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K48
25th Oct 2007, 18:11
Hi all.. In the ole ATPL(H) material Hydraulic Lock is described as different to Jack Stall- which if I remember correctly is a hydraulic force overload.
Hydraulic Lock as I understood it from the ATPL(H) studies is a failure (design or mechanical) in which the hydraulic pressure gets around the back of the relevant actuator(s) and the controls become hydraulically 'locked'. Turning off your HYD may make no difference..? Does anybody know of this?
While training in NewZealand I was flown over the site of an AS350 accident where the pilot had pulled a hard right turn (fully loaded with 4 Pax) to show a view of something. He had (I was told) got 'Hydraulic Lock' and continued into the ground at high speed. I was told it was well known with As350s, in NZ at least, that high positive G and especially right turns in the As350 was to be avoided.. (If I recall correctly). I asked which type of hydraulic failure he meant and was not given a definite response either way..'Is there a difference?'
For interest in this Dauphin clip... (http://www.youtube.com/watch?v=9mzT13Hd5Gw)he seems to be straight and level, but this looks more likely to be just Jack Stall from an aggressive pull back on the stick. see here (http://www.youtube.com/watch?v=9mzT13Hd5Gw)
Can anybody shed light on this issue of Hyd Lock...? (not a big discussion about Jack Stall that has been talked about in depth in other threads).
(Note: My previous refs to specific recent accidents have been removed out of respect and sensitivity to those affected. I ask to keep the thread on the technical issue proposed, Hydraulic Lock:))

Bravo73
25th Oct 2007, 18:18
Ahhh, the power of 'search'. :E

Edited to add: Sorry, I linked to the wrong thread. Try this one:

http://www.pprune.org/forums/showthread.php?t=254165




PS A quick word of advice - be very careful about playing 'accident investigator'. Jack stall probably didn't have an influence on the Morecombe Bay accident. And nobody really knows what happened to Colin McRae yet. Be careful about adding 2+2. It's all too easy to come up with 5.

killabeez
25th Oct 2007, 18:32
Do you realy know WTF you are talking about ?????

Dont bring up old and ongoing investigations to explore 'YOUR' mind, !!!

K48
25th Oct 2007, 22:59
CHC. Very sorry to offend.
Killabeez. The issue is what I am looking to answer?

Bravo, I did search.. thanks.. but no answers on Hyd Lock as described above. Thread continues with orginal references removed due sensitivity/respect CHC.

Bravo73
25th Oct 2007, 23:28
From how you describe it (I've never come across the term but I'm by no means an expert), Hydraulic lock sounds like what would happen to any actuator if it failed (ie hydraulic fluid in both chambers.)

Jack stall occurs when the actuators are still working but they can't apply enough force to overcome the aerodynamic forces. So they 'lock' momentarily.

So, 'is there a difference?' Yes. One is a permanent failure of a component. And the other is a temporary exceedance of a design limitation (to put it kindly.)

FH1100 Pilot
26th Oct 2007, 00:12
Tut-tut, K48! You should know (or should have known) that on PPRUNE there is at least a two-year moratorium before *any* accident can be discussed, other than the obligatory, lengthy thread in which condolences are wished to the pilot and crew. When an accident occurs, no matter how big or small, we must always wait until the "official" report comes out (for as long as that may take) before the event can even be spoken about out loud. There must be nothing mentioned, analyzed, postulated, theorized, hinted, discussed, surmised or even educated-guessed at because...umm...because...uhh...because...oh yeah, because the lords of PPRUNE say so, 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 accidents are 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.

Remember: Accident talk here = Verboten!

Happy to help.

Scissorlink
26th Oct 2007, 01:16
Got jack stall.....reduce collective..no more jack stall, now that wasn't to hard was it

SASless
26th Oct 2007, 02:18
Oh oh! The dreaded "jack stall" question....did we not have a detailed hashing of this topic not so long ago? Perhaps we should revive that thread and carry on with it.

Senior Pilot
26th Oct 2007, 02:27
SASless,

This thread (http://www.pprune.org/forums/showthread.php?t=233275) here, or this one (http://www.pprune.org/forums/showthread.php?t=254165) maybe?


FH1100,

Harsh words: I know of no edict from PPRuNe that forbids healthy discussion, but you always run the risk of criticism from other Rotorheads should the discussion become inappropriate.

Senior Pilot

killabeez
26th Oct 2007, 08:34
FH1100 Says 'There must be nothing mentioned, analyzed, postulated, theorized, hinted, discussed, surmised or even educated-guessed at because...umm...because...uhh...because...oh yeah, because the lords of PPRUNE say so,'
ERM NO, the reason is and always has been because why try to educate-guess when WE ALL dont know the full facts !!
If you want that sort of information you can always just pick up a daily paper and read the full 'bull**** and missinformation' stories to satisfy anybodies appetite for postulation, theorization, hints, or NON educated guesses,
How would your grieving family and relations feel if we was discussing an accident you had been involved in without the facts !
Good luck,

Said my lot, thanks to the original poster for editing the post, cheers chap ,

26th Oct 2007, 08:51
K48 - jackstall is where the aerodynamic backloads from the blades (specifically on the retreating side during manoeuvering) overpower the hydraulic jacks because they are not man enough for the job. Aerospatiale (as they were then) claimed this was designed into the system for Gazelle but most people are of the opinion that they just under-engineered the hyd system.

I have heard of, but not experienced, similar problems in Squirrels and another label that was given to the condition was 'control transparency'.

However, a hydraulic lock is a hydraulic lock with pressure trapped on both sides of the actuator, usually due to a blocked port or failed pilot valve. Only a detailed stripdown of the components would reveal the source of the problem and even then might not be 100% conclusive.

K48
26th Oct 2007, 09:26
Crab and Bravo thanks for reply on subject...
I just read that Hydraulic Lock is actually used to hold down undercarriage in some light fixed wing a/c, perhaps in some helis too. Anyone know of their type's u/c design?
I have just dug up the ole notes.. (the power of search that Bravo taught me;):E):
It seems most Power Control Units consist of "a balanced double acting actuator where the body of the actuator is attached to the flying control surface input and the ram is attached to the structure of the a/c".
The pilots selector is linked to a valve, moving the selector will open one side of the actuator to pressure, the other to return, thus assisting the movement. Things equalise in a follow up action (not sure exactly how)and the control therefore assists only.
However in the event of fluid being lost (I assume after accumulator exhaustion) an interconnecting valve drops to break the 'hydraulic lock', allowing the control to be moved manually.
Of course most bigger helis are not really controllable manually. But it is one thing to be dumped with manual control and it is another for the interconnecting valve or equivalent to fail and hold the controls in place = hydraulic lock.
Now of course this is just me digging out exam material of old which was mostly fixed wing related and says no more... So I wonder could people familiar with their type/hyd systems e.g AS350/365 dual system and As332s etc please volunteer more detail? For example how does a dual system work in practice. Thanks Crab for that...
Cheers

charliegolf
26th Oct 2007, 09:48
From B73:
Hydraulic lock sounds like what would happen to any actuator if it failed (ie hydraulic fluid in both chambers.)

Don't the jacks always have fluid in both chambers?

Or do you mean pressure to both chambers?

CG

HeliComparator
26th Oct 2007, 09:56
On the 332L & L2 the flight control servos are in hydraulic lock when there is no control input - ie the fluid is trapped both sides of the piston and the piston cannot move. Operating the flight controls (with or without hydraulic pressure) operates the distributor valve thus breaking the hydraulic lock and letting the hydraulic pressure motor the piston (or in the case of loss of a hydraulic system allows the other piston in the jack to motor the piston, circulating the unpressurised fluid in the duff system).

The main undercarriage legs are held both up and down by hydraulic lock (nosegear has mechanical lock however).

Jackstall can occur on the 332L2 following failure of 1 hydraulic system. Remembering that force = pressure x area (area is fixed and is the area of the piston head) if the pressure from the hydraulic system results in a force less than the feedback forces from the rotor head, the controls will appear to lock or even perhaps motor the wrong way. This can happen during high speed right-banked flight (with 1 hyd system out) and so there is an accumulator on the RH jack to allow level flight to be obtained should the hyd system fail in this flight condition, after which there is a bank limitation imposed by the EOPs.

The EC225 also has the possibility of jack stall when on 1 hyd system though new servos make this less likely than on the L2. As well as the EOPs specifying a bank limit following a hyd failure, there is also an aural warning calculated depending on mass and load factor - if the audio sounds you are approaching the jack stall limit and its time to back off (again, only following failure of 1 hyd system).

HC

Devil 49
26th Oct 2007, 10:46
There's very good reason why one should discuss an accident without the illusion of perfect knowledge- survival. There's lots to be learned in the discussion of what is known of any accident circumstances. It's my belief that almost all accidents start with a a reasonable pilot.

FH1100 Pilot
26th Oct 2007, 11:46
I hate to play devil's advocate here (heh-heh-heh, I kill me) but I completely agree with him.:D

On the other hand, Killabeez asks: "How would your grieving family and relations feel if we was discussing an accident you had been involved in without the facts?"

They'd feel fine because we was doing exactly what *they* was doing. See, I'm pretty sure *they* would want to know what happened too - the known facts and circumstances, the possible causes along with those things that might be immediately ruled-out (e.g. "Could Bob have been drunk?" "NO FRIGGIN' WAY!!! Uhh, well maybe...yeah, possibly...okay, probably."). *They* wouldn't want to just sit around, shrug their shoulders and patiently say, "Ahh, no point in asking questions - even non-expert ones, let's just wait a couple of years for the formal report to come out." :rolleyes:

No. That's not human nature. Human nature makes us curious and inquisitive. If a pilot like myself were to be involved in an accident, at least some people on this planet would go, "How did THAT happen?! ...And WHAT happened?" That's called being normal. I know some of you won't understand that.

NickLappos
26th Oct 2007, 12:05
K48 might have helped us uncover another myth! The distinction that someone told him about a mysterious hydraulic lock condition that runs around waiting to infect your servos, and that somehow explains the cases where "straight and level" aircraft lose control (because someone thinks you can't get jack stall in an aircraft that is not at weird attitudes).

For the record, you can make an aircraft that is prone to jack stall get the condition in every flight attitude known to man. The stall of the rotor is the key. Rotor stall causes the servos to be loaded up by the changing pitching moment from the blades. In a helo that gets jack stall, the servos are too weak to fight this condition, and the forces overwhelm the servo, which then can lock the controls or even cause them to whip around the cockpit. Jack stall is a euphemism for "out of control because the servos are too small for the rotor". 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.)

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.

JimL
26th Oct 2007, 12:25
Devil and FH1100,

I'm with both of you on this - silent speculation is worthless; best that we discuss these issues and improve our understanding. Long gone are the days when we used to stay behind after flying and discuss all current issues with our peers (I really did learn about flying from that).

We should not tread on the sensitivities of relatives or friends but, waiting for the accident report - which from experience takes years to emerge, is a vow of silence that is way too long.

Jim

Bravo73
26th Oct 2007, 14:55
From B73:

Don't the jacks always have fluid in both chambers?

Or do you mean pressure to both chambers?

CG

Erm, yes I probably do. :O But I refer the learn'd gentleman to my previous comment:

(I've never come across the term but I'm by no means an expert)

Either way, the actuator is knackered. And it's not really related to jack stall.



With regard to speculation about accidents, it is my view that informed speculation (before the accident report comes out) might well have some merit. And what I mean by informed is speculation or input from people who have experience of either the aircraft, the operation or the environment. What K48 did was particularly ill-informed and as such is really no better than what one might consider as 'tabloid speculation'. ie 2+2=5 :=

JimEli
26th Oct 2007, 16:31
Actually, Jack Stall is a character, played by Ashton Holmes, in the 2005 movie “A History of Violence”. So, can we drop the colloquialism and refer to the phenomenon as “Servo-transparency?” Furthermore, servo-transparency is discussed under the normal operating procedures section of the POH, and described as “smooth” and “presents no danger.” I draw your attention to the tagline of the aforementioned movie, “Everyone has something to hide.”

Devil 49
26th Oct 2007, 18:49
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.

K48
26th Oct 2007, 19:48
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.>

Revolutionary
26th Oct 2007, 19:55
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.

FH1100 Pilot
27th Oct 2007, 00:07
Well that was original.

K48
27th Oct 2007, 01:31
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 (http://www.youtube.com/watch?v=9mzT13Hd5Gw) Is this Jack Stall or a Hyd Lock...? Is it common?

Bravo73
27th Oct 2007, 08:35
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:
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.. ?

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)

Graviman
27th Oct 2007, 13:09
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.)

It will be interesting to see whether brushless DC electric servos have as big an impact on small helicopter control system design as they have had in automotive. Some interesting papers by Joseph Horn / Derek Bridges (Comanche).

Aser
27th Oct 2007, 13:45
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?

We have even another thread for you! :E

The Dauphin & the Pole (video)
http://www.pprune.org/forums/showthread.php?t=225261&highlight=jack

Regards
Aser

Revolutionary
27th Oct 2007, 14:56
FH1100 Pilot, you know, imitation, sincere, flattery and all that.

Devil 49
27th Oct 2007, 15:14
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.

K48
27th Oct 2007, 16:13
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:E). 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:confused::confused: 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:eek:....oh and it will swerve right and lock up too.:ugh: 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.:confused:: 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:E... maybe their insurance would pay...? :E:D better than pilots/pax with their lives?:( Or maybe I am missing something....? :\ $$$

K48
27th Oct 2007, 16:36
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.

Bravo73
27th Oct 2007, 18:17
Hmmm, K48. You don't seem to be very good at listening/reading. :ugh:

Deep Jack Stall sounds likely to be the Hydraulic Lock that I opened the thread with.

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!:O) 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.


I confess to being on a learning curve here

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 (http://http://www.pprune.org/forums/showthread.php?t=158490) 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... :}

K48
29th Oct 2007, 11:01
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.
Sorry, that's a misunderstanding due to various thread diversions and lazy typing on my part- I was referring specifically to the orginal thread - While I have had confirmation of the true definition of Hyd Lock as per ATPL material (courtesy NLappos et al), I was stating that I now have come to the conclusion that what my Kiwi friend was describing as 'Hyd lock' was most likely in fact Deep Jack Stall - i.e when he was describing the cause of an AS350 accident NE of Auckland, to which I referred at the beginnning of the thread. (Bravo I'm surprised you didn't spot that. Were you off thread again? ;):E. ) 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.:ok:

A Nony Mouse
29th Oct 2007, 11:55
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!

A Nony Mouse
29th Oct 2007, 12:08
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,

SASless
29th Oct 2007, 14:23
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.

rjsquirrel
29th Oct 2007, 19:08
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?

K48
29th Oct 2007, 19:35
What precisely is wrong with expecting the hydraulics to be strong enough to allow the pilot to do his job?

Right on the nail....

Scissorlink
29th Oct 2007, 19:40
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