It is the term to describe when the blades overpower the hydraulic servos, causing the controls to whip around, and usually causing control loss.

It is the product of having servo hydraulics that are too small for the helicopter in question, because the servos should be able to muscle the blade without feedback. No modern US Military aircraft is allowed to experience servo stall or jack stall, as the hydraulics are designed to have enough force to overcome the most extreme blade forces without being back driven.

The forces produced by the blade are generally the stall forces due to the strong pitching moment changes produced when the stall occurs, usually due to extreme maneuvering.

It doesn't need to be particularly aggressive. If you are travelling at high speed and a bird appears in front of you, you tend to pull the stick back and perhaps to the right.

When i did this, the controls moved a bit, but the cyclic then locked solid, and the aircraft, which had started to turn right and nose up, suddenly flipped back to a level attitude. When I stopped trying to fight the controls, and the aircraft stopped reacting, all returned to normal, though my heart rate took a little longer.

Lucky it flipped back to the left and not further to the right, as I would have been upside down.

Agrees with DD, it does not have to be that violent. On a straight B model at max gross and MCP, a dive up to 135 kts and just a bit aft stick will give this symptom. Lessen the collective or aft stick and it goes away. Not any diffrent load than servo off in cruise. IMHO I think it is vital to have felt this during initial training, to recognize it and act accordingly.

I think the idea with this is to limit the load being fed into the swashplate, the pilot will feel the "jack stall" and lessen the load. On the first 355 with dual servos they did not have any limit switch, and to much load was feed into the swashplate with permanet deformation seen as a result. After that the limit switch was installed on top of one of the servos.




CB

Disguise,

What altitude, OAT, Indicated Air Speed and gross weight were you when this occurred?

Collective Bias,

I think your description is quite correct, but let me translate the logic just a bit:

The swashplate is too weak for the rotor blades, because the rotor forces generated can create high enough stresses to bend the swash plate. As a result, the manufacturer reduced the strength of the hydraulic servos, so that the servos would back-drive before these high stresses could be generated. This safety feature prevents over stressing the helicopter, but also reduces the pilot\'s ability to control the aircraft during relatively mild maneuvers within the flight envelope.

Is this reasonably correct?

Errrr...Nick...guys....let me get this straight.....the 350 is designed and certified with this "capability" or as I see it....built in lack of control or questionable handling ability?

What you guys are describing are somewhat "normal" situations that easily result in the loss of control of the helicopter....frozen controls....feedback during cruise flight maneuvering?

Am I getting timid in my old age or is this a desirable situation? Has this a bearing on some recent crashes due to hydraulic failures....feedback forces that preclude safe landing of the helicopter?

For Nick...have you encountered...or know of other aircraft that have similar characteristics....or is this like unique to Euro-choppers? (of the French variety)?

I couldn't possibly comment but I'll have a go anyway.

Any aircraft will have an envelope which it is dangerous to be outside (even if you feel you can fly well beyond it in terms of your own abilities)

Jack stall is easy to encounter during manouvering such as quick stops where the blades decellerate the aircraft rapidly against the air mass, jack stall in this situation will cause loss of tail rotor authority,

In the same way you can over torque, you can jack-stall.

good pilots know the limits of their aircraft and will fly accordingly.

That said I have no problem with manf's fitting more powerful actuators.

I have rarely heard a discussion such as this that does not relate to EC350/355

'hydraulic jack stall' as everyone refers to it is something that can be avoided.:E

I agree with what everyone else says,but here's some more info.

When this accurs, the aircraft will normaly roll to the left with slight back pitch. The correct action to take is to not fight the controlls and the aircraft will fly itself out of this situation.
All of the accidents I have read about have been low level with high speeds and aggresive control inputs.:}

We used to demonstrate (nearly said 'teach' then!) Jackstall to ab initio students in the gazelle during basic trng.

If memory serves me right:

Dive the helo to close to Vne (160 in Gaz piece),
pull like f**k on the cyclic (aft) and follow me through bloggs :uhoh:

A/c then reared up and rolled (I think) towards the retreating blade side, quite violently.
In so doing it 'recovered itself' because the helo slowed down and the forces on the blades eased somewhat.
But during that 3-5 seconds she was in JS, the controls locked solid and we instantly became - passengers :ooh:

What stresses this imposed on the a/c, God only knows, but each a/c went through this about 50 times/year and not one bent pitch change rod was ever found..........

The students cra**ed themselves:\

A10

I really don't know how you would get jackstall during a quickstop, as the aerodynamic surfaces are fairly lightly loaded during this manoeuvre. The only way I've ever been able to demonstrate it is by fairly harsh rearward movement of the cyclic while flying at high speed, normally in a dive and approaching VL.

Dynamic C

The recovery action is to 'reduce the severity of the manoeuvre'. That is, whatever you've just done to cause it - stop doing it.

Jack stall can occur due to several reasons. From a design point of view the hydraulic pump is not properly sized to provide the necessary fluid flow when all three servos are actuated. There is still a charge in the servo accumulators but when this bleeds off the pilot is mechanically connected to the blade feedback forces. What is needed in this case is a constant pressure variable delivery pump,which is installed in most helicopters. With this type of pump you do not require accumulator(s).

Another reason for jack stall is the slippage of the belt drive that turns the pump. I believe this is the reason given by Aerospatiale.


:E :E

I've experienced the famous Astar "Servo Transparency" in a 350 B model.

The flight conditions were:

AUW 4200 lbs (GW 4300)
80 Kts
4,000'
+30c
Light winds
15 degree LH bank

No aggressive flight, no sudden flight control movements, the controls just simply froze when circling a spot fire.

Pub user

Apologies, perhaps I was using the term "quick stop" too loosely , I defer to your greater knowledge.

What I actually meant was going at max chat then stopping as quickly as one could, I would describe this as extreme handling (as described by Thomas Coupling) rather than gentle handling associated with slowing an aircraft under normal circumstances.

It all depends on how quick one's quick stop is, don'cha find?

A10, in a normal quick stop you lower the collective to stay level, that in itself is going to stop any chance of a problem, plus I think the g loading required is normally well above 2-3 g.

Lu, are you saying AS350s have belt driven hydraulic pumps? Not disputing it as have no knowledge either way, just curious that they are not MGB driven directly.

212 Man, yes the AS-350 has belt driven hyd pump. Looks like something that came from a Citroen or Peugeot (French cars!)

I have never really heard of problems with the belt or hyd pump in the AS-350 other than the aforementioned hydraulic jack stall. Never experinced it myself flying the series but maybe that´s because I fly them very gently.

I always heard that the controls really "freeze" on you rather than it feeling like a hydraulic boost failure.

However I have from a Dauphin AS-365 pilot that he has also experienced momentary stuck controls in extreme handling situations. I guess that you really have stuck controls if you loose dual hyd boost in the AS-365 and just really heavy controls in the AS-350.

This is why I prefer to: "FLY SMART, FLY BELL" :)

Jack Stall was taught to AAC students so that they would know in which situations JS could occur. The severity and onset of JS differed with each a/c and one could experiment to discover the limiting point, at and from a safe recovery situation.
Later flying the AS350 series I discovered that if the cyclic inputs were violent enough the cyclic would baulk and go into a sort of JS situation. My thoughts are that if one moves the cyclic fast enough you can feel that the fluid is not moving as fast as your input. OR it could well be that the pitch changing just cannot keep abreast of the inputs. The hyd pump is designed to provide adequate pressure and flow for all normal requirements and the system is so designed to protect the a/c from extreems of G.

QHI course, 1976. Staff used to demo jackstall on the Gazelle in a straight descent and with 60 degrees AOB to the left. My instructor, bless him, decided to do this to the right. He pulled hard from 150 odd knots. The next thing I knew was that Newport and my chinagraphs were above my head. Aircraft flipped right under. Next day, asked for a change of instructor! Jack stall on Gazelles has certainly written off a few at low level - usually when pulling hard in a descending right hand turn (but you have to pull very hard). Never had a problem in 2000hrs with the 350.

please excuse my ignorance here, but I have always wondered this:

Are the cyclic & collective in a 350/355 purely a hydraulic linkage (like the brakes in a car) rather than an assisted mechanical linkage (say like power steering) as in a B206?

In the latter case jack-stall couldn't occur could it?

thanks!

The symptoms of jack stall are caused by blade stall pitch change link loads pushing through the servo, not by fluid supply limits. The hydraulic pressure warning lights would illuminate if the pump capacity were reached, since the pump could not keep up the system pressure if the fluid demand were too high.

The blades are always fighting the servos, and the pitch link loads get progressively more severe as the rotor is progressively stalled more and more (blade stall is not a flip of a switch, stalled or not-stalled).

as A10 Thundybox said, "Any aircraft will have an envelope which it is dangerous to be outside (even if you feel you can fly well beyond it in terms of your own abilities)" The real question is not that helos have envelope limits, but rather if those limits occur in normal required maneuvers. Military regulations forbid jack stall anywhere near the operational envelope, and most companies strictly avoid allowing it to occur, even with one failed hydraulic system (down to a single servo).

The consensus here seems to be that the situation in jack stall of the 350 is manageable, the propensity is predictible, and the outcome is not catastrophic. Without doubt, the French authorities examined the jack stall thoroughly in the certification tests and deemed it acceptable. Were any accident to be blamed on jack stall, I would recommend re-thinking that attitude!

Frankly, I know that Sikorsky would deem that behavior unacceptable, and require stronger servos (and swashplates, if the parts could be bent in maneuver!) I believe it is a governing philosophy of US manufacturers (certianly Sikorsky) that the controls must not lock up and the rotating control system not be damaged by virtually any maneuver the pilot can conceive, and it is a strong requirement in US Military regulations. I am also quite certain that the FAA would not approve such behavior, absent the bi-lateral agreements that make it necessary to overlook some things from foreign certifications.

Having reviewed my retirement portfolio last night....and considering my advanced age...seems to me....knowing the 350/355/Gazelle/365 probably the 155 can engage in recalcitrant control behaviour (....that is locking up the cyclic at a minimum....or doing its very own thing.....) which might be counter to what I (the Pilot-in-Command) desires at that moment and phase of flight.....maybe sticking to non-French gear is the answer. There's been times that I would have been much better off leaving things alone....but I think I want that to be my choice rather than some Vin swilling Gaul version of Lu.

Nick's post certainly convinced me of the advantages of riding Igor Iron.

If what you guys are talking about is "servo-transperency" in the 350 series, I have some info. I see little bits and pieces in some of the posts above that are involved. The easiest way that I've seen to get into this phenomenon is abrupt control inputs. The higher the gross weight/airspeed, the less aggressive the inputs have to be in order to cause it. I've never had the controls actually "lock-up" on me. You can tell when you are getting close to the onset. The controls start to feel a little heavier. If you stop/decrease the input you were doing at the time, it won't progress any further. The only time I've ever felt it was when performing a hard turn at high airspeed close to max gross.

Now as far as the system itself goes, from what Eurocopter told me, its isn't a matter of the pump lacking the capacity to overcome the high control loads. The pump has the capability. It is intentionally limited to a certain boost pressure (I can't remember the exact figure in bar) as to not damage any of the components in the head.

(212man It is belt driven off of the input shaft to the m/r transmission) The belt driven pump doesn't inspire a hell of a lot of confidence in people (especially the older style green belt) but I've never really heard about as many problems with the belts. I've heard about more failures of the splines inside the pump than actual belt failures.

At high airspeed the contol loads are very high, probobly too high to be manageble at close to Vne. For this reason the aircraft has a servo accumulators is that they allow supply sufficient hydraulic pressure for inputs to be made to bring the aircraft back to about 60 kts in the event of a hydraulic failure. Other than that, it isn't much different in operation from the Bells.
Hope this helps. BTW alll this information is based on the 350 B2/B3, I don' t have any experience with the earlier models.

Great thread!

One thing about the FAA and US manufacturers...

NickLappos said
I believe it is a governing philosophy of US manufacturers I am also quite certain that the FAA would not approve such behavior, absent the bi-lateral agreements that make it necessary to overlook some things from foreign certifications.

Isn't a U.S. manufacturer together with FAA responsible for introducing us to the term "LTE" to cover a design-compromise, or am I completely wrong? -That happens alot :O
I know that Nick is partially referring to the military but everything flying on the civilian market is a compromise, and those are beeing made by every manufacturer, no matter where they're based.

Well, I'm learning alot anyway.

Cheers!
/2beers

If servo transparency and jack stall are being used interchangeably and incorrectly, could somebody explain the difference?

As to servo transparency in the 350/355-
In more foolish days, I'd fly these like ordinary state-side helos.
Flown vigorously- Say, at better than cruise speed- load a little "G," like a zoom and control RPM with collective, add a turn- and the normally impressively agile aircraft's cyclic will stop moving in one direction( or you'll get a "limit" light in a 355). A little less turn (left, last time), or a little less collective and you get some back. Load it again, even with less pitch- and there's the wall, once more. It ruins your plans for hotting up the dog. If there's something that you were turning or zooming to avoid, well- too bad- you're not going to push the stick in that direction, right now. I hope it's a forgiving obstruction, or you left an "out."

I've never encountered this in any other mode besides playing around. And never in any other helo.

The terms can confuse you. We call it servo stalling, or jack stalling but "'Transparency" is a good ephimistic way to describe the same thing - the servo reaches its maximum force and then passes the forces to the crew (becomes "transparent").

The idea that this is used to protect the rotor components from flight loads in certainly novel! We always thought it was a good idea to make them strong enough to not bend!

Frankly, the FAA "Proof and Operations" tests on the helicopter controls forces the rotors to be strong enough.

Regarding LTE as an example of the pot and kettle calling each other black, I don't think you would find me supporting that either, much to Sultan's ire!

I wish I had had the benefit of this thread some years ago, cos it would have saved me putting some embarasing photos in my flying album.

Having sadly been on the receipt of "jack Stall" in a French made heli, there is one aspect to this topic that has not been considered. If you are taught that if you place the aircraft in a 160kt dive and pull back harshly on the cyclic it will 'js'. Why bother with all that when it does the same thing at 30deg AOB/5deg nose up and 60kts in a RH decending turn.

If I could offer any advice it would be that the 'envelope' is something of a vague line that exists in the grey areas only probed by the BOI. Dont be under the illusion that your handling has to be harsh for the aircraft to Jack stall, and the feeling through the sticks can be minimal when you are in full blown 'js'.

All the above is naturally 'IMHO'

Since the question was if any other aircraft have this kind of behaivor, yes sort of the same, the Sikorsky S-55T (sorry Nick). It might not really be a jack stall I think, more like a very veak servo system to very heavy blades, or it might be same thing but just feel diffrent to the pilot.

The S-55T is VERY easy to get in to a bladestall situation if not adhering to the VNE table and follow the WAT reduction closely, especially in mountain flying with gusts. But before it bladestalls on you it starts letting control forces through the servos to warn you that you are getting close. And on the S-55 you can't miss if you loose the servos.

I have never had the questionable "honour" to experience a blade stall in any helicopter, and I hope I never will, but I have for sure had some frightning cases of control forces through the servos on the S-55. I know of at least 3 cases of bladestall on the S-55 at our company in the past, and all went well.

The T version is flying with roughly 20 rpm higher MR rpm than with piston engine (199 to 219), so i wonder how bad the original was. But I guess it did not have the power to reach VNE with max gross as the T version does. In the RFM on the original S-55 it is actually a great deal of text regarding how to avoid and how to cope with bladestall.

Good ol days ;)


CB:{

quote

Nick's post certainly convinced me of the advantages of riding Igor Iron.

Did you really need that post to be convinced ?

I know of some people who would have been more than happy to ride a jackass Star when a blade of the Igor Iron they were on decided to part.

Don't want to start another Airbus vs Boeing or Bell / SK vs EC, though.

Cheers

ATN

ATN,

If you are referring to the Bristow S-76 that shed the blade after it was put back into service after being struck by lightning....I would suggest one might look towards the operator that trashed almost every moving part on the Lightning struck aircraft and after having done that for safety sakes....then sent the blades off for inspection and then put it back into service. The 76 had two other blade failures in its very earliest hours....and knew one of the guys killed in the second accident (a man I respected highly in all regards I might add.)

The same company lost Bell aircraft to blade issues, Wessex aircraft to unknown causes....but these are all catastrophic failures.

My point is I have concerns about knowingly flying a machine that in "normal" flight can have control problems. That does give reason for pause or should anyway. Logically, it does not follow that one would wish to fly a helicopter whose controls "lock" up in the cruise....or while maneuvering near the ground.

Having only flown in the back & front of helicopters for nearly 50 years, I seem to have missed out on all these jacking problems you guys seem to have had.

The closest to it I can recall is in a Bell 47 & 206 when flying in mountainous areas parallel to a cliff face in very windy conditions, maybe 30 + kts, a gust has hit me towards the cliff face and I could not move the cyclic in the opposite direction. The cure was to move the cyclic towards the cliff to unjam the cyclic and then put in opposite cyclic. Is this what you mean by jack stall? I just considered it as running out of hydraulic control.

I can't imagine this in normal cruise unless you are flying through a massive thunderstorm when anything can happen.

ATN,
I certainly don't want this to become an us and them thing. I believe that the servo strength of virtually every helicopter I know, civil and military, does not show any jack stall in regions anywhere close to the operating envelope. This 350 discussion is teaching me plenty. I do believe that many/most/all of the helicopter world (British, US, Russian, etc) has grown past the need for the pilot to worry about having his helo take control away from him in most maneuvers.

Collective Bias, that S-55 condition you mention is most certainly stall related servo load, but happens at or beyond Vne, and to an aircraft that is arguably three generations old. If jack stall was only experienced at Vne in 1949 (S-55 first flight Nov, 1949!), one would have hoped we stayed the same or got better in 55 years!

I did the servo adequacy tests on the S-76, and took a loaded S-76 to Vne, turned off one servo system, then maneuvered to 1.7 g's to clear the aircraft for certification. Not a hint of jack stall, believe me.

The hydraulic belt on the AS350 has caused some problems. One was lost in the GOM a few years back when the belt broke and the pilot tried to land on an offshore platform. Sadly, there were no survivors. I have around a thousand hours in the AS350D, and always had mixed feelings - lots of fuel, plenty of speed and comfort, but if things went wrong, they went badly wrong.

Two tales, but both concerning SA/AS/EC type helicopters and servo/hydraulics:

1. SA-341 Gazelle (MIL version) suffered a fatal accident at Farnborough around 1973. The helicopter performed a low level, right-hand turn at high speed. The roll to the right continued unchecked and the helicopter crashed inverted. The conclusion was that by increasing the angle of attack on the advancing blade, which provides most of the lift, the forces on the blade at high forward speed were sufficient to overcome the hydraulic servo and jack stall occurred, and the pilot was unable to counter the roll.

This occurs mainly when turning to the right - French helicopter = advancing blade on the left side of the helicopter. When turning left the angle of attack on the advancing blade decreases, and the forces on the servo decrease accordingly.

Even though this was a known phenomenon, and demonstrated under training, it was the presumed cause of another Gazelle fatal accident in 1975, during a low level sortie over Dartmoor, killing the instructor and student.

2. AS-350B2 – When this type was introduced it had new spherical bearings, new single hydraulic system (both taken from the 355 dual hydraulic system), a new power plant, beefed up rotorhead, & etc. Better, more powerful version of the B & B1……?

The hydraulic pump is driven by a belt (“rubber band” - see previous postings on this). In cold weather (under - 25oC) the hydraulic fluid increases in viscosity and the belt starts to slip. As it cannot drive the pump at normal speeds, the belt deforms, due to the friction from the accessory drive, and eventually stops turning the hydraulic pump, or slips off the drive wheel. OK you think, small helicopter, no hydraulics, what’s the problem ?
Well it turns out that the new spherical bearings (“rubber balls” from the 355) freeze solid at temperatures under - 25oC, and without a hydraulic servo the whole control system locks up !

The pilot then becomes a passenger in the helicopter, and only by using extreme force can the controls be moved.

AS/Eurocopter say they have fixed this problem with new types of spherical bearings, but the fact remains that if you lose the hydraulic drive belt on a 350, it becomes extremely difficult to control – see the news gathering AS-350 that plunged to a rooftop in New York earlier this year

Reading Collective Bias's story about the S55T reminds me of an incident I had some years ago when a leak in the cockpit roof caused a drip resulting in a bridging of the hydraulics Primary off, Secondary off test switch.

Both sets of hydraulics failed on me leaving only the emergency system - driven I think by transmission oil pressure on the lateral jacks. All could have been restored by switching off the electrical master switch (fail safe on) but I lacked the courage and free hand to reach for the switch.

From that incident on I made a special effort to learn the aircraft systems and not just skim over the text to pass the type rating exams.

Yes I did manage to get the aircraft down and land it after 20 minutes flying in that condition - pure luck.

Jim

Reading about the accident involving a hard right turn near the ground....and being unable to stop the roll and for sure probably not wanting to reduce collective at that point....a question arises.

The BO-105 and BK-117 have a similar trait in that situation....one can run out of cyclic authority if a high roll rate occurs.....the recovery is to apply "full" opposite pedal.....fully and quickly...."stomp" was the word used but something slightly short of that seemed to work during demos.

Adequate control is quickly gained and as the nose pitches up to level or more....then the collective can be lowered and cyclic authority is regained.

Just a thought!

This is a very intresting subject and I have to send my 2 cents again.


BB I think the problem you refer to was from an accident on Greenland in the mid or late 80 ies. This was due to (if I remember right) a broken drive belt to the hydraulic pump in very cold conditions and with a new style of Spherical Bearing (load carrying rubber bearing) fitted. Not to the fact of slipping drive belt.

The fix was a new style of bearing, and a new lower temp limit of the previous one.

The RFM also calls out for warming up the spherical bearings before takeoff in cold conditions by moving the cyclic 3-4 cm fwd for 2 min and to check the force to move the cyclic without servo.

We have been flying B, B1, B2, B3 in very cold conditions (down to lower limit) for a long time without problems, we started with B in 1979. We even tested a cog belt driven pump for EC, but it never went into production. Even if the belt drive looks very simple, it has just failed on us once in all these years, and it was a successful landing afterwards.

I have always as a training captain had the opinion on single hyd system helicopters that if there is a procedure in the emergency checklist that calls for turning off the hyd system ASAP, then it should also be trained at cruise speed. Normal procedure is to bring down the speed to around 60 KIAS and then turn it off (even at ECF they do not train this at high speed if they have not changed there way of training). But if you get some sort of hardover you need to get it off immidiately, no matter the airspeed, without having tried it before it could be intresting

:ooh:

Therefore when I train someone on the 350 I demonstrate this and then let the pilot try it with increasing airspeed up to cruise. At cruise it is hard work, but since the cyclic want to go right and aft, it is very much controllable. But since many 350 pilots from time to time hold the cyclic "very light" to get good feel, I think it is important to know what they are up against if you turn off the servo at cruise speed.

:ok:

CB

I taught on AS 350Bs for a few years. One of the course demonstrations was"jack stall". The point of this demo was to show the trainee that the phenomenon was possible and could be dangerous close to the ground.

It was a while ago but there was very rapid rolling and pulling to achieve it. Once it occured, it felt much like the aircraft did hydraulics off. Although the controls were heavier they could still be moved and the aircraft recovered. You really had to work hard to make it happen.

It's a limitation to operations, like left crosswinds and LTE are to Bell 206s, left pedal stops and crosswinds to Bell 205s, vortex ring is to any helicopter and the size of the fuel tank is to any aircraft. No big deal.

As for the "rubber band", the fleet of about 20 to my knowledge never had a failure, even in a temperature range from -5 deg C to 40 deg C. The biggest problem with them was getting them on and off. Undoing drive train etc. They were lifed for 10 years so when the fleet hit 10 years old, not enough rubber bands to go round.

I've seen a few cases of sudden belt slippage when arriving in the hover in loose dry snow (read - - big nasty white snowball ! )

This not the time you need control issues, horns, etc as you are searching for the ground in a white-out ! I have also seen a few broken belts, plus a lot of burned - glazed ones.

I work with a 100% Bell company now( :ok: ), but my past employer used to have a spare belt fastened around the drive-shaft of each 350, so the complete dis-assembly of the drive system was not required to change the belt -- once anyway.

I think a lot of the hydraulic problems mentioned above during high speed turns are not really hydraulic problems but retreating blade stall which causes a euro machine to flick right and a US machine to the left. For this reason when teaching steep turns, you get the student to turn the opposite way to the flick, so that if it goes wrong, you flick upright.
I well remember being number 5 in a tail chase in a S55 when the leader sped up close to vne and wrapped on lots of right bank. A few seconds later, trying to follow number 4, I was doing a steep turn to the left. Very worrying but not really a hydraulic problem.
Maybe the Gazelle had this happen? :confused:

The Gazelle's controls give a definite feedback "jolt" when jackstall occurs. I saw retreating blade stall in a Whirlwind 10 (at 150 feet agl) and if I recall correctly, it didn't give the same effect.

Both have a similar effect on the pilot though...... :ooh:

This is a very good example of how prone the ASTAR is to jack stall. It doesn't take very much. At high DA's in combination with a High gross weight, light to meduim turbulance can result in jack stall. Anyone who has flow an ASTAR in the mountains has probably experienced this.

Mr Osborne, my experience is contrary tp your speculation regarding blade stall. I've had it happen in turns of both directions, and vigorous but not terribly rapid roll rate or exceptionally high speed- well within the green arc and low DA. The surest way I've induced it is cruise or higher, pull some g, and roll. The stick just stops, lateral. I'd hate to force it, as the onset is sudden and unpredicted- it could well cease with me leaning on it- That would introduce new and exciting issues. Pitch reduction (both senses of the word), slow, and the aircraft's normal again.

As to belts- An Arizona 350 had an air conditioner compressor drive belt break and take out the hydraulic drive belt, too. It's a chintzy system in an otherwise very satisfactory helo.

devil 49,

The reason for the jack stall is that the blades are stalling, and when they do, they progressively add more and more force to the swashplate. This is due to the pitching moment of the airfoil shifting with the stall. When the swashplate gets heavily loaded, it pushes the servos backwards despite the hydraulic pressure in them. this is called "transparency" or "stall" of the servo.

here is a web site that talks about the dynamic stall of rotor blades. Scroll down to where they talk about the pitching moment (the Cm plot) to see how the moment of the blade takes a big turn at stall. This is the reason why the nose drops on an airplane when the wing stalls - the wings pitching moment shifts sharply downward.

http://aerodyn.org/Dstall/dstall.html

I am glad there was a very simple answer to my original question. I would hate to think I raised a complicated issue like why some places in the world still use the QFE altimeter setting vice the World-wide accepted QNH method.

Dear all,

A search for "jack stall" shows the amount of previous discussion. I, like 'scrubba',

http://www.pprune.org/forums/showthread.php?s=&threadid=19913&highlight=jack+stall

did all sorts of things in the AS350 that deliberately generated jack stall. I found it to be predictable, progressive and at the far edges of the envelope compared to normal operations.

While I note Nick's view in 2001 and now, I never felt frightened by the phenomena because I knew it existed and I knew the extremes to which I had to go to induce it. The other "mid-envelope" experiences reported just did not gel with my experience.

Stay Alive,

4dogs,

Thanks for the link to the past! It is interesting to see that old topics don't just go away!

I have to note one issue with your comment,"did all sorts of things in the AS350 that deliberately generated jack stall. I found it to be predictable, progressive and at the far edges of the envelope compared to normal operations"

Could I ask you to add the note, "so far" to the end of your comment? One thing I have found in testing is that when a problem surfaces, it is not likely to just fix itself. When other pilots have loss of control events, and lose their aircraft in an accident, your evaluation has just been trumped by theirs. We all lose if we decide that something which hurt a buddy is really his fault, so that we apologize for the aircraft, blame the pilot and march on to the next accident.

I coined an aphorism to describe the loop we get into when we are trying to decide if a problem we have found really needs to be fixed. I would write this on the chalk board before we started the meetings to decide if it was a "feature" or a problem:

The size of your problem is proportional to the efforts needed to convince yourself that it is not a problem.

IMHO, Jack Stall is like LTE, a sign of a marginal helicopter that has bitten some of us, but others want to simply blame the pilot. Safety of helicopter flight operations will only be achieved when I, and my counterparts at the other manufacturers, face a raft of indignant pilots constantly trying to make their aircraft better, not a group of apologists who want to blame each other when an aircraft fails them.

Regardless of our collective opinion about how much out of control we will accept, the authorities should not let us debate it. In good military aircraft, there is no debate, and I can promise you, it would be a cold day in Hell before the FAA pilots I fly with would accept jack stall at 1.5 g.

4Dogs,

My personal experiences have shown a complete disagreement to your post. I have unknowingly entered the "servo transparency" in a flight condition I feel was very routine and quite gentle.

I say to you, be careful of this situation, don't approach it with such casual disregard.

Given a higher gross weight ( Did you practice this with a full load ? ) a different flight altitude, a different 350 model, a different Outside air temperature, and most importantly, a flight situation where you MUST turn to aviod terrain, you may find that the aircraft may surprise you in how quick it bites.

You end your last post with "Stay Alive", good advice, I say ...practice it !

Fly the type smoothly....
Always leave yourself an "out".....
Anticipate that the control transparency may occur at the worst possible time.....

"The size of your problem is proportional to the efforts needed to convince yourself that it is not a problem."

This one I will remember.

Again Nick hits the nail squarely upon the head!

Great discussion throughout.

Why is an ASTAR called a Squirrel? Is it because it looks like one? Who called it a Squirrel first? The French or the Yanks?

Thanks.
WB

i believe that would be because the manufacturer originally called it the "ecureil" which i believe is french for squirrel...

AStar was a north american name attached to it...

Aerospecial called it Ecureuil - Squirrel - cause it was supposed to be a money saver for the operators just like the animal is provident and thrifty.

That was changed to A Star for North America since the name does not mean the same there.

Cheers

ATN

does anyone have any time or experience in one of these?

never flown an Fx, did some time in a F2 though

Good Morning All,

Just wondering if anyone out there knew of any good low time AS350B2 or B3's for sale. Looking to purchase ASAP. Thanks in advance.

Cheers

Sorry Auscan not much help to you but looking for a B2 in the UK and looked in all the usual places.

Can anybody recommend a Twin Squirrel sim based over the channel in Europe?

Try ringing +49 2382 82082. they have just bought a B3 with good hours and I KNOW he always likes to sell his helicopters, nearly got a 212 rating until he sold them all from under me...drat!
Don't buy it too quick though, I might still get to fly it :E

Sorry, slip of the keyboard it\'s a B2 NOT a B3

Rick

auscan: pm me if your interested in a b3 in north america
dr

Never heard of one, certainly is something that would be useful though:ok:

Never heard of a 355 simulator. Hell they didn´t even have a SA 365 Dauphin sim until about 3 years ago.

Its in Marignane France.

I would imagine that the flight hour cost on the sim would not be much less than the DOC's on an actual aircraft.

Bond Air Services will shortly have an EC135 sim that may be configurable.

http://animalpicturesarchive.com/animal/Animated_GIF/Squirrel/sqtiny.gif

The French Army Air Corps have some but no visuals just an IF trainer. I don't know if they'd let anyone else use it though.

Heli Union training center has a FNPT2 which is a fixed base sim featuring the cockpit of a Fennec - Twin Squirrel with Arrius engines.

Héli Union Training Center
Aéroport d'Angoulême - Brie Champniers
16430 CHAMPNIERS FRANCE
Tél :33 05 45 90 33 30
Fax : 33 05 45 90 33 33

www.heli-union-training.com

Cheers

ATN

Does anyone have any information about the Arriel 1b engines in the AS350 BA. Apparrently a small piece of metal has fallen off the shroud on module 2 and has gone through the whole engine causing total destruction......engine write off 240,000Euros !!
To make it better , this probably happened 2 years ago and it has been flying around on public transport all this time....like a time bomb. Turbomeca deny there is a design problem but how many engines have had this happen and how many crashes ??? Any info really appreciated.

Arriel 1B huh? Now that seems to be one damned fine engine if it has tolerated FOD some two years back that has apparently taken out the interior of the engine, yet no-one has noticed it.

No vibes? No power loss? Just kept on haulin' a*s.

Doesn't seem that there's any design problem if the chain of events are as written.

I saw a copy of the IFSR for the Arriel a few years back and it was impressive for its reliability. If I recall correctly I could expect an in-flight shut down from all causes (fuel exhaustion, false indications, minor fault precautionary included) each 100,000 or so hours and a catastrophic type engine event each 500,000 or so flight hours.

Going on the data I saw it seemed that I could expect the thing to go BANG once each couple of thousand years at the rate of effort I was doing. Then again, it could be tomorrow, couldn't it?

I still feel real comfortable with them though.

(O.K you guys, I know it's French)

STL

Does anyone have experience on a good replacement unit for the AS350 airconditioner? Specifically, the electric blower motors are hideously expensive for what they represent and they seem to only have a short life.

Is there a modification that can be made to a Squirrel to make the air vents as good as the Bell air vents (on the 206/407 models).

Many thanks.
:cool:

What system is fitted ? Aero AIre , or Integated ( jack keen version).

http://www.maverickhelicopter.com/

If you talk to these guys I think they have had experience with both versions.

http://www.platinumaviation.com/
now sell the integrated flight system.

http://www.aeroaire.com/ is now run by enviro systems.

I think the french factory installed system was based on Aero aire .

Integrated Flight Systems, owned by Platinum Aviation are the best in the business for air con systems for the AS350. Give them a call and talk to owner Leroy Aday.

www.integratedflightsys.com

and

www.platinumaviation.com

Cheers

Ned

Thanks Widgeon and Phoenix. What the Squirrel needs is better air vents like the Bells and then there's no need for airconditioning (unless in extremes of temps)!

rgds

Mods, this is offered for free so I don't think it can count as an advert.

We have an A-frame towbar which is built to fit the Twin Squirrel; we no longer use that type so we want rid of it. It fits via pins to the jack-up handling wheels and the tow point is about a metre in front of the nose [it started life as an apprentice's project].

It's nowhere near as useful as the heli-lifts etc currently available....but it's free if you want to collect it, obviously UK only; it seems a shame to scrap it. I'm too short of time tonight to post a photo, so PM me if you're interested.

Just what I want....

Any Ppruners out there that have flown the AS355FX?
WOuld like your thoughts on the C20R and FX conversion's performance.Does it really make a difference?:E

Sorry don't know much about it-is there a web site?

It's a customised STC version, at present only Certificated in North America. See www.helilynx.com.

Has anyone experienced either abnormally high cruise fuel consumption or problems with the accuracy of the fuel indicating system on the AS-350 B2 or B3?

There have been some problems and possible related accidents in regards to accuracy of fuel gauges in the older B2' and BA's. They had a float type fuel senseing sytem that would stick when it wore and got old. I believe there was a SB or an AD out on it. All the new A/C have a capacitance system and you can buy the kit for 11k to replace the old one.

The B3 sucks alot more gas than a b2, and the b2 more than the ba. Noticeably so.

RB

Thank you for your rapid reply. This is a brand spanking new B2. The fuel consumption appears to be closer to a B3.

Having some time in both, here is my 2 cents worth.

180-190lts/hr or 30% per hour for the B2 and 220-230lts/hr for the B3.

Beer in mind that is just what I have experienced

Big Beres,

Not picking a fight, but 30% of 540Ltrs is 162Ltrs/hr.We burn about 168 Ltrs/Hr on our B2:}

Would appreciate a Eurocopter citation for securing the rotor.

I'm having a technical disagreement- one party is concerned about the starflex, the other with the blades and the effect of unrestrained flapping. Specific issue- The blades must be immobilized, braced and tied above "x" windspeed (40 knots?)? Up to that point, autorotation is the only issue?

I believe this is addressed in the maintenance manual.

10% = 20 minutes
10% = 40 miles
10% = 100 pounds

The higher you are the better these numbers. But for anything between 3,000 ft and 9,000 ft thes numbers have been very constant fo me.

This is purely from memory, and I'm assuming the 350 limits are the same as the 355; beyond 20kts tie downs required, beyond 60kts hangarage is recommended. I could get you a maintenance manual reference in a few days if no-one else comes up with it.

I remember having several AS355 in for an overhaul and all the blades where scraped, because they where never tied down. I can only suggest to tie them down all the time.

Droopy, the maintenance manual citation is exactly what I'm looking for- if and when it's convenient, I'd appreciate it. The aircraft subject to this disagreement is a B2, same head and blades as a 355.

Rotorbee- It's an EMS A/C, so time is important, the tie-down kit we're using is horrible and prompted the discussion. Specifics motivating change and supporting documents...

I have never split a starfex head using tie-downs. Here is the method taught in Donouworth and Marsaille.

Tie the main rotor down at it's median point..ie leave it where it is when no wind is blowing, let it jerk all over the place all night, check it in the morning before you fly, 99 percent of the time it will be worth flying.

If you tie it down FFS don't drop it two inches as you might on a different head you will bust that starflex and that equals an expensive repair.

Para 2 applies to factory courses as taught on As350, As355, as365 and EC135.

Talk to the guys who design and build the things if you don't believe me.

I have been fixing these types for over 20 years,some just happen (no wind, no flex), some are engineer/pilot/handler lack of knowledge), most are avoidable.

Take care

4R

In my experience, with the B model STA 1000 cracks occurred due to not tying the blades down in even the slightest amount of wind. The cracks are on the lower side from compression.

The 355 grey blades tend to crack on the upper side at about mid point. Why - who knows.

IMHO Starflex damage comes from droop stop pounding on shutdown with the cyclic not centred.

Not a definitive answer, just personal experience.

My experience over a lot of hours is 180L/hr on a straight 350B, (ie not B2/3) 235L/hr on the 355N at S/L, 210L/hr 5000ft, all at fast cruise.

I thank one and all for your responses. I did a fuel consumption check of the subject aircraft and found that it agrees with your inputs. It appears as if we had a pilot experience issue. Your responses will help with our training.

Jack

I gave myself a surprise on a long ferry flight in a B2. Experience was an issue then as well since I had 1:30 on type when I left UK. Cruising at 1000ft through Europe was giving me 35-36% per hour (instead of the 30% I had been expecting) and an endurance of 2:35 to chicken fuel. Later, through Egypt I was up at 11,000ft and it was around 24% per hour and I was staying up for 3:25. Subsequently I did some graphs for my own use in Ethiopia which was very helpful.

The fuel consumption presentation in the flight manual was not very useful on the subject.

Great aircraft though, I wish I had one now!

Over the 12 years of operating the 350, we have had great success using blade stands when ever the helicopter is on the ground, in a hanger or otherwise (under all wind conditions). The blade stand consists of an adjustable aluminium pole with a blade cradle which slides over the end of the blade, and then is adjusted to unload the starflex whilst supporting the blade at the end in a lightly loaded configuration.

We started doing this religiously following some blade and starflex issues and we have never had a single problem since (over 10 years). Our starflexes always go to SLL and the first problem we suffer with the baldes shows up in paint erosion, no delaminating of leading edges or anything else. It works extremely well.

Hope this helps.

MJB,
I believe that we experienced the same situation that you described. The long leg was flown at 1000MSL. If he had climbed to 7K or 8K, he would have had plenty of fuel. You are right the AS 350 is a sweet aircraft to fly. That comes from an old S-76 pilot.
Thanks Again
Jack

The Transportation Safety Board of Canada recently released the report of a fatal AS350 accident.

Report:

From the report:...
3.1 Findings as to Causes and Contributing Factors

After experiencing a hydraulic system failure, the helicopter departed controlled flight and crashed while manoeuvring for landing. The reason for the departure from controlled flight could not be determined.


It is likely that the hydraulic pump drive belt failed in flight, precipitating the hydraulic failure.


It is likely that the hydraulic circuit breaker was in the tripped position in flight, rendering the hydraulic CUTOFF and HYD TEST switches inoperative. This would result in hydraulic pressure from the main-rotor servos being depleted asymmetrically

Report (http://www.tsb.gc.ca/en/reports/air/2003/A03O0012/A03O0012.asp) http://www.tsb.gc.ca/en/reports/air/2003/A03O0012/A03O0012.asp

I agree completely with 407D, don't ever think this is somthing that will give you warning. I consider myself VERY lucky to be able to describe when I first experienced this situation. I was in cruise flight, no pax, looking for an oil rig in northern BC (this was 1980, before GPS) I got down low over the trees to see if I could see the derrick over the tops, there it was a mile away. I stayed low and once over the rig started a what I would not call an agressive cyclic climb to the right. The cyclic froze in my hand, the next few moments seemed like an eternity, really maybe 2 or 3 seconds but something I will never forget.
Don't get me wrong, I love the Astar, one of the nicest a/c I have ever flown, but as in all a/c treat it with respect.

Hi gents, the freezing control problem with the Astar, from what I have been teach during my initial, can be created by negative G because of the pump. I have experienced it in that situation and it is not really confortable situation.
Cheers
FH

An interesting discussion. Our company employed a few senior ex army Blackhawk instructors and jack stall was a frequent topic of theirs and related a number of accidents which were a result of the phenomema. Until their employment I had never heard of the term. They also told of how it was demonstrated to pilots under going conversion onto the Blackhawk. In light of your comment Nick it would seem that an educational program may be in order.

Brian

As you say Brian, very interesting indeed.

This is new to me and I suspect most others. Didn't think it happened with Blackhawks. Any chance of it with the S92?

Were there Blackhawk jack-stall accidents in Australia? I seem to recall reading that a couple of Aus BH's had a night mid-air but haven't heard of other accidents down there.

What Red Line,

From an earlier post in this thread by Nick Lappos, now ex-Sikorsky....but still somewhat knowledgeable about the issue under discussion......

"I know that Sikorsky would deem that behavior unacceptable, and require stronger servos (and swashplates, if the parts could be bent in maneuver!) I believe it is a governing philosophy of US manufacturers (certianly Sikorsky) that the controls must not lock up and the rotating control system not be damaged by virtually any maneuver the pilot can conceive, and it is a strong requirement in US Military regulations. I am also quite certain that the FAA would not approve such behavior, absent the bi-lateral agreements that make it necessary to overlook some things from foreign certifications."


Now we hear that this did occur in some Australian BlackHawks? Or is there some question as to whether it did for sure happen? Or what actually happened? I cannot imagine the Oz Blackhawks are any different than the original marks in that regard anyway.

Brian Abraham said:
"An interesting discussion. Our company employed a few senior ex army Blackhawk instructors and jack stall was a frequent topic of theirs and related a number of accidents which were a result of the phenomema. Until their employment I had never heard of the term. They also told of how it was demonstrated to pilots under going conversion onto the Blackhawk. In light of your comment Nick it would seem that an educational program may be in order."

OK, Brian. Let the education begin here. There is NO Jack stall in any Black Hawk, nor in any modern Sikorsky type. There are NO accidents caused by, related to or involving jack stall.

Maybe you could have those guys who you think said this log in and share their thoughts, I would like to discuss it with them and clear up the misunderstanding.

Nick, the guys Brian is mentioning learn to fly in Astars through the Australian military. I think there has just been a misunderstanding.

While on this subject: Does anyone remember the accident in the US where the Astar on a news job ended up crashing onto a rooftop with all of us trying to decide whether it was hydraulics or a tail rotor failure?
We all watched the footage and I was today just thinking if there had been a resolution to that accident.

Nick and Steve,
The individuals have since left and returned to the army but they were definately talking about the 'Hawk. Would seem perhaps to be one of those urban myths that develops some where and has a life of its own although they did talk of demonstrating it to students. Will try and contact one of them and see if they will post.

Brian

Nick,
An after thought. The guys mentioned read the list so your emphatic reply should give them the message.

Brian

Steve76,

I had heard rumour that the A-Star news copter was subject to the pilot mistakenly selecting the hyd test button rather than the collective mounted switch he had hoped for.

I stress that this is rumour. I have no AS350 time so am unfamiliar with the exact hyd set up on this machine, but seem to recall other A-Star incidents of a similar nature due to poor ergonomics by Eurocopter.

C'mon you guys, don't get too deep into this thing. Leave it as one of those mysterious things that can still be used as the probable cause of those un-explainable accidents that happen from time to time. You know the story, "Musta been jack stall, couldn'ta been anything else. He's too good a pilot".

On the other hand, if someone can provide real evidence that boosted flight controls commomly lock up while the particular type is being operated within its certificated flight envelope, then we need to ask some really serious question to the various airworthiness authorities who have certificated it. I would think that the FAA for example would cancel that ship's type cert in a heart-beat if this were the case.

'nuff said.


STL

Brian; that's interesting. I will be enlightning to hear what they have to say if they bother to post. I think Nicks position is pretty clear and I understand the S70 variants to have similar hydraulic pressure to the S76, (I think it's the S92 with 5000 psi?) so a jackstall situ seems surprising. Hey! next time you are at FSI, see if they will let you have a pole of the Blackhawk sim... that will put a grin on your face :)

STL - read this thread from start to finish and then re-think your post. See the light...

As to accidently engaging the hydraulic test switch:
Boost disabled, controls stiff;
Caution panel segment illuminates;
The horn blasts.

I find it hard to believe that disabling the control boost inadvertently would be more than a transient problem. The aircraft would tell you in many different ways, that the button you'd just pushed wasn't the landing light.

Had an occurence of servo transparency yesterday- cruise flight, vulture sails into path, left bank and descent, resistance to roll back to horizontal. This was not an aggressive maneuver. It's so common I barely recall the circumstances.

Devil,

Were that "engine transparency" the howls would start. That it is "servo transparency" makes it ok!

I think it is properly labeled "servo inadequacy".

Earlier in this thread I posed the question...."Why would I want to fly an aircraft that had this problem?" I also asked how the FAA granted an airworthiness certificate knowing this occurs?

Nick, you said you did not think the FAA would go for such a thing as I recall.

Does that mean the FAA is unaware of this event in the 350 series and thus the aircraft can continue flying?

What happens if someone complains to the FAA about this....will they jerk the C of A of all the 350's in the USA?

Part of the problems with servo transparency is the bilateral airworthiness agreements under which the helicopter was originally permitted to enter the country.
The helicopter was certified originally in France, and because of a bilateral agreement between France and US, if it is certified in France, then it is accepted with minimal fuss in the US for Part 27 helicopters. For part 29 machines, the process is a bit more rigorous but not much different.
The French seemed to have few problems with the servo transparency in certification, and the US was relatively powerless to not accept it (or they may not have seen this during the FAA familiarization flights).
Things like this that are discovered later in life become more a political issue than a technical issue - and political issues are nearly impossible to solve any time.
As an example of this - there is no such thing as night VFR in Europe for single engine aircraft. So the EC-120 didn't have much beyond a single wander light to light the instrument panel when it was first certified. That was caught in the approval for use in North America (both FAA and Transport Canada caught the problem) and the EC-120 had to have the instrument panel lighting changed significantly for N. American sales.

That must have been what happened with the electrics, then.

Phil

SawThe Light: have a read of the accident report I posted, link is on page 4 of this topic.

Steve76 & IHL

Took your collective advice and re-read the entire thread, my post and the TC report.

What I see is that the post is still headed "Astar jack stall" .

In my post (slightly tongue in cheek if you didn't note) I made an apparently simple observation that "if someone can provide real evidence that boosted flight controls commomly lock up while the particular type is being operated within its certificated flight envelope, then we need to ask some really serious question to the various airworthiness authorities who have certificated it." I also went on to say that the regulatory authorities would take appropriate action if someone could provide real evidence etc etc.

What's difficult to understand about that? Have you any real evidence that this has occurred while operating within the certificated flight envelope?

In the matter of the TC report here are a few notable points as follows:

- The hyd CB was likely out in flight and probably un-noticed by the crew

- The hyd belt apparently failed in flight

- The hyd test switch was activated

- The M/R accumulator pressures were less than 50% of normal pressure

- No other anomolies were noted in the hyd components

- Para 2-3 said in part "As a result of not slowing the helicopter to the recommended . . . . "

- The report said in part " The reason for departing controlled flight could not be determined. . .

Don't see anything anywhere relating to jack stall (The thread title).

STL

I had heard rumour that the A-Star news copter was subject to the pilot mistakenly selecting the hyd test button rather than the collective mounted switch he had hoped for.

In subsequent interviews the pilot maintained that he had lost his tail rotor, or control. If you look closely at that crash you can see where he tried to fly it into vertical stab control, realised it wasn't happening, and deliberately flew it into the chimney to stop the whole thing in its tracks. A brave thing he did and lucky that it worked, seeing the built-up area he was over.

An AStar is quite controllable without hydraulics, and you can pick up, hover and land without them. I find it funny that there is so much criticism regarding this "servo transparency" issue as being
a failure of the French to build an adequate or safe machine, while the issue of LTE with certain Bell products is still ongoing. To be honest, I think I'd rather have jack stall than LTE any day. Until the perfect helicopter is built, there will be flaws, quirks, etc to be taken into consideration by those that fly them.

I think that the point here is that until as Nick says the problem is addressed by the manufacturer, there can be no substitute for knowledge and training.

Regarding the Limit light on the 355/365, as I understand it it is there primarily for when the machine is on the ground with no load on the head to alert to excessive cyclic displacement. You would have to be pretty severe in your maneouvring in flight to get that to light off.

The "Limit" light- at least on the 355- mirrors the servo transparency on the 350. It's not uncommon in flight.
The difference between the two situations is important. In a 350, you have inequality in control forces, and thus compromised control at an unexpected, unplanned and potentially dangerous time.
If you're in the 355, the same situation results in a light on the caution panel, and the controls remain fully effective. Hmm... so much for the blades stall and mechanical control issues....
The airframe differences between the two types are minimal beyond the power plants, electrics, and tankage. The biggest difference is the 355 has dual hydraulics and direct drive pumps. The vert stab differences probably aren't germaine.
My guess is that the servos and the hydraulics just aren't robust enough to overcome flight loads in the 350.

Regarding the hydraulic system circuit breaker- in 17 years I've only flown one (of dozens) that had CB's in place of the factory fit fuses. Remember that it requires electrical power to disable the boost...

Excellent dialouge Gents.

Here's a line from the report that may be of importance to the outcome...just as important as C/B's switches and procedures...


"There were good visual meteorological conditions at Mekatina, with clear skies, calm wind and a temperature of -30ºC.

The elastomerics tend not to be quite as "elastic" at minimum temps...giving much stiffer than normal control forces with out HYD assist.

Just my thoughts...

407,

The elastomers are not any stiffer while in flight, because the internal heating from the flexure is quite sufficient. In any case, the stiffness of the elastomer is a very tiny force compared to the stall forces from the blades as they produce high thrust.

The stiffness of the elastomers is high during warmup after cold soak, that is why many helos have warmup procedures for the rotorhead, and restrictions on the amount of flapping until a few seconds of running has passed, allowing the internal friction to warm up the elastomers.

As a recap for this thread (and a chance to awaken the arguments!):

The "transparency" is experienced when the rotor pitching moment forces (blade stall forces) become great enough to overcome the hydraulic forces of the servo. It is not actually caused by low hydraulic pressure, it is a function of the design being so marginal that the servos are too weak to push the blades around as the helicopter gets near stall. The maneuvers that cause "transparency" are often quite normal, and sometimes the effect is alarming and dangerous.

The limit light on the 355 is second cousin to "transparency" in that the servo forces trigger the light when they get large enough to signal impending loss of control. However, the 355 seems to have less propensity to enter jack stall, mostly because it has a more capable servo design than the 155.

NO US helicopter, civil or military, can have such "transparency" issues, since these signal that the controls no longer are controlling, and the pilot is a passenger. I also wage my friends at CAA would have similar thoughts, were they able to post here. Only the weakness of the bilateral regs (Shawn's excellent post above discusses this) allow such marginal controls to be put into service in countries other than France.

Why do the French approve such marginal systems? Je ne sais quoi! Perhaps it is because the French government owns the manufacturing company, the design engineers, the test engineers and the approval agency, and they dislike arguing with themselves. It is so unseemly to actually regulate yourself, n'est-pas?

I stand corrected, thanks Nick

It does beg the question why has the limit light not been fitted to the AStar - does anyone know if it was a post - FAA/TC mod on the 355/365?

Sandy,

Good question! Any EC people out there who can answer?

There's a Limit light in the AS355F-1 I'm flying right now. Don't have the manual here, so I'm not sure if it's a mod or if it's original.

We flew an intentional jackstall on the Gazelle. It takes quite a bit of effort to put yourself into that condition. I agree that if it could be designed out of the system without consequence then it should, but it's not as if there's a very large accessible and easy to use "DO NOT TOUCH THIS" button in the cockpit.

Like many things helicopter, it does require the pilot to understand and be aware in able to prevent and if required, recover.

Nick,

The French may not have a fondness for arguing amonst themselves...but they sure enjoy arguing with everyone else. Eeeet issss Lodgeek!

Let’s not turn this into a Francophobe forum.

As anyone in the business knows that the design and certification of any helicopter is a series of trade offs. In a good design everything is sized perfectly, keep the weight down is the battle cry in any helicopter design office, US, UK, France or where-ever. Each manufacturer has a different take on how to design a helicopter and how to achieve compliance, were that not the case then every helicopter would be the same. In the same vein safety cases rely on different mitigations; you can keep the pilot alive by making the crew station survivable in a 30 g impact but that is costly and heavy, alternatively you can reduce the risk of such an impact in other ways that do not necessarily make the aircraft less safe. Each design must be taken in entirety and a direct comparison between manufacturers design priorities in a single area will not result in an objective comparison.

Eurocopter will argue that the hydraulic system is designed to ensure that the rotor head cannot be overstressed. Something that in the early days of the Starflex head was paramount given the lack of operational data associated with any new technology. The fact that technology works and other manufacturer use elastomers is testament to a successful technology. In later Eurocopter models the Limit light is an indication that the head is close to its limiting stress loading, just as mast bending moment is displayed in other semi-rigid designs (BO105 for example). As an aside there are many in the Eurocopter who believe that hydraulics should run at the lowest possible pressure in order to minimise the safety implication of leaks and minimise weight, as SASLess put it.

Be in no doubt that the French take civil certification very seriously, in fact unlike the ETPS & USNTPS the EPNER Rotary Syllabus is based on US FAR certification and not European military compliance. After all Eurocopter has worked very hard to break into the North American and international markets and has had considerable success, they can’t be doing things too badly.

We are all different and from differing backgrounds, to really know your aircraft you need to understand the philosophy behind it not fight against it.

Fly safe chaps.

GA

I don't want to turn this into a Francophobe rant either, but....
It does make one wonder when the hydrualics off control forces on the AS-350 series are huge (a technical term we use in flight test) and others (like the Australian military) found significant problems with the handling hydraulics off.
I remember instances of 'there is no problem with the helicopter, it is how you are flying it' on more than one model of helicopter from this manufacturer, which does lead one to wonder about the politics of the situation.
I think it will also be found that as a result of the cold weather re-test, several changes were made to the AS-350 series hydraulic systems.
Don't get me wrong- there are some wonderful design features in French helicopters, but like everything else in this world that is designed by man, they ain't perfect.

I totally agree, and if there is a flaw in the helicopter I would certainly expect Eurocopter to sort it out. My point is that if the product flys as designed then there may be a transatlantic training/philosophy issue that needs addressing.

Lets face it no manufacturer wants the users to lose faith in their product, look what the DC10 tail engine issue did for MD sales.

GA

There are two types of servos in the 350, Dunlop and SAMM.

On the types I have flown there have only been Dunlop servos, and these are "easy" to demonstrate "jack stall" on.

Anybody out there that knows if the SAMM servos are the same, or better than the Dunlop. Dunlop seems to be more common.



CB

Gray Area said:
"Eurocopter will argue that the hydraulic system is designed to ensure that the rotor head cannot be overstressed. Something that in the early days of the Starflex head was paramount given the lack of operational data associated with any new technology."

Balls! Stated another way, you contend that because the rotor is so very structurally inadequate (that it can be damaged by pilot maneuvers,) thus it is a good idea that they weaken the hydraulics so that the pilot instead loses control in the critical maneuvers!

How about simply building a helo strong enough to start with? And if it isn't strong enough, how about fixing it?

I think it is not a Gray Area. Your profile says that you are a RN TP. Is this something you think the UK military would buy?

Nick

It is your contention that the rotor is "structurally inadequate" not mine.

The fact that you so strongly disagree simply supports my argument that there are cultural differences and different design philosophies.

I simply do not believe that bigger is always better. Whilst in military applications there is a greater need for redundancy, in the civil sector, particularly the light single market, weight eats payload and payload pays the bills. How many successful overweight or overly complex helos have there been in the civilian market? None, WG30 is a great example of how a complex military design does not necessarily translate into a commercial success.

FYI Single Squirrels operate at RAF Shawbury primarily in the Basic Helicopter Training role but also used for QHI training and misc tasks. Twin Squirrels are operated by 32 (The Royal) Sqn in the VIP role. So in answer to your last question yes, I think, in its time, the AS350 was a good design compromise. Although the Gazelle is much more fun!

GA

The British Army has always known about this with our Gazelles. When carrying out any hard right turn, I would always reduce collective a little bit to reduce the load on the servos, and never had a problem.

Is it a design fault? Possibly, but the aircraft concerned are fairly light aircraft with generally light control forces. Therefore the pressure within the hydraulic system only needs to be fairly low in order to control the aircraft. Hence the ease with which this pressure can be overcome.

Larger, heavier aircraft have heavier control forces therefore require higher hydaulic pressures. The Lynx hydraulic system is at around 3000psi and doesn't have a jackstall problem, but you can't really put a 300psi system on a 350/355.

Of course, all of the above could be b****ks. :D

Nick,

Remind me of my hydraulics theory....something about pressure...ram diameter....and cams....could we not get the same snoot out of two systems with different pressures but different sized components? The compromise is not just operating pressure but the sheer size and weight of the rams we would need....low pressure on the bulldozers....but really huge heavy metal bits...and higher pressures on smaller lighter bits?

Say what you want to about yer 350's.....if the rotor forces can overpower the flight control hydraulics....it seems a bit daft to me to say it is okay so long as you are aware of it. When I holler whoa....I want some thing to move besides my butt in the seat as I slide forward while pulling back on the cyclic.

Seems to me...if I put the controls to the mechanical stop...collective full up....cyclic full over and forward...and pedals full right (in the french model)....I want the hydraulic system to cope with that....full flow, constant pressure, and no feedback or "jacque stalling".

Anything less than that is sub-standard engineering design.

Before anyone says anything about...."come on...no one does that....they have not seen me flying an underslung load!" I scare myself sometimes.:uhoh:

Gray Area,
Inadequate is the definition of a rotor that can be bent by the pilot during relatively normal maneuvers. This is not hypothetical, it is (according to you) why the hydraulics were weakened to the point where the control of the helo is sometimes removed. This is not cultural, it is engineering, and we are not dealing with beliefs, we are dealing with hardware.

Sasless,
The issue is not hydraulic, it is rotor structure. The Squirrel can bend and break its rotor if handled near stall. Weakening the hydraulics is the "fix" according to Gray Matter.

MightyGem, The thread was about another model, not the Gazelle. Read the first several posts to see. In my understanding, the Gazelle is very much less prone to jack stall than the 350 series, which has relatively normal maneuvers causing loss of control (a cultural problem, according to Gray Area.) I agree, because if control is lost close to the ground, the pilot will end up looking like cultured yogurt.

Also, the hydraulic pressure is applied to a piston area, so that almost any hydraulic pressure can be used, if the piston is properly sized. It is not a pressure issue, it is a design issue, where the designer has chosen a servo that gives up during some maneuvers, and the pilot becomes a passenger as a result.

The difference is that, with the gazelle, it's reproducible in similar circumstances almost every time, whereas in the 350 it can catch you any time. Thus, with the gazelle you could call it a limitation, and with the 350 a design fault.

Phil

Rumour network, indeed!
Shawn, what's this about the Australian military finding significant problems with the hydraulics off handling?
AS350Bs and BAs were operated for years with few dramas and lots of practice hydraulics off landings. Very predictable and easy to handle, once the 'fault' was detected and the hydraulic isolate switch operated.
'Jack stall' was a discussed and demonstrated phenomenon in training courses, but I never experienced it or heard of it being a problem in normal aircraft use, and they got a bit of a caning manoeuvre-wise, much more so than the teetering-head types that were also used by the Aussie forces, because they could take it!
To paint this phenomenon (which certainly does exist but is only in my experience a problem if you like to throw the controls around like a gorilla, although to be fair, I don't know much about how they respond in extremely cold conditions) seems to be hysterical over-reaction based on a lot of hearsay.
Over...

Collective Bias:
The present aircraft I'm in is the only one I've ever flown any significant time in that has SAMM servoes. There's no apparent difference as to jack stall.
The SAMMs have other bad habits unique to the type- they "kick" when the pressure comes up. It's in the RFM....

First of all we need a EC tech rep on the line who actually knows what is going on - anyone, anyone?? Ken where are ya?

Secondly, has this phenomena ever led to loss of control causing an accident? Not that I am aware of, so is it really a design flaw or structural inadequacy? - Most incidences of jack stall that I have heard about have involved aircraft close to MAUW and close to Vne. Are those "normal" operating conditions?? Generally accepted procedure is to back off collective and cyclic, and control is regained. Why would you want to be in a full speed cyclic descent anyway????

And Nick - is it really a structural issue as opposed to hydraulic??

The issue is not hydraulic, it is rotor structure. The Squirrel can bend and break its rotor if handled near stall. Weakening the hydraulics is the "fix" according to Gray Matter.

Because if this is the case, wouldn't one expect to see cracked blades, splintered stars, or bent pitch links?? I have never heard of this happening as a result of jack stall.

The aircraft has been designed to be flown with out hydraulics if necessary, and is controllable at speeds of up to 70 knots, without damage to the rotor system. If you are incredibly strong and willing, probably more - you just aren't getting any help from the hydraulics.

I believe it is more of a 'characteristic', that perhaps should be investigated a little more thoroughly, same as LTE for the 206 series, the T/R problem with the 407, or the phenomena of mast bending in the 204,205,and 412 that led to the RIN and limited torque settings in the RFM limitations.

Is it necessary or practical to change a major design feature such as the hydraulic system?? I think I can answer for Eurocopter.
Knowledge and training I think are the key to this "issue".
After all its not what you know that will kill ya...........
Arm out the window...I'm with you on this one

Inadequate is the definition of a rotor that can be bent by the pilot during relatively normal maneuvers.

Nick that is plain spin - In the world of the articulated head that may be true but any rigid or semi-rigid design can be damaged by a pilot if he does not adhere to his limitations - mishandling the cyclic on the ground being a prime example, rapid manoeuvres at high speed another. Depends how you define normal. Put an unbriefed 206 driver in a Squirrel and get him to land on a decent slope and I'll give you good odds that he'll over-stress the head. I've seen it, or rather prevented it, many times converting pilots to Lynx.

All that aside this is a not a real issue. The recovery from jack-stall is simple, ease the manoeuvre. It is not a safety issue if the pilot flys within the capability of the aircraft - just like any aircraft there are manoeuvre boundarys.

The argument from SASLess that he should be able to "put the controls to the mechanical stop...collective full up....cyclic full over and forward...and pedals full right" is frankly daft, at low speed you might get away with it but in the cruise or faster,with the contol authority of a semi-rigid head you would end up in a very hazardous situation.

GA

Gray Area,

I think you are missing the point....we are discussing the 350, not the Bell two bladed head. Not withstanding that, there are things that I will not do in various helicopters for various reasons. In any Sikorsky I or Bell helicopter I have flown....the hydraulics always kept up with the control inputs...take from that what you will. In the MBB products....except for some roll coupling...the hydraulics keep up with control inputs. In the Boeing-Vertol products I have flown...the hydraulics keep up with control inputs....it is only on the 350 we hear of this "Jacques Stall" event.

Yes, in the Bell two bladed heads...if you show your butt you can snap the mast off at the top....yes, if you enter negative "g" you can get into mast bumping and snap the head off...or lose control. Yes, in really aggressive maneuvering you can get yourself into a pickle in very high speed, high "g" pullups following a gun-run in a Cobra. Yes, you can over stress the Mast on the Bell 204-212 series if you pull too much power at too high an airspeed....but in all of these events...the hydaulics work with full control authority.

Your question "why would anyone want to operate near Vne at max weight?" Everyone of us who fly these things for a living will do that at some time. As long as the power utilized remains within the set parameters....we usually go for whatever speed we can get on long distance flights....Vne is the limit.....not near Vne....otherwise the Vne would be lower than it is.

There is no denying the fact....the controls should not enter "Jacques Stall" and remove the control of the aircraft away from the pilot. It is poor engineering at best in my humble opinion.

SASless

Applying that line of reasoning then to other aircraft...............
You should be able to be low and slow and heavy in a 206............
You should be able to punch in as much pedal as you want in a 407......................
You should be able to push over a teetering system into low G.........
You should be able to fly into icing conditions.....................
Is fuel REALLY necessary??................................

Point is, every aircraft has its deficiencies, quirks, characteristics etc etc, and granted some are of grave enough concern that they eventually find their way into RFMs as a pilot procedure, or a limitation, while others remain as a known phenomenon to be discussed, taught, trained.

Vortex ring state, or settling with power, doesn't imply a design flaw on a particular helicopter (or does it???)

I do see your point on a system that maybe should perform better, but if it is a known characteristic, isn't the first and obvious fix not pilot technique?? As in not pushing over a teetering head, not putting yourself into LTE, or getting into settling with power?

I've been flying, among others, A stars for 18 years now and have to say that I've experienced jackstall only twice on B models and when I was doing quite an agressive flying. Never had any more on twins (F's and N's) although I have to say that it's been a long time since I don't fly the hard way anymore. So for me it has not been an issue but I've never flown them -25 ºC and it seems that some pilots have encountered that situation in normal flight envelopes:confused: , if really so it should be something to take care of.
I fly my AS 355 N with total confidence in flight controls. Just my 2 cents
Buen vuelo

Sandy,

In response....in each situation you mentioned...the pilot has the control....not the aircraft. When the controls quit working...the pilot does not have control.

LTE...the aircraft is fully functional...the controls work...might be the tail rotor does not have the ability to cope with the yawing moment but the controls are working. Judgement is the main issue there....keep your nose into the wind...don't let a yaw rate develop.

407 and its tail rotor....seems like the controls work too good there.

Bell Helicopters and their tail rotors are much akin to the "Jacques Stall" issue. Thus you will not get much argument from me about those issues.

Zero "G"....again the controls got you there....judgement is the issue.

Icing....the controls are working....judgement got you into the ice.

Low, slow, and heavy in a 206.....again...judgement got you there.

Fuel....pilot judgement again.

In the 350....with "Jacques Stall"....too many reports of it happening for it to be a simple judgement thing....gets back to engineering and the controls not working all the time.

I got hydraulic feedback in a Huey once while manoeuvering 'positively' to avoid hitting someone else in a formation, which felt just like the dreaded Jack Stall - unusually fast and large cyclic movement leading to forces through the controls which went away as soon as the severity of the manoeuvre was reduced.
That's the same thing as we're talking about with the Squirrel, isn't it?

For sure hydraulics or pylon mount issues that felt like feedback...or mast bumping....? Used to get hydraulics failure on the Alouette III in severe turbulence....hit a real down draft...all the fluid went to the top of the resevoir....pump cavitated....feedback in the controls...till the down draft was replaced with more normal forces.

During testing at Patuxent River we experienced a form of Jack Stall in the AH-1T (PT-6 powered AH -1 with a 214 rotor and tail rotor). Even with a 3000PSI hydraulic system the servos were not able to react the flight loads during a symmetrical 3 g pull up. During this maneuver we experienced significant levels of control feed back in pitch. Review of the data also revealed that we exceeded test cards imposed limit of 3 g's. I do not believe that the weak hydraulic system is actually capable of protecting the airframe. Limitations do that.:E

Can someone help me with the specs of the AS350D and its differences compared to the B series?

Thanks

NB

It is powered by a Lycoming engine that had nil respect in the early days, but is now workable. It is not supported by EC

phil

The "B" series used to be called "Falling Stars". However, paco is right: the newer version of the LTS101 is apparently much better.
See:
http://www.pprune.org/forums/showthread.php?s=&threadid=18877&highlight=lts101

SO who knows what the AS350C was ?. One of the early Canadian ships shows c to d to b on its registration.

Mark C-GMEY Serial No 1004
Common Name Aerospatiale Type Certified Model AS 350B
Identification Plate Model AS350C TRANS D TRANS B
Base Of Op. - Country CANADA
Base Of Op. - Province Quebec
Base Of Op. - Location Les Cedres
File Location Dorval Basis for Eligibility for Registration Type Certificate - H83
Type of Registration Commercial
Category Helicopter Weight (Kgs) 1950
Manufacturer Societe Nationale Industrielle Aerospatiale
Year of Manufacture 1979
Country of Manufacture FRANCE


Link to all you need to know about AS350 models

http://www.aviationtoday.com/cgi/rw/show_mag.cgi?pub=rw&mon=1003&file=1003as350.htm

Rotornut,

I believe the "D" was the falling star, otherwise known as the Death Star.

RB

I read somewhere recently that a soloy conversion is on the way for the AS-350 using the updated LTS engine with much increased output and twin channel fadec which will give even the B3 a run for its money with MUCH lower DOC's.....would be a great conversion.
With regard to the AS-350 series all the basic airfames are more or less the same not including the engine / airframe interface parts, the t/rotor compensator fitted from the B1 onwards and some minor frames added to the underside of the tranny deck for a/frames modded from B upwards...... The vertical and horizontal stabs are a little different for almost all models. There is a fence on the tailboom of the B1 and B2 that must not have achieved a whole lot because it is not to be found on the B3....

OCTANE100,

I beleive also that Bell will introduce a version of the LTS 101 into the 407 from 2006 thereabouts!..should be interesting.

Here in NSW the National Parks have a 350BA with a C-30 Fitted to it

apparently, the b3 doesn't have a strake because it doesn't need it as it has enough tail rotor authority as it is.

Soloy (pappilon ownes the soloy/ STC ) does have a STC for the LTS101, they are calling it a B2 101 or someting. They had one at the show this year. Supposedly the 101 is a super eng now. One thing about the 101 in the d model is it burns dirty, turns the tailboom black in a hurry.

The 101 DOC is a fair bit lower than the french eng.

rb

Someone (the name escapes me, but was located in Broussard, LA) had an STC for a conversion of the D model to an Allison C28 or C30 engine. I can't remember if there was a model change or not. It never became very popular.

When I transitioned into the AS350D I thought it was heaven at first - a heater, 3.5 hours fuel, fast, comfortable, roomy, and very responsive. The B206 paled in comparison. And it was a nice ride as long as everything worked the way it was supposed to. When things started to go wrong, it could be a handful. I still recall doing a postflight and wondering where the water on the engine deck had come from. Turned out to be kerosene, and the fuel manifold that was mounted behind the combustion chamber, in a circle around it, had sprung a leak, spraying fuel directly onto the combustion chamber. The good news was that the leak was large enough that the amount of kerosene being sprayed provided cooling, and was too heavy to ignite. :eek: :yuk: :ooh: :ooh:

AS350C was the first with a LTS 101 600A and preceded the B model in being type certified.

AS 350D came after the C with LTS 101 600A2.

AS 350D1 is the same as the D with a LOWER MTOW.

AS350B came along with Arriel 1B engine.

All of the above have "Blue" MR Blades.

AS350BA is a "B" with 355 "Grey" blades and 355 TR blades and a few mods to the transmission deck.

AS350B1 is like a BA except with a Arriel 1D engine and TR compensator and boom strake.

AS350B2 is as above with a Arriel 1D1 and different tailpipe.

AS350B3 is basically a B2 with an Arriel 2 engine (FADEC) VEMD and NO boom strake as it has the TR off a 355N Model.

EC130B4 is EC120 at the front, B3 in the middle except with Dual hydraulics and EC135 in the tail although a mirror image due to direction of rotation.

There is/was a Soloy conversion to install a 250C30. Ones I have seen have some probelms with exhaust re-ingestion and if you look at the installation it is very "draggy" compared to the Lyco or TM.

There is a "Super D" with an LTS 101 750 and effectively B2 running gear.

Some people who have stuck by the Lyco love them. Low fuel burn and the engine can be operated "on condition". You can do a lot on the Lyco yourself. TM are very reluctant to let people outside their organisation mess with their engines.

And there is an odd one out there - AS350BB UK Military training aircraft (HT1) which I think is a BA with a 1D1 in it.

Does the LTS 101 600A2 have all the problems soughted out or is one to stay away from and stick with the Arriel donk ?

I am looking at a machine with an approx 2500 hrs TSN.

Thanks

NB

Judging by the terminology you are using - look to the East of you. There are a few operating and there is a bit of experience there.

Talk to someone at Airwork (NZ) they look after 350D's and BK's with similar engine.

One O Wonderful's have some form in NZ. The Cresco Ag machine had the LTP although now carries a PT6.

Be aware of the component times , between 2500 and 3000 hours most of the dynamic components need major overhaul or replacement.

ENGINE (Lycoming LTS101-600A-2 with 2,491 hr TSN)
GP Rotor Assy 5000 3837 77%
GP Disc 5000 3837 77%
GP Spacer 15000 12617 84%
GP Sealing Plate 15000 12617 84%
Impeller 15000 12775 85%
Axial Rotor 15000 14485 97%
Compressor Shaft 15000 13362 89%
PT Rotor Assy 12000 12000 100%
Fuel Control 2400 397 17%
Fuel Pump 2400 1625 68%
T1 Sensor 2400 2221 93%
O/S Limiter 1800 1760 98%
PT Governor 2400 1430 60%
Air Flow Modulator 2400 1742 73%
Fuel Manifold cyc 2000 1821 91%
Start/Gen 1200 1200 100%

Should also pay attention to Starflex , upper and lower sleeves MGB and Epicyclic module. Starflex was abour 3000 hr retirement ( If I recall correctly though it is more for the D now I think about it )

If you change your mind later I think it is still possible to convert from a D to a B via SB.

ANY engine would be cheaper than turbomeca, their service is **** and they when you bend down to pick up the penny they left you with they **** you again.!! I had small part of mod 2 go through engine and it cost E250,000., all i get is a Gallic shrug!!

Anyone know of weight and balance software for a PDA? Any other good PDA software (aviation) that you guys can recomend?

Thanks

RB

There's a spreadsheet at www.electrocution.com/aviation

GB

I made an Excel S/S, converted it with "Documents to go" to run on a Palm OS. It does every thing I need in EMS- existing W&B and compares it to fore and aft limits, computes max wt on the stretcher with exisiting crew and fuel, and a very few other conveniences...

If you'd like it, PM me, I'll send it on. It's not fancy...

For more general computing, I use CoPilot on the same Palm OS unit, and like it great deal.

Ok 350 guru's I have a question?

I have a fair amount of time the in the 350, but recently have been working it at a Pa of >7000-12K. I have noticed that starting the initial light off tends to be pretty hot and requires maniuplation to keep it in the 700-750C range, even bringing it back just a hair to mudulated it, cause it to flame out (0ver 9000 pa). EC want you to immeaditly induce fuel when you hit the starter. Just as an experiemnt I waited unitl 10%n1 before I came forward with the FCL and got a much cooler light off (as expected) .

Anyone else seen anything like this. Tips for running these things up high?

RB

Are you, as a standard practice, introducing fuel at the same time as you press the start button? The only time you should use that particular technique is when the OAT is below freezing. (As per the flight manual) Standard start procedures for the B-2 are:

"-When the Ng reaches 10%, move fuel control lever forward
about 1/3 of its travel range (When OAT is below 0 C, open the
fuel flow control at the same time the start push-button is
pressed)"

Firepilot is correct mate... as it reaches 10% then introduce the gas. On the 1S1 arriels you can intro from initial igniter activation.

Should it not be modulated at 650 - 700 degrees?

Smell burning yet? :)

Check your battery, Rotorboy. If you have bad battery, you need to move your fuel control more forward during start. It great's of course T4. Be aware it. Change your battery ASAP if it's the fault.
(That you need to do only if you are in the middle of nowhere!.)

Normally I'm doing my starts like this: Move forward fuel control when it's front edge is front edge of the hole. (I mean hole where fuel control is during flight) Then push start button and t4 rise to about 670 degreeses after Ng is thru 10%. You dont have to move fuel control before t4 is going to fall. Keep t4 between 650-700 degrees during start. That is easy way. It works our As 350 B and B2 helos. (Still monitor T4 all the time!!.)

(hope thet you are understand what i'm trying to type) Languages are not my best part.

Dear aviation friends

I was wounder if someone have an information or where can I find about dual belt hydraulic pump for the 350B3.

Thanks for the info.

FELIPE

I believe Eurocopter offers the hydraulic backup as an option on the B3. It's listed as such on the spec sheet.

Felipe,

I can't help but wonder why you would go to the expense of adding that option when a simple daily check will show the condition of the single "uprated" belt...ie the vee type, they are very reliable...

Not trying to second guess you but the only real reason for the change from the original green flat hyd belt on the earlier AS-350's in my humble opinion was the lack of regular "condition" monitoring which led to the inevidable......There are plenty of other areas a B3 could do with a little work/modification....

all As350's( Both twin & single) with auto pilot have been grounded worlwide.

Eurocopter have discovered a defect with the weight & Balance issues and have declared them grounded.

The only way you can fly them is if a fully certified engineer, who has been certified via Eurocopter to carry out these check's, carries out a check A before if flies every day.

This is regardless of whether the flight is classed as a private or commercial.

Intill Eurocopter come up with a solution this is the procedure you have to comply with.

Can anybody shed some light on the situation.

As always I stand to be corrected.

Could you provide the details from whence that grounding order comes.....Emergency AD's or something maybe?

IS it all autopilots ?. ( 2 axis , 3 axis , coupled )
For the twins it would probably be more significant . I would guess that less than 5% of singles have autopilot .

Nothing on federal register .

goose boy

Is this rumour or news?

WIDGEON

As far as I know it is all.

SASLESS

I dont know the answer to that question.

HELIPORT

My source is from a very well know maintanaince company, I dont want to mention there names for obviouse reasons but the company begins with M.

Also I have had first hand dealings with a AS350 owner who is currently dealing with the situation.[

Heliport...I went to faa.gov and checked for AD's in both Emergency and Past 60 Days catagories and came up empty handed.

Seems a strange thing.

What has the check "A" got to do with weight and balance?

If it's a secret, it shouldn't be!

Sorry When I say Check A it's more of a engineers check A ( totaly irelavant to a pilots check A)

More of a certificate of release to service for one day

goose boy

"very well know maintanaince company."

If your info is kosher, what's the problem about naming it?

You may be right - I don't know - but "AS350's Grounded Worldwide" is an eye-catching headline. You got the wrong end of the stick on another thread you started recently - and since removed.
I'd be much happier if we had a checkable source to confirm what Eurocopter has actually said.


Heliport

(I've changed your title for the moment, and will change it back if what you say is confirmed.)

Heliport,

It would seem there would be lots of response to such a situation....here and other web sites.....but other than the original post....there seems to be no smoke signals from any fires showing.

But then....maybe there are not all that mamy 350/355 aircraft with autopilots out there to be affected.

"Sorry When I say Check A it's more of a engineers check A ( totaly irelavant to a pilots check A)"

??

Is there a difference? There isn't on the aircraft type I fly and hold a check 'A' qualification for. We use the same checklist as the engineers.

My sources tell me that it originated from a faxed warning from Eurocopter concerning a cracked vibration absorber. Requires checking daily by an engineer due to the need to take the belly panel off.

news to me my company operates both and they where both flying today as where a number of other 350/355s.

If the belly panels had hartwell latches could the pilot carry out inspection ?. If i recall correctly if the panel can be removed and installed without the use of a tool then an engineer is not required, is this correct . If it is a cracked vib absorber then to me it sounds like an isolated installation problem , I recall the sfim/sagem system had one of the computers mounted adjacent to the vib absorber. Can't see how a W and B problem would cause damage to the vib absorbers .

Eurocopter issued an alert telex on 9th June to inspect the right hand cabin anti-vibration damper. The inspection has been included in our Daily Mandatory Inspections. All the pilot does is drop the right hand side of the belly panel to check the damper. If it breaks it could foul the trim actuator. Our engineers showed us in a few minutes what to look for. No fuss, no drama, no grounding.:ok:

VH....but if it breaks in flight then what? Possible for it to foul the control linkage and thus be a bit bothersome?

Sasless;

You are absolutely right. Sorry, I meant no trouble about groundings or complex inspections. If it did break in flight it could cause a serious buttock clenching moment. I haven't heard if this fault has actually happened or whether someone has realised the possibilities and reacted accordingly, if so good on them.

VH

If this slight irregularity is of enough concern to require a daily visual inspection....one would assume the FAA, et al....would be issuing an Emergency AD on the issue. Another argument for operators to buy bare bones helicoters....see what happens when you add fancy avionics...nothing but extra costs and inspections!!!

SASless, you used to complain about barebones aircraft flogging around the patch at night, now you say that barebones aircraft are better (is that a gotcha?)

Nick,

Sorry old boy...that is not a gotcha....just another chorus of the same refrain.

I said....yet another excuse for operators to argue against buying the fancy kit....citing the increased costs of yet another inspection.

If the aircraft did not have the servo....and the chance of interference with it....would it be a "daily" visual inspection vice a periodic inspection as are a multitude of other things?

A question is begged here....did the engineers drop a clanger on this one by not anticipating the conflict?

Just revising for my 355 OPC next week and the anti vibration resonator is not part of the autopilot. It just reduces vibration around the cabin floor area. The aircraft has to be checked once a day by a qualified engineer (not the crew) and details are available from macs

Yes, the problem is that the antivibrator could detach and fall onto an actuator. The check is a one-off, and not required daily.

thats not what I have heard from 3 different owners now as they all have to get it checked off by an engineer daily

For us barebones chaps, What kind of device is the AntiVibrator, how and where is it connected and what effect does it have in real life?

TFS

squirrel: pm me, have some very detailed jpegs of the anti vibe weights if your interested.
dr

Goose boy - we operate 27 AS350s with 2 axis autopilots, and that's what my chief engineer told me a couple of days ago.

TheFlyingSquirrel - as I understand it, the Squirrel was found to have numerous vibe problems. Some were removed/reduced by the antivibrator on the rotor head - some ground resonance (or something similar) difficulties were reduced by adding the springs on the back of the skids and dampers to the skid mountings. The anti vibration units under the floor are lumps of lead on flat springs and are mounted one under each pilot's seat. They are tuned in the factory to reduce the vibration levels felt by the front crew (engineers speak of 'nodes' whatever they are). It's probably the size and weight of the lead that makes them a problem if the spring or mounting fractures in flight!

Thanks for the reply Oldbeefer - how effective are the lead devices? A little or loads?

Thanks.

I have been told that they reduce vibration substantially , they were not going to be installed on EC120 but after first flights they changed their mind , with a 20 to 30 lb weight penalty there must have been good reason.

A "node" is a stationary point in a vibrating system.

Visualise a skipping rope, or tail rotor drive shaft. Start shaking it at one end, keeping the other held firm. As it vibrates, one part of the rope/shaft won't move - that's the node. Shake it / turn it faster, the node moves.

The lead weights I assume move the nodes in the AS350 cabin to near the seat attachment points - less movement, less bounce in the pilots' step when they get out.

AD's just issued here in Australia: AS350 (http://casa.gov.au/airworth/airwd/ADfiles/ROTOR/ecureuil/ecureuil-112.pdf) and AS355 (http://casa.gov.au/airworth/airwd/ADfiles/ROTOR/as355/as355-088.pdf).

Hmmm...how can it not become effective until the 20th, or have I misread it??

Thanks for the pics Chopperdr - know I can see what everyone is yappin about. I personally can't see how a dumb piece of lead can have any significant advantage - but I presume it acts as a counter-balance? I've glued it up if you don't mind - i'll remove it if you like - thanks again. Also, how can it fall onto an acutator?

TFS

http://img.photobucket.com/albums/v650/theflyingsquirrel/Dsc01283.jpg

The relevant Eurocopter Alert Telex equires a visual inspection at the next, and each, ALF check (after last flight of day) until they introduce a modification to prevent any interference with the trim actuator rod in the event of failure of the vibration damper blade.

No mention of engineers needing to do it. Extension of Check A, so effectively daily.

Anyone ever come across such a damper blade crack/failure or know the TT/history of the incident that triggered this?

rechecked with techies - you're right. A daily visual inspection is required. Seems a bit OTT?

So, can we take it that AS350s are not 'Grounded Worldwide' and all that's happened is Eurocopter has issued an AD requiring an additional check to be added to the other daily checks?

Heliport

Yes, at least seems clear to me.

Oldbeefer

Tend to agree it is OTT, which is why I'm interested to try and find just how many incidents anyone knows of. What worries me is the added risk of finger trouble on a pretty big cowling that I reckon could cause some serious damage if it came undone.

OK it's got 3 latches but it is not light and a bit awkward. History tends to prove that if pilots (and engineers) open cowlings, sooner or later they'll forget to close them properly.

Balance of risk then. And allocation of responsibility!

TheFlyingSquirrel-


That thing is a vertical vibration absorber, designed to "twang" probably at 4 per revolution frequency, kind of like a person standing on a diving board can make the board bounce at its natural frequency. It is resonant at the frequency, and so it absorbs those vibrations from the surrounding structure. It is very effective, that kind of absorber is used in the industry quite a bit. If it is not tuned right, that area of the cabin will feel like a rocky road. Two absorbers like that are located in the UH-60L near the pilot's step. The stiffness of the diving board and the amount of lead are selected to make it "like" the 4 per rev (which is probably about 21 to 25 Hz).

The place near its mount that is to be inspected is where the vibration gets passed through, so it is subject to high stresses, and thus the crack inspection.
I think I see a place on the weight for a vibration pickup to be mounted (the circle with a hole). If so, this is probably used at the factory to fine tune the absorber by reading how much it shakes in flight, and adding or subtracting weight until it is peaked out.

nicks correct, you can see the cross hairs where the 6 attach bolts p/u the airframe, that is the pickup point. also note the washer glued to the hammer weight, this is very common to see washers or various amounts of loose change glued on the hammer face to fine tune the airframe.
dr

chopperdr,

If that loose change are Franc coins, it means someone has found a use for the Franc!

If you guys would like, I can post some comments on the type of absorbers commonly used.

Nick,

Please do provide us a topic for some vibrant discussion....hopefully the frequency of posts in reply will vary with the source. Maybe that bit of information will dampen any misunderstandings and smooth any inconsistencies.

nick: your correct, however if you order by part no. from eurocopter, the face value increases by a factor of 4, lead time approx 90 days and the service bulletin requires that the head side is up : )

What, even for that hose that is plainly labelled 'Made in USA' in the picture?

hilico: for that a/c hose your okay, in stock, ready to ship, reasonable price, call platinum aviation.
now if i can just figure out how to finance an stc installation of PW207E engine we would really be cooking with gas.
dr

CD I thought first plan was a RR250 in EC120 , surely with all the disposable income on this site we could raise enuff capital !!! As350b207E is a bit long , any shorter names ? Is Jack K still around talking of platinium ?.

widgeon: so many more eligable airframes with regards to the astar. the 120 is ok as long as its kept light. as for jack K not sure if he is still involved.
will be at ecl monday

Gents

Are there any AS355 operators still having problems with this inspection?

Anyone know of the pilot being authorised to conduct said inspection or does it still require an engineer?

Thanks

Right pain in the preverb.
We're lucky that aircraft is based where gingerbeers work but the flexibility of the beast is hampered for 'overnights'

Pilots are not auth'd to carry out the additional check - unless they're also a certified engineer

I was told this morning by a CAA maintenance surveyor that the decision of whom to authorise [pilot or engineer] was being delegated to the maintenance organisations...

Cheers guys.

I will chase it up.

Now....... where did I put that number.....

:O

I got told by a little dickie bird that the whole reason why this check can not be carried out by a pilot is because the A.D that was sent out did not say to be carried out by engineer's & crew on it like all the rest and it was supposed to be on there.

which mean's this whole knightmare is all down to a typing error.

They are now letting pilot's carry out the A.D check if you get certified from a maintenence organisation.

I know McAlpine's are certifieing people to carry out this check

Hopefully no more messing around and that we can all get back to haveing a social life again .

Yep, likewise, back to auth'd pilots carrying out the check!
Not a good advert for EASA, CAA, Blah

EESDL

So True

As far as I understand Eurocopter have Given all operatores a choice.

You can either check the damper daily before first flight or you can have the damper removed all together.

It's only taken them over a month to come up with this solution.

They must of had half a dozen monkeys working around the clock on this one

Any opinions on this

I am looking to buy a set of floats for the 350 B3 model. If you have any ideia of who may have one available for sale, please let me know. this is hard to find and to expensive if you buy new at Eurocopter. Any ideia!!!!!:(

Air Curiser and Apical. The advandage with the aircuriser is they pop on and off and the gas is in the float itself vs the aricraft. The Apical's are retty much permantly mounted on the skids, configured with several differnt bags.

good luck,

just remember never trust the floats, the electrial firing and alwys double check the rigging on the MANUAL release. Nothing more nerve racking than pulling the T handle and not hearing the floats go when your falling from the sky

rotorboy

Anyway these could be automated, in a similar manner to airbags, to save pilot workload?

The simplest system would be a float in a small chamber, that triggered a fast inflation. OK it wouldn't stop partial submerge, but it would stop it becoming a more serious situation like inversion. Once the pax and pilot had walked away, the heli would also be recoverable.

Maybe even link it into the hard landing airbag system suggested in an earlier thread, although airbag/float shape might not be compatible.

Mart

That really isnt practical. Most floats I have flown on an astar are fired by a trigger on the cyclic, that shoots a charge into the mechansim that inflats the floast (rather rapidly). There is usualy and secondary failsafe system ( I have seen fail) which is a mechanical linkage to the float firing device.

I as a pilot would rather have control of when the floats fire. Condiser the Autorotational charectaristics change dramatically with two huge airbags on the side. mo drag!

Floats may get you on the water but most of the time the a/c is lost due to capsizing.

rb

There have been a number of accidents where aircraft have impacted the water in an uncontrolled manner, the flotation equipment has survived the impact but has not been manually activated by the crew. Research carried out by Westland Helicopters in the UK and independently in the USA on behalf of the FAA has identified drowning to be the major cause of loss of life. Aircraft occupants having survived the initial impact then failed to safely escape from the hull.

In March 1992, an AS332L crashed into Sea State 7 conditions during an offshore night flight. Only 6 of the 17 occupants survived. Although the impact was severe, post crash investigation indicated that the flotation system may have survived and been at least partially available, had it been activated. The crew did not have time to manually activate it and there was no automatic means. The accident investigators considered that inflated flotation bags would have prevented the hull from rapidly sinking and assisted passenger evacuation from the inverted cabin by allowing it to float higher in the water.

In September 1996, an AS350B1 was carrying out low level overwater filming with 2 persons on board. For reasons unknown, but suspected to be inadvertent closure of the fuel control lever, rotor rpm dropped and the aircraft descended into the sea. Although the pilot attempted to, he did not have enough time to manually activate the emergency flotation equipment. The helicopter impacted the sea, inverted with the subsequent loss of the passenger.

Provision of a means to automatically inflate both ditching and emergency floatation equipment could have prevented loss of life in the above accidents.

Most helicopters working offshore in the North Sea now have automatic inflation of floats.

ADvantage of apical floats is you can take off again ( get a bit of spinning happening until the TR gets thrust ). The floats are fairly easily removeable it is just those pesky skid extensions that take some time. Phoenix in NWT are using them on their EC120 to land on lakes to collect water samples. I am not sure if any flotation system can recover a helicopter once it has ditched. ASide from the Sea king there are not many that will float for any appreciable time after impacting the water. Flying at high speed close to the water I do not think even automatically activated floats would be of any use

widgeon: your correct, with the apical emergency floats you can land and take off as they have enough bouyancy to keep the tailrotor out of the water. ditching floats are approved for water landing only. operators must be careful to make sure they have emergency floats vs ditching floats, if they decide to alight from the water.
with regards to the extensions, have seen a number of operators keep the extension installed and just remove the bags when not flying over water.
one more advantage to apical floats on the astar is the mechanical pull system, no electrical system. apical also has the astar floats available with the liferaft built into the float bag, thereby freeing up cabin space.
dr

Who or what is the best thing to use to get accurate operating costings for UK aircraft? Is there anything like C&D or who are the best to speak to? The a/c concerned is an AS350B2.
Any advice from them older and wiser greatly appreciated.

I operate a BA and all i can tell you is...............A LOT !!! About double that at least of a 206 , and when it comes to the engine side.....well you are bent over and R****ed by Turbomeca....circa £200,000 if you are unfortunate enough to have FOD damage and have to have an exchange !! I can buy around 7or8 allison C20 engines for that. I cannot imagine a B2 will be much different.........great machine though!

Just confrontated with an AS 350 BA accident i'm interested if anybody of you guys have experienced a LTE on a AS 350. I have a few hundred hours on this type of helicopter but never encountered such a problem.

The ship was taking off with an external load on a 50ft rope when suddenly in 100ft it began to spin to the left. At this moment the IAS should be round about 10-20kt. There is no indication of any technical malfunction. The helicopter was short before the MTOW but not overloaded.
LTE would declare the reactions of the ship seen by the witnesses.

the As350 has tremendus t/r authority but altitude and high Gross Weights you can get your self in real trouble.

I had a 350B2 swap ends on me picking a sling load at nearly 10K. The load wasnt that heavy. light and varible winds 0-5 from every where. I went to pick the load up vertically at 75-100 feet the thing just swapped ends , weather vained into the wind and stopped. My heart went in to my mounth and I was nano seconds from punching the load off.

A good friend an someting similar happen on approach to land , near MGW at altitude, real light squirrely winds, shallow approach 10-15 off the ground swapped ends and stopped.

I have a heard a few other storys , all at alt near mgw.

hope this helps

RB

The ship was taking off with an external load on a 50ft rope when suddenly in 100ft it began to spin to the left

Need some numbers here. Like What was the Aircraft Weight, Altitude, Temperature and what was on the end of the 50' rope.

After you get those, Im sure you will see what makes the world go around............

Most LTE's are due to rotor rpm drooping when too much power is commanded. Lowering the rpm reduces the available tail rotor authority, and is really not LTE, but rather over-pitching, a good British term. What was the power/rotor rpm during the incident?

thank you nick, thank you,

overpitching at last, instead of more of this crap about lte.

obviously if you run out of main rotor rpm you will lose tail rotor effectiveness. if the wind changes speed you get loss of tailrotor effectivness.

the chance of weather cocking with a heavy load load at altitude is to be totally expected and not a consequence of lte but a case of no more power available, something has to give.

i know why pilots like to think lte was to blame, it's because it is a good excuse for bad handling or inattentiveness.

better than telling the boss that you overpitched his machine and bent it.

"it had nothing to do with me boss", "it was that bloody lte phenomena", or "I could still pull pitch so i must of had more power left, then it started spinning all by itself".

thanks again nick for the reality check. :ok:

Imabell,

if the wind changes speed you get loss of tailrotor effectivness. or perpahs direction.

Ok explain to me your deffenition of LTE.


When you have a light varaible wind, you position into the current/ most prevenlant wind direction, then wind shift slightly and you are at a high power setting and you "weathercock" or have an uncommanded yaw. Recoverable or not, how is that not a symptom or byproduct of LTE?


So all these 206 accidents at altitude with uncommanded yaw on short final to spots are all over pitching? not lte? Tailrotor authority has nothing to do with it?

rb

Terminology: the bane of understanding!

Rotorboy, I see your points, but I think you are mixing the terminology between LTE, Authority and perhaps not understanding imabell's oevrpitched call. So we are all singing from the same sheet of music, I suggest the following terminology cut and pasted from another thread:

Loss of tail rotor control: You are not able to control the tail rotor pitch mechanism.

Loss of tail rotor thrust: Little spinning thing at the back stops spinning or falls off.

Loss of tail rotor effectiveness (LTE): "Newly" discovered and named in the 80's after many (in particular OH-58/B206) accidents. Although somewhat awkwardly named (as the tail rotor is still effectively working and must be providing thrust) LTE refers to what is thought to be an ingestion of main or tail rotor vorticey through the tail rotor which causes an onset of yaw in the direction induced by torque that cannot be overcome by the application of full "power pedal". The yaw rotation can build up quickly enough to fool most pilots into believing they have experienced a loss of tail rotor thrust. The concept has come under fire lately because of the early thoughts that the tail rotor enters vortex ring state being a little hard to prove. Oh - and then there is fenestron stall that possibly fits into this category too, although strongly denied as a possibility by the manufacturer whilst allegedly being strongly experienced by the pilots!

Loss of Tail Rotor Authority (LTA): Also a new term to make the old Huey war story of "..and then I ran out of left pedal and..." sound a little more sophisticated and technical. In this situation, the tail rotor does not produce enough thrust to counteract the torque/crosswind combination you require, your power pedal hits the stop, and around you go - though often quite gently when compared to LTE or loss of thrust. A lot of aircraft are susceptible to this, but the UH-1D/H Huey is famous for it - and many people have had the earth come up and smite them as a result.

This is somewhat semantics, but the reason I used the term Loss of Tail Rotor Authority instead of “Over pitched” is that it confuses the situation a bit. Over pitched infers that the blade pitch angle is too excessive either for the engine power to overcome the induced drag, or that the blade may be in some sort of stall condition. Most commonly, over pitching refers to the main rotor case (as Nick says below) causing a RRPM droop and therefore LTA, or it could mean a T/R blade overpitch causing LTA. Either way, both manifest in a LTA situation - not an LTE.

But not all LTA is caused by over pitching. LTA also covers the other conditions where niether the M/R or T/R blade is over pitched but the T/R still cannot produce enough thrust to counter act the yaw. IE the T/R blade pitch angle is at it's max, but the resultant thrust is insufficient to overcome the yaw conditions caused by power, DA, adverse wind, pilot handling, etc.

So in green thumb's case, I don’t believe that the tail rotor or main rotor has “over pitched”, although as imabell points out, this common term has been clouded by the LTE hysteria, and somewhat forgotten - and with the forgotten term comes a forgotten condition and a forgotten recovery technique - and I share imabell's concern with this. Fly a UH-1H and you will be forced to remember.
:oh:
In the AS 350 case, though you have yet to provide weight and DA details, I think an LTA case can be made: the T/R was unable to provide enough yaw authority for the power/DA/wind combination. Given that it was an AS 350, it is unlikely that the T/R blade was over pitched/stalled, and unlikely to be a main rotor droop – though the term over pitched certainly describes the aircraft reaction accurately, and the recovery actions are the same. (Unlikely does not mean impossible!)

edited to include corrections by AOTW!

rotorboy,

In an LTE study I did about 7 years ago, based on worldwide accidents of all helos, using four different data bases, this is what it showed:

95% of all LTE accidents involve Bell 206 models.

Virtually 100% of all LTE accidents involve Bell helicopters (one Robbie in UK was reported as LTE, but was probably over pitching).

My conclusion was that the inadequate size of the Bell 206 tail rotor was the principal cause of its LTE woes.
A second finding is that all tail rotor authority events were being called LTE because the marketing campaign conducted by Bell was effective on removing the heat from their design.

LTE really does not exist, it is a label used to blame the pilot when a marginal helicopter loses yaw control within its approved envelope. That does not mean that a 206 can be milked by an experienced pilot to not lose tail authority.

LTE cannot be experienced by any helo built to modern standards (larger tail rotor). It is impossible to get LTE in a Black Hawk, Apache, S76, H-500, EH-101, Lynx, etc because they have adequate tail rotors.

Overpitching (as I understand the term anyway) is when you pull too much collective for your engine's available power to overcome the drag, so the rotor system slows down; it doesn't necessarily imply a stall (even though I guess you could say that bits of the blade are stalled all the time). The only way to recover would be to lower the collective.

What I'm getting at is that in an 'overpitched' situation you'd have drooping Nr and the associated loss of main and tail rotor thrust, not necessarily the case in these so-called LTE situations.

As you say, helmet fire, the 206 LTE situation as we have had it explained to us is a rapid onset yaw probably caused by vortex ingestion.
I think that tends to support the Huey 'running out of left pedal' case being different to that, because you can sit there in the hover with the pedal bouncing off the stops but not be scared of whipping around to the right at a great rate - it feels controllable, while not necessarily comfortable.

thanks again nick, "lte does not exist".

but its not a way to blame the pilot it's a way for the pilot to move the blame to the helicopter.

only ' thought' to happen to the bell 206.

and your right too arm out the window, when you demand more power than any helicopter engine (piston included) can supply you end up with full left pedal and no tail rotor authority, ergo loss of tail rotor effectiveness.

fly the aircraft properly and it won't happen.

Thanks for your answers. I will try to describe the accident better.

An AS 350 BA (converted from "B") hauling loads with a 50ft rope in 3000ft PA, OAT 20°C, light and variable wind. Take off weight seems to be round about 1950-2100kg. (the load is destroyed and it's not possible to determine the weight of the load exactly) The >5000h experienced pilot lifted the load without problems and began to climb and to accelerate when suddenly the ship turns to the left. The left spin accelerated and wasn't to stop, even not with lowering the collective or full right pedal the pilot later explained. The ship and the load turned around the heads of the ground crew some full 360's and chrashed 50m ahead into the ground. The pilot doesn't opened the hook and released the load because he afraid to hurt someone on the ground.
As i wrote before there are no indications of a technical malfunction. The experienced ground crew reported the tail rotor was turning all the time. I' m surprised because the whole thing seems to me to be a kind of loss of directional control. That's not easy to understand because i thought LTE is a problem of the 206 or 500 series. Of course a loss of directional control is also possible on a AS350, but i have never heard about such a problem on AS 350 and never experienced personally on this type of helicopter. But i believe the pilot is really experienced on this kind of work, doing such flights a lot of years and will not loose the a/c out of control on such a "simple" flight during accelerating. But we are all humans and nothing is impossible.

Good to say the pilot isn't to bad injured and we all hope he will made a good and fast recovery.

Would it be better to explain the "overpitch vs LTE" in this fashion?

It takes a fixed amount of horsepower to keep a helicopter hovering. For any horsepower, as RRPM goes down, torque (as expressed about the rotor mast) goes up. This demands more thrust from the tail rotor to maintain heading.

At the same time, the tail rotor RPM drops, therefore demanding a greater AOA just to maintain thrust. So you have two factors demanding left pedal, and there's only so much left pedal...

However, for most helicopters, the tail rotor is able to effectively counter any torque the engine/main rotor can develop as long as you keep the RPM in the green (and under most flight conditions). So for most helicopters, "LTE" can only happen if you overpitch, and droop the RPM while pulling a lot of power.

A few helicopters (B206, H269A) can, with RRPM in the (normal) green, regularly produce more torque about the rotor mast than the tail rotor can counter. So even if you are doing nothing "wrong", at high power settings you can find yourself running out of left pedal because the tail rotor is incapable of sufficient thrust even when operating at full RPM.

Flingwing,

The only quibble I have with your observation is that LTE is the wrong term to use if the overpitch causes LTA.

LTE is the moniker established by Bell to describe how a helicopter can lose control while within its normal envelope (in spite of imabell's statements otherwise). In contrast, if a pilot takes on an excessive crosswind (beyond the flight manual limits) or is he pulls too much torque or operates at too much gross weight or pulls the rotor rpm down below normal, the resulting loss of yaw control is not really LTE, it is LTA.

If we call every loss of yaw control LTE, we blur the reason why it happened, and thus blur the responsibility for who caused it, and also blur the method used to prevent it.

helmet fire's post above slices nicely thru the definitions, and is worthwhile, I think.

To imabell,

Your protests are noted, some people can fly a crummy helicopter and stay out of trouble, I agree, but when 95% of the mishaps are on one model helo, it says that model has a problem. I really dislike blaming the pilot when it is clear otherwise. As a former test pilot, I worked to try and make helos that helped us stay out of trouble.

When the Bell Cobra experienced LTE, the tail rotor was fixed, after an extensive campaign that the Army insisted upon.

When the prototype Bell Kiowa Warrier was flown by Army test pilots, they experienced LTE, and grounded the aircraft to require that the tail rotor be made more powerful.

When 10% of all JetRanger accidents are caused by LTE, Bell published an elaborate procedure that tells you how to baby the aircraft, and how to blame yourself if it happens.

As long as we apologize for our aircraft, we are doomed to have to deal with their shortfalls. When we as a pilot community stop blaming ourselves, we stand a chance at becoming a legitimate transport system. Please stop blaming your brother pilots and start focussing on how to get us better aircraft. Perhaps you could start by changing your username so that your biasses are slightly more hidden!

Thoroughly agree with Nick here about the procedure on how to baby the aircraft and blame yourself when it all goes wrong! It was the same on the Skycrane thread: LTE is thrown about with such misunderstanding that it has succesfully hidden a design flaw in a shroud of aerodynamic faux-legitimacy! (I think I shoud resume drinking after that phrase - sorry!).


What green thumb describes is most assuredly not LTE, but that is the only one we can rule out from the description thus far. Without more info, we can only rule out LTE, we are left with Loss of tail rotor thrust, Loss of tail rotor control and LTA. We have a high power demand, with adverse wind direction ?? at relatively high DA (approx 4560 ft - plus humidity?) More questions are still required: was there any rotor droop? If so, was this due to N1 limiting, or governor malfunction? If not, was the tail rotor being driven (or just windmilling? The tail rotor was spinning - but was it powered? Were the t/r control mechanisms functioning? Was it a hydraulic event? Sounds like he held the load and crashed the aircraft? Was he able to move the aircraft away from the ground people, but not the load? Did he have the cargo release system active?

And others will bring more to the table I am sure.

Hi Nick,

Yep, I'm just a poor ol' head CFI trying to thread the briar patch between reality and what's printed in the textbooks we still have to answer to come checkride time. Since it was OVC002 all day, I got to engage a couple of my instructors in a discussion of this very subject, trying to find the balance.

We decided that if you get the "uncommanded yaw", you have just that. a yaw. If you react promptly and correctly and stop the yaw, it was not LTE. If the yaw stops on its own, not LTE. However, if you respond promptly and correctly but cannot stop the yaw, you have LTE (this still keeps us safe with the FAA). If you don't respond promptly or correctly, then you goofed - and the result cannot be truely classified as uncommanded (even if the first bit was) - hey you had your chance, Tex.

So if Sammy Schweizer gets his tail pushed around by that 12G20 tailwind, but ends up facing the wind going "wha'happah?", not LTE.

Rebecca Robbie gets sideways on a steep approach but stomps the left pedal and stops things, not LTE.

Joey Jetbanger starts seeing the word go 'round while OGE and downwind, and full left pedal won't stop it, LTE.

I agree that it is not altogether appropriate to call low-RPM induced "unstoppable yaw" LTE, but at that point, it ends up the same - (even if you initially screwed up by drooping the RPM).

Nice work with the names there Flingwing!
Considering the start point of the thread, you'll have to come up with another one like 'Simone Squirrel' or 'Etienne Ecureil' now - or 'Anatole A-Star' for the Americans.

O.k

So L.T.E may or may not exist, but whats it called when you stick in the left pedal on a AS350 on take off? Is that L.T.E as well?

wow flingwing - you really an instructor?

wow flingwing - you really an instructor?
I strongly suggest you review those text books with your mates. Perhaps you could quote them here because your conclusions do not match current aerody theory. There is a real difference between LTE and rotor drooped LTA, Loss of control or loss of thrust.

And guess what - they all have different recovery requirements, no matter how much you and your buddies decide it is all so simple.

Smash -
Mate that is not LTE, though let me assure you, LTE does exist. If you are putting in left pedal, that is due to streamlining unloading the T/R by enabling the vertical fin to provide some thrust and translational lift reducing inducd power, nothing to do with LTE, LTA, etc. The T/R is working too well, not well enough. Call it translational lift.