Hydraulic Lock /Jack Stall
"Just a pilot"
JimEli posted- 'Furthermore, servo-transparency is discussed under the normal operating procedures section of the POH, and described as “smooth” and “presents no danger.”'
Very similar to LTE, I guess, in that somebody has accepted a control limitation by design. One runs out of control effectiveness, sometimes. Not an issue for the engineer (It's in the RFM- just avoid doing that.), they're not involved in the crash because of the loss of an axis of control at the worst possible time.
Very similar to LTE, I guess, in that somebody has accepted a control limitation by design. One runs out of control effectiveness, sometimes. Not an issue for the engineer (It's in the RFM- just avoid doing that.), they're not involved in the crash because of the loss of an axis of control at the worst possible time.
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Thread diversion.. accident speculation...
I have already made apologies to those concerned and re-focussed the thread back on subject. If someone dare start a thread on accident speculation go for it..
As my thread has been hijacked there is one thing I will say in finality before it goes back on track:
If you hear of my fatality, (touch wood) Please note: I am saying now: Please do discuss my error, go ahead and analyse, talk, brainstorm and figure out my error(s). Spread the word on my possible mistakes so you can at least say.. well K48 ate it in these conditions with that equipment.. So maybe we'll take it easy in those conditions with that equipment.. I would be grateful. And I mean before the AAIB report comes out... the day after would be best. Thanks.
So, now you know my final wishes, back on thread? Hyd Lock.. dual systems..
NicKlappos, thanks for that. Very helpful. That has probably answered my question. Yours copied below. I wonder if you know this example, re The Hyd check at 60% N1 on the 206 during start up.. is this check for 'stick jump' for servo weakness (and perhaps potential Hyd Lock) as you describe.. ?
<Nicklappos wrote:>The new item that K48 throws out (he calls it hydraulic lock) has nothing to do with a maneuvering helo, it is a condition that old worn out servos might get, or servos with worn seals, and it is rare enough indeed. When it does show up, it can be seen during the controls check during runup, when each servo is felt while the other is turned off, and weak servos usually tell themselves by producing jumps as the systems are switched, and odd forces when the bad servo is manipulated.>
As my thread has been hijacked there is one thing I will say in finality before it goes back on track:
If you hear of my fatality, (touch wood) Please note: I am saying now: Please do discuss my error, go ahead and analyse, talk, brainstorm and figure out my error(s). Spread the word on my possible mistakes so you can at least say.. well K48 ate it in these conditions with that equipment.. So maybe we'll take it easy in those conditions with that equipment.. I would be grateful. And I mean before the AAIB report comes out... the day after would be best. Thanks.
So, now you know my final wishes, back on thread? Hyd Lock.. dual systems..
NicKlappos, thanks for that. Very helpful. That has probably answered my question. Yours copied below. I wonder if you know this example, re The Hyd check at 60% N1 on the 206 during start up.. is this check for 'stick jump' for servo weakness (and perhaps potential Hyd Lock) as you describe.. ?
<Nicklappos wrote:>The new item that K48 throws out (he calls it hydraulic lock) has nothing to do with a maneuvering helo, it is a condition that old worn out servos might get, or servos with worn seals, and it is rare enough indeed. When it does show up, it can be seen during the controls check during runup, when each servo is felt while the other is turned off, and weak servos usually tell themselves by producing jumps as the systems are switched, and odd forces when the bad servo is manipulated.>
Last edited by K48; 27th Oct 2007 at 01:21.
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Tut-tut everybody! You should know (or should have known) that on PPRUNE there is now a two-year moratorium before jack stall can be discussed again, other than the odd thread in which references are made to movie characters or fluffy animals. When you encounter jack stall, no matter how big or small, you must refrain from reporting your experience on PPRUNE. On this board, there must be nothing mentioned, analyzed, postulated, theorized, hinted, discussed, surmised or even educated-guessed at when it comes to jack stall because...umm...because...uhh...because...oh yeah, because all of us here at PPRUNE are tired of flogging that dead horse, that's why. And if you don't like it, just take your curious kiester over to any of the other aviation discussion boards in which jack stall may be discussed in a manner that might bring up some useful, timely, or worthwhile information.
I do apologize that you weren't fully briefed on this procedure. However, if you'll be so good as to put a tick-mark in the appropriate box on the form, initial it and then fax it to me, I'll sign you off so you'll know better for next time.
I do apologize that you weren't fully briefed on this procedure. However, if you'll be so good as to put a tick-mark in the appropriate box on the form, initial it and then fax it to me, I'll sign you off so you'll know better for next time.
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thanks
Thanks for those contributions, Nickkappos.
Devil, you make a valid point. In the smaller helis with hyd systems that can't cope with all flight envelopes it's accident potential that perhaps should not be tolerated in a/c design at all. This is refering Jackstall though. Any further comments on Hyd Lock appreciated. Perhaps someone knows the facts behind the scary clip from the beginning of the thread..which could easily have been an accident.. here Is this Jack Stall or a Hyd Lock...? Is it common?
Devil, you make a valid point. In the smaller helis with hyd systems that can't cope with all flight envelopes it's accident potential that perhaps should not be tolerated in a/c design at all. This is refering Jackstall though. Any further comments on Hyd Lock appreciated. Perhaps someone knows the facts behind the scary clip from the beginning of the thread..which could easily have been an accident.. here Is this Jack Stall or a Hyd Lock...? Is it common?
K48,
Hydraulic lock and Jack Stall are not related. Other than by the fact that they both involve actuators.
Like Nick has already said, please stop trying to start another 'helicopter myth'. If you want to find out about some other 'helicopter myths', try searching through the threads that Nick has started. It is a very, very interesting thread.
re the Dauphin incident - it has been mentioned (and analysed) already in the other Jack Stall threads.
And finally:
Essentially, no. Why not? Because you can't selectively turn off the individual servos in a B206. You are just checking the general state of the hydraulic system - ie is it working or not? In his example, Nick is probably referring to much larger helicopters (ie S76, S92 etc)
Hydraulic lock and Jack Stall are not related. Other than by the fact that they both involve actuators.
Like Nick has already said, please stop trying to start another 'helicopter myth'. If you want to find out about some other 'helicopter myths', try searching through the threads that Nick has started. It is a very, very interesting thread.
re the Dauphin incident - it has been mentioned (and analysed) already in the other Jack Stall threads.
And finally:
Essentially, no. Why not? Because you can't selectively turn off the individual servos in a B206. You are just checking the general state of the hydraulic system - ie is it working or not? In his example, Nick is probably referring to much larger helicopters (ie S76, S92 etc)
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Originally Posted by NickLappos
Jack stall is preventable by designing proper controls for the helicopter (servos big enough to always tell the blades to keep their forces out of the cockpit.)
Perhaps someone knows the facts behind the scary clip from the beginning of the thread..which could easily have been an accident.. here Is this Jack Stall or a Hyd Lock...? Is it common?
The Dauphin & the Pole (video)
http://www.pprune.org/forums/showthr...highlight=jack
Regards
Aser
"Just a pilot"
206 hydraulic shutoff check
K48, I was told that the hydraulic check you refer to checks that the hydraulic cutoff switch works normally. This is also common to other helos.
Quick review of the fundamentals- the hydraulic cutoff switch energizes a valve that blocks flow to the servos, thus reverting to non-assisted control, and, hopefully eliminating boost issues by eliminating assist. If the switch is defective, it won't shutoff flow and whatever hydraulic assist issue you had could continue until you land.
Quick review of the fundamentals- the hydraulic cutoff switch energizes a valve that blocks flow to the servos, thus reverting to non-assisted control, and, hopefully eliminating boost issues by eliminating assist. If the switch is defective, it won't shutoff flow and whatever hydraulic assist issue you had could continue until you land.
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Aser
Aser thanks for that. It's the same video clip on that thread as given above for those who can't see it. The thread is a good read on Jack Stall. Deep Jack Stall sounds likely to be the Hydraulic Lock that I opened the thread with. Thanks for the highly regarded experience donated above. I can't help feeling quite astonished that this be regarded as an acceptable design compromise in this day and age. It reminds me of my Laguna bonnet flying up last year on the motorway...nearly killing us. When I complained to Renault they said that I had not been using the car within limits..... I shouldn't accelerate over a hill into the wind like that... (joking). But seriously they did say that I had not maintained it properly etc etc! My own RoadAI revealed that the 2 main catches are under-designed pathetic little things... and over the years grease plus dust had made a paste that prevented them from locking closed..(not visible) the backup centre latch that is supposed to be the last-chance-saloon backup was/is also under engineered with a weak spring that was not doing it's job, (also not visible). 3 failures... and I was made to feel that it was my fault? I am not ever buying a renault again... nor will I ever a helo with jackstall issues for that matter.. isn't it just poor design mentality? How hard can it be to increase the specs of your Hyd system? I wonder how can a dual system like on the Dauphin suffer the same issue as a single system? This may mean that you are twice as likely to get a serious failure... and so actually being worse than a single system? In contrast an As332 with op limits imposed for one system inoperative makes sense.. but not for both Operative
Is it not fair to wonder why is this a tolerated state of affairs? Surely it's an undisputable certainty that accidents will and have happened as a result. I acknowledge that all helos/a/c have limits... but this just doesn't seem acceptable.. it's like... your nice new car manual reads: 'Occasionally when your laguna is full of passengers and you have to break hard from near vne 70mph the hydraulic breaks might stall and leave you with no brakes
....oh and it will swerve right and lock up too.
I confess to being on a learning curve here but sometimes it takes fresh eyes to see how ludicrous a state of affairs has become. I was a mechanical engineer and do feel this design compromise is totally unjustified in such an a/c. We all know the stability comparisons of helos vs fixed wings.. now consider cars -with a 2 dimensional advantage: Brake failure would still not be acceptable. So I do wonder how this situation ever got past certification for helos.: I know it's all probably been said before.. Perhaps the problem is lack of evidence after such a catastrophic accident?....
(How many are possibly absorbed in pilot error or IMC stats?...anyone from AAIB volunteer a suggestion?)
Sorry for the rant.. no rant should finish without a suggestion of a solution... Perhaps the solution could be a refit of all under-spec Hyd systems at manufacturers cost... maybe their insurance would pay...? 
better than pilots/pax with their lives? Or maybe I am missing something....? 
$$$
). But seriously they did say that I had not maintained it properly etc etc! My own RoadAI revealed that the 2 main catches are under-designed pathetic little things... and over the years grease plus dust had made a paste that prevented them from locking closed..(not visible) the backup centre latch that is supposed to be the last-chance-saloon backup was/is also under engineered with a weak spring that was not doing it's job, (also not visible). 3 failures... and I was made to feel that it was my fault? I am not ever buying a renault again... nor will I ever a helo with jackstall issues for that matter.. isn't it just poor design mentality? How hard can it be to increase the specs of your Hyd system? I wonder how can a dual system like on the Dauphin suffer the same issue as a single system? This may mean that you are twice as likely to get a serious failure... and so actually being worse than a single system? In contrast an As332 with op limits imposed for one system inoperative makes sense.. but not for both Operative Is it not fair to wonder why is this a tolerated state of affairs? Surely it's an undisputable certainty that accidents will and have happened as a result. I acknowledge that all helos/a/c have limits... but this just doesn't seem acceptable.. it's like... your nice new car manual reads: 'Occasionally when your laguna is full of passengers and you have to break hard from near vne 70mph the hydraulic breaks might stall and leave you with no brakes....oh and it will swerve right and lock up too. I confess to being on a learning curve here but sometimes it takes fresh eyes to see how ludicrous a state of affairs has become. I was a mechanical engineer and do feel this design compromise is totally unjustified in such an a/c. We all know the stability comparisons of helos vs fixed wings.. now consider cars -with a 2 dimensional advantage: Brake failure would still not be acceptable. So I do wonder how this situation ever got past certification for helos.: I know it's all probably been said before.. Perhaps the problem is lack of evidence after such a catastrophic accident?.... (How many are possibly absorbed in pilot error or IMC stats?...anyone from AAIB volunteer a suggestion?)Sorry for the rant.. no rant should finish without a suggestion of a solution... Perhaps the solution could be a refit of all under-spec Hyd systems at manufacturers cost
... maybe their insurance would pay...? better than pilots/pax with their lives? Or maybe I am missing something....? $$$
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Devil re 206 hyd check
Thanks... that must be the interconnecting valve then.. if you have any more detail on that I would appreciate it. Is there a double acting actuator (two pistons on one shaft) in this 'servo control unit'? At60%N1 you are looking for a jump in the stick.. Perhaps this check detects a sticky/damaged piston on one side of the double acting actuator?
I am not sure I see how this particular check might reveal a failure in the interconnecting valve itself though as surely there would be no change if it were to not operate? The later check at 100%N2 when you move the sticks will prove the interconnecting valve has released the hyd pressure though and would do as you described though...? I may be thinking of a totally unrelated system though as I have no specific info on the 206 system.
I am not sure I see how this particular check might reveal a failure in the interconnecting valve itself though as surely there would be no change if it were to not operate? The later check at 100%N2 when you move the sticks will prove the interconnecting valve has released the hyd pressure though and would do as you described though...? I may be thinking of a totally unrelated system though as I have no specific info on the 206 system.
Hmmm, K48. You don't seem to be very good at listening/reading.
Jack Stall, no matter how 'deep', IS NOT Hydraulic Lock. Jack Stall is temporary. Hydraulic Lock (due to a failed component) is permanent. The two are very different.
You might not be willing to listen to me (and don't worry, you won't be the first!
) but please listen to Nick. He is a bona fide expert on these matters. If you're not sure who Nick is, try Googling him quickly. His 'resume' tends to lend a bit of gravitas to his arguments.
You are indeed. And it would appear that you are right at the bottom of it at the moment. Take a bit of time to read all of the previous 'Jack Stall' threads. Particularly Nick's contributions. Everything that you have said above has already been discussed. A lot. (Apart from the Laguna bit, of course.
)
And whilst you're at it, here's the Helicopter Urban Myths thread that I was telling you about. Have a read through that as well. Although I've got a feeling that Nick might be adding to the list soon...
You might not be willing to listen to me (and don't worry, you won't be the first!
) but please listen to Nick. He is a bona fide expert on these matters. If you're not sure who Nick is, try Googling him quickly. His 'resume' tends to lend a bit of gravitas to his arguments. You are indeed. And it would appear that you are right at the bottom of it at the moment. Take a bit of time to read all of the previous 'Jack Stall' threads. Particularly Nick's contributions. Everything that you have said above has already been discussed. A lot. (Apart from the Laguna bit, of course.
)And whilst you're at it, here's the Helicopter Urban Myths thread that I was telling you about. Have a read through that as well. Although I've got a feeling that Nick might be adding to the list soon...
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The nEd?
Jack Stall, no matter how 'deep', IS NOT Hydraulic Lock. Jack Stall is temporary. Hydraulic Lock (due to a failed component) is permanent. The two are very different.
. ) Although this Kiwi was very experienced he was perhaps unaware of the difference in terminology, as many are not over here either, even though it is now taught in the latest ATPL material. But to me it has all been cleared up, with thanks to all - and I have to say that I am extremely honoured to have the input of those such as Nick (and your own good experience Bravo) in the thread.
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As an ex- military pilot I would like to support those who are saying Jack-stall is a tempory condition induced by flying the aircraft out-with it's safe flying envelope (i.e. tearing the arse out of it!). Commercial/ Private pilots should never be in this position. Hydraulic Lock is a mechnical failure.
There we are, my first post!
There we are, my first post!
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Jack-stall doesn't just happen unannounced! There are warning signs of incipient stall, such as heavy 1 R vibration in a tight turn, with a high power setting. Reduce pitch and level the aircraft will put you out of danger,
Jack stall, Full Jack Stall, Transient Jack stall, Minimal Jack Stall...normal Jack Stall, Blade stall, cyclic/collective interaction....can we produce a definition for each distinctively different response for when the Main Rotor subverts "normal" control response?
It might help to organize the arguments here.
It might help to organize the arguments here.
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A Nony Mouse has lots of strong opinions about the non-problem that jack stall represents. Of course, he is wrong! If he took that marginal machine up to altitude, he could stall in simple maneuvers, and he would have chocolate brown pants instead. He doesn't know how to tell the severity of his maneuver, since no means is provided. Also, the myth that vibration must increase prior to blade stall is as dead as a dodo with today's helicopters.
We should take jack stall seriously, the number of aircraft that flip upside down and crash because of jack stall is small but significant, as is the testimony of those who survived it in spite of the cool assurances of those apologists like Mouse.
What precisely is wrong with expecting the hydraulics to be strong enough to allow the pilot to do his job?
We should take jack stall seriously, the number of aircraft that flip upside down and crash because of jack stall is small but significant, as is the testimony of those who survived it in spite of the cool assurances of those apologists like Mouse.
What precisely is wrong with expecting the hydraulics to be strong enough to allow the pilot to do his job?
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How many machines have crashed due to jack stall from everyday within the envelope normal flying??...Don't count high speed low level passes over buddies with hard cyclic climbs at the end,or hard tight turns at speed on or above MAUW,flying at speed, heavy in bad turbulence. Its definitely not high on the list of things to worry about when I go to work in the morning.
SL
SL
