TR Failure Drills
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How nice to have a safety discussion that is not about engine failure for once. Thanks to the original contributor for raising this topic.
Certainly during my PPL training all the emphasis was on engine failure and autos but the whirly thing at the back was hardly ever mentioned. I do think that there should be more time allocated to this during training.
Keep the discussion going guys - I am learning a lot.
Certainly during my PPL training all the emphasis was on engine failure and autos but the whirly thing at the back was hardly ever mentioned. I do think that there should be more time allocated to this during training.
Keep the discussion going guys - I am learning a lot.
Avoid imitations
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Nick,
A question regarding reduction of rotor speed. The minimum RFM figure for N2 / Nr on the S-76 is 93%, how would reducing it further, for example to your figure of 90%, affect the aircraft mechanically?
What about the engine to transmission torques increasing as the Nr is reduced for the same power? Is there likely to be a problem with breaking something else?
A question regarding reduction of rotor speed. The minimum RFM figure for N2 / Nr on the S-76 is 93%, how would reducing it further, for example to your figure of 90%, affect the aircraft mechanically?
What about the engine to transmission torques increasing as the Nr is reduced for the same power? Is there likely to be a problem with breaking something else?
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Carefull Cowboy !
I would be very carefull on generalizing on what a "tail rotor control failure" is
In ze french FMs(EC120) it talks about "tail rotor control failure", but seems to follow the procedures of tail rotor drive failure(Auto)
This could confuse dumb pilots like myself
In ze french FMs(EC120) it talks about "tail rotor control failure", but seems to follow the procedures of tail rotor drive failure(Auto)
This could confuse dumb pilots like myself
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Shy,
Good questions, and important ones.
generally, no parts will fail for a 10% overtorque (at least on the helos I have deep knowledge of). Remember, this is a very broken machine you are flying home, and when you land safely, and get down from the shoulders of your passengers who have been carrying you around singing "For he's a jolly good fellow" with true passion, you can write up the over torque! A few seconds on touch down are no sweat, IMHO.
For the rotor rpm on touchdown, most helos suffer those transients on HV engine cuts, and touch down at somewhere around 80 to 85% rpm as part of the certification testing. We have to show the FAA some reasonable data to show that this is not a catsatrophic event, so we know that is ok.
If you ever saw "The High and the Mighty" then you will understand what I am discussing. The old former captain, now a washed up co-pilot, brings the crippled airliner back across the Pacific by vastly over boosting the remaining two engines, knowing he is damaging them, but also knowing that his fuel consumption is now low enough to let their fuel last to shore. He has to smack the young, by-the-book captain to make his point. Sometimes the limits can be "reinterpreted a bit" in a true life and death emergency!
Here is that clip, which illustrates my teaching style, the one I learned from SASless:
http://www.s-92heliport.com/highmighty.wmv
Good questions, and important ones.
generally, no parts will fail for a 10% overtorque (at least on the helos I have deep knowledge of). Remember, this is a very broken machine you are flying home, and when you land safely, and get down from the shoulders of your passengers who have been carrying you around singing "For he's a jolly good fellow" with true passion, you can write up the over torque! A few seconds on touch down are no sweat, IMHO.
For the rotor rpm on touchdown, most helos suffer those transients on HV engine cuts, and touch down at somewhere around 80 to 85% rpm as part of the certification testing. We have to show the FAA some reasonable data to show that this is not a catsatrophic event, so we know that is ok.
If you ever saw "The High and the Mighty" then you will understand what I am discussing. The old former captain, now a washed up co-pilot, brings the crippled airliner back across the Pacific by vastly over boosting the remaining two engines, knowing he is damaging them, but also knowing that his fuel consumption is now low enough to let their fuel last to shore. He has to smack the young, by-the-book captain to make his point. Sometimes the limits can be "reinterpreted a bit" in a true life and death emergency!
Here is that clip, which illustrates my teaching style, the one I learned from SASless:
http://www.s-92heliport.com/highmighty.wmv
Purveyor of Egg Liqueur to Lucifer
Interestingly enough, IMHO, no-one has yet mentioned the actions required for the MD 500/600/900 series of helicopters.
I think that zxcvbn would need to reconsider his theory.
I think that zxcvbn would need to reconsider his theory.
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The NOTAR aircraft have a tail rotor, it is inside the tailcone, out of sight (and better protected, to be sure!)
The types of emergencies are the same, I would imagine, because the fan, its shafting, the control system for it, as well as the nozzel control mechanism are all subject to Mr. Murphy and his Law.
SilsoeSid you are also right to call into question the idea that an autorotation is the cure for all tail rotor failures. At high tail rotor pitch failure, an auto is the worst answer, possibly leading to loss of the machine (to say nothing about its occupants!) This is especially damning when, with a TR control failure to high thrust (so called "stuck left pedal") you could fly home first, and make a powered landing.
The types of emergencies are the same, I would imagine, because the fan, its shafting, the control system for it, as well as the nozzel control mechanism are all subject to Mr. Murphy and his Law.
SilsoeSid you are also right to call into question the idea that an autorotation is the cure for all tail rotor failures. At high tail rotor pitch failure, an auto is the worst answer, possibly leading to loss of the machine (to say nothing about its occupants!) This is especially damning when, with a TR control failure to high thrust (so called "stuck left pedal") you could fly home first, and make a powered landing.
Cor! Nick finally admitted he learned something from me! But then with my applied psychology who would not learn!
I prefer to call this method "The Pentacostal Method" in that its core belief is the "laying on of hands" results in the most effective rate of of learning.
It definitely is more fun teaching this way than by mere Rote learning. Primacy, intensity, effect, and exercise are all enhanced by such a technique.
One caution however....never use this technique on people who have arms longer than yours, who enjoy pain, carry guns, knives, dirks or daggers. Otherwise, the post flight de-brief can get a bit involved.
I prefer to call this method "The Pentacostal Method" in that its core belief is the "laying on of hands" results in the most effective rate of of learning.
It definitely is more fun teaching this way than by mere Rote learning. Primacy, intensity, effect, and exercise are all enhanced by such a technique.
One caution however....never use this technique on people who have arms longer than yours, who enjoy pain, carry guns, knives, dirks or daggers. Otherwise, the post flight de-brief can get a bit involved.
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Some help guys, this is my pattern of thought when faced with uncommanded yaw or loss of tail rotor control. I would like some input and suggestions on safer/ perhaps more efeective methods
- TR control failure : high pitch angle(TR) , set up approach with nose yawed off towards retreating side of disc, by decreasing collective pitch, test speed at which nose aligns with direction of motion at safe height(500'), approach long flat smooth surface for a run-on landing, get within a few feet(safe tail rotor height clearance ) of the ground and slow down and thus incr. collective untill nose straightens out and run-on to ground.
- Neutral pedal(control system) stuck : similar but higher run-on speed. and the more it leens toward minimum tail rotor pitch stuck, best to enter auto/ semi-auto and do slide/run-on.
- Complete loss of tail rotor thrust/ tail rotor blades/ gearbox failure etc. I was tought to enter autorotation and do heigher than normal flare and then try to flare off all speed before cushioning onto ground. With the bigger twins (10t+ ) higher inertia will alow possibly a bit of yaw towards retreating side during flare before sink starts, thus a run on perhaps possible (gearbox drag). Once entered autorotation and sufficient height and time, inc speed to manuf. recommended V for loss of tail rotor thrust and start to increase coll pitch and correct with bank, as mentioned by 'NickLappos', but down to what altitude would you follow such an extended glide to (agl) before entering full auto again ? and also what sort of flare would be best for small and large heli's ?
Any replies appreciated greatly guys
- TR control failure : high pitch angle(TR) , set up approach with nose yawed off towards retreating side of disc, by decreasing collective pitch, test speed at which nose aligns with direction of motion at safe height(500'), approach long flat smooth surface for a run-on landing, get within a few feet(safe tail rotor height clearance ) of the ground and slow down and thus incr. collective untill nose straightens out and run-on to ground.
- Neutral pedal(control system) stuck : similar but higher run-on speed. and the more it leens toward minimum tail rotor pitch stuck, best to enter auto/ semi-auto and do slide/run-on.
- Complete loss of tail rotor thrust/ tail rotor blades/ gearbox failure etc. I was tought to enter autorotation and do heigher than normal flare and then try to flare off all speed before cushioning onto ground. With the bigger twins (10t+ ) higher inertia will alow possibly a bit of yaw towards retreating side during flare before sink starts, thus a run on perhaps possible (gearbox drag). Once entered autorotation and sufficient height and time, inc speed to manuf. recommended V for loss of tail rotor thrust and start to increase coll pitch and correct with bank, as mentioned by 'NickLappos', but down to what altitude would you follow such an extended glide to (agl) before entering full auto again ? and also what sort of flare would be best for small and large heli's ?
Any replies appreciated greatly guys
One other thought....
I prefer to fly the aircraft with an aft CG vice loaded way forward. Seems the aircraft handle better when loaded aft and a secondary thought of positively affecting the CG shift should the TRGB and rotating bits depart the aircraft. Maybe it is just that I like to recline in my cushy seat rather than hang in the straps all day.
I prefer to fly the aircraft with an aft CG vice loaded way forward. Seems the aircraft handle better when loaded aft and a secondary thought of positively affecting the CG shift should the TRGB and rotating bits depart the aircraft. Maybe it is just that I like to recline in my cushy seat rather than hang in the straps all day.
Avoid imitations
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RedAnt,
I don't think there is a "blanket" answer. Each aircraft has slightly different characteristics and the multiple failure modes cloud the issue. There may also be more than one way of flying the aircraft to a safe landing.
My own main strategy for a TR control failure is the same as your own, namely to aim to get the nose out to the retreating blade side for approach which allows a gentle tweak on the collective to bring the nose straight whilst cushioning the landing.
This has been proven to work for both clockwise and counterclockwise main rotors from my own experiences in a number of different simulators (my own personal practice and also instructor duties). If there is no pressing need to land, I would consider a dummy approach or two at altitude to discover what will work best.
There is an obvious trap for pilots who fly different types, with opposing main rotor directions - it is possible to become confused about what is happening with regard to yaw directions, especially as during a complete rotor thrust loss situation the pilot action may need to be almost instinctive if control and structural integrity is to be maintained. I have always tried to avoid the advice of "lucky left / rotten right" for this reason. I am very confident that a very high percentage of us can remember which way the rotors were turning at startup (!) so the retreating blade is a very useful answer. *The lucky side is the retreating blade side , both for the safe side for the nose to be and the best side for the crosswind to be from on landing*.
P.S. *unless the pilot is faced with a very high TR power situation, which isn't too likely unless a servo runaway has occurred.
With regard to your question about C of G change.... a very significant change is very likely, to the point of the situation being non-recoverable.
I don't think there is a "blanket" answer. Each aircraft has slightly different characteristics and the multiple failure modes cloud the issue. There may also be more than one way of flying the aircraft to a safe landing.
My own main strategy for a TR control failure is the same as your own, namely to aim to get the nose out to the retreating blade side for approach which allows a gentle tweak on the collective to bring the nose straight whilst cushioning the landing.
This has been proven to work for both clockwise and counterclockwise main rotors from my own experiences in a number of different simulators (my own personal practice and also instructor duties). If there is no pressing need to land, I would consider a dummy approach or two at altitude to discover what will work best.
There is an obvious trap for pilots who fly different types, with opposing main rotor directions - it is possible to become confused about what is happening with regard to yaw directions, especially as during a complete rotor thrust loss situation the pilot action may need to be almost instinctive if control and structural integrity is to be maintained. I have always tried to avoid the advice of "lucky left / rotten right" for this reason. I am very confident that a very high percentage of us can remember which way the rotors were turning at startup (!) so the retreating blade is a very useful answer. *The lucky side is the retreating blade side , both for the safe side for the nose to be and the best side for the crosswind to be from on landing*.
P.S. *unless the pilot is faced with a very high TR power situation, which isn't too likely unless a servo runaway has occurred.
With regard to your question about C of G change.... a very significant change is very likely, to the point of the situation being non-recoverable.
Last edited by ShyTorque; 5th Dec 2004 at 21:16.
From the accident reports I have read, it would appear to be almost inevitable that one noses over and goes in inverted, at approximately 120 degrees nose down.
N.B. The above is not scientific; just a conclusion I have cobbled together over many years of reading the crash comics.
N.B. The above is not scientific; just a conclusion I have cobbled together over many years of reading the crash comics.
Bomber....
During a time and place far far away....a AH-1G Cobra took a hit from a SA-7 missle that removed the entire tail boom and related bits.....the crew (despite being at altitude) survived the incident. The aircraft remained right side up but spun like a top as I recall. One of the pilots is flying in the GOM today.....everytime I see him I touch his shoulder hoping some of his good fortune will rub off on me.
Some very good accounts are around about 412's that shed TRGB's.....some guys actually survived the events....though most do not.
During a time and place far far away....a AH-1G Cobra took a hit from a SA-7 missle that removed the entire tail boom and related bits.....the crew (despite being at altitude) survived the incident. The aircraft remained right side up but spun like a top as I recall. One of the pilots is flying in the GOM today.....everytime I see him I touch his shoulder hoping some of his good fortune will rub off on me.
Some very good accounts are around about 412's that shed TRGB's.....some guys actually survived the events....though most do not.
For the story of the Cobra / SA-7 mentioned above, see http://www.vhfcn.org/missle.html for full details.
SASless - can you get me a lock of his hair ?
SASless - can you get me a lock of his hair ?
How's this for TR jammed in low power, ie cruise. I've tried it in the simulator and it seems to work well.
Start to reduce speed, at some point the nose will start to yaw right(non French rotors). Set up an approach at this speed. The reduction in power for the descent will help. When happy with the approach, retard one engine to idle or shut it down. Maintain the speed all the way down. At the landing point flare off the speed. The reduction of power to more or less zero will stop the nose going right, it may indeed swing slighty left. As the speed decays to zero, start pulling in power to establish a hover, roll off the throttle on the remaining engine or get the second crew (or well briefed pax
) to retard the roof quadrant, and cushion the touchdown.
As I said, it works well in the sim and may be preferable to a double engine off landing.
Start to reduce speed, at some point the nose will start to yaw right(non French rotors). Set up an approach at this speed. The reduction in power for the descent will help. When happy with the approach, retard one engine to idle or shut it down. Maintain the speed all the way down. At the landing point flare off the speed. The reduction of power to more or less zero will stop the nose going right, it may indeed swing slighty left. As the speed decays to zero, start pulling in power to establish a hover, roll off the throttle on the remaining engine or get the second crew (or well briefed pax
) to retard the roof quadrant, and cushion the touchdown.As I said, it works well in the sim and may be preferable to a double engine off landing.
Back in 1981, the RAAF had a UH-1B which crashed. The T/R pitch change cables ran beside the drive shaft in the upper tunnel (in later models they were moved to the lower one). One cable came off the pulley and wrapped around the drive shaft, causing a full control deflection. The T/R blades flapped way past their limits and struck the fin, causing part of a T/R blade to depart the scene. This imbalanced the gearbox which tore itself out of the fin.
The resulting CG change pitched the nose down, and combined with the yaw, caused a mast bump. The main blade separated, but on its way out, it sliced through the left cockpit, bisected the copilot, removed the left door and then the tail boom. The remainder dropped / fluttered to earth, 3 fatalities.
No time to react.
The resulting CG change pitched the nose down, and combined with the yaw, caused a mast bump. The main blade separated, but on its way out, it sliced through the left cockpit, bisected the copilot, removed the left door and then the tail boom. The remainder dropped / fluttered to earth, 3 fatalities.
No time to react.
For anyone interested , `Gallery` p19 shows what can happen when a blade comes off; took the other blade and gearbox with it; just had enogh stick left to flare into/onto a small clearing on top of a hill.....
