hehehe After a complete loss of T/R and having a place to autorate, I almost break the pedals in the 412 simulator when in ground run after the flare!
:}

Carebear and Aser,

Having helped build and qualify several training simulators, I can assure yu that they can teach you virtually nothing about extreme emergencies like tail rotor failure. I suggest that you do not be fooled by their seemingly perfect ability to mimic the real aircraft. Their behavioor for tail rotor failure, as well as all other flight beyond the normal envelope, has never been verified, and is based on assumptions that have no real flight data in them.

When you draw conclusions about the REAL helicopter's response to situations beyond the normal flight envelope based on flight in the simulator, you are probably wrong, but definately beyond the sim's ability to help.

Nick, you have beat me to it! I, too, was going to say don't believe the simulator when it comes to TR failures. If you compare the FSI 212 sim with the SAS one the behaviour is at opposite ends of the spectrum. The FSI one displays pretty benign characteristics and is not a big deal (I even autorotated onto the carrier at night) the SAS one will tumble instantly and freeze to prevent damage to the jacks. The truth is probably somewhere in between but closer to the SAS one.

Even a brand new level D sim for the 155 does not accurately replicate the TR drive failure and requires a run on landing about 40 kts higher than experience has shown true.

At the end of the day, the sim can only reproduce chracteristics derived from test flight data and checked against the QTG; anything outside of that is extrapolation and guess work.

My first and only experience with a level D sim was in SAS (the 412) and men... it was really AMAZING!
I'm just a guy that flew only r-22 and b-206 before, so I don't have much idea about the reality in the flight model, but after a complete t/r faiulure in hover , 2000' hover , final, etc. and being able to put down the chopper without a "red screen" I was feeling very confident to react for the unexpected.
Maybe it isn't very real , but I thought it was a wonderful tool to develop "instinctive reactions based on the procedures" isn't it? :sad:

Obviusly I'm not going to check if the rolls and fall back from hover maneouvers that I saw in the sim can be done with the real aircraft. ;)

Regards.
Aser

John Eacott amaizing pictures!! glad you are with us to tell the tail and share the experience................ CARRE BEAR...... is right about his method for TRF and yes it works very well and easy in the 206, its your only option when a zero speed landing is needed, no need to roll the throttle off though any collective applied must be late / last sec and snatch to avoid early torque rotation, use then the pwr as long as you can ( even a second) to help prolong rpm, letting the nose rotate to match ground travel, if any, B4 using throttle to maintain it, done right and with practise you it is very effective and in the 206 very easy (dont try it in an r22):D ... one point to make, the flare, apart from the obveouse is used to put the machine at best full right angle to ground travel if you do this then you got it won, also easier to get closer to the ground not worrying about the tail, anymore than a few Kts of wind and you will land it zero speed. And yes i show this to advanced students to show the "more ways to skin a cat"thoery and just to get them thinking, obveousley comes with practise and experience.

T/R failure practice
 

Just to add a few notes regarding the R44 failure and as mentioned already, many FIs in the UK offer specific training so pilots have a sporting chance of coping with the condition ... albeit being outside the EASA/CAA approved PPL syllabus. Yes, it is a fact that too many T/R failure cases result in a major accident involving fatalities but I'd like to think that given a reasonably amount of dedicated instruction and subsequent practice, plus a slice of luck at the moment of failure and a fairly flat piece of ground, most pilots should be able to land the helicopter safely.

So to add my pennorth can I continue. When in practice exercises, I have my pilot place both feet on the cabin floor clear of the yaw pedals. I then make a 'best guess' at the yaw angles that would be experienced by observing the power settings in combination with the airspeed being used. I accept that these may not be exact, but the exercise does provide, as near as I am able, the changing yaw angles and attitudes required to maintain control.

For the exercise, the major items to be considered are ... power in use at the moment of failure ... then the next three being airspeed, height and aircraft weight. Helicopters having a large keel surface such as the Big Bells and the Enstroms generally allow a better level of control relative to airspeed selected. Taking a standard current production American aircraft as our example, a partial or total failure of the T/R system does, as we all know, produce an immediate loss of directional control as Newton's third law of motion takes over and engine torque drives the nose rapidly RIGHT (left in most European makes).

To remove any mystery of the condition, I teach my pilots that they don't actually have a problem! Pause to think! What they do have is an engine that they can no longer control. So initially we just carry out an exercise we have practiced many times ... ie to get rid of the source of the problem by lowering the collective lever and closing the throttle to enter autorotation. With a reasonable airspeed (say 70 knots) and lowish power (say under 50%) the RIGHT yaw might extend out to the 'two o clock' position but whatever, the pilot's immediate action of power reduction prevents further yaw, while the lowered lever drops the nose either increasing or at least maintaining speed. Using cyclic the pilot's first task is to level the 'wings' and maintain at least 60 knots. With the RIGHT yaw stopped, transmission friction take over causing the nose to slowly commence a yaw to the LEFT but again highly dependent on the speed being maintained.

With the nose rotating toward the LEFT 'ten o clock' position, the pilot can now use engine to control left rotation and by raising the collective lever increasing power to yaw the nose once again RIGHT ... the plan being to discover the maximum power setting that can be used at a given airspeed to allow a controlled yaw to the original 'two o clock' position. It should be borne in mind that the resultant 30 degree yaw involves large ASI errors. Opposite use of cyclic assists control, ie with right yaw use left cyclic, the plan being to achieve straight & level flight if possible, or at least a reduced rate of descent ... much depending on aircraft weight.

IF control can be achieved with steady height and airspeed at the 'two o clock' position, the world becomes your oyster! Or at least allows more time to select a suitable emergency landing area. If the former, you may even have time to return to your base airfield or at least reach a better landing site, alert the emergency services and carry out safety emergency drills.

Once over the selected landing site, the helicopter should be positioned so that a shallow rate of descent can be made to the landing site. Lowering the collective lever allows the nose to yaw LEFT back to the 'ten o clock' position while maintaining speed and directional control with a combination of lever position (power) and cyclic (speed). Ideally the approach needs to be made at progressively reduced speed bearing in mind the ASI errors.

So far, the procedure hasn't been that difficult but if a non-damaging landing is to be achieved, the handling co-ordination requirement to control the final rate of descent, the airspeed and yaw is now at its highest. At this point the pilot is aiming to bring the helicopter to within a few feet of the landing surface with as much power as can be used to achieve the lowest rate of descent and minimum forward speed.

At around 20 to say 30 feet the helicopter is initially flared with aft cyclic to further reduce speed but then pushed forward to level the skids for the landing attitude. As the helicopter sinks collective lever is raised allowing the nose to yaw RIGHT back toward 'two o clock' but at around the 'one o clock' position the throttle is closed quite rapidly and as the nose yaws back toward the 'twelve o clock' position the cyclic is pushed forward to make rapid skid contact with the surface. With skids on the ground, collective lever and perhaps throttle is used to keep the helicopter straight allowing skid friction to stop forward movement.

It needs to be borne in mind that once the landing site is reached and descent commenced it will not usually be possible to make a 'go-around' and the pilot is committed to a landing.

I appreciate these suggested handling techniques are more applicable to a failure from a fairly benign configuration and may not apply to a worse-case take-off or landing or low height zero speed hovers where more advanced handling would be required.

I also hasten to add, that these notes are for guidance only and perhaps to promote discussion on such an important life-saving exercise, but I'd have to say, I've never been a supporter of the usual PFM recommendation to handle the T/R failure problem by ... "entering autorotation." For sure that technique will stop the rapid right yaw problem but will not allow the helicopter to be landed safely since the initial right yaw will, as outlined above, be followed immediately by a yaw to the left and in my view it matters not a lot whether the helicopter impacts the ground in a right or a left spin. And just to remind pilots that our European friends turn their rotors differently so where I say RIGHT .... use LEFT and vice-versa.

Just to close, much of the above has been learned from my four 'actual' T/R failures I've experienced in 14,000 plus hours over a forty-year career. Luck allowed me to survive the first in 1973 when a T/R shaft sheared on a sales demonstration, the second was a hover failure when a licenced engineer obligingly fitted the T/R blade assembly in a reversed 'trailing edge' first configuration which being an 'ace' pilot, I did't spot on the pre-flight inspection. With some experience under my belt, I completed a high speed run-on landing at Cranfield in 1986 and a later further occasion when I landed on a cricket field at one of Noel Edmonds 'Mr Blobby' events in Somerset. The final episode occurred at the 1999 Biggin Hill Air Fair when, with the hoped for 'slice of luck', I managed to get the Enstrom FX down without further damage. But Guys & Gals out there, I'm still waiting for my first engine failure!

Safe flying to all and I sincerely hope my words will help another pilot one day. DRK

Thank you Dennis ...a very useful explanation , as always:D
Would it be fair to say that landing with the wind off the left side would also be helpful ? ( USA heli )

T/R Failure
 

Hi Nigel ... interesting you should raise that point. For my Biggin Hill recovery, I made a point of landing in a 'Three o Clock' cross-wind making an initial touch down on the right skid so once I'd achieved ground contact the right side wind and right skid friction held the nose straight in the 'twelve o clock' position until the last few yards. With both skids down M/R friction took over and the machine completed a 100 degree left spin as it stopped, fortunately I was on a hard grass surface. IF I had been able to make more accurate use of collective lever/throttle, no doubt I could even have avoided that! Regards. DRK

Nigel
Very interesting, personally I think it is better to be straight into the wind so you keep precious airflow over your stabiliser to help keep it straight as one runs on. Remember it is accleration that kills us, so touching down at the slowest possible speed must be the best, thus landing into wind. An example in a 500, stick about 1.5 inches of right pedal forward you can do a zero zero landing without moving the pedals and keeping straight in 15 ish knots of wind ( 2 up half fuel) drop the wind to less than 10 kts and you cant do it without closing the throttle to remove the tq reaction as you slow down

The word benign was used which is easier to understand that what I usually say as - arrive at nothing with nothing - instead land in the most benign manner.Skating along close to the ground washing off even a little airspeed, you will end up pulling too much power and thus yaw, or too steep an approach the same applies.

With practice with wind from either the quarter or nose a zero zero touchdown can be achieved and allow the last little rotation to wear itself off as you hold off with the toe of right side skid down. That is with T/R fail simulated with 2/3 pedal in the '47 or R22.

As it finally falls you will see the cyclic all the way over toward the skid toe with lever fully up.

A good pre exercise is to fly along at slow airspeed and wind the throttle on-off-on-off a few times to learn the torque /rotation control and heading effect of the throttle.

Hughes500 - be very careful who you give advice to here...Dennis wrote the book and you are advising him on how it should be done:ugh:

Tail rotor failure - my pet subject. A VERY complicated phenomena, made much much more difficult to understand when the main aerodynamicists the world over, aren't fully comfortable with what happens and how best to handle it. We teach this malfunction on a daily basis to the best pilots in the world and the data we get from Westlands / AW / Sikorsky is a little scant, to say the least.

Very few helicopter pilots fully understand what to do when the tail rotor stops. 99% think they know and a tiny proportion prepare as best they can for the time it may happen to them. BUT like most aviation related skills it is a perishable skill and needs constant rehearsal.
Mosy military pilots allow for this in their training repetoire, but I suspect once a civvy qualifies and gets their ticket, they rarely if ever train in anger with this phenomenon.
There is a world of difference between tail rotor control failure and tail rotor failure. The former will allow most helicopters to arrive safey on terra firma in most instances (except with gross mis handling) The latter relies heavily on luck more than on judgement.
I won't drag on with more detailed explanations but what I will say is anyone who successfully lands a helo after a tail rotor Failure deserves atleast a Distinguished Warfare Medal , to say the least.
(Actually a DWM would be an insult - but I couldn't resist it after reading in the nes today that the yanks are awarding these for Drone operators :eek:)

What Dennis and TopendTq did / said is as close to copy book as one can get.

Ok TC ...we will keep this one civil:ok::ok:
With all due respect to you superior training and experience ( actually not being sarcastic ) ...I would have thought that t/r malfunction , as in stuck , controls could be far worse . If we take it that a t/r with no drive produces little to no thrust , other than a small weather vain pull or push , you then have the ability to change heading by use of collective and throttle either way ...yes ?
In the event of the t/r sticking on a high power setting , say max take off ....ie fullish left pedal ( in yank machine ) then your options are vastly reduced . You can pull full power to get straight ....but then how do you lose height and make a landing .....if you reduce power you are going to spin . The only way I thought you could cope would be to do very tight turns using a lot of power but still managing to sink until close to ground . I would be interested to hear how full left pedal would be easier to cope with .
Ps. For these purposes we are not including c of g issues which you would have with the departure of blades , xmsn etc

Nigel - TC beasts us with these complex TR malfunctions on a regular basis and a stuck pedal in the manner you describe is a regular exercise - the answer is to reduce the Nr if you can because that will reduce the amount of TR thrust and make things easier to handle.

You still end up in a slow, high power approach but it is manageable, even with very high TR pitch settings.

If you mend your fences with TC he might even let you have a go:)

Ok ...but can he supply the helicopter ??!! I recall I have done that exercise with drooping NR but I don't think with max left rudder . I shall do it with someone like JJ next LPC for sure . Certainly a good exercise to keep up to speed on ( we all spend so much time practicing engine failures when they are probably the very least likely bad scenario to happen . Hence DK with none .... Touch wood :ok:)

NigeH, We have an opportunity here to publicly discuss, probably the helicopter pilot's worse nightmare - Tail rotor failure. Excepting of course all those who fly tandem or contra rotating helicopters.
If you're happy let's start a separate thread on Tail rotor malfunctions and see what comes of it.:ok:

I suspect this has been discussed time and time again on Pprune but my search didn't throw much up :yuk:
It would actually bring together some of the best and worst views and opinions, experiences and suggestions. People like Dennis et al could tell us what actually happens.......
Let me know what you think?

That is true and where wind from the quarter can come in handy.

However may I register a small divergence.

I always aim to enter with 100% RRPM as i look at the critical surviving factor as the highest remaining RRPM to retain flying control after throttle is wound off for heading control.
Torque variation gives heading control, therefore maximum torque is required under the prevailing benign power required condition
If RRPM is decayed then so too is torque and if you wind throttle off to straighten up starting from low RRPM it gets spooky real quick.

A separate thread could be a good idea.

Yeah I'll stick my mitt up for one those dang DWMs too although i got one of those company star and bar turnouts for surviving with no damage a T/R drive shaft pop out at thirty feet with zero airspeed.

Because of that we initiated T/R failure at the hover OGE (1500 feet min please for lighties) as well as the usual in the hover IGE.

TET, your point regarding Nr is certainly valid for horrid low inertia rotors like the R22 and R44 - I would want as much Nr as possible in one of those - read the R22 accident report from the latest UK AAIB, it makes for sobering reading about low inertia heads and how quickly low Nr can turn into NO Nr!

Ref torque though, as you slow the rotor down the torque goes up so your max Tq will be as you try to accelerate the low Nr back up to normal setting.

In the high TR pitch scenario we are talking about, you can use lower Nr to help manoeuvre and get a rate of descent - then, once you are near the ground at low speed (with a higher power demand) you can wind on the throttle a bit to help directional control.

Nigel, what TC can supply is a top-drawer simulator where such things can be practised over and over again.

Tail rotor issues and the FFS
 

Just before you get carried away just remember that unless your simulator has been programmed with actual flight data then it would have been programmed using a mathematical model and given the evidence I have seen thus far I would be a touch sceptical.

The major instinct you want the trainee to grasp is an instantaneous (or as near as) recognition of a TR malfunction and if it is one that involves total loss of directional control to then lower the collective fully whatever the phase of flight.

A few seconds later then you may have a chance to reassess the collective position according to your circumstances but I believe we can say with some confidence that the longer you delay your reaction the more problematic the outcome.

G.

hovering downwind
 

hye...i'm new here...can anybody tell me why tail rotor is more sensitive when we hovering down wind...

Selamat ,diraf, all helicopters have a measure of directional stability;that is,they are like a weathervane,pointing into the relative wind,in the normal flight case,going forwards,and or sideways; that is a generalisation,as some,those withe long streamlined fuselages,are better than those with `skinny` tails.However, hovering tail to wind/downwind alters the airflow pattern around the fuselage,tailcone,tail-rotor,horizontal stabiliser,and you are now in the regime of the weathervane,with a larger `side-area` being affected,and any slight yaw will attempt to make the aircraft want to turn back into the natural wind. So,it requires a lot more `work` on the pedals to keep the helo pointing `downwind`.Anyway, most helicopter pilots are very `light on their toes`,and the really good ones wear `dancing shoes` anyway...!!!!.

Stuck pedal - low power scenario
 

Geoffers stated: "just remember that unless your simulator has been programmed with actual flight data then it would have been programmed using a mathematical model and given the evidence I have seen thus far I would be a touch sceptical"
I'm with you 100% on that! They're good for teaching the initial recognition and reaction but I'm not convinced thereafter.

Hughes500 stated "I think it is better to be straight into the wind so you keep precious airflow over your stabiliser to help keep it straight"
I think you may well have a point in the H500 as the front of the skid tends to touchdown first (as does the R44). However, on the Squirrel (which is the type I've taught this on most often), with a slight nose-up on the skids as it runs on, it's posssible to touch the back of the skid down first which acts as an 'anchor' and straightens the aircraft up as it slides on. Therefore, a slight cross wind (from the right on the Squirrel but from the left with Yankee helis) helps this to happen. It takes practice but if the surface is smooth, it's possible to slow down significantly with only the aft of the skid in contact before gently completing the landing. Remebering not dump the lever during the slide-on as you breathe a sigh of relief.

Nigel H stated: "I shall do it with someone like JJ next LPC for sure"
Although I've got my FE(H) suspension revoked, I've not completed the renewal flight and seminar so I'm not in a position to do your next PC. I've had the wind knocked out of my sails wrt examining over the last few years and am not sure I'm ready to take on the responsibility again. I'll gladly spend an hour or two doing some revision of techniques though if you come over to Sleap (FOC of course).

My only addition to the discussion is that if it starts to get away from you at the bottom ofthe approach, it's almost always possible to go-around if done soon enough using gentle cyclic to build translational lift. Then re-organise your thoughts, learn from the mistakes of the last approach then have another go.
If you don't make that decision to go-around soon enough and the aircraft starts to spin, try to wash off all the speed, chop the throttle and cushion the touchdown. If done over a hard surface, the probable yaw at touchdown will be inconsequential if the aircraft is kept level.

JJ

Edited for typo

Thanks JJ , i will def come and do that soon .:ok:
With ref to examining etc i dont think you have a choice .....you cannot let the lunatics run the asylum :ugh: We need you back in service making people better , safer pilots ....ASAP .
ps I still remember being a bit heavy handed in FIBS , i think doing a go around , and doing part of my climb out almost backwards :eek: I remember thinking ...hes got to take the controls now !! I thought you were bloody brave leaving me to sort it out ...but it gave me huge confidence that i could bring the nose back myself !! ( All this not quite so easy in a civvy 350 as against the Mil version with coll throttle ..)

Fiddling with the RRPM.....
 

........ is not an option when you have a FADEC and NO THROTTLES poking from the roof. No such thing a a manual reversion and no possibility to play with the RRPM. (You can tell I've just started my 189 course!)

G. :ok:

welcome also to diraf4410

Possibly funny terminology there, maybe sycamore is funny fellow, but I don't think so. Most of us may prefer to be known as quick on our feet rather than have any pixie toed connotations attached.

I tend to fly around in socks only with boots kicked off after the first coffee pour time, because they give my feet cramps.

Ref tail feathers into wind; It's a bit like shooting an arrow out of a bow backwards. It will be very unstable and the pesky tail feathers will take over very quickly and reverse the order of flight.

cheers tet.

189 course Geoffers? Positioning for UK SAR perhaps???;)

Crab
 

UKSAR ?? Only if they want me to look after the zimmer frames. My day has been and gone I'm afraid, but I'll draw my pension this year and be happy to know that with 44 years in the flying game I can continue to embrace the latest technology and have teaching opportunities that are only available to a few.

The very first pilot 189 ground course is underway and AW are keen to have all in place by the time the aircraft enters service.

At first glance the step up to the 189 (electrically and avionically(?)) will be straightforward for 139 guys and gals, slightly more uphill for those with 92 and 225 and one giant leap for mankind for 61 drivers.

We live in exciting times.

G. :ok:

TC
Sorry havent replied earlier been in Peak District load lifting. Not trying to give advice to Dennis, just pointing out that on the type I examine a lot on that is what you can do. Do it regularly with all students as well as high power settings such as hover power, simulate by sticking pedal in and leaving it until one reaches best rate of climb speed, students really enjoy it.
Now should try it in a Notar, makes life much more interesting !!!!!!

Crab: stop hijacking the thread - get a life outside SAR :)

Hughes500 what type you examining on?

Hm

500's, 300's and 341/2

Sat in the office, a little bit bored, I decided to re-read Dennis K's original post about t/r problems.

What struck me is that the advice, although I am sure it is accurate, was also quite confusing. I've also found lots of pilots that are confused by t/r problems with many choosing to bury their heads in the sand and hope it never happens to them.

One of the causes of confusion is the widespread use of the words 'tail rotor' when referring to either drive-shaft failure or control failure/stuck pedal.
At my current place of work, the t/r problems are referred to as 'Tail Rotor Drive Failure' or 'Tail Rotor Control Failure'. Both problems are distinct and seperate and require different responses from the pilot, but in the heat of the moment, the drills can get muddled. I think that some of this may be due to the similar names given to the problems.

What I tried to suggest at work, but sadly there appears to be too much inertia in the system, was to rename the drills to avoid confusion; my suggestion fell on deaf ears. I'd like to see 'Tail Rotor Failure' referring to a loss of power to the rotor, ie Shaft failure. As for a control problem, I'd like to see it referred to as a 'Yaw Control Malfunction'. A distictly different name which should (may?) prompt distinctly different drills.

Thoughts........?

JJ

JC/JJ,don`t forget that the big eye-popper is a loss of t/r and or gearbox leaving,and the resultant change in Cof G,depending on the loading may well take you outside your limits ,and leaving marginal f/a cyclic control. Another point is whether you have wheels or skids..

One step at a time !! I agree with JJ that the two scenarios are totally different and require different reaction .....so why not make them toally different by calling them different things . Look at LTE and LTA etc etc
I think its fair to say that having a big chunk of your chopper fall off is a different thing again and will probably be very painful .

Think the problem really revolves what you can show a student when flying
Yes you can stick the pedals to try and represent a failure but you cant stop it turning ! As one of my customers who had a blade pitch horn failure you cant simulate the massive vibration, banging round and the smell of fear !!!!
Does puuting full right pedal ( US machine) in the same as having no tail rotor turning ? Would love to know what thrust the tail rotor actually gives for say every inch of pedal movement ie full right pedal is 10% thrust etc etc

Surely there must be a way of finding out where zero pitch is on the t/r ??

Having talked offline to a number of contributors, the general consensus is that an attempt should be made to simplify the dynamics associated with tail rotor problems – the pilots nemesis.
I'm applying the mnemonic: KISS.[Keep it simple stupid!] on purpose so that all helicopter pilots might understand or relate to it. :)
There are aerodynamicists, test pilots, victims, individuals out there who know much much more than I and it is hoped they will contribute too. All I ask is that they remember the golden rule throughout: KISS. This is not meant to be a technical blow by blow description of vectors and forces. It is meant to shed some light on a poorly understood malfunction(s).

My main reference is the comprehensive CAA report:

http://www.caa.co.uk/docs/33/capap2003_01.pdf

It discusses many aspects on this subject. Some are fascinating, some are complex...all are thought provoking. Aviators can never stop learning and if it helps one guy out on the day of the race....job done.
Warning: This is not, in any way to be seen as subject matter expert advice. It is background chatter; something to bolster your confidence if and when the day comes. Enjoy.

I invite as many people out there to spread the word and accept the following:

Tail Rotor Failure [TRF]: Mechanical failure resulting in the TR ceasing to act as an anti torque device, either by stopping rotating or breaking up or by departing flight.

Tail Rotor Control Failure [TRCF]: Mechanically sound, still rotating, restricted movement.

Catastrophic TRF: If the tail gearbox departs flight, the associated change of CofG will almost certainly cause the aircraft to pitch out of control due to the (weight x moment arm) change caused by the removal of “x” Kg of metal at the end of that moment arm. ENDEX.....

Contained TRF: If the tai rotor stops rotating due to bearing failure; gearbox seizure, drive shaft failure or (closest to my heart): thomas coupling failure! Its raison d'etre ceases.
In the hover: A/c will yaw and pitch immediately and uncontrollably. Time permitting, chop the throttle(s) to reduce (not stop) the yaw. LAND ASAP. Hope for a safe touchdown. Another reason why you should not hover too high. ENDEX......
In flight: There will be an undemanded yaw and pitch input
TRF's will result in the a/c yawing in the opposite direction to the rotation of the blades.
(Whereas an engine failure causes a yaw in the same direction of rotation).
More often than not, a TRF in the cruise where the tail rotor is still attached to the airframe, will result in some form of controlled landing (as opposed to a crash). Invariably a running landing or an EOL. The controlling factors for a successful landing (for the pax not necessarily the a/c) are:
Height at which failure manifested itself.
PRT (pilot reaction time).
Level of experience of the flying pilot.
Training.
Speed of a/c.
Stiffness of airframe (weathercocking ability).
(To name but a few.)
Height: The higher you are, the longer you have of regaining control.
PRT: The average PRT is estimated at 2 seconds for most instances. Any longer and the a/c could exceed airframe stress limits and in flight break up could occur.
Experienced pilot: Speaks for itself – they have trained and practiced for these occasions so some of it shouldn't come as a surprise. They are therefore less likely to 'overload'.
Speed of a/c: The faster you are travelling the more likely the a/c will remain cocked in the direction of travel. Atleast the yaw disturbance would be minimised.
Stiffness: Some a/c are more benign to TRF transgressions [Dauphin / Fenestron a/c / Squirrel etc]. Others may not be so forgiving [R22, Alouette etc]. The stiffer a/c will reduce the amount of yaw making it more likely to prolong fwd controllable flight in an attempt to reach a LZ.

These factors combined will decide the eventual outcome: EOL / running landing. The general 'expert' advice gleaned from actual and simulated experiences, suggests that a TRF in fwd flight and at height should be concluded with an EOL with the minimum of delay. This - because you are purposely putting the a/c into a know, tried and tested flight regime (auto) which also reduces the offset of yaw and pitch and culminates in a minimal fwd speed landing reducing the chances of high impact trauma. Prolonging flight leading to a resultant running landing could exacerbate the fault, cause unrecoverable departures from flight at height and below a minimum speed or increase the chances of a traumatic ending if speed and/or heading are uncontrolled at touch down.
In summary then it is suggested that a TRF in fwd flight and at sufficient height should be handled thus:

TRF in fwd flight results in uncontrolled yaw in the opposite direction to main rotor rotation.
Playing with the collective results in more yaw (applying collective), or less yaw (lowering collective). Regain some form of fwd controlled flight accepting yaw and or height loss. Continue fwd flight only if absolutely necessary. (IE: flying over hostile terrain).
Turn into wind if possible remembering to turn away from direction of yaw.
Enter auto (yaw reduces), establish autorotation and then chop the throttle(s). Yaw further reduces slightly.
Flare (yaw further reduces), level and cushion touchdown by cross controlling for yaw offset and sideslip. The reducing Nr will cancel out any tendency for the a/c to yaw substantially thereafter. Attempt as close as possible a zero fwd speed landing.

-------

TRCF: This is where it gets tricky for the incumbent, because it allows the pilot time to ‘experiment’ and we all know what happens then :{
The plan therefore is to apply KISS once more. Here goes:

The pitch on the TR blades is controlled (normally) by cables or rods. The pitch changes the amount of anti torque available to offset yaw due to the rotation of the main rotor.
If you RAISE the collective, the helicopter yaws in the OPPOSITE direction of main rotor rotation. And visa versa. When you RAISE the collective, I call the pedal that is pressed to keep the a/c pointing straight: POWER PEDAL. When you lower the collective, you ease off the power pedal to keep the a/c straight..or apply pressure to the other pedal, dependent on helo type.

When the ability to change the TR pitch stops, the a/c will yaw in direct proportion to the amount of collective lever movement and the pilot will not be able to prevent this happening.
Raise the collective without applying power pedal and the a/c yaws in the opposite direction to MR rotation. Lower the collective and the a/c yaws in the same direction as MR rotation.

For me, as I was learning about permutations for power/speed/heading offset/collective position/fiddling with throttle settings (and then changing to a new helicopter where the MR rotation was in the opposite direction! I felt I needed a ‘crutch’ to rely on, that would remain a constant. Here it is:

The moment I discover I have a possible TRCF, I remember the torque setting it happened at. I remind myself that a millisecond before the a/c became ‘unserviceable’ it was under control and flying in the direction I wanted it to fly in. Therefore if I can get back to that Torque setting prior to touchdown, the a/c will be pointing in the direction I require.
Example 1:
Flying straight and level – everything appears normal. I decide to descend (by lowering the collective) and in so doing, the a/c immediately yaws in the same direction of MR rotation without permission. I raise the collective back to the original torque setting and the a/c resumes ‘normal’ again.
I then commence my procedure for dealing with a TRCF i.a.w. my aircrew manual and my experience (or lack of it). However, when I finally wish to land safely at the end of this procedure, I know that by attaining that original torque setting, the a/c will be under some form of ‘recognisable’ flight regime (ie: straight and level).
In the above instance, the malfunction manifests itself at cruise power (say 50% Tq). I must therefore find a way to reproduce a relatively sustained profile at 50% Tq immediately prior to touchdown to achieve a survivable outcome.
Example 2:
I am in the climb where everything appears normal (70% Tq). As I lower the collective to level off, there is an undemanded yaw in the direction of MR rotation. I have a high power TRCF @ 70%. .
Example 3:
I am in the descent to land (30% Tq). I level off and there is an undemanded yaw in the opposite direction of the MR rotation. I have a low power TRCF @ 30%.

In all of the above examples, provided I can reproduce those ‘safe’ Tq settings (30, 50, 70), I will be in a relatively safe flight configuration. Now all I have to do is reproduce those steady states long enough to land:

Low power TRCF:
Where do I witness low power settings in my helo?
Bottom of a normal approach prior to arresting the descent.
Bottom of an auto prior to levelling.
Or if you look at the “KISS” power required curve below – Vy .
Vy varies for different helos but is around 60-70kts.

https://www.dropbox.com/s/hzt232ckxgb7ieq/Prfig2.gif

So, with a low power TRCF, I would initially endeavour to level off by raising the collective and accept the offset yaw in the opposite direction of MR rotation. I would then fly at Vy (minimising power, thus minimising this offset yaw) to a suitable landing strip. On arrival at the landing strip I would then initiate a SHALLOW descent at 60-70 kts (offset yaw reduces even more because you lowered the lever to descend). Prior to and just above the touchdown point, whilst still at 60-70kts, initiate a very gentle and prolonged nose up attitude (I specifically did not mention the word ‘flare’!). Allow the speed to decrease whilst still maintaining a gentle descent to land.
[*WARNING: If you reduce speed too much, you could end up dropping through your descent angle and have to apply collective to restrain the increasing R.O.D which could lead to uncontrollable yaw in the opposite direction to MR rotation and subsequent loss of control of the helo. In low power TRCF therefore be prepared for a relatively fast (50+kt) running landing].
Speed should now be inside the safety parameters for a running landing and either the skids / wheels can be used to maintain straight as you raise the collective to cushion the remaining touchdown, or if you are able (in a single pilot helo) bring the throttle back commensurate with the rate of change of yaw to remain relatively straight. In a twin pilot a/c the other pilot can play with the throttles at this stage.
[The bottom of this approach requires practice if it is to produce a polished outcome, but in an emergency, an unprepared landing without previous practice should still save your life].

Cruise power TRCF:
In the above low power TRCF scenario, I was trying to mimic the Tq I had when the TRCF manifested itself (30%). On the graph, 30% Tq or SHP relates to a minimum speed of Vy (ish).
This time though, with a cruise power TRCF I am looking to achieve 50%. From the graph it appears that the respective speed for this power is slower than Vy (as I move up the y axis from 30 – 50 Tq). So if I employ the same tactics as in the above scenario, at the bottom of the SHALLOW approach I can afford to slow down even more, prior to touchdown by raising the collective further to try to achieve 50% Tq/SHP. The result being that my touchdown speed is even lower than the previous scenario’s final running landing speed.

High Power TRCF:
The “easiest” outcome of them all. Using the same scenario as both of the above and in the best interests of KISS – I now have to go even further up the y axis to find 70% Tq/SHP. This means that at the bottom of my SHALLOW approach, as I begin my progressive nose up attitude immediately prior to touching down, I can bask in the satisfaction of knowing that the collective will need to be raised significantly as I slow down more, and more and more en route to achieving 70 Tq/SHP. In fact I might even (wind permitting) be able to come to a hover, or a (trickle) fwd drift.

In summary:

TRF: Provided the gearbox assembly remains onboard the probable outcome is a land as soon as possible (LASAP) auto and/or an EOL.

TRCF: Memorise the shape of your helicopters power/drag curve and picture where on the Tq axis your malfunction manifested itself and how you are going to return to that figure immediately prior to touch down. LASAP.

Remember: the more you practice this manoeuvre the more likely you will be able to survive it on the day of the race.:ok:

Nigel: When on deck stationary. Play with the tail rotor blades until they are in the zero pitch position, then memorise where the pedals are:ok:

T/R problems
 

Mainly for TC please ... congrats on a neat, informative and not too technical resume of the dreaded T/R problem. Can I suggest that all new and less experienced ppruners "mark, read, learn and inwardly digest TC's words" ... as my old RAF aerodynamics tutor would say.

But TC, having suffered two total failures, (one T/R drive-shaft shear and one T/R gearbox seizure) can I ask you to note, and as I wrote in my earlier contribution, that simply entering autorotation and closing the throttle (in the Enstrom 28/280 series) does not just REDUCE yaw opposite to the direction of M/R blade rotation ... having accomplished that ... a continued throttle closure produces an INDUCED yaw in the direction of M/R blade rotation as main rotor gearbox frictions take effect and at low speed would result in loss of control to left yaw/spin.

Once in steady state autorotation, my fix has been to use engine power (collective) combined with air speed to allow the nose to hold at the '10 o clock' position in the descent until just before the flare when the procedure you outline should get the machine safely on the ground with little residual run-on speed.

I agree with the axiom ... plenty of study of the principles and plenty of practice offers a significant increase in the chances of coping should the lights go out!

'Twould be good to hear from others who have experienced total T/R failure especially for we guys mostly flying on the bottom rung of light helis.

Dennis K.

DK: Thanks very much for your contribution. Worth its weight in gold:ok:
Can I confirm that for the Enstrom (where a/c 'stiffness' is lacking) , you established auto shortly thereafter the TRF and kept the engine running to retain a modicum of left yaw (in direction of MR rotation all the way to the deck, or did you convert to an EOL just prior to landing on as fwd speed was virtually eliminated?

Having said all that I think we are striving to achieve the same aim - go for an auto/eol rather than a running landing - yes?

Thanks again for your time.

Had a minor TRCF as a stude. After pulling to a hovering stop on the helipad I turned the H300 around and began a hovering taxy towards the hanger. As I picked up speed and started relaxing the left pedal I got no response, a slight push on the right pedal did nothing, so I tapped the left pedal a few times and normal control resumed for an uneventful landing. Although the problem was a binding cable it didn't seem like a big deal at the time. Reported it to maintenance nonetheless.

TC in your notes would you include something in there about short shaft failure as on some models full T/R performance is still available when it happens. Does anyone know if the engine surges and overspins the T/R before the fuel control eventually compensates for the sudden loss of engine load?

Cattle can u explain 'short shaft failure' please? Also what are you trying to say w.r.t. TR overspeed????
I'm doing TRCF later - much more 'complicated':eek: