Tail Rotor Problems
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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
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
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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!!
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Thermal runaway.
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!!
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Thermal runaway.
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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!
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!
Guest
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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.
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.
Guest
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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
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
Guest
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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.....
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.....
Guest
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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
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
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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
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
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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.
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.
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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
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
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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
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The Cat
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
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The Cat
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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
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
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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?
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?
Guest
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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.
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.
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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
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
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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...
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Thermal runaway.
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...
------------------
Thermal runaway.
Guest
Posts: n/a
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
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Peter B
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
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Posts: n/a
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!
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!