little coaching, usually the guys would get it right, they offloaded the rotor by entering autorotation and usually could fly the aircraft on cyclic, accepting the out of balance situation that resulted. Having done that, it was relatively straight forward to make a controlled landing PROVIDED that the engines were completely shut down before flaring at the bottom for the EOL. If the engines were left running even at ground idle the residual power caused loss of yaw control during the landing.

However, when we later didn't pre-brief them to expect it and gave no warning to the pilot by missing out the vibration, they tended to be slower with the collective lever and quite often lost control because with power applied the aircraft yawed rapidly and then rolled out of control. These guys were no dummies, believe me.

I do know of one notable exception to the above. A military Super Puma operated in the middle east in the early 1990s had a tail rotor drive failure at a high cruise speed (140 kts). The pilot found that each time he tried to gently slow down the aircraft yawed very badly. He admitted afterwards that he didn't attempt to enter autorotation, possibly as he was not too confident of his ability to carry out a good EOL. He elected instead to find a long runway, made like a fixed wing, and ran the aircraft on at 140 kts! He managed to keep the aircraft upright, but he used an awful lot of tarmac to stop! I would not personally have risked that technique but then I was fairly good at engine offs, having had lots of training and given lots of instruction in them on that type (including in the dark and on instruments to ground level just to make it a bit of a challenge if you like!).

I think following drive failure the tail rotor auto-rotating stuff is a red herring. If you react to yaw with pedal you will rapidly slow and probably stop the tail rotor. An auto-pilot heading hold will do the same. I don't think we should kid ourselves that it is going to start up again!

Sorry for the long drawn out post but I think it's very important for people with not much training on tail rotor malfunctions to get it right in their minds before it catches them out for real. Good topic!

Shytorque: Yeah - agreed .......I misunderstood where you were coming from.

CONCUR: TR failure - forget throttle playing!

Nr variation with a CONTROL problem can make all the difference and is something to be practised and thought about. Again ONLY - with someone who knows how.

Thanks for the reply - I too saw the same video it is very scary stuff.

I assume you were on PUMA sim?

Shytorque - good post.

To have access to a sim would be a god send to us all, I could only dream of getting my hands on one.

Just to clarify - the tail rotor auto thingy was just a scenario. A thought provoking question really. There was no intention of trying to use it to help in a T/R problem. I know for a fact that I would instictively try to boot in opposite peddal if I lost the T/R drive - that alone would be the end of the conversation of T/R auto.

I did throw in a comment on whether you could overspeed a tail rotor by having it in the 'auto' pitch setting (zero pitch) with a drive failure. Could there be a risk of exacerbating the problem if you threw off a T/R blade without even knowing it was going to happen?. Once again just a tongue in cheek thought. No need to do the tests.

I am going to have to back peddal a little now cos' on a previous post I talked about using a small amount of engine power on descent and landing when confronted with a T/R drive failure. As mentioned previously it is very important to know how each aircraft responds to various problems. I wrote the response with the B47 in mind. It was not my intention to use it as a generic answer to tail rotor problems although I guess it was centred on collective mounted, throttled helicopters. I was 'lucky' enough to work with a bloke who had a short shaft failure in a B47 whilst mustering. To this day he does not know how he flew away but I presume he had just enough residual forward speed and a hell of a lot of crossed controls. Anyway he was able to fly back to the station which had a gravel strip. When he rolled off the throttle completely to enter auto he found that the aircraft yawed to the left by a considerable amount. In the end he had the engine ever so slightly past the idle all the way to the ground and as he leveled he wound the throttle off completely and landed. All of this to the benefit of us young blokes.

To this date I have taken the example as gospel but always wondered whether the tail rotor had some residual thrust or if the position of the free wheel unit in the transmission played a part in the outcome. I don't know.

Reading the posts I have come to the conclusion that I could be in varying degrees of trouble if I use the same thought process for different aircraft. I am therefore following the thread with renewed interest and an open mind.

Shytorque's experience in the sim may be invaluable. Please note, as mentioned earlier there really does need to be a distinction between collective mounted throttles and power levers. The rules do change.

keep it coming.

I have been holding back as I thought this may have been mentioned before but so far I haven't seen mention of this so I thought I might add my 2 cents. I have been shown a recovery from a low speed high power JAMMED pedal event. As the aircraft starts to rapidly rotate cyclic can be aplied toward a constant heading ie "stir" the cyclic in the opposite direction of aircraft rotation. It allows you to gain airspeed in a constant direction and lower power post translation to a point where the aircraft will once again fly in something close to balance.

Interestingly enough the instructor who demonstrated this tecnique subsequently experienced a loss of tail rotor and tail rotor gearbox in the hover and landed without rolling into a ball.

I agree that simulator training is a very valuable way to experiment with handling TR problems but would add the proviso that the simulation may be innacurate.

Having flown the FSI 212 sim at DFW several times it is easy to come away with the impression that a TR drive failure can be controlled fairly well. In an extreme example which was basically a bit of 'wazzing' I took off from the simulated aircraft carrier, had a loss of TR drive at about 65 KTS, flew the thing horribly cross controlled to about 1000' abeam the ship then autorotated back down to the deck and survived. I don't believe that to be a true representation of the a/c's behaviour. The SAS sim at Stockholm, on the other hand, is a newer generation. TR drive failures can be truly aerobatic events, generally resulting in the sim freezing with the 'world' inverted, to protect itself.

Having spoken to pilots that have had TR drive failures in two separate AS332 accidents, one happened in a relatively high power setting in level flight and even entering autorotation did not stop the rolling/pitching/yawing; the PNF had to retard the speed select levers before things settled down. The handling pilot compared the manouver to a lomcevak! (negative flick roll going vertical, in an aeroplane). They executed a text book ditching and were all saved. The other one happened in a descent at 70 kts after the pilot had diagnosed the probability of impending TR drive failure and was a far less dramatic event, again resulting in a perfect ditching with no casualties.

Yet another accident with a 330J in the cruise resulted in the a/c tumbling all the way down to the sea.

So, being aware of the variables and trying it out in a sim is great, but come the day there is a very good chance things may not go to plan.

I suppose that is one thing in favour of fenestron a/c; they should fly happily in a straight line at about 100 kts with no drive.

------------------
Another day in paradise

Having experienced a tail rotor failure in a rather large Wastelands product from a 40ft hover over the sea, I can assure you all that the previous theory lessons, good though they are, go straight out of the window!!.
In my case there was no warning, the helo just started to turn. Both myself and the other pilot automatically applied full opposite boot, thus we were both aware that tail rotor control had been lost before the end of the first 360 degrees. The rate of turn was rapid and disorienting but lowering the collective immediately significantly reduced the rate of turn - albeit in mid plummet.
We hit hard and bounced out of the sea into hover No2 where the a/c started to turn again before droppping into the 'oggin and rolling over. All escaped with no injuries.
Two lessons learnt from this. 1.In a hover you must lower the lever quickly, hack the engine if you can and cushion the touchdown with collective. 2.If you dont have your shoulder harness locked in every hover you are a prat!

Flypro - are you the "Certsmith"? who transitioned from Dark to Light? - Sorry If I have mis id'd you and if I have -I'm sure you have no idea what I'm talking about.

GOOD POST THO'

212 Man and Flypro,

Glad we all agree then, on the simulator thing about possible inaccuracies. (Please read my post of 13th Feb, 22:43 hrs if you haven't already; where I mentioned "off model" programming by the sim manufacturer). My experiences on the 332 sim carrying out T/R failures of all types were interesting to say the least.

Some (very experienced) pilots were quite alarmed by the response of the "aircraft" (sim). However, they unanimously agreed that they had a far better chance of a survivable outcome following their sim training. If nothing else, a discussion of the possible different scenarios is extremely useful. The proof of the pudding came a few years after we began training RAF pilots; a military 330J (no floats!)was successfully ditched following a tail rotor spider failure. The pilot said afterwards that had he not done his sim training he knew the outcome would have been different.

Personally, I would rather have a total drive failure than a runaway to FULL maximum or minimum tail rotor pitch, at least on the Super Puma. Either of those was in our experience, uncontrollable in most flight regimes. If the tail rotor ran away to maximum positive pitch on that type we found that even pulling the collective up as far as it would physically go (clunk) would not stop the right yaw caused by this failure. You then end up in a rapid spiral climb at full power and rapidly run out of ideas (throw baggage into the tail rotor to fail tha drive? It was suggested by one pilot!).

Similarly, if the pitch ran to fully "negative", even shutting down the engines did not stop the left yaw. This results in a spiral descent, very nasty too.

This may well be so on many other types, which is probably why many are fitted with some sort of centering device for the hydraulic servo for the cable break / malfunction situation.

One thing is for certain these days. I always check the tail rotor components very thoroughly when it is my turn for the check 'A'! I have already discovered one newly re-conditioned (!) and faulty tail rotor control spider.

ShyT.

Eden.
Sorry, I aint he. Not a clue what you are talking about,and I certainly did not transfer to light blue - there is a code you know!! http://www.pprune.org/ubb/NonCGI/eek.gif

Shytorque (now where have I seen a bar with a very similar name?)

The RN and RAF SeaKing Simulators are both very good for practising tail rotor problems and certainly in the case of tail rotors stuck at high or low pitch they fly very much as the real aircraft does. For a tail rotor failure at height they rely on data supplied by Wastelands as nobody has had one for real yet (I think).
In the Sim, to retain any control whatsoever the a/c must first be dropped into autorotation (and quickly at that). Once established, if possible go for an engine off landing, if not you can try to reapply power and sometimes manage to arrest the rate of descent for long enough to position the a/c over more suitable terrain for the subsequent engine off.
Another unofficial technique for tail rotor failure that works well in theory and in the Sim is to shut one engine down and set the other one at low torque, just enough to counter friction within the transmission. The a/c then handles almost exactly as it would in a normal auto.
I think the large keel area of a SeaKing prevents it from immediately spinning after losing the tail rotor in forward flight and give one time to lower the lever.
Hope this helps!

Finge Et fuge (Bodge it and Scarper)

[This message has been edited by Flypro (edited 23 February 2001).]

Eden,

Intrigued but I don't know where your bar is.

I thought of my user name after spending a few years dodging large hawks that circle eastern parts looking for - Shyte! Torque is appropriate for someone in our line of work. I also now circle looking for - Shyte!

Someone else on this forum has copied it but he's not as subtle as me!

it seems that a full right or left stuck pedal would be a highly improbable situation - simply because they aren't used to the extremes all that often - unless there's some reason why the pitch would continue to increase or decrease to its full stop position, I guess.... seems that most "stuck" pedal situations would occur during flight regimes where the amount of stuck pitch was appropriate....any thoughts?

Does it not depend where the centre of pressure acts relative to the feathering axis and hence how the centripetal turning moment moves the pitch?

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Another day in paradise

Shytorque.

I was thinking of *****hawk (though I reckon someone else posts under hat name)

Imlanphere.

A hydraulic hardover that you can't switch out would do the trick ie full range deflection.

212man.

Ask LZ - he's the theoretitian!!

The RAF Puma flew for 20 years plus in a condition likely to give a hardover in yaw due to the lack of a centre-ing device in / on the servo mechanism. It would happen if you lost one of the 2 pull cables to the tail rotor hydraulic servo valve. On this type there is no manual reversion and no way of isolating the hydraulics.

We looked at this type of failure in the sim, and discovered it was probably irrecoverable, as I intimated earlier. I did some personal research in the mid 1980's and discovered that the Norwegian aircraft had a centre-ing device fitted. Myself and other QHIs afterwards bleated long and hard about this and I think we eventually got through to the powers-that-were, as all the RAF aircraft are, I believe now modded with a centre-ing device. If not, they Bl**dy should be!

Even with such a device fitted, a broken pitch control spider can still give a hardover. Check the UK AAIB site for the report on the S.Wales police helicopter that landed on the roof of a house last year.

It's worth all heli pilots training for this in a sim. It doesn't matter which type as long as the main blades go round in the same direction as your helicopter (otherwise the yaw directions can get a bit confusing). Many heli pilots believe that closing down the engines is the answer to all tail rotor malfunctions. It ain't!

ShyT.

[This message has been edited by ShyTorque (edited 24 February 2001).]

I believe I read somewhere that if the pitch control mechanism were to be severed somehow the tail rotor blades would work themselves back to zero pitch automatically, but maybe thats type dependent

ShyTorque,

If the centering device you refer to is the tail rotor spring bias unit, then I think we are still waiting for it to be fitted (along with a torque meter/anticipators/Makila engines!). As you have said, the simulator is an invaluable tool to get you thinking about tail rotor malfunctions. I'm pretty sure that if it happens for real however, the 'What the f...' factor will precede the 'THROTTLES!' call by some distance!

Been following this thread with some interest. A couple of points/questions. I had a TR drive failure in a 204 over trees during longline ops (just powering up for a lift). I found the most surprising element of the failure was the severe nose tuck almost immediately drive to the TR was lost. It required almost full aft left cyclic input to maintain a wings level attitude during the early part of the rotation. I was lucky in that I identified the failure early and shut the throttle after 180 degrees of rotation which immediately stopped the rotation and levelled the aircraft. The trip down thru the trees was "intersting" but both myself and my co are here to tell the story today.
I have never done any sim time but I am intereted to know whether the 212 sim replicates similar tendencies to what I experienced. Also over a number of years of flying I have never heard any instructor discuss this point when briefing for TR failure. Any thoughts?
PS
Loss of drive to the TR was caused by the failure of the grease coupling on the TR driveshaft immediately aft of the TR output quill on the Trans. As a point of note never trust the Zinc chromate paint lines on the couplings to indicate high coupling temps. The Bell temp indicating strips (like they use on the R22) are the only way to go!

This will probably be common knowledge to most of you, however, it was certainly news to me at the time.

Flying the 412 sim at DFW I was given a tail rotor drive shaft failure in forward flight. The drill is to enter autorotation immediately but my instructor suggested that I continue flying (80kts) and see what happend.

Horrible right yaw and nose tuck ensued, but it was certainly controllable, so we decided to return to the airfield for an autorotation. As the airfield was in our 4 0'clock position I began a gentle turn to the right (into the yaw). Bad move. We very quickly lost all airspeed and began to lose control of the beast.

If you need to turn, then turn away from the yaw as it is much easier to maintain airspeed.

Lama Driver: your input must be worth its weight in gold...thanks for sharing your experience, hope some of it is remembered by others. http://www.pprune.org/ubb/NonCGI/eek.gif


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Thermal runaway.

To:212 Man

“Does it not depend where the centre of pressure acts relative to the feathering axis and hence how the centripetal turning moment moves the pitch”?


Hopefully this does not start another international incident due to semantics but I believe you are talking about “Centrifugal twisting moment”. The centrifugal twisting moment coupled with the aerodynamic forces are what you feel when you move the pedals during flight, or in other words, you experience the associated feed back. Propellers on aircraft have the same condition. If say on a Hydromatic propeller you lose oil pressure the centrifugal twisting moment will return the blades to low pitch and if you don’t catch it quick enough you can have a runaway engine.

To: Imlanphere

“I believe I read somewhere that if the pitch control mechanism were to be severed somehow the tail rotor blades would work themselves back to zero pitch automatically, but maybe that’s type dependent.”

You are correct in stating that the return to low pitch is type dependent. Some helicopters that do not incorporate compensating weight would return to flat pitch if the control were severed. Many helicopters incorporate dynamic or static counterweights. The static weights are incorporated as a part of the blade on the Bell 407. Helicopters like the Sikorsky S-58 incorporate dynamic counter weights that move when the tail rotor pitch is changed. The purpose of these weights is to counter the centrifugal twisting moment so that the pilot only experiences the aerodynamic forces if he has to fly with the tail rotor boost shut off. On this type of tail rotor the dynamic or static weights will under ideal conditions maintain the blade pitch in the last commanded position when control is severed.




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The Cat

Lu: calm down, we are do'ers not thinkers...who the hell cares anyway if one has suffered a TR failure the god damn thing has stopped!!!!Feathering or no bloody feathering!!!

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Thermal runaway.