AS350 Astar/Squirrel

[Heliport]

LOS ANGELES POLICE DEPARTMENT
PRESS RELEASE

"LAPD Grounds Eurocopters Temporarily"

Los Angeles - On Saturday, March 17, 2001, the East Bay Regional Park Police experienced a complete engine failure in one of its Eurocopter AS350B-2 helicopters while it was being operated on patrol over San Leandro. The pilot landed safely and the crew sustained no injuries. The aircraft sustained minor damage.

Because the Los Angeles Police Department operates eight of the same model helicopters, it began a study of the East Bay Regional Park Police (EBRPP) incident to discover the facts associated with that incident. Following examination of the helicopter and discussions with key personnel, helicopter maintenance representatives, Eurocopter Corporation and Turbomeca, LAPD has temporarily grounded its AS350B-2 helicopter fleet pending further investigation. The Department continues to work closely with Eurocopter Corporation, Turbomeca and appropriate federal authorities in an effort to determine the cause of the EBRPP incident and ensure that LAPD aircraft are properly equipped for return to service.

It is expected the AS350B-2 helicopters will be returned to service during the next six weeks.

sf

[Thomas coupling]

No-one is going to convince me that one engine is as good as two for emergency service work. That would have been good for the industry if that happened over London or any other city here in the UK....

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Thermal runaway.

[Hoverman]

I can't comment on the emergency services, but why good for "the industry"?

Do that stats support the theory that singles are, in practice, safer than twins
Aren't most heli accidents in the UK weather related - very rarely power failure?

[Deeko01]

I have to say having been a helicopter crewman, If you were to put me in a AS350 with an Arriel engine or an AS355 with Allison engines over water for 100 miles then I would chose the AS350 any day.

The feeling of the Twin Squirrel or TwinStar to US was that if you got an engine failure then the other engine took you to the scene of the crash.

My personal belief is with regard to the CAA's view on single engine helo ops near cities that it is not what the US can do it is what we cant do, the statistics prove I am right.

CAA = Jobs for the boys.

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Better to be up there wishing you were down here than be down here wishing you were up there!

[HeliEng]

An opinion I heard once, was a Twin is O.K. But having two engines, makes you twice as likely to have engine failure!

Don't know quite how that works statistically!

"Some days you are the pigeon, some days you are the statue"

[hoverbover]

I was doing a conversion course in the states, and asked the factory instructor/test pilot (as we were practicing engine offs in a single at the time) How many engine failures he had experienced in his time (20 years in various mil roles I think)And he said just two,to this I asked wether it was a single or a twin, the reply:
"Oh it was a twin and both quit, an Apache actually !!!!!!" Apparantly it was quite exciting.

So maybe only Merlins/Eh 101(or anything with threeengines) should be allowed for EMS(joke).

The one thing you can be sure of,if its got an(y) engines they will stop! It may be at your request or it may not!

Regards
hoverbover

[army427]

The organisation that I work for use a medium twin on 24 hour SPIFR SAR/EMS tasks. When the twin is unavailable we use an AS350. Although I do feel safer flying with two engines, my main concern is that the single is not equipped for the tasks we perform. Small cabin area, VFR, no autopilot etc.

Single engine VFR helicopters certainly have their place in a variety of roles but when it comes to emergency services work, particularly at night, they have limitations. Combine that with operations over urban areas at night and I feel that a twin is essential.

Most of our pasengers (patients) have little choice over which type of helicopter they are flown in. I think that they deserve the more capable twin.

[widgeon]

Am I crazy or was there an AS350C model , B is Turbomeca D is Lycoming, textron, allied signal / honeywell ( GE ? ). I recall seeing on the transport Canada site an early serial number (1004)C-GMEY that was converted from C to D and then to B.

[rotormatic]

The AS-350-C was an astar powered by an early model lycoming engine, a LTS-101-600A

[Pac Rotors]

Hey All

Just had a question re the B3. Have been here with one in Alaska and it proved itself to be a very capable machine. We lifted a hut up on one of the glaciers and did it very nicely.


Was wondering what other pilots or mechanics thought of re this machine. Good and bad points.

[Intersection]

If your talking about the squirrel then yes they are a very good a/c and the RAF use them as a basic trainer are you talking about the twin or single both are good and i assume the twin would be able lift pretty large underslung loads. As the single does with relative ease they are comarible i beleive with the 206.

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"Vacate next Left at intersection...., contact ground on 121.9"

[Larry]

After the terrible reputation these aircraft (engines)obtained in the 1980s does anyone know how the engine is holding up now on the remaining AS-350Ds out there ?....At one time they were called "EXPLODING STARS"

There are a few operated in Southern California that ive seen lately and its made me wonder.

From what i heard the problems are a thing of the past and considering the LTS-101s are about 1/3 the cost to overhaul and burn less fuel than the turbomecca they are now worth considering. Ive even been told some people are reconverting Turbomecca REengined AS-350Ds back to the LTS-101.

ANY COMMENTS ?

[ 04 September 2001: Message edited by: Larry ]

[CTD]

The older LTS-101 engines were indeed troublesome and were terribly unreliable, but the later versions (A-3) shouldn't be saddled with the same reputation.

Nowadays, things have changed and the engine has become all the things you say in your post. I haven't flown one in 6 years, but I have friends who operate D's and B's together and find the D to be a much better ship. Easy on gas, easy to start, more reliable and MUCH lower DOCs. The company you speak of is now marketing a 'Super D' using BA components with the LTS powerplant, and by all accounts it's a great ship.

[tgrendl]

I'd agree, the LTS 101 is now a superb engine. Great power margins, inexpensive etc.

SSShhhhhh, don't let it get out or the prices will go up. ;)

[BigJim]

I work for a company that has a lot of D's and a Super D. Seem to be pretty good with the updated 101, having said that I had an early 101 distroy itself on the side of a hill, not a good feeling.

The super D pisses all over the BA and would fly it any day. All our landings are around 8000 feet and we have no troulbe with 7 pob and good fuel.

That's my 2 cents worth - hope it helps. :)

[spinwing]

LTS101 engine of today is a very different engine to the engine of the early eighties...lots of development taken place with turbine wheels, burner cans and such like ...it is now a very good engine and as indicated in a previous post...having said all that I only operate the engine in the BK117 not the AS350!
;) ;)

[RotorMod]

Does anyone know what the real costs are to convert an AS350BA to the new LTS101 power?

[rotormatic]

Here is an example of the improved Honeywell engine....
http://av-info.faa.gov/ad/PublishedADs/011715.html

The fuel pump needs to be pulled every 600 hours, and sent to CECO for inspection...not field maintainable.....

[HeloTeacher]

AS 350 servo transparency

If anyone knows where to find accident write-ups and analyses related to this I would really appreciate finding out where they are.

[Lu Zuckerman]

To: Helo Teacher

The way this condition has been described to me it is the jamming or loss of servo boost under certain maneuvering conditions. For the life of me I don’t know where the term transparency came from to describe this condition but then again maybe someone else can.

To me it is a design defect in the hydraulic system that should be corrected by Aerospatial because under certain emergent conditions if the “transparency” manifests itself the helicopter could crash but then again that is what you are looking for.

[Grey Area]

As far as I remember Servo transparency is a nice name for "jack stall". It is common in smaller helicopters with parallel jacks. AS350, SA340/341/342 Gazelles etc. Jack Stall is often included as part of the flight envelope definition. Sorry, I don't know of any repositories of knowledge but I'll ask my contact at Marignane.

PS Lu, thanks for the input, I'm sure the Eurocopter Bureau D'Etudes will jump for joy.

[Steve76]

An AS350 crashed in NZ in the early 90's. The pilot was in a high speed decending turn when 'Jackstall' occurred.
My understanding is the huge feedback forces generated by a high 'G' manouver cause the controls to lock.
Correct? :confused:

[Grey Area]

1. Servo Transparency - Discussed with a Eurocopter flight tester engineer today. The phrase is a direct translation from French - To a Frenchman it makes perfect sense, interestingly another ALAT pilot I spoke to translated the French phrase immediately to "Jack Stall" (heavy French accent required). The implication in French is that the jack appears to be no longer there.

2. Steve you are just about there. The point is that the aerodynamic loads fed back by the rotor system to the flying controls exceed the maximum force that the servo-jacks can exert. In effect you now have manual flying controls which, given that the jacks are stronger that you (I assume ;) ) is impossible to move in the desired direction. If you ease the loading the problem disappears, ie reduce the manoeuvre or lower the collective. Unfortunately as you are most likely at the edge of the flight envelope if you are close to the ground the consequences can be disasterous.

This is not so much a design flaw as a flight limitation, and common on small helicopters with parallel flying controls.

[Lu Zuckerman]

To: Grey Area

“This is not so much a design flaw as a flight limitation, and common on small helicopters with parallel flying controls”.

You’re statement above is basically the same as the cautions placed in the Robinson POH which restricts the pilot from flying out of trim and from sideslipping the helicopter as something bad will happen if the pilot violates the cautionary statements in the POH.

Both the restrictions on the Aerospatiale products and the Robinson are to compensate for a design flaw.

From what I understand the Aerospatiale helicopter in this discussion has a hydraulic system that could be considered low pressure by comparison to the systems used in other helicopters. I would assume that the pump used is a constant displacement pump and I would assume that because of the existence of the jack stall problem it does not have an accumulator and if it does, then it is of low displacement.

What I visualize happening is that under certain maneuvering conditions there is a high demand on the hydraulic supply system. This causes a pressure drop in the system and if the pressure drop is sufficient, the bypass valves in the servos open and the jack is now part of the control linkage and the feedback forces can pass through the jack. Upon the cessation of the demand on the hydraulic system the pressure builds up and the bypass valves close and the jack is now operational.

This is a killer just like having high flapping loads on the Robinson. The protection of the pilot rests on a few words in the respective POHs and not by proper system design.


Regarding the French logic in using words to describe something when I was working in the Service Department at Sikorsky we got a telex from the French Forces in Algeria asking something about the dirty link. This caused some confusion so we asked them to identify the part number under discussion. The number provided was for the sloppy link on the primary servos. It seems that the French did not have a word for sloppy so they figured that sloppy equated to dirty.

[ 05 December 2001: Message edited by: Lu Zuckerman ]

[Grey Area]

Lu,

What you invisage happening is not what I described and is, frankly, rubbish. The feedback forces exert a force equal to the maximum available from the jack so it can no longer move. It has nothing to do with bypass valves.

"From what I understand the Aerospatiale helicopter in this discussion has a hydraulic system that could be considered low pressure by comparison to the systems used in other helicopters."

Really? Its the same as many production helicopters.

"Both the restrictions on the Aerospatiale products and the Robinson are to compensate for a design flaw."

Helicopters are designed to do a job. If you exceed the design spec or limits you lose your right to sue. The helicopter concerned conforms to FAR 27, I would suggest you back your comments up with hard facts before making sweeping and rather slanderous allegations about things you patently understand close to nothing.

Why not get a copy of FAR 27, or even AC27 (flight test specs), read it then sue the FAA because you don't like what it says?

[Steve76]

Grey Area, as soon as I read your last paragraph I could hear Lu's fingers tapping.
It is also unfair to the Astar/squirell/AS350 to be mentioned in the same context as a Robinson. A far superior aircraft.
:rolleyes:

[Lu Zuckerman]

To: Grey Area

“What you invisage happening is not what I described and is, frankly, rubbish. The feedback forces exert a force equal to the maximum available from the jack so it can no longer move. It has nothing to do with bypass valves”.

The very purpose of a hydraulic servo is to not only resist feedback forces from the rotor but to be able to overcome any and all feedback forces. To do this it must be properly designed and be supported by an adequate supply system. If you have what you call jack stall then the system is not designed properly. In order to do this; the hydraulic system must be able to support the maximum demands placed on the system by manipulation of the controls. That is why hydraulic systems incorporate an accumulator large enough to take care of these maximum demands while the pump catches up. Most new hydraulic systems do not incorporate an accumulator but use a constant speed variable displacement pump. In a few cases the system may incorporate both an accumulator and a constant speed variable displacement pump.

Again, I state that if you get jack stall then the system is not designed correctly and I don’t give a damn what Aerospatial thinks.

I have seen helicopter flight control systems that incorporate constant speed variable displacement pumps and in monitoring the pressure gage the system pressure can drop by one third or more when the cyclic stick is moved in a circle or if the collective is raised and lowered. When the movement stopped the pressure immediately went up to the green line. At two thirds rated pressure the system could still resist the maximum design feedback forces. If this type of pump can’t keep up with the heavy demand then think about what a constant displacement pump does relative to system pressure when a high demand is placed on it.

On a Sikorsky servo on the H-34, H-37 and H-19 the bypass valve would open at pressures lower than 750 pounds PSI. Please tell me what the hydraulic pressure is on the AS-350 and tell me at what pressure the bypass valves on the servo open up?

[helmet fire]

To GA: I agree.

To Lu: your sweeping statements are why I love this forum so much. Lets look at your call that >>something bad will happen if the pilot violates the cautionary statements in the POH<<

Hello?

Lu?

Isn't that WHY there is a POH? :eek:

As for "design flaw", I assume you were joking. :D :D

Jack stall is a detail inless you execute a high G (generally high speed) manuever. Why would you do that? The condition was demonstrated on the endorsement course (and all AS350 pilots should have seen it). The AS355 even has a limit light to tell you that jack stall is approaching (though I cannot imagine having my eyes inside during high G rapid manuevering).

Is this a design flaw compared to the Bell teetering head which will come off under negative G if not handled IAW the POH? Or compared to fixed wing aircraft which will stall and spin if not handled IAW the POH? Or compared to Loss of Tail Rotor Effectiveness in the B206 if not handled IAW the POH? You getting the picture?

The AS350 is an outstanding aircraft. Enjoy it's huge capability and dont fly it against the POH - like EVERY OTHER AIRCRAFT.

:)

[Lu Zuckerman]

To: helmet fire

“To Lu: your sweeping statements are why I love this forum so much. Lets look at your call that >>something bad will happen if the pilot violates the cautionary statements in the POH<< “.

This is probably the tenth time I have said this. The cautionary notes in the Robinson POH were incorporated as a result of an engineering study made by the Georgia Tech Aero department and the FAA commissioned the report. The FAA wanted to know the causes of over 22 mast separations and rotor incursions on Robinson helicopters since they entered into service. The report was made just prior to 1995. Although the engineering study was never completed there was sufficient evidence that prior to the mast separations or the rotor incursions the helicopter experienced violent flapping excursions. (I will explain the design problem later in this text). It was determined that these flapping excursions could be initiated in three different ways.

1) By flying out of trim

2) By sideslipping the aircraft

3) By the application of left cyclic while recovering from a zero G incident.

In 1995 Robinson incorporated an unnumbered page in section 4 of the POH outlining restrictions from performing the above (1-2-3) and instead of making the information mandatory they made it in the form of a suggestion. The CAA indicated to me that they would make it mandatory in all POHs for G registered Robinson helicopters. That was about 8 months ago and nothing has been done. During the past year or so there have been several mast separations in GB.

This is what I meant by the pilot being protected by words and not design.

Regarding the design problem on the Robinson head it involves the “droop stop” which is referred to as a tusk. The tusk establishes the low position of the rotor blade while static. Once the rotor is up to speed and collective applied the tusk moves downward from its' limiting stop. Under normal flight conditions the tusk will never contact the stop. However, when you experience extreme flapping excursions and the tusk hits the stop then it turns the rotor system into a first class lever with the fulcrum at the teeter hinge. If the kinetic energy is sufficiently strong the force exerted by the blade will cause rotorhead contact with the mast.

Regarding your comment about sweeping statements this is what I get paid for as a RMS Engineer and that is to identify and eliminate if possible design problems that will impact Reliability, Safety and even Maintainability.

No helicopter should be designed and certified if there is a possibility of experiencing “jack stall” or to have a mechanical part of the rotorhead that under certain circumstances can cause the loss of the helicopter.

Now, here is something to think about. If the Robinson was restricted from certain flight conditions in 1995 because these conditions could result in the loss of the helicopter, how could the helicopter pass certification if these same situations had to be demonstrated (sideslip and out of trim).

[helmet fire]

Lu,

I see we are getting some where. I point out that jack stall is a detail, and you talk about the rotor heads flying off Robbos. I talk about the comparison of Jack Stall to other design gotchas, and you talk about the rotor heads flying off Robbos.

Shall we ignore the Robbo, and return back to the fact that Jack Stalls are NOT a design flaw?

You said : >>No helicopter should be designed and certified if there is a possibility of experiencing “jack stall” or to have a mechanical part of the rotorhead that under certain circumstances can cause the loss of the helicopter.<<
:)

I say: Dont all helicopters have a certain circumstance that can cause loss of the helicopter? What negative G and applied roll rate in a teetering head helicopter? What about fully lowering the collective at the bottom of an auto? What about flying them into a fog bank and trying to hover? How did anyone manage to get any of them certified? :rolleyes:


Again: The AS350 is an outstanding aircraft. Enjoy it's huge capability and dont fly it against the POH - like EVERY OTHER AIRCRAFT.


:) :)

[Arm out the window]

I must endorse helmet fire's comments here - the fact that the AS350 hydraulic jacks can reach a point where they can't overcome the flight loads being placed on them is just something that happens with this particular machine (and others, no doubt) and defines a boundary on the flight envelope.

No matter what type you fly, there will be physical limits to what you can do with it because of the design - for instance, don't try to do a level slow roll in a teetering head helicopter, and whatever other such ridiculous examples you want to name.

I have seen incipient jack stall demonstrated in an AS350, and shown it to others myself as a controlled learning exercise to promote awareness of what can happen if the aircraft is mishandled. This is not a design flaw in the aircraft, it's simply a facet of the machine that people need to be aware of, like VNE or the transmission torque limits; or vortex ring for that matter.

I have flown agressive manoeuvres in the aircraft on many occasions, and have never come anywhere near to jack stall. I would go so far as to say that if you get in a situation where jack stall occurs and you crash because of it, you have caused the crash yourself by placing the aircraft in a situation from which it couldn't recover - something which can be done in any aircraft type!

[heedm]

This does bring up an interesting question. What is the difference between a design flaw and a published limitation?

Obviously if a flaw in the design is discovered and it is found to be more economical to narrow the envelope than fix the flaw, then that flaw becomes a limitation. Doesn't mean it's not a flaw anymore.

______________

My take is this. When you design a helicopter, you have a purpose for that helicopter in mind. That purpose defines a minimum envelope. A published limitation that narrows the envelope to an extent that any part of that minimum envelope is excluded could be considered a design flaw.

Let's say that to post on Pprune, the programmers decided you must hit the "Add Reply" button. They write the software and find that you have to double click it. They are perplexed and can't fix it. Instead, they add some text to say to double click the button. It's still a flaw.
_______________

It sounds like the AS350 limitation is at an extreme of an envelope. From my line of thinking, that means it's not a design flaw.

What's been said about sideslipping a Robinson seems unusual for a training aircraft. That may qualify as a design flaw that became a published limitation.

________


Of course, I haven't flown or touched either aircraft so what the hell do I know? :D

[Grey Area]

Lu,

You said "The very purpose of a hydraulic servo is to not only resist feedback forces from the rotor but to be able to overcome any and all feedback forces."

1. In fact in many helicopters the hydraulic systems exist only because the AFCS needs it. In the case of the AS350 you can fly an AS350 hydraulics off but because of the loads from the starflex head you wouldn't want to for too long.

2. If you took a Model T Ford to the Indy 500 would is survive? Is that a design fault? Remember that whilst reasonable margins must exist (and are defined in FAR / JAR 27 and 29) they are there for a reason.

[ShyTorque]

I have flown both Aerospatiale (3500 hrs) and Sikorsky products (1500 hrs), both military and civilian types. Each of them have good points and some not so good points..

(I also flew a Robinson helicopter. Only once and I have since had no desire to do so again).

If mud is to be slung about it could be done at any manufacturer, for a variety of reasons. However, as a professional pilot and Military taught QHI I do not see jack stall as a design flaw but merely as a limitation. It has already been pointed out that jack stall only occurs outside the normal flight envelope under high power and "G" (I have seen a roll off the top in an AS341 without experiencing jack stall - surely that is enough for most pilots and engineers)? The phenomena is preceded by warning signs including a big increase in vibration. I would far rather the aircraft calls "enough" by stalling a jack than something else letting go instead, either on that occasion or later for someone else to deal with.

Jack stall is just like a heart attack - it's nature's way of telling you to slow down a little...

[Mark Six]

I have to agree with Arm Out The Window (and others) on this one. With more than 3000 hours in the AS 350 series I have never experienced jack stall except when demonstrating it to students. Even then it usually took a couple of attempts at extreme manoeuvring to achieve incipient jack stall. As I recall the aircraft basically recovers immediately by itself as the pilot "automatically" (you have to be there) relaxes pressure on the cyclic. Any aircraft will experience problems if pushed far enough, as others have pointed out. This is not a design flaw. By the way Lu, the 350 hydraulic system does have accumulators.

[Lu Zuckerman]

The reason I mentioned the Robinson head (tusk) in the same post with the AS-350 Jack stall problem was that if you do not comply with the POH limitations you can experience a problem. How severe that problem is on the AS-350 with jack stall is totally dependent upon the conditions under which it is experienced. We already know the seriousness of the problem on the R-22 and the end result of exceeding the POH instructions.

As an RMS engineer I would think that if this condition was known at the onset of the certification process then from a safety point of view they should have eliminated the problem through redesign of the hydraulic system (if that is the root of the problem).

Here are several questions, which relate to the R-22 but are directed towards the AS-350 jack stall problem.

1) At what point in the certification process was the problem identified? Was the limitation placed in the POH and the jack stall warning light installed on the instrument panel at service entry?


2) If it was not identified in the certification process then at what point after entry into service was the problem identified? When was the warning light installed


3) At what time was the POH modified to reflect the problem and establish the flight limitations?


4) How is the jack stall light turned on? Is it by a G sensing switch or a pressure switch in the hydraulic system? Or, is it by some other means?

5) If the problem was identified after service entry was any attempt made to modify that part of the system that allowed jack stall to manifest itself?

Regarding the statement about the servos being necessary to support the AFCS or any other electronic system that requires hydraulic boost most of those helicopters had these systems installed as after market items. On those helicopters (large) that have this type of system the electronically controlled servo valves are installed directly on the servo or on systems like those on some Sikorsky helicopters there is a primary and an aux. servo system and the electronic servo valves are on the aux. servo. On the EH-101 they have dual servos at the swashplate and the electronic control is incorporated as a part of the flight control linkage. This is similar to smaller helicopters that had the system installed during production and as after market items.
However the servos are not installed to support and AFCS their primary purpose is to resist and overcome feedback forces at any level.
Even though the AS-350 can be controlled without hydraulic boost I would question what the POH indicates if you encounter this condition.

Anybody that has the knowledge please respond to the questions above.

[widgeon]

By POH I assume you are talking of the flight manual . Folowing Lu's logic operating the aircraft over gross weight is OK because the baggage compartment is large enough to take 10 cu ft of depleted uranium .
To suggest that you cannot change the flight manual based on service experience is patently absurd . In a perfect world the flight test program and design review would find every possible fault that might occur. I think that flight manuals carved in stone may be a little overkill not to mention overweight. Can you give a single example of an in service helicopter where the Flight Manual is still at Revision A ?. ( unless you forgot to sign up for revision service ).

[Grey Area]

1. What "Jack Stall Light"?
2. If you really understand the certification process why not take issue with FAR 27 instead of aircraft that conform to it?

[Lu Zuckerman]

To: Grey Area

To: Grey Area

Someone in a previous post alluded to the fact that although the warning light was illuminated he did not have time to look at it as his eyes were outside the helicopter during the maneuver. I was speaking in generalities about the jack stall condition relative to the hydraulics system and the control boost servos I assumed that since a pilot mentioned the light it must be there.

What kind of warning do you get with imminent jack stall? If it is a light or a bell or a voice alarm it doesn't make any difference as I asked what caused the alarm to go off.

To: Widgeon

I did not say that the flight manual should or should not be changed due to things that occur in operation. This happens on both the POH and the maintenance manual. What I was asking, was the entry in the POH for the AS-350 jack stall problem entered at rev A when the helicopter went into service or, did the problem occur at a later date after entry into service with the entry telling the pilots to avoid this flight regime and, there was no attendant design change to prevent this from happening in the future. This is exactly what happened to the R-22 relative to sideslip and out of trim flight. It warns the pilot but no design change was made. I also asked the question, why didn’t this show up during certification testing? That goes for both helicopters.

This leads us back to the basic premise that the pilot is protected by words and not by design. Please everybody; do not attack this last statement as we have already gone through the various arguments.

I would still like to have all of the questions answered.

I should have asked a sixth question and that is why do you as pilots accept this form of protection? One day you might find yourself in an emergency situation where the last thing you need at that time is Jack Stall.

Here is a test you can perform. It works on a Sikorsky helicopter and I assume it will work on the AS-350. Go into a hover and take the cyclic stick and move it in a circle in the same direction as the rotor is spinning. Move the cyclic stick through this circular path four or five times. Do the controls get stiff. It does not happen on the Sikorsky and it may not happen on the AS-350. However if it does, it indicates that the hydraulic system can’t keep up with the demand.

[ 06 December 2001: Message edited by: Lu Zuckerman ]

[ 06 December 2001: Message edited by: Lu Zuckerman ]

[ShyTorque]

My personal SWP just gave me a caution light because I hope this thread isn't going to degenerate into another where manufacturers (except Lu's apparent favourite, the big "S") get a slagging for alleged poor design.

I haven't flown the single Squirrel but Lu's cyclic stirring test doesn't let the manufacturer down on the twin with basically the same hydraulic system. On a different AS type we used to use that same test to check for a suspected faulty drag damper rather than try to test fly for a suspected design limitation of the hydraulic pump output.

Lu, a pilot is taught to understand and respect the idiosynchrasies and limitations of each machine that he flies. Most aircraft have them, because there is no such thing as care-free handling just yet although it is obviously a desirable design aim.

For example, I would not try some of the manoeuvres I have flown in the AS341 or AS355 or even AS332 in an S-76 because the rotor would overspeed as soon as you tried them. Similarly, one or two manoeuvres I used to do in my display sequence in the AS332 would possibly kill you in the S-70 due to aircraft design peculiarities (and in fact one of them was specifically prohibited). These things are not generally design faults, but aircraft limitations. I don't have any problem whatsoever with this, it's what I get paid for as a professional pilot.

From your many previous posts I can fully understand that you would like to redesign many items on many aircraft and I can sense your frustration that you haven't been able to do so. Unfortunately we don't live in an ideal world where all aircraft are 100% compliant with & safe iaw your own personal design parameters!

I used to safely enjoy 360 and 540 degree handbrake turns in the snow in my small hatchback. I wouldn't try handbrake turns in my people carrier or an articulated lorry or on a ride-on lawnmower. Does that make people carriers, artics and lawnmowers inherently dangerous or poorly dsigned? I don't think so, it would make me stupid for trying.

Watch out Frank, I think you might need your tin hat on again any minute now....

:rolleyes: :D

[Lu Zuckerman]

To: Shy Torque

I can totally accept the fact that limitations are placed on helicopters and aircraft. In most cases it has been determined that to perform certain maneuvers you can overstress the structure. That is why they have a SCAS system in some helicopters to keep from overstressing the rotor system or the structure. In one case you described that if you performed a certain maneuver in a specific helicopter that if this maneuver was performed in another helicopter you could overspeed the rotor system. So, this maneuver is restricted on that helicopter and that is OK with me. The problem I see on the AS-350 if I understand it correctly is if you perform a specific maneuver you get jack stall, which means that there is a failure to deliver adequate fluid under pressure to combat the feedback forces generated in the maneuver. If the pump had a greater delivery capacity or they used a constant speed variable delivery pump or if they had an adequately sized accumulator the pilot would never experience jack stall. To allow jack stall to happen in a helicopter design is unconscionable in respect to systems safety and from a reliability point of view if the lower controls are exposed to flight loads.

[helmet fire]

round & round & round &..............

Lu some answers for you:

1. The LIMIT switch is fitted on the twin (I have never seen it on the single) on a servo. It illuminates a cockpit warning light only, no bells, whistles or voices. The action required is to "reduce pitch or open out the manuever (i.e. relax the G)"

2. An actuator supplied by the LH HYD system is fitted to the end of the servo control. During flight, when the load is below an preset value, the servo pressure keeps the piston against the upper stop and the light is off. If the flight load on the servo control exceeds the limit threshold, the microswitch is actuated and the light comes on.

3. NONE of this is relevant to your statement that it jack stall is "unacceptable".

4. I have never heard of anyone getting jack stall other than during aerobatic manuevering (prohibited) or demonstrating it during endorsements. You need to be taken up and shown this how violent the manuever has to be before you reach incipient jack stall. It is unsettling. The again Lu, you COULD just believe the experienced pilots who are all telling you it is not an issue......... :rolleyes:

5. You ask why pilots accept these seemingly dangerous limitations? This is easy Lu, they ARE NOT dangerous. More fixed wing guys die through stalling close to the ground than ever even see jack stall demonstrated (let alone experienced). Should they immediately ground all fixed wing?

Actually, thats not a bad idea....... :D :D

6. The "someone" who said they dont have their eyes in side during harsh, high G manuevering was me. Can you not look back through what has been said? If you were going around a 60mph signposted corner in your car at 100mph, would you have your eyes inside reading the speedometer? Perhaps not. Understand?

I'll say it once again (in case you cannot read previous posts):
Is this a design flaw compared to the Bell teetering head which will come off under negative G if not handled IAW the POH? Or compared to fixed wing aircraft which will stall and spin if not handled IAW the POH? Or compared to Loss of Tail Rotor Effectiveness in the B206 if not handled IAW the POH? You getting the picture?

The AS350 is an outstanding aircraft. Enjoy it's huge capability and dont fly it against the POH - like EVERY OTHER AIRCRAFT.


:)

Edited for spelling

[ 06 December 2001: Message edited by: helmet fire ]

[Jiff]

Oh Please,
Are you lot just arguing with Lu because you can?

Lets draw this comparison, you buy a particular hand gun knowing full well that if you wave the gun around a lot, the safety catch can move to the off position.
You are aware of this limitation therefor you don't wave it around a lot, but if you do, you always check the position of the safety catch. Anyway this hand gun in most other aspects is superb and as every one is aware of this problem it is generally accepted and called a good gun.

Now here's the revelation
Guess what
The design of the safety catch on this superb gun that every one loves is still crap.

Jiff

[ 07 December 2001: Message edited by: Jiff ]

[ 07 December 2001: Message edited by: Jiff ]

[Arm out the window]

Your analogy doesn't really hold water, Jiff.
The hydraulic system in question performs perfectly well under any reasonable inflight circumstances, rather unlike a safety catch that might fail at any moment.

If anyone knows anyone at Aerospatiale they should ask them, but I'd imagine that beefing up the hydraulic system and servos to fix this so-called problem would incur a weight penalty and be not worth doing considering the performance reduction.

[heedm]

With Jiff's handgun analogy, we come back to my question. If a problem is solved by publishing a limitation, is it still a design flaw?

I posted my thoughts on this. Appreciate others'.

[Grey Area]

"If a problem is solved by publishing a limitation, is it still a design flaw?"

The point in THIS case is that the aircraft operates quite safely within the designed limits; if you exceed this limit you will reach a possible loss of control that is refered to in the POH.

Note/ AS350 - No limit caption - CAT B
AS355 / AS365 Limit caption - CAT a

[Jiff]

To Arm out the window,

I think that my analogy does hold water because I did say "wave the gun around a lot", that certainly doesn't imply that it will fail at any moment.
The beefing up of the hydraulic system in this case is probably just a very small pump capacity increase.

Heedm,

"If a problem is solved by publishing a limitation, is it still a design flaw?" Yes and no, If a helicopter can carry an underslung load of 2000 lbs. I think it is reasonable to say that's its not a design flaw because it cant carry 5000 lbs, but in the case of the hydraulic system we are talking about, it clearly is.

Grey Area,

I have designed the control systems for several safety critical systems (non aviation) which involve servo jacks and hydraulics, and I know for a fact that if the mechanical guys did not design in an additional 10% capacity above and beyond what the worst the control system could ask for, the design would have been questioned at the review stage.

Jiff


:)

[Lama Bear]

In 12,000 plus hours I have never flown a helicopter that would not "Jack Stall" if the aircraft was over flown. Has anyone besides Lu flown one that is immune to this?

[sling load]

I suppose VNE is a limitation to cover up for a design flaw, I suppose VNE limits with doors off are cover ups of a design flaw, I suppose the Torque limit is a cover up for a design flaw, I suppose the Flight Manual should say "don't fly helicopter into powerlines" and I suppose the Flight Manual should have a special supplement that says, all flight test data conducted by Test Pilots and Flt Test Engineers are superseded subject to the opinion of Lu Zuckerman.

This forum is basically Lu taking the position of argument for the sake of argument, not for the sake of learning or sharing. I have never seen a person ignore the opinions of highly qualified people quite like this bloke.

Test Pilots found the feedback limit during flight test Lu, they call it transparency Lu, Its in my Flight Manual under NORMAL PROCEDURES, Sect 2 Paragraph 7, Crusing Flight Manoeuvres, Para B "-Maximum load factor in turns is felt in the form of servo-control "transparency"; this phenomenon is smooth, and presents NO DANGER."

Limitations Section, Para F 'Prohibited Manoeuvres'- Aerobatics.

Pretty well much says it all, once again Lu, you stray way off the subject and turn it into a design flaw of a helicopter which you have absolutely no knowledge of, aren't you glad pprune has no forums for astronauts, imagine the crap he go on with there..

[Lu Zuckerman]

To: All

Once and for all understand this: Since in my work it is imperative to try to eliminate any problem that effects reliability and safety I made a few assumptions. These were eventually proven wrong and I learned something in the process. Jack stall is an acceptable condition on the AS-350 and it does not cause a danger. I saw it as a problem because I felt that the hydraulic system was incapable of overcoming the forces and on any other helicopter I have been associated with, this problem was never addressed. I saw jack stall as a problem related to the reliability because in my misunderstanding of the conditions I felt the lower control system could react the flight loads. I saw it as a safety problem because in an emergency situation you would not want the jacks to stall. I also saw another potential problem and that was how the warning light was triggered and I was told that the warning light is on the Twin Star and not on the A Star. I thought the trigger was the system pressure and I was told that it is an external device that is mechanical with a micro switch or possibly a strain gage. The danger that I saw was that once the jack stall was taking place the pilot could not move his cyclic. To do so, would displace the servo (pilot) valve(s) opening the lower part of the cylinder to the return system and then the feedback forces could enter the control system and displace the cyclic stick quite hard and seriously hurt the pilot depending on which way the cyclic was displaced. But then again I am just a worrywart.

[ShyTorque]

At risk of doing this to death...

Why not fix the problem of jackstall by inceasing the pump output (and possibly having to upgrade the whole system and redesign the airframe to cope with the consequential increased feedback forces, adding weight and reducing the useful load of the aircraft)?

Firstly, because jackstall occurs outside the normal flight regime and it requires high power, high speed and harsh manoeuvre to induce it. For example, we used to demo it to basic students in the military Gazelle AS341 by diving the aircraft at high power then pulling hard through the heavy vibration until a jack stalled. It was very unnatural to do it, we didn't like doing it because it felt awful to the airframe and I believe it was later removed from the syllabus. (It also scared the $hit out of most students).

The parameters required to induce jackstall will sound familiar to any helicopter pilot because they are also exactly those required to induce retreating blade stall.

There is little point modifying an aircraft already in safe and satisfactory service to prevent jackstall if retreating blade stall will subsequently occur at only a slightly higher speed, power, or manoeuvre limit.

Secondly, market forces rule. It's a fact. Any aircraft can be redesigned (at a cost) to perform better but we aren't talking about an agile fighter here, it's a small helicopter for goodness sake! Who would pay? The manufacturer, or the customer, especially if there is nil perceived benefit?

Finally, jackstall tends to result in the aircraft throwing off pitch so that it is a short-lived phenomena, unlike retreating blade stall. As I said earlier, I would rather suffer jackstall than get RBS a few knots later. The aircraft limitations are there for a reason. Observing them is what we get paid for.

[helmet fire]

ShyT: well said. Especially that the aircraft limitations are there for a reason and that pilots get paid to observe them.

Lu: I appreciate where you were comming from, and I am glad you were able to take the points on board.

Jiff: Re your handgun example. I agree with your proposition, however, it is in no way comparable to the AS350 situation. In particular, you might note that several pilots have described how jack stall only appears during extreme maneuvering, not during normal ops. To draw the analogy with your handgun more accurately, it would be like saying that the safety catch had a design flaw if it came lose after repeatedly (and harshly) bashing the gun on a hard surface when you are reloading. In other words, the "flaw" only appears after gross mishandling. To continue the analogy, there would even be a note attached to the gun warning you that: "if you repeatedly bash the gun on the ground to reload it, the safety catch MAY come loose. To correct this, check safety catch before lifting the gun." Does this put it a little closer to context?

To heedm: The point you raise is an excellent one. Basically you are asking: where do you draw the line. Who defines flaw Vs limitation, gross mishandling Vs routine operations? I guess that is the manufacturers and certification authorities, perhaps Nick might know?

[Nick Lappos]

Uh, Oh, I might have to agree with Lu on this. heedm, note the date and time!

Jack stall is a sign of a servo system with too little force capability, and is not acceptable in modern helicopters, as a rule. It is caused when the stall of the retreating blade causes the blade to change its pitching moment sharply downward, which makes the blade try to dive. The strong downward force is fought by the pitch change links, swashplate and servos. At Sikorsky, we set the design requirement of the servos so that with one stage failed, the other has the full capability to fly the flight envelope. That means that we have twice as much servo force capability as needed in normal unfailed circumstances.

I personally set the S-76 flight test points to prove this, with max weight, one servo turned off, we pulled over 2 g's at Vne with no change in stick feel.

A helicopter that shows jack stall is on the edge of taking over for the pilot, and turning him into a passenger for what could be a very short ride. Treat all jack stall cases as bad ju-ju, because the difference between a stick that throbs a few cycles, and one that thrashes around and allows the aircraft to go ape is a very small difference in maneuver load factor.

[ShyTorque]

Nick,

2G equates approximately to a sustained level turn at 60 degrees of bank, if I remember correctly.

The manoeuvres I have experienced as required to induce jackstall are beyond that.

If the aircraft are flown within their published limits there is no problem.

However, I may well agree that Sikorsky aircraft may be built with more margin in hand in some areas, obviously in the case of the S-76 and other aircraft with an input from your good self. It doesn't mean to say that another manufacturer's product is unsafe though. ;)

[sling load]

To get transparency in the AS 350, the manouevers are so severe that you could fly without ever experiencing it, i have had it demonstrated and as one of the other posters said,it is quite a deal to set it up, I don't see it as a design flaw, it was designed at the time with the technology available, its an excellent aircraft and an absolutely stable platform to work from. Ive flown up to and including the B2, i havn't seen or read the B3 data, but if it was a serious concern, the B3 may have changed.

Anyone who operates an As 350 outside the performance specs and limitations is asking for trouble, doing anything, its a light helicopter with limits, the manufacturer has identified them for the pilot, fairly straightforward.

It is an extremely violent manoeuver to get to transparency. I have only had it when its demonstrated, never encountered it in normal ops or had other pilots experience it in normal ops.

[Arm out the window]

Funny term, transparency.
You would think that in the normal course of events, the servos would feel 'transparent', i.e. you wouldn't know they were there, so to speak.
I'd say that jack stalling would be when they weren't transparent!

[baranfin]

maybe servo freeze or something like that would make more sense.

[Nick Lappos]

Shytorque,

I agree that the 2 g's is not terribly severe, but recall that is with half the total servo force, since we had turned one system off prior to the maneuver.

The test pilots who took the AS-365 through air combat trials frequently experienced jack stall to the point that the aircraft would wind up tightening its own turn. This occurred at 2.4 g's or less, which is not terribly far out in the spectrum of possible maneuvers. One can argue if this is acceptable or not, but the ideal helicopter should not have the ability to out-fight its pilot, in my humble opinion. None of this should be interpreted as impuning a very fine helicopter, just stating what we should be striving for.

In any case, the concept of jack stall is clearly understood by the bunch, we can argue (politely, of course!) the specific level at which it should occur (clearly far out in the envelope).

Like weak tail rotors (which create the need for careful LTE training), jack stall is a fact of life, but I hope we all get to help raise the bar and make it something we tell newbies about with the phrase, "Sonny, I remember the time when...." :D

[ 08 December 2001: Message edited by: Nick Lappos ]

[IHL]

Hey Nick : I always wondered why the S-76
has such High Hydraulic pressure (3,000 psi)for a helicopter with a Gross Weight under 12,000 Lbs. Is it because the servo actuators are relatively small ? ?

[ShyTorque]

Nick,

I certainly agree that a combat aircraft should be able to endure more than its pilot can stomach.

But the AS-350 could hardly be described as a combat aircraft! :eek:

[helmet fire]

Not a combat aircraft? - dont say that around the French! :D :D

Nick, What you are saying makes sense, but again I harp on the severity required to enter jack stall in the AS350 (not the 365), I am guessing from experience, but I would say around 3 Gs, or slightly less. As you say - jack stall occurs in or approaching RBS, but that is the point we have been trying to make - why are you flying the aircraft into RBS? Fighter maneuvering aside of course!! Thus the majority opinion was that as it only results from gross misshandling - perhaps calling it a design flaw was a bit over the top. Does this level of severity have to occur during certification? Or do you restrict it to 2 or so Gs as you indicated for the S76?

Lastly, do you think that the RBS under these conditions is a G stall?

[Nick Lappos]

IHL,
The higher hydraulic pressure allows more energy to be transmitted, and it allows smaller piston areas in the servo for a given force, so it saves weight. 3,000 pounds per square inch is now considered old hat. The S-92 is 4,000 psi, and the V-22 is 5,000 psi (!!) The tradeoff is against the leak potential and the need to protect against line burst.

ShyTorque,
The real issue is a subject dear to my heart. Our machines should not execute the pilot for an error, I think, but the levels of jack stall we are discussing are really just annoying characteristics, so I really agree with the group, I think.

Helmetfire,

Generally, few helicopters can pull 3 g's, and I'll bet the 350 cannot. High g capability robs hover performance, so designers give it out gingerly. The Black Hawk can pull 3.5, and an Apache can get close to that, Comanche can pull almost 4. I have hit 2.7 in the S-76, doing stuff that would make many pilots toss their cookies (I used to demonstrate helo aerobatics to the Army when they were deciding how to specify LHX maneuvers). Estimating g's is hard, I really can't without a g meter.

Max G capability is actually easily estimated based on blade chord, tip speed and diameter. I can give you a reference, if you'd like.

The issue here is really the nature of carefree handling. As long as jack stall does not cause control loss, it is not a major issue, and we really agree. If it robs the pilot of control, it should be fixed, even if the maneuver is considered extreme. FAR states that we must test to the maximum the aircraft will experience in flight, so if someone comes back and pulled more, we didn't test enough. Flight manual cautions and the "pilot error" rubber stamp are quick outs for poor designs.

We used 2 g's with a servo failure in the S-76 to assure that nobody would ever get jack stall, reasoning that folks would not pull near stall loads after a failure. With both servos on, the controls can never get to jack stall under any case, as is true with the Black Hawk.

Something I must calrify is the notion that any helicopter can hit any g if the pilot gets wild enough. The max g's for a helo are set by the rotor design, especially the solidity (amount of blade area relative to the disk area). The rotor can only pull a few g's before it stalls, and sometimes the maneuver can be quite mild. The typical rotor stall g level drops quickly with altitude, so if the maneuver took 3 g's at sea level, it might stall at 2 g's at 10,000 feet DA, a much more achievable level, and near Vne, it might stall at only 1.5 g's.

If my helicopter could lose control in jack stall at 1.5 g's, I'd find another!

You ask about g stall as opposed to speed stall, I think. There is no difference, really. The relationship between g and speed is that the stall g drops with speed until at some speed beyond Vne, the aircraft stalls at 1 g. I will be glad to email you some charts of this relationship, or give you some references, if you'd like.


You ask, "Does this level of severity have to occur during certification? Or do you restrict it to 2 or so Gs as you indicated for the S76?" Please note that the S-76 is jack stall free with only 50% of its servo strength, and jack stall with both systems healthy is impossible. The manufacturer must test to a maneuver level that he then declares to be the maximum (the phrase is that the test maneuvers are extreme enough so that the probability of exceeding them in service is "extremely remote" which is FAA speak for 1 in 10e9 hours. In other words, if 1,000 helos are building 1,000 hours per year, in 1,000 years we will have one event! Using this definition, it is not good design to experience jack stall (to loss of control) in service, having certified that your tests were so thorough.

[helmet fire]

Thanks for your response Nick. I should have clarified the G stall - what I was asking was: do you think the RBS we are talking about here was primarily induced by the G loading being experienced (as opposed to the retreating blade speed)?

your point about having the pilot executed by the machine design is well said, and I do not dispute, but I am curious as to where the limits of manuever harshness during testing are set. For example, you stated that you tested the s76 to two Gs with half the servos because you couldn't imagine anyone pulling to the stall with a servo failure. This is the point being made above - very few (none of the above so far) AS350 pilots can imagine pulling so hard as to experience jack stall, it is as you say: a manuever in which you mightlose your cookies! So if the Bell teetering head can get away with not being termed a design flaw because it can come off during gentle manuevering, and fixed wing stalling can too - jack stall is surely not a design flaw, or at least labelling it as such is a little harsh isnt it?
:)

[Nick Lappos]

This is truly a study in sufficiency, because you are quite right, the issue is subjective. The jack stall we are discussing is a benign type, where control is not compromised, so it could be termed a marginal but acceptable characteristic.

Regarding the differences between retreating blade stall and g stall, there really is none. The stall is at the retreating blade, and is due to too much angle of attack. This could be achieved at 1.25 g at Vne, or 2.0 at 80 knots, the cause and results are the same. If you plot the slope between those two hypothetical points, that is the relationship between thrust and speed that defines retreating blade stall. If you toss in the effects of density altitude, you create a parallel line that is at lower g for higher altitude. Another parallel line could represent the effects of lower rpm.

In other words, more g or more speed or lower rpm or higher altitude all effect retreating blade stall.

[Devil 49]

In my paranoid imaginings (result of this thread) I'm wondering where in "Chickenman's" flying life he could expect this problem to roast him?
Lots of cyclic demand, even at normal G? I can envision being rather busy if I suffered complete antitorque failure at a high hover- what with the throttle on the floor and probably over a hover hole... :eek:

[scrubba]

interesting discussion.

i also used to fly the as350 and i used to do aerobatics in it (different environment so settle down!) and teach others to do them. i believe that jack stall was an intentional design feature and i believe that it was a carry-over from the gazelle.

the facts are that jack stall was progressive and you could fly through it if necessary. i saw it as the rotary equivalent of the plankwing "buzz" that accompanied impending stall - in other words you knew you were at the limit and if you continued there were identifiable consequences.

after my AS 350 experience with jack stall, i had cause to rethink some previous experiences in uh-1 gunships where we thought we were regularly getting thrown out of maneuvers due to retreating blade stall. some might have been rbs, but i came to believe that many of them could have been jack stall (the benign ones) and others could have been jack stall followed by rbs when we couldn't back off in time.

anyway, despite the lu hysteria, it still seems to me that "transparency" is a good design feature because it alerts you progressively to an impending limtation that in effect is being sensed through the feedback load on the control horn.

[paco]

I took this from another discussion.

"except the only time I ever got into the "Servo Transparency" in my 2,000 + Astar hours was in a B model (Approx 4000 lb AUW) in a gentle turn around a fire on a calm August day at 4,000 Ft....go figure that one out??? "

I only mention it because somebody said that it only happens under extreme conditions. I have found that things like this that could happen often do just when you don't want them, despite what designers and test pilots say. In that respect, I think it should have been fixed before now. The accumulator is there to allow reduction in speed in a timely manner without going to the expense of adding a second hydraulic system.

And talking about hangovers from gazelles.... our Twinstar has a crap electrical system as well, but I won't go there....

phil

[Nick Lappos]

scrubba,

Save us from such wonderful design features, please! The issue is that the hydraulics are too weak to keep the blades from arguing with you. As Paco relates, the incidence of stall can occur at relatively low maneuver states.

You have been lucky that the "transparency" occurred where the recovery is simple. The problem is that the mild stick wiggles you have felt are nothing compared to what could be dealt to you in other circumstances. Should the stick simply whip around the cockpit and let the aircraft suddenly take over, you would probably not declare that a design feature! The 365 family does that, and the maneuver ends when the aircraft finally runs out of airspeed, so control can be regained. Should the aircraft find some comfortable dirt or rock to nestle into before it lets you become PIC again, the flight might come to a rapid halt, thanks to that handy-dandy design feature you like so much.

I hate to agree with Lu (and I think hard about it, believe me!) but let's all push for power steering that works all the time, and helos that don't stall too early.

I hear the same apology for LTE in this group ("crummy pilots deserve to be punished"), and I ask us all to please seek helos that don't require budding Astronauts to keep them safe. The helicopter mission is hard enough, with the demands for extra judgement, fine motor skills and great airmanship to keep the outside world from hurting us and our machines. Let us at least ask our machines to be our partners, and not our adversaries, in the quest for better safety. If our safety record can't be raised, we might always be a mere sidelight in the world of aviation.

Paco, that incidence illustrates what I was talking about above in this thread - that stall is stall, it is not g stall or speed stall. The August day was warm, I'll bet, and the aircraft was heavy, and that turn crossed the stall line by a bit. :cool:

[ 15 December 2001: Message edited by: Nick Lappos ]

[paco]

Yup, stall is stall, as many beaver pilots have found when turning low and slow...

here's another from the same thread, a sobering thought...

"110 kts, straight and level, collective bottomed, 500 lbs below max gross, descent off the top of the mountain - wind sheer, a/s up to 155kts, a/c snapped to the right 90 degrees. both arms could not pull it back, cyclic was solid. you can get ST any number of ways."

You know, I don't like aircraft that bite. I know the Astar is a good machine, and has had a lot of good stuff built in from the design stages, but that sort of thing should have been fixed. To my mind a limitation is something that results from natural causes, such as something that all engineers know about, such as, say helicopters don't fly faster than a certain maximum speed. This is a design flaw. like the electrics, but I'm not going there... :)

Phil

PS Design features are a Microsoft euphemism for bugs

[ 16 December 2001: Message edited by: paco ]

[Lama Bear]

"110 kts, straight and level, collective bottomed, 500 lbs below max gross, descent off the top of the mountain - wind sheer, a/s up to 155kts, a/c snapped to the right 90 degrees."

So you exceeded the max autorotation "collective bottomed" airspeed by 40 knots at sea level and it's a design flaw? Sounds to me like you put the aircraft far out of any reasonable design reserve.

[paco]

First of all, I just copied that from another bulletin board - it wasn't me (read the post).

Secondly, it is a typical situation in the mountains, POH notwithstanding, and a 90 degree snap to the right is not what you want right then. It shouldn't be what you get at *any* time.

When senior test engineers or pilots admit that it was a bigger factor than originally catered for, I would suggest it is something that ought to be fixed, n'est-ce pas?

Phil

[ShyTorque]

Seems to me there are two polarised opinions here.

One from pilots who observe the published aircraft limitations and have no problems.

The other from people who think that limits are to be ignored when it suits them, suffer a fright as the consequence and then call it a design fault.

"Whaddya mean, stressed to 4G?
I've only been pulling 5G all morning and then the wing came off this afternoon!! :rolleyes: I think you're a crap designer!"

[Lama Bear]

"First of all, I just copied that from another bulletin board - it wasn't me (read the post)."

Sorry about that. I thought you were re-posting something you had already posted.

"Secondly, it is a typical situation in the mountains, POH notwithstanding, and a 90 degree snap to the right is not what you want right then. It shouldn't be what you get at *any* time."

I'm not sure what mountains you fly in but where I fly the "V" limitations are exactly that. Anyone near gross weight that puts the pitch down, rolls the nose over and approaches an airspeed limitation, in anything but the smoothest air is asking for exactly what happened."

"When senior test engineers or pilots admit that it was a bigger factor than originally catered for, I would suggest it is something that ought to be fixed, n'est-ce pas?"

Who are these senior people that have all this Astar experience? Lu probably has never even riden in one. Lu knows lot about why helicopters fly but he knows little about how a helicopter flies. And Nick has already stated he does not have that much experience with the AS350/355 series. What I've been reading is that the pilots with considerable Astar experience are saying there is nothing wrong.

I haven't been fortunate enough to fly one of the new generation attack helicopters but every helicopter I have flown will exhibit "Jack Stall" if pushed past it's published limits. Which model do you consider immune?

[Nick Lappos]

Lama Bear said:
I haven't been fortunate enough to fly one of the new generation attack helicopters but every helicopter I have flown will exhibit "Jack Stall" if pushed past it's published limits. Which model do you consider immune?

Nick sez:
The servo strength does not have to be infinate to counter the stall forces from the rotor, because the moment the blades generate reaches a practical limit in deep stall. Therefore, there is not a relationship between the designer building ever stronger servos to counter the pilot doing ever more aggressive maneuvers. A properly designed control system always wins against the blade stall forces.

In US Military service, the maneuvers must be tested to extreme limits in a structural demonstration where we squeeze everything out of the helicopter and make sure that controls, structure and systems all support the pilot. Jack stall is not allowed, and any helicopter that demonstrates it must be redesigned (usually by making the servos stronger).

In short, no Boeing, Sikorsky or Bell product of the last two generations has or can experience jack stall.

[paco]

No, it's not something i already posted, but I had already alluded to the same thread a couple of messages ago - I thought you had read it, sorry :)

It's just that I'm watching two threads at the same time on the same subject. In the other one there are a lot of experienced pilots giving examples of when they have encountered this phenomenon, which range from the relatively benign to the extreme, such as the last example I gave above. When I say "typical of the mountains", I meant the situation, where windshear will often take you a great deal above your target airspeed very quickly, obviously something to be watched for, but you can't always catch it.

Obviously, one shouldn't fly aircraft to their limits, and none is bulletproof, but my problem with this one is that it isn't repeatable under the same circumstances every time. If it were, you would just avoid it and regard it as a limitation, which it clearly isn't. I still maintain it should have been fixed as part of ongoing product development, while recognising that you can't design everything right first time.

Actually, Lu (or anyone else) wasn't on my mind when I posted - here is yet another quote from the other thread:

"Within the first 50 hrs of flight after my endorsement there I was with fire crew on board headed out for the old day base in Alberta - so very close to max. gross internal. 800' ceiling "zipping" down the siesmic line enroute to day base, spring black bear eating grass on siesmic line, fire fighter wants picture, tight right hand turn at about 110knts., rate of descent approximately 200-250fpm. you do the math on how long it is prior to controlled flight into terrain. Actually it would have been uncontrolled flight into terrain as I experience "servo transparency" - cyclic & collective FROZEN - the only controls left to help reconfigure the disc loading were the pedals - however I was unaware of what was happening and it was only #$%^house luck that I was able to regain control. If I had not the A/C plus 5 people would have been spread over the Alberta jackpine muskeg for a mile and no one would ever have come up with the reason.
It took me until 1997 for a eurocopter test pilot to admit to me in "private" that yes it was a bigger factor than had been anticipated. There are at least 3 fatal's I am aware of where it is my belief that "jack stall" was involved.
My advice - for what it is worth - enjoy the A/C but learn your product well, be careful of: subject discussed, vortex state ring, Hyd. failures and although a nimble and responsive A/c is should be flown more like a medium. If you have a penchant for being a cowboy - leave the boots and spurs at home on this one. This is not meant to frighten, however knowledge is one of the gateways to professionalism. Have a awesome season."

Phil

[Big Beres]

My work mates and I have been discussing wether or not the AS350 has a "turbulance penetration speed". One of the guys we work with(ex Mil) says it does :80kts which it clearly states in his Defence Force Flight Manual. But when we look for it in our civil flight manual there is no mention of it.. .I can't remember anything said about in my type rating(years ago). .So is there such a figure?. .Do the Mil guys know something we don't?. .or has Eurcopter just forgotten to add it?(which I dought)

. ."Wise man says 'make haste slowly that way accidents don't happen" <img src="rolleyes.gif" border="0">

[sling load]

Ive never seen it in a Squirrel flight manual either, 80 knots sounds right, its in my RAAF AS 350 pilots handbook. Perhaps it had to have a turbulence penetration speed for military acceptance.

[Big Beres]

SlingLoad. .The 80kt is in the RAAF fligth manual that I had a look through today... .Must be a Defence Force standard.

[Big Beres]

SlingLoad. .The 80kt is in the RAAF fligth manual that I had a look through today... .Must be a Defence Force standard.

[copternrd]

I am looking at doing my endorsement on a AS 350B2 soon.Anybody out there have any tips or info on these machines that I won't find in the FM?

[Dynamic Component]

Does anyone know what a new AS350 B2 costs?. .Lets say in utility configuration.

[whatsarunway]

try a bell , not as nice to fly but when somethinh goes wrong the eurocopter backup is abismal

[Dynamic Component]

Been there, done that.There arent any Bell machines that can compare with the AS350.All machines have their ups and downs. <img border="0" title="" alt="[Wink]" src="wink.gif" />

[Dynamic Component]

Any one out there with some info on this subject please?:confused:

[Aesir]

www.savback.com in Sweden has a B2 for sale for 720.000$ and a B3 for a little over a million$US.

Walter

[407 Driver]

That was a fairly broad statement Dynamic, would you care to elaborate?
We just sold our 3 remaining B2's in favor of moving to an all Bell fleet, we feel that the safety, servicability, and economics are much better.

[widgeon]

Is that an all 407 fleet ? , if so you aint comparing apples to apples.

[Dynamic Component]

407 Driver,

Would you please explaine why you say Bell is safer than the AS350?I know the AS350 has problems with so called "jack stall", but then on the other hand it does'nt chop its own tail off.

I do not have much experience in 407s, but all owners and operators I have spoken to have something bad to say about it.Be it "not living up to expectations" or"the interier falling appart". :p

[407 Driver]

Widgeon, I don't quite understand your question.

We now have an all Bell fleet, from 206B3's to 212's. We had 3 - 350B2's but sold them and bought more 407's. We currently have 6 and are looking at adding more. The 407 had been a very reliable and safe aircraft in our fleet.

I personally have over 2,000 hours on the 350 series, and now about 1,000 hours on 407's. My experience with the types is that the 407 is superior to the B2 in performance. All of my work is at altitude, and in a general charter / utility role.

I have had the unfortunate experience of attending 3 -350 accidents in my career, all of which have resulted in injuries and death. I feel that the 350 series does not offer the protection that other types do in a crash situation. The cabins of each of these 350 wreckages were demolished, and each aircraft was a complete write-off.

In addition to my personal experience in dealing with the aftermath of these accidents, I routinely study the information available on the NTSB website (www.ntsb.gov). This information may not be a complete look at a given type worldwide, but it is readily available and gives a good look at the US stats.

The 407, introduced in early 1996, has 20 reports filed, and is now numbering over 500 ships worldwide. There have been 15 fatalities, including a night wirestrike (4) several M/R blade strikes (3) a mid-air with a 355 (1 - 355 pilot fatal), but only approx 7 fatalities directly related to the failure of the aircraft/structure. in that same time period, the US 350 fleet had 60 reports and 50 fatalities. This is not an "apples-to-apples" comparison, as the 350 fleet numbers are larger.

Dynamic, you wrote..."There arent any Bell machines that can compare with the AS350". I disagree with this statement, there are several Bell models that can compare directly with 350B, BA, and B2's.
I also suggest that if you feel that Hydraulic servo transparency is the only item of safety effecting a 350, you should do some research. There have been several AD's issued recently that could have a profound effect on your safety.

The 350's may be wonderful aircraft to fly, but do not be lulled into any false sense of security. When they bite, they bite very hard!

[Dynamic Component]

407 Driver,

You now have my full attention.I thought I had done my homework:confused: .
Would you be so kind as to please broughden my view on the 350?
What ADs are you talking about?there are more than 80.

I must say that you are the first person I know of saying that the 407 is better than the 350.Ofcourse everybody is entitled to their own opinion.Could you explain to me why you say so.

[widgeon]

My point is comparing B2 to 407 is not apples to apples.407 has purchase cost about 300K usd more than b2 and DMC about $40 usd / higher ( like having a free pilot on the b2 LOL) . If you want to compare performance compare L4 to B2 and 407 to B3 .

[CTD]

Each has its ups and downs. The Bell vs Eurocopter thing has been going on for years like Ford vs. Chevy, and we may as well be arguing about our favorite colour. One could tit for tat for hours on end.

Dynamic, you'd be well advised to pay attention to 407 Driver. He is among the finest of helicopter pilots anywhere, and has reached a level of knowledge and experience in the Canadian Rockies that most of us can't even imagine. As you may have noticed, he doesn't talk through his hat, and can back up his words.

I can only speak from my own experience, which is operating 350s commercially for 1500 hours, and flight test on 407s for about 1000. I don't work for Bell anymore, and have no particular allegience to them or anyone else. I can tell you that I know the 407s problems intimately, but would not hesitate to operate one anywhere. It is a superb helicopter.

We have just over 200 AS 350s operating in Canada. They have had their share of growing pains, like anything else. The Turbomeca engine, once the savior of the type, is quickly falling out of favour due to reliability issues and horrid product support (Widgeon, a quick call to Irving in NB who operate a 350B1, L4 and 407 will enlighten you). In fact a 355F1, with two Allison engines has a lower operating cost than a 350B with one Arriel. You are correct that Conklin and DeDecker do indeed list the 407 DOC at $36 more than a B2, but I think the servicability issues and performance more than make up for it.

The hydraulic failures persist, in spite of being identified eons ago as a problem. In the past 8 years in canada we have had 9 reported hydraulic failures in Canada. Some of the belts had 200 hours.

In the same time, there have been 15 forced landings due to inflight power issues. Admittedly, it's likely that not all have been directly engine related, but that's still one out of every 13 helicopters in 8 years of data (assuming there were 200 A-Stars 8 years ago - and there was nowhere near that). Of the 25 407s in Canada, there have been two engine power incidents, one is still under investigation as to cause. There have also been 520+ production models and several thousand hours of experimental which have been built at Mirabel without a failure in flight test. Touch wood.

There have been several accidents involving main rotor spherical bearing failures. Very serious problem.

My biggest worry about them is the survivability in an accident. Lawn furniture surrounded by ping-pong ball skin. Give me that box structure of the 407 anyday. It's even stronger than the L with the added composite. Another misconception is that the 407 is an L4 with 4 blades. In fact, there is only 14% commonality between the two ships, and one cannot build a 407 out of a 206L-4.

End Rant.

[407 Driver]

Well, this thread is getting WAY off topic, but I'll respond one last time. Thanks CTD for those kind works.

Widgeon, I'd GLADLY compare my 407 to a B3 anyday, as you know, the B3 is a fantastic aircraft, but Eurocopter failed to raise the Internal Gross weight above B2 levels, (last time that I checked anyway) so all that power, but still only 4960 Internal? Given it's probable heavier EW than a B2, one would be worse off...unless you dare to depart over the Internal Gross wt?? You wouldn't do that would you??
Slinging, well, the B3 is great, no doubt about that!

We feel that our 407's are operated for less $$ than our B2's were, plus with some innovative purchase methods, (build them) we have aquired them cheaper than a 350. We had B2's parked in the summer for 5 weeks waiting for parts...figure that cost into your equations and the Bell products suddenly look more attractive.

I don't take safety lightly, and feel good about strapping into one every day. We have excellent maintenance personnel, who have developed some great ideas on dealing with T/R shafting balance issues, some of which have been incorporated into Bell's maintenance proceedures.

As CTD said, this is turning into a Ford-Chevvy debate. I initailly took up the issue re: the comment that Bell has nothing to compare....

[tigerpic]

today i experienced an oscillation in the eurocopter as350b3 for the first time. the b3 has just been returned to service after a 1500 hours (i believe). it had been flown a couple of times since then, until i departed the airport to ferry the helicopter out in the woods for sling load. i flew at 1500', 135 kias, 82% torque (90% on the fli, i believe), OAT 5 deg C. i had put lots (!) of friction on the collective, not touching the control, and gently keeping the cyclic to maintain the attitude. no turbulence in the area. suddenly, with no power or attitude changes, i got a oscillation up and down in the whole helicopter that corresponded to the main rotor rpm, same intensity, like the rotor system wasn't tracked properly. i gently reduced power just before the bleed valve opened (appx 91% ng) and the oscillation stopped. i returned to base with this power setting and landed normally.

i have heard of new b3's having this problem; but this was my first time. i want to make clear that this was no pilot induced oscillation, since the friction was almost max on, my left hand was on my thigh (until it had lasted for about 3-4 seconds), and i was not moving the cyclic, it was completely still. momentarily i thought it was turbulence, but it turned out to be rythmic. the technicians are checking the helicopter tomorrow morning, since i was on a night flight. my guess is that this could be the collective linkage (somwhere between the collective and the servo). is this the case? i have heard of other pilots who have had the same problem, and even worse oscillations than what i had.

the thing that worried me was that it came without any warning in smooth, calm air, with no changes in power/attitude, like lightning from clear sky, and disappeared when i reduced power.

[tgrendl]

tigerpic,

I would have lot's more questions about the indications, ranges etc for you.

When you say "oscillation" do you mean a vibration in the rotor system or a movement of the airframe?

Were you close to vne?

What were these secondary indications;
1. TOT
2. N1
3. NR
4. Acft yawing back and forth?


5. Indicated airspeed change during the event?
6. Audible pressure change?
7. Change in groundspeed?
8. Close to vne?


If the secondaries 1 through 4 were varying I would work the engine/ bleed valve side of it.

5 through 8 would lean me towards unforeseen turbulence/ frontal passage/ lee eddies from something


If those were clean;

And the event was happening at a small power range I would work the engine some more,governor, power demand, load demand etc.

If it's a small airspeed range it's happening at I'd look at the rotor system/ flight controls from the blades back to the servos and then further back the chain to the place you do the touchy feely stuff to.

Keeping in mind that the flight control side of this problem is the most dangerous I would go through all I could on the ground first and with heavy emphasis on the flight controls.

Please let us know what your technicians find out,


(disclaimer....not a eurocopter guy, just tom generic):D

[[email protected]]

Tiger, could it be described as a vertical bounce?

[The Nr Fairy]

tiger :

May be applicable, may not be but I saw this in a CAA safety publication I received in the post yesterday.

SA350 - Cruise.

An investigation by the aircraft manufacturer into two reports of in-flight oscillation concluded that the problem was due to the Fuel Control Unit's ( FCU's ) lack of success in filtering drive train torsional mode. This 4Hz torsional mode causes velocity variations for which the FCU tries to compensate. However because the NTL ( free turbine ) and NG ( combustion chamber ) are in phase lag, the FCU doesn't solve the problem but sustains it. By modifying the flight conditions, the balance is broken and the phenomenon disappears.

It is noted - with no more stress on it that a pure mention - that this was a military Squirrel used for ab-initio training by the UK military.

Hope this helps. You modified the flight conditions - reduced power - and the problem disappeared, so this may be something after all.

[Devil 49]

Aircraft has started hitting the unsat side of the graph on a regular basis, after bouncing around near the line for the 10 months it's been here. We've checked for compressor section visually, looked for leaks, checked the free air temp and torque calibration. NG remains to be checked, and most interestingly, something internal to the module 5 of the engine. For which I've been requested to perform a "climb power check"-but can find no rotorcraft flight manual entry describing the test. If you can point me to it in the RFM, or describe the test and your experiences, I could sure use some insights...

All other suggestions welcome.

[mikeferg]

I would perform a power check at 97%, 98%, 99%, and 100%. Look for a trend to see if you are generating progressively less power at higher settings, or 'better' power the higher the Ng you pull.

The 'climb power check' you are referring to is the 100% Ng setting. You have to climb in order to perform it. Try doing it straight and level and you'll see what I mean. Be careful not to exceed any airspeed/power setting limitations.

Pull the p2 filter and clean it. Perform an engine wash, and follow it with a thorough rinse. Pull all the stainless steel lines on the engine and check the flares for any sign of contamination, especially the fuel line. Run the engine with the cowl open to make sure there isn't anything leaking around any of the lines.

What has Eurocopter said about any of this? Have you spoken with a tech rep yet?

[MASTER_CAUTION]

also, disconnect and cap off all customer bleeds, (heater/demister valves notorious for leaks),particle separator, etc.

[Devil 49]

Now I feel really bad-I can pull 100% NG at 3000 hp and 22 C, and not hit tq limit in cruise...

Turbomeca is on a call back, forwarded a pile of numbers from previous power checks.

My opposite got a sat power check with a max power climb to 3000, establish cruise and then autorotate to 2000 for the power check, or so he claims.

[chopperdr]

looking for operator feedback concerning the as-350 b3 with crash attenuating seats.
question: do you find the cyclic grip too low, or uncomfortable, and would you be interested in an adaptor to raise the height of the cyclic grip.
thanks

[tigerpic]

i wished the world could be more black&white when it comes to helicopters.

starting up and shutting down the arriel 2b engine is described in the operating handbook something like this:
- to start the engine, go from OFF to ON (flight) with the starting selector, except when below -20 deg C when you must wait until oil temp is >0 deg C before switching to ON.
- shutting down: after setting down the helicopter, wait 30 sec on full RPM (flight idle) and the go from ON to OFF directly with the selector

the technicians in marignane, france, told us that the shutting down procedure is to prevent carbon build-up in the engine.

what happened to the cooldown issue? i was at the american eurocopter factory, and the test pilot told me what the book said as stated above, but good procedures was to wait at IDLE both up and down.

what do you b3-pilots out there think? what do you use for procedures?

cheers,
tigerpic

[John Bicker]

Believe the frenchman. I remember guys coming from Allisons to the Arriel and doing 2 minute rundowns. Longer on the Arriel is not good for it. The temperature in the bearings initially goes down but after 30 secs it goes all over the place. The problem is low oil flow at idle. In fact if you do idle an Arriel it is better to run it back to "Flight" for a period prior to shutting down. Operate IAW the RFM, simple.

[cpt]

I have always complied with the RFM on the B3. This sort of procedure, based also on experience, is not lightly determined by the manufacturer, and untill now I have never heard of something different.

[Steve76]

Hey Lads,

Does anyone know anybody with an Astar engineering ticket who needs some work for the Canadian season?
It will be contract on fires with employment during winter at a major SW Ontario city. Really good conditions and a great boss.

Immigration assistance will be provided for the right person.

Kinda getting urgent too....

Thanks in advance :ok:
Please contact:
[email protected]

[Rob_L]

email address is failing, can you correct

[Steve76]

Mate,
There should be a underscore between the collective and bias. I think the underline is absorbing it.
Try again and if it doesn't work I will get another address for you.

[EESDL]

Thanks, thought there would be more to it!

[beetlenut]

Hi all,

Can anyone clarify the system used to record cycles operating the AS350.

I can understand 1 start--shutdown = 1 cycle...............but have been told a percentage of a cycle is recorded each time during a landing when N1 reduces below ???%

Can't remember the figures.....................anyone?


Cheers

Bn

[Devil 49]

Without cycle count sheet or RFM handy, I hope the following is helpful-
A normal NG cycle is one start and warmup, takeoff, and 30 sec ground idle cooldown. IN that instance, your cycles would be determined by your maximum NG, a K1 value.
In the real world, you may have many power changes with various high power settings, the highest of which would determine your K1.
You could also have low power settings between starts, so you add a cumulative K2 to the max K1.
Example- I start and takeoff, normal power on approach and cooldown- max Ng 96%, cycles logged 0.6.

Alternate, 1 start and takeoff 96% Ng, K1 0.6, log 0.6 cycles
HOGE power check, max NG 97%, new K1 0.7 log 0.7 cycles
Agressive approach, min NG 85% adjust cycles with a K2 of 0.1, terminate at hover without exceeding previous high NG. No change K1, cycle calculation K1 0.7 + K2 0.1 log 0.8 cycles.
I land from hover and roll back to ground idle, adding a K2 of 0.15 to previous 0.1, total K2 0.25. If I shutdown, cycles would be K1 0.7 + K2 0.25, log 0.95 cycles.
NO engine shutdown, max power departure 100% Ng yields a K1 of 1.0. Then sobered by previous hairy approac, I make a normal power on approach (without exceeding previous high NG) to hover, land and cooldown. Cycles K1 of 1.0 and sum of K2 0.25, Log 1.25 cycles.
Not as complicated as it sounds. Max NG between starts equals K1, add sum of K2 events yields cycles to log.

[Jez]

After just starting to operate an AS350 along side our Bell 412 I know what you are going through .

I made up this sheet for our pilots to help work through the calculation of NG cycles. This will have to be read in conjunction with the table of Max. and Min. NG found in the Maintenance Manual (Arriel).

Hope it helps

Arriel 1B Cycle Counting:

(I) REFERENCE CYCLE (Ng): Theoretical cycle used a reference for setting service life limits. Includes one start, one power acceleration corresponding to the "takeoff power" and one shutdown.

(ii) OPERATING CYCLES: A flight may consist of two types of cycles:

- Complete Cycle: An engine operating sequence including one start, one power acceleration and one shutdown.
- Partial Cycle: An engine operating sequence corresponding to a power decrease followed by a significant increase without engine shutdown. It may be defined as the number of hover events and landings.

(iii) Free Turbine: All components. One flight = One cycle

Gas Generator Equation: N = K1 + (n x K2)

K1 = Coefficient corresponding to maximum Ng (see table over page)
K2 = Coefficient corresponding to minimum Ng (see table over page)
n = Number of partial cycles carried out between start and shutdown

;) :confused: :confused:

[Arm out the window]

Absolutely impractical, is it not.
You'd think in this day and age of dirt cheap computers someone would be able to design a $20 box that would record it all for you, eh?

[paco]

Quite agree - I've got better things to do than count how many times I've w*nked the handle

Phil

[Dynamic Component]

beetlenut,

We use max NG pulled during the flight + min NG used(only 85% or below)x the amount of times you droped the collective below 85% inflight for NG cycles.
NG95=0.6,NG96=0.65,NG97=0.7
NG81-85=0.05

I can't remember the rest of the figures, but you can find them in the Turbomeca Manuals.
As for NF cycles, 1 startup +1Flight +1Shut down= 1cycle

[bellsux]

If your boss has enough coins in the bank you can buy a cycle counter that works it all out for you but it is pretty straight forward to record the cycles after a while when you get your head around it.

[beetlenut]

Thanks to all respondents, think these comments sum it all up



Absolutely impractical, is it not.


Quite agree - I've got better things to do than count how many times I've w*nked the handle

Especially on a up/down/up/down survey trip the number of landings gets a bit blurred.

Cheers BN

[Giovanni Cento Nove]

It seems you may have "summed it up" without any thought about the consequences. In a country that seems to have "diificulty" counting hours and cycles maybe you should have asked your maintenance engineer "Why?".

Apart from the possible financial implications it has a lot to do with the design of the engine..

The catch is the injection wheel. This wheel is subject to considerable thermal cycle fatigue. If it fails, most of the gas generator rotating assembly will leave the engine rapidly. It has been proven a few times, so don't bother.

There are units which will record what you want - 1 is a tacho box from Turbomeca and there are a few aftermarket units. Or is this a case of "can't be arsed?"

[beetlenut]

GCN Maaaate!!,

It seems you may have "summed it up" without any thought about the consequences. In a country that seems to have "diificulty" counting hours and cycles maybe you should have asked your maintenance engineer "Why?".


Nope, you got me completely wrong. This system is impractical and can be a challange to keep correctly. I personnally will get a "click counter" to ensure my tallys are right.

It just seems stupid that these "after market" accessories are not included in the initial A/C build.............. a bit like auto-relight systems (don't get me started).

Cheers BN

PS: I dont think everyone has problems with truthfully recording Hrs or Cycles.

[Buitenzorg]

Don't have a flight manual handy, and I'm looking for the wt & balance information for the BA model Astar - Squirrel for Europeans. Basically, all the info required to calculate a weight and CG position - weight/CG envelope, cg positions and limits of seats and bagage compartments, etc. - except for the empty of the individual machine. Browsing the web hasn't turned up anything, does anybody know a website with this info?

Many thanks in advance.

[Aesir]

Check out: http://www.electrocution.com/aviation/

Excellent W & B spreadsheet.

[Gordy]

Here you go

arm inches
Front seats (right hand pilot) 61.02
pilot (left side) 63.00
front bench seat high back 65.00
rear seats 99.99
side baggage 125.98
rear baggage 181.1
fuel 135.81

[paco]

I'll be putting a new spreadsheet up in a day or so - just added density altitude/pressure altitude - amazing the things you do to pass the time in an oil lease.....

Phil

[Buitenzorg]

Many thanks to all you gentlemen. Just what I was looking for.

[Flying Lawyer]

Five-times 500cc motorcycle world champion Mick Doohan has taken delivery of Eurocopter's 400th AS350 B3.

http://www.mickdoohan.com.au/photos/1997_doohan_flag.jpg

The keys were handed over by Eurocopter's President at a ceremony at Marignane.

This is Eurocopter's second sale to the Ozzie star who's been Honda's Head of Racing since he retired in 1999.

[Hilico]

For those unfamiliar with Doohan's racing record, Flying Lawyer's picture shows him three laps from the end of the 1994 Spanish Grand Prix, having lapped the entire field twice and deciding to ease off a bit.

[sprocket]

:D

Which country does Mick reside now? or was the ceremony purely for the AS 350?

[Steve76]

I think Mick is in Spain.

[chopperdr]

saw the original ship in texas the other day, truly a beautiful paint job, i heard that the gentleman that paints micks helmets did the aircraft. nice work
dr

[Aussierotor]

Mick is General Manager of Racing for Honda and his home address is Monaco.
Think he still has a place at Surfers Paradise to visit,but with attending all Grand Prix,s etc both his places would be a haven for cobwebs.

[wobs]

Mr. S

If you're around caloundra i know Jacko has some copies of a roll of film i shot of it when Mick's pilot picked it up.

And I think Rob has my negatives!! he's on Central Coast NSW somewhere. rumbles would probably have a contact 9pass it on to me if you get one - wouldn't mind my negs back!)

These are the two guys who painted it. They don't paint helmets! I think Jacko was painting buses again when I left Qld.

Also believe Eurocopter in Sydney has some copies.


T

[Danger Boy]

Greetings all,

Your inputs would be greatly appreciated, especially those rotorheads who have experience with this particular aircraft.

I am presently working with the Red Cross Air Mercy Service, in Cape Town South Africa. They render an airborne emergency service countrywide. Our Helicopter Wing in the Western Cape, utilizes two platforms to render this service.

A well suited BO-105, equipped as an Air Ambulance, for all our Primary calls (trauma,transfers etc); and an Alouette 111, equipped for Mountain Rescue and Surf Rescue.

Unfortunately as much as we all love and respect what the Alo has done for us, we find ourselves restricted to 1.5 hrs airborne capability on Surf Rescue calls, and just under 1 hr on Mountain calls. That is with our present operational Payload. Work in your average ferry, and this doesn't leave you with much time for an all important thorough search, and even less time for the actual rescue. Obviously we have made alternative plans wrt strategic fuel placements and off-loading of certain crew on site where necessary. Unfortunately this has often proved to be time consuming, which can be fairly criticall for certain patients.

Hence our need to replace the Alo with a suitable platform. we have looked at many alternatives, and seem to have narrowed it down to the AS350 B2. We have been frantically trying to source a suitable, reasonably priced second hand B2 for quite some time now. If anyone has any suitable contacts please post or send me a PM; not to sure of the protocol on this forum?

More importantly though, we would really appreciate pilot and operator inputs wrt the suitability of this aircraft. This before we commit to purchasing one.

Here then our worst case scenario Payload and conditions:

Pilot
Winchman
1xParamedic/Doctor
2x Mountain Climbing Specialists
Stretcher approx. 15 kgs
Life support Gear and Climbing Gear approx. 30 kgs
Suitable Winch/Hoist
Floatation Gear
Highest Mountain in Area 7000'amsl
Max possible OAT @ 7000'amsl 20 Deg cent.
Approx Density Alt 8500'
Endurance 2 hrs

Any feedback greatly appreciated! :ok:

DB

[davidi]

In my opinion you'd be hard pushed to find a better single engine helicopter for what you describe. Purchase cost is one of the few things against you. You'll be in a relatively simple machine, easy to maintain, simple to fly, certainly reliable (especially if flown most days), stable platform, relatively robust, it is unlikely to be the cause of your crash however if you do you're in one of the worst seats/harnesses so see if you can get the as350b3 seats but they are expensive and are also not perfect (but then what is). Lack of tail rotor authority can be a problem but good pilot techniques will help, you'll struggle to get into vortex ring unlike two bladded bells (but poor piloting will help if you insist), the standard landing lights are not that good. The main rotor blades are "on condition" but you're unlikely to get more than 4000 hours out of a set, if you purchase a b2 a new or newish set of main rotor & tail rotor blades would be high on my list, you must have high skids. I could go on. If this is of any help give me a phone number to ring and I'll give it some real thought. Good luck!

[widgeon]

http://www.eurocopter.com/site/FO/scripts/siteFO_contenu.php?lang=EN&noeu_id=3#


A few for sale , the 9000 series are factory re builds , will prob cost as much as new. very important is time left on ENgine , overhauls can be as high as 200K though I think TM have an assure OH rate now.

[Autorotate]

You might also want to check with Johan Nels at SA Dept of Ag at Lanseria as they have their unused B2 sitting in the hangar there. Since he got the new B3 he hasnt used it at all, except for a few flights to stop everything rusting up.

Also Eurocopter Africa are pretty good to support operators from what I understand.

Autorotate.

[Dynamic Component]

I would like to know where I could find those large windows they fit to the AS350?:confused:

I've seen them on pictures,but can't find a website for them.

Any help would be apreciated:}

[rotorboy]

I looked in ours, I assume you mean the ones that "bulge" or bubble out a little. Tech Tool Plastics, I believe it is called the "comfort window"
www.tech-tool.com

RB:ok:

[Dynamic Component]

Thanks rotorboy,

But its not the "bubble windows" I'm after.
I have seen windows on AS350s that almost take up the whole door.:E
Those are the ones I'm after:}

[Autorotate]

The ones that Air Kauai have were made by Eurocopter Canada.

Heli Ops

[rotorboy]

I believe those are made by tech tool too. I wasnt alking about a "bubble" window for VR work. I would give then a call. If they dont make em, theyll know where.

RB

Autorotate, I sent you an email the other day and didnt get a reply.

[chopperdr]

send a p/m, have some information on pdf concerning the full length vis doors which are a eurocopter canada product
dr

[widgeon]

http://www.tc.gc.ca/aviation/stc/stc_e.html


stc Sh00-1 first canajun STC of the new millenium.

Also installed on LA police I believe.

[goaround7]

Great helicopter and love everything about it except landing which can make one look a complete twit. Everyone asks why it wiggles ? Anyone know ?

[Vfrpilotpb]

I asked a pal of mine the exact same question, he is a CPL and used a twin Squirrel every day, he passed it over by saying he had never really tried to work out why, but he went on to say, it did make you look a little under-experienced.

But yet I watched an RAF FI and student land a single Squirrel and never saw the same wiggle, could it be big engine covers create dead spots when trying to come down slowly?

Vfr

[Steve76]

My understanding is that the tail boom becomes a lifting surface under the rotorwash. IE: Corianda effect

Later models of Astar had strakes to prevent this. Still wiggles thou...
Probably pilots with not enough coffee.

[paco]

Just relax a lot more - you'll do a 5 ft hover smoothly quite soon

phil

[ShyTorque]

Steve 76,

"Corianda effect" :confused:

Isn't that the "Turbulent lifting under the tailboom" one suffers after a good curry the night before? :\

Or did you really mean "Coanda effect"? :p

[Devil 49]

My best but completely unscientific guess is that the low tail rotor placement causes it's rotor wash to interact with the ground, varys thrust efficiency. Add a horizontal stab that's at the margin of the main rotor down wash and you've got a lot of changes happening in the control trim position.

Good news, forget the tendency and fly the aircraft all the way down. Concentrate on no translation as you slowly descend and above all- don't try to feel for the ground- and it lands like any helicopter.

[ATN]

Interference between the rotor downwash bouncing back upwards and the frame. Put it in hover at 4 or 5 m and it's steady as a still life. The engine cowlings have little influence, yet I find the twin wiggles more than the single engine.

Cheers

[John Eacott]

Low skid/high skid? From what I can recall, the high skid Squirrel puts the airframe spot on the top of the ground cushion, just before the skids touch (depending on weight, power, etc), whereas the low skid is through the downwash and stable before the skids touch. The Squirrel dance is basically trying to get on the ground whilst the ground cushion has other ideas: that was my excuse for the erratic landings, Guv!

[Steve76]

Thanks Shytorque...:O
Back to basics for me.

[407 Driver]

Devil49 has the answer....don't hover it in, just do a smooth no-hover run-on landing ( we're talking just a few inches of dragging the springs)

Smooth as silk every time.

[Milt]

The guru is stumped!

Ok then what is "coanda" or "corianda" ?

Ever had any PIOs in a chopper?

And does the throttle turn the same way in all of them?

[Ascend Charlie]

Coanda effect - a cylinder can generate lift in an airflow by rotating on its axis, or by inducing the air to flow faster on one side.

Coriander effect - big night on the beer and curry, can cause urgent visits to the bog.

Throttles on the collective seem to rotate in the same direction, throttles on the floor (Squirrel) or roof (twins) have the same orientation of forward for full throttle.

Bell 430 is the odd one out, with throttles looking like motorbike setup, but (I believe) rotating the opposite way.

[RobboRider]

Coanda effect

As stated by Ascend Charlie - in an aviation sense.

The coanda effect goes back to even more basics. Any liquid or gas if flowing along a surface will tend to follow that surface even if the surface changes direction.

If its air - add in the changes in air pressure that occur with air flow changing direction and you get lift in funny directions

[[email protected]]

Milt - Henri Marie Coanda was a Rumanian engineer/ scientist/ aircraft designer born in 1886 and he designed what could be considered the first turbofan/bypass engine in 1910, exploiting an effect he had observed where engine exhaust gases from a piston engined aircraft tended to follow the curved shape of the fuselage much further than expected.
He took the propeller off the piston engine and used the drive to power a compressor that forced air into a ring shaped combustion chamber and produced sufficient thrust to get the aircraft airborne (albeit briefly).
As ascend charlie has said, we see coanda effect on tail-booms as the downwash creates lift on one side of it (the angle the air hits the boom forces it around one side faster than the other).
The effect can be enhanced by blowing air through a slot along the length of the tail boom (NOTAR does this) which encourages and enhances the boundary layer.
The Sea King had a long strake added on the port side of the tail boom to break up this powerful lift because, with a wind from the right, the aircraft was trying to yaw right and full left pedal was frequently insufficient to prevent it.
I have seen pictures of a rotor system built in the 60s with circular section blades that had a blown slot long the top surface - it apparently worked but the engineering problems (weight and power required) associated with getting high pressure air up the rotor mast and along the blades meant it didn't see full production.

[rotorboy]

Well, some of you are close. there are 2 main things that make it a little squirely in a hover.
1) the shape of the belly .. has a tendancy with the rotorwash to recirculate.
2) The 146 gallon unbaffled fuel tank under the M/R transmission... its called fuel slosh.. very noticeable when your really light and it has under 40% fuel... and once it starts.... if you try to correct it... youll make it worse. My theory, is it came out of a Pugeot... its got the same gas cap;)
3) its french and they make everything difficult like getting in and out of the thing.. like the blades turning the wrong way

I love flying the thing, but the fuel tank a couple of other things makes me wonder about the people who designed it. Like whay cant they put the damm throttle on the collective and why cant the seat be 4-6 inches closer to the window!

Oh lets talk about my HYD failure last week and the whimpy green belt where the gule came apart....hmmm can you say weak link.

You know they have a saying in france " that may work in practice, but it does not work in theory, there fore we can not do it.


you tend to see guys in a really high hover, or a really low hover... that be why..

OK I am done rambling

RB:ok:
"still bouncing on the concrete with the best of em "

[goaround7]

Thanks Guys !

Now I've got a straightfoward explanation - shape of the belly and recirculation plus large tail boom - and a scientific name for the whole thing - Coanda effect - that I can tell students to go research so it all seems terribly aerodynamically complicated and they'll stop asking me questions ! Perfect.

It's a high skid B that I 'm flying and I must admit to being a bit nervous at a zero speeder on the hard stuff, especially when light. Will give it a few goes when no-one's looking.

As for sitting nearer the windscreen, I'm fairly tall and as it is I can't easily see the red marks on the torque gauge. Any nearer and I'd have to crouch. Seat won't go back as far as I'd like. Is this more 'design for short ar$e French people' again ? (No offence to short or French people but the ergonomics don't seem quite right for a relatively spacious cabin.)

We also have a Squirrel, that I haven't flown yet, that does have the twist grip throttle - believe it's a mod or you can request it from the factory. Not for the twin though I don't think...?

As for 222, yes, the throttles are the opposite way to a motorcycle.

[PPRUNE FAN#1]

Many things conjoin and conspire to make the Squirrel squirrelly right near the ground. If it were "simply" the low tail rotor, 206's on low skids and certainly 222's would be similarly afflicted. Unless there's one on the left side also, the strake on the right side of the tailboom would seem to be Eurocopter's attempt to take advantage of the Coanda effect to lessen the right-pedal demands at a hover.

Rotorboy correctly brings up the fuel sloshing in the unbaffled plastic tank (although at 146 gallons it must have come out of one really long-range Peugeot). This can be uncomfortable, not to mention the source of PIO, and one that is certainly not needed when other factors are coming into play.

People have mentioned the rounded belly and how it affects the hover airflow. I suppose that's as good an excuse for my squirrelly hovering as any. And it probably does play a part.

I've never figured out Eurocopter's philosophy on control harmony. The D-models I flew had notchy collectives even with the friction all the way off, the pedals were strangely stiff considering they were boosted, and the cyclic was your typical "wet noodle." The cyclic, collective and pedals all ought to move with the same perceivable effort and effect, and this did not seem to be the case with the Astar. Ease in some pedal and nothing happens at first. A little more and...whoa, that's too much! Eh- maybe it was that limber, elastomeric tail rotor.

Adding to this was the puzzling cyclic linkage. The French do like a "sporty" feel to their helos, but the gearing of the Astar cyclic linkage and bellcranks seemed to me to be needlessly "quick" considering how responsive the rotor system is. Perhaps in designing the AS-350, the Aerospatiale engineers used the same basic control linkage ratios that they used with the (non-starflex) Gazelle and wet-head Dauphin, which were both sporty without being twitchy.

Although some pilots seem to adapt to the Astar flying qualities quickly, it takes awhile for many others to develop a feel for the aircraft. Fly an Astar at night, when the landing light illuminates the very front arc of the rotor disk. Even the tiniest movement of the cyclic causes that arc to jiggle up and down. To my mind, that's a control system that's not got the right bellcrank gearing.

High-skid or low, the Astars I flew all seemed to get weird right near the ground. It's aggravating because placing a skid exactly where I want it is neither as easy nor predictably accurate as it is in a Bell (or virtually any other helicopter for that matter). Flying shouldn't be that much work.

[2Sticks]

The French have another saying:
"It is not my fault, I am French"!
(said with a heavy gallic accent and an Elvis-like sneer to the top lip) :D

2Sticks

[CyclicRick]

Sorry to whinge at the previous participant but:
The rotor does not turn the "wrong way", merely the other way ( much more ergonomic if you ask me)
The space in the cab is excellent, you can shove all sorts of bits and pieces left and right and most of it doesn't fall out of the ddor when you open it (ie 206)
The throttle is fine where it is, never had a problem with it at all!
The tank, well at least it's big enough to get you somewhere without having to re-fuel every two hours.
NO I am not French, but US helicopters are certainly NOT gods gift to us pilots.

PS anyone else had Nr, Ng and TOT needles all wobble(fluctuate) at the same time in a 206? Bloody strange if you ask me

[Giovanni Cento Nove]

2 things are happening -

1/ The cyclic induced PIO. Friction up the cyclic as per instructions in the Llama RFM to the point where it is quite difficult to move. You'll get used to it. The controls are obviously fixed to the frame and if the mast/transmission start to oscillate it subsequently moves the controls more. The better the balance of the MR the better the hover as well. Don't stir the pot. With friction on you'll soon tire of trying to.

I have had a 355 hover for 45 seconds or more without touching the cyclic. This is with .02 IPS.

2/ The wake from the MR OGE misses the tail rotor due to contraction and when IGE moves across the tail rotor and causes translation lift in the TR but not consistently. This causes a yaw roll couple and gets worse the closer you are to the ground. This can be proved by hovering in a tail wind. Keep it straight with your feet. The wake around the cabin is minimal.

The strake on the B2 was to create a Coanda effect to help the tail rotor by destroying lift on the right side. I doubt there is much Coanda effect without it as per B, D. Interesting the B3 doesn't have it.

The tank sloshing is limited to earlier unbaffled tanks and will NOT be noticed in the hover unless your a stick stirrer, only in the cruise at about 60-70%.

Try it. Works for me, steady as a rock.

[Collective Bias]

Ok, two cents from me as well:ok:

I once had the pleasure to talk to one of the designers of the AS 350, and one of my questions was of cource why it is so unstable. Should not have said unstable:E I got an instant reply "It is not unstable, it is precise". I guess it could be argued. Anyway he said they (Eurocopter) where not really sure why exactly is was a bit twitchy (he agreed on that), a lot of contributing factors he said, no magic item.

He also said when they installed the long tailpipe on the exhaust on the B3 it became much better, and this was a surprice to them.

I have had the pleasure to fly many diffrent versions (all but the D) and in my opinion there are some diffrences.

Low skids are worce then high( I know it was argued the other way, but this is my opinion).

Short T/R output drive worce then long (standard now).

Twinstar blade with trailing edge tab much better than without.

B3 exhaust also much better.

Best contributing factor - lots of houres on the machine and to have it recent. Look on a high time 350 pilot not flying anything else - steady as a rock, but do not put that guy in a steady dampend platform, such as the S76, he will make it look bad by overcompensating:E

[rotorboy]

Cyclicrick,

I totally disagree with you that the throttle is OK where it is. I guess you havent had too many emergency's that require throttle manipultion.

High side gov failure in an Astar is a little differnt, you must immeaidtly lower collecitve and take the FCL out of the govering range.


Stuck pedals, kinda hard to adjust throttle to help control yaw.

There are several other things i wouldnt mind having it on the collective for.

They shouldnt have waited for the B3 to do it , but put it on the B2 years ago.

RB

[goaround7]

....so then why DOESN'T the EC120 wiggle ?

That you can put down like a feather... not enough coriander ?

[as355f1]

THE REASON THE SQUIRELL WOBBLES WHEN IT LANDS IS THE RESULTING FORCE CAUSED BY THE MAIN ROTOR HEAD AND THE POSITION OF THE TAIL ROTOR BEING AT DIFFERENT HEIGHTS
THIS RESULTANT FORCE CAUSES THE HELICOPTER TO "HANG" RIGHT SKID LOW .
THIS COUPLED WITH THE "STINGER" {FITTED TO ALLEVIATE GROUND RESONANCE} CAUSES THE HELICOPTER TO INITIALLY LAND ON THE RIGHT REAR STINGER TIP WHICH IN TURN CAUSES A PIVOTING/ BOUNCING MOTION-USUALLY OVERCORRECTED BY MOST PILOTS I AGREE THAT THE BEST WAY TO LAND IS A GENTLE RUN ON LANDING

[pilotwolf]

as355f1 you sound more qualified to comment than me as I ve never flown the squirrel and guess I m not likely to in the near future :( but...

Are there any helicopters where the main rotor head is at the same level as the tail rotor?

In my limited experience all helicopters tend to hover with one skid low - or is that just my flying?

I always thought the stringer wa the part which stopped me dinging the tail rotor - what is it on the squirrel?

And surely one of the bonuses of helicopters is you don't need to 'run on' during 'normal ops'?

PW

PS - got a headache so please don't shout! :)

[chopperdr]

pilotwolf, i believe the stingers that 355f1 refers to are actually the small "beavertails" installed at the aft end of each skid tube, those are for ground resonance attenuation. remove those and things can get interesting. also there are tolerances for the tails and they need to be replaced if the angle / clearance is out of limits
dr

[Governormalfunction]

I don't recall a major problem with a 355, I always found a BO105 much more sporting, especially when landing on a trolley!!
Maybye it was just my gash 'hands on'??

[Squirrel]

"Run-on landings" on a mountain log pad or when placing your heels on a log to keep from sinking!!?? - In my opinion, not a good way to get around the handling characteristics - if you are never going to land anywhere other than an airport, well you may be able to get away with it, but if you fly utility, and the times you have to be precise, you won't have the practice or technique down to do a good job.

Follow the advice on frictioning up of the cyclic (although lots of smooth Astar pilots use no friction), and not stirring the pot (actually hardly even moving the cyclic), staying in trim and keeping a steady approach right to the ground, and not hovering before landing, will help you master the beast. If every landing is a no hover landing, with your descent controlled by collective and not by moving the cylcic, you will be on your way to perfecting the landing.

[Devil 49]

Y'all, I've done 30k+ landings in this airframe, in calm to 50 knots, level ground to elevated (all varieties), and my observations-

1) Yes, it ordinarily lands right side skid heels first. If you put that down without translation and not descending too quickly, you won't know when it touches. Translate a little over the ground except forward and all bets are off. If I "feel" for that first touch, I always mess it up. Yes, the control trim positions change suddenly, but nothing unacceptable. If you have a stabilised and slow descent going, it'll be a quick small movement or two and the collective will be on the bottom.
So- eyes out front, hold it in place, and slow uniform descent until the collective stops going down. Just like any helicopter.

2) The aircraft will land fine, as above, unless winds anywhere but on the nose- Then it darts and jumps a bit more, especiialy sporty with 10-15 knots on the right rear quarter! If you're up to form, you can still do the "Technique 1)" but it's not easy. Don't feel for the ground!!!
10-15 knots at the right rear quarter can get real interesting, especially on an elevated pad with turbulence. Those conditions can bounce the automatic leveling device, a/k/a tail skid. It'll pitch up suddenly, commence a descent, and yaw suddenly.
A bunch of wind improves things (and stabilises the airflow, which I think supports my tail rotor wash theory), and it does better in all quads, as long wind steady state. Plenty tail rotor authority and few surprises.

3) If all else fails, a little forward as the right rear skid heel touches. Good when you absolutely gotta plant this pig as it's pointing, and "good basic helo technique" is kicking your keester today.
Whenever I lapse into the slide-it-on routinely, I'm soon back feeling for the ground and jarring teeth. 350's will show you where the pilot is wanting.

This aircraft is "precise" and little change in trim and effect is apparent in the seat of one's pants. More than once I've thought I was definitely down and bottomed the collective only to have it drop the last couple inches. "I" was "down and through flying" but the helo wasn't.
When all else fails- stop overcontrolling, hold it still- and land it like any helo. The slide on is admitting defeat and she knows she whipped you.

[NickLappos]

as355f1

It is an old belief that the height of the main rotor vs the height of the tail rotor is a reason for hovering one skid/wheel down, this is really not correct. All the forces developed by the machine are summed at the center of gravity, which is considerably below the main rotor head.

The aerodynamics of the machine make it such that the higher the tail rotor, the LESS it leans in a hover! Helos with the lowest tail rotors have the most lean, believe it or not.

High tail rotors produce a rolling moment that subtracts the left lean (for a US type system). For a given helo, if the tail rotor is centered on the tail cone, the left lean is about 5 to 6 degrees. If that tail rotor is moved up a few feet to the top of the tail, the lean is reduced to 3 degrees or so.

A question for the group:

In what axis does it wiggle - yaw or roll?

How fast are the wiggles _ in wiggles per second?

[Gomer Pylot]

From my days flying the D model, lo these many years ago, ISTR that the answers are Yes and I can't count that fast. :D

I always tried to keep my hands as still as possible and my feet moving as fast as possible - land the thing using the tail rotor instead of the main rotor for precise positioning. But nobody alive can set one down gracefully every time. Most of the time, but not every time; eventually it will embarrass you. I've never flown any flavor of B model, and never one with a high skid gear, so those may be different. If the fuel tanks are baffled now, that's a big improvement, but I only noticed that in cruise, the notorious AStar shuffle. When landing, I was always moving things faster than the fuel could move in the tank, so the inertia never seemed to build up.

I loved the space between the seat and the door. When I moved into the AStar from a 206, all that space was wonderful. I finally had a place to put my bag where the pax couldn't get it and take it downstairs with them. 140 gallons of fuel, speed to get somewhere before burning all of it, a heater, a defroster - hell, I was in paradise. A little twitchiness in landing was only a minor annoyance. The hand grenade LTS101 built by Lycoming was what worried me. Those who still use them say they're much improved now, but the offshore operators abandoned them long ago.

[matador]

Having flown over 3000 hours on AS 350/355 series and landed most any kind of place, I don´t dare to explain WHY is so hard to do a soft/Bell type of landing, mostly on hard surfaces, like concrete or others alike, but my two cents on HOW to deal with it are trown in:
It's a nice trick to land moving a bit forward as it is to put the wheight on the right aft skid and maintain it in that position until the bouncing stops, then really easy on the cyclic, put the rest of the right skid on the ground, maintain again without stirring the pot, and low collective to land the left skid. I find that if you want to land without feeling that frustating sensation of rebounding on the right skid first and then on the left, due to a really stiff landing gear (cross tube), you have to go through three fases:
1.- Right hand aft skid
2.- Right skid
3.- Left skid
If you don´t move the cyclic nothing more than strictly needed, you might get a soft landing out of every 10 tries.
Good luck :ok:
P.D. In the other hand there is no better landing gear to do toes or partial landing in stones and other weird places in mountain terrain IMHO.
Buen vuelo

[Squirrel]

Agree totally with Devil & Matador...

Re: the ugly wind, yes, right quartering and/or straight up the tail upslope is very tough - mix in some down drafts from high surrounding trees and you have your hands full. The advantage with the Astar is you do have lots of range fore and aft cyclic, vs others where you have to be very careful not to run out of aft cyclic when facing a slope. I have had to hold it in a hover (against my wishes) when a precise landing plus or minus 8-12" fore and aft and left and right is required, until I have that moment of respite from the tailwind, then plant it on the log or log pad .

As far as moving the pedals, everyone has their own technique, but I try to move the pedals as little as possible - the tail rotor is so powerful (which is good), that even small movements of the pedals back and forth exaggerate the wiggle (at least I have found that).

[ralphmalph]

An interesting thread......

As a very! inexperienced pilot who has flown a number of different types I always found the Squirrel to be a fantastic aircraft.

I learnt to fly rotary in it and although it is a bit jumpy in the hover after some practice I never really noticed it.

As for the throttle I know other aircraft where the throttle is poorly placed for single pilot ops......i.e. Gazelle

Ralph

[Devil 49]

Mr Lappos, I don't know why the question was framed as a "wiggle." That's a PIO, everytime, in these. 350's hover just fine, but as one descends and the flow changes, it'll pitch, roll and occasionally yaw, small but quick attitude changes, and start translating in response, if correction not expeditious and accurate. Controls are quick (the engineer type was right- "precise"), so small changes in position gotta have really fine control adjustments. That can be a challenge some days when the death-grip cramps are constantly being shaken out...

It's one of the few helos I've flown that seems as quick in the hover as in cruise. Real joy, harmonious and stable without being ponderous. If only the hydraulics were as nice...

[JNo]

Thinking back to PoF, I think the right skid low issue is actually a result of tail rotor drift??

[John Abersynth]

As John Bicker told me during my early squirrel days, "It's all in the pedals."

Thanks JB, You're a legend, and I love you!

[NickLappos]

Devil49,

Thanks for that info, it does seem to me the comments center around a yaw control that is both powerful and sensitive, and that we are talking about a bit of Pilot Induced Oscillation - PIO. Not much, I'll bet, and easily compensated for.

The reason why it gets worse as the aircraft descends is probably little to do with flow and such, and lots to do with the pilot getting tighter on the controls as the ground nears.
The reason why I asked about the frequency of the wiggle is that the airflow around the machine cannot generate a 2 or 3 Hz problem, because the aerodynamics are slower than that, but the pedals surely can. NOTARs are a bit slow on the yaw response, for example, and they captiolize on that aerodynamic force.

Generally the PIO can be fixed with a bit of damping on the pedals - like a door closer, a small hydraulic cylinder is imposed that makes the pedals hard to move too fast, but easy to move slowly.

Even a Huey is sensitive in the pedals, and likely to get a tad squirley when a pilot dances a bit too much on the pedals.


JNo,

Yes, I agree the right drift is exactly why the skid is low. The tail rotor is producing a force, (all US convention hereon) that pushes the helo to the right, a factor called "translating tendency". When the pilot corrects the right drift, he automatically rolls the aircraft a it to the left. When everything is settled, the roll attitude is about 2 to 3 degrees to the left, so the main rotor thrust is tilted a bit to the left to counter the tail rotor thrust to the right. 3 degrees tilt equals 5% of the main rotor thrust.

There is a hard to kill belief that the height of the tail rotor makes this worse, as if the comparison between the tail rotor hub and the main rotor hub height is somehow a part of the aerodynamics. Sadly, this one will not quite go away! Actually, the higher the tail rotor, the LESS the hover bank angle is!

Those who fly S-76 note about 2 to 3 degrees, those who fly a center line tail rotor (A-109 and any fenestron bird, for example) can you tell us what you see on the roll gyro when in a steady hover, no wind? I predict about 5 degrees or so. Comanche leaned at 5 degrees with its centerline fantail.

[Head Turner]

My thoughts are that all of you that experience this wiggle are ex Bell pilots.
I have never had the problem, nor have my students.

Around all helicopters close to the ground there will be patterns of air flow that are random due to a multiplicity of reasons. These air flow patterns will effect the tail and main rotors and as pilots you are trained and practiced in hovering. May I suggest more hovering practice with a relaxed and alert brain!
Coanda effects and the like are possible reasons. Some tail booms have strakes, some have had strakes and have had them removed, some do not have strakes. I think strakes were/are fitted for other reasons.

[Shawn Coyle]

Head Turner:
There are lots of those who experience this who are not ex-Bell pilots.
Seems to be unique to the AS-350 series, although I have seen something similar, with less intensity in the Bell 407.

[goaround7]

My company's looking at buying a Squirrel that comes with both high and low skids.

Planning to fly it in both configs and see but apart from the obvious change of ground clearance and dynamic rollover potential, what else is different when flying the low skid version ? Less 'wiggle' ?

[GLSNightPilot]

All my time is in low skid models, and IME the low skid makes it harder to set one down gracefully. Also, the tail skid is below knee level when on the ground, and it is entirely possible to strike the ground with it when hovering with an aft CG and/or a tailwind. Avoid low skid gear at all costs.

[goaround7]

Thanks GLS,

Useful to know, especially as many of our landings are confined and high skid model can be 'squirrely' enough.

[magbreak]

Is it nothing to do with the front and rear legs being a different length, and the bushy tail moving from side to side as they run???:confused: :O :O

Is there a difference between grey and red versions as well??

[teeteringhead]

Are there any helicopters where the main rotor head is at the same level as the tail rotor? The answer is yes, they all do in a certain part of the flight envelope - probably the cruise.

Certainly Brit military Principles of Flight teaching is thus: put simply, tail rotor roll (ie hovering left or right skid/wheel low, depending on main rotor direction of rotation) IS a consequence of the different height of main and tail rotors and is designed in to avoid being left (or right) side low in the cruise. As the fuselage pitches further down with increasing speed, at normal cruise, you have a (laterally) level floor. Much more comfortable, and less disorientating in IMC. However, inevitable design compromise means that laterally level fuselage in cruise (tail rotor and main rotor level) inevitably means in the hover when more nose up (tail rotor and main rotor NOT level), there is a lean to one side (towards the advancing main rotor blade).

Check out side on pictures of most conventional helos in the cruise to see that tail rotor is usually level with (or closer to) the main.

And I did say "put simply"!! With due consideration for Danny's bandwidth.

[Steve76]

Surely it has been asked before, but what's with the clockwise direction of travel for the rotors?
Just the french engineers being french??

[Thud_and_Blunder]

Steve,

Looked at many single-rotor Russian helicopters lately?

Maybe anti-clockwise is just the Americans being American...

[NickLappos]

Jonathon Swift wrote a whole book about the ability to argue about arbitrary things!
As lately seen, Americans go Right when more power is added, the French and Russians have always gone Left!

[Shawn Coyle]

There is obviously no 'better' way to have the rotor rotate.
Legend has it that the French got one part of a Flettner machine as war reparations and used that for their engineering, and since it turned clockwise when viewed from above, they stuck with it. Given the relative maturity of the French rotary wing engineering prior to the second war (they had the first hovering helicopter in 1909) that's a bit far fetched.

[212man]

Anything to do with the relative conventions of piston engine direction of rotation in the early days?

[Arkroyal]

(they had the first hovering helicopter in 1909)But that had two contra-rotating rotors, didn't it :confused:

[ATN]

Hi,

Have a look here

http://www.pprune.org/forums/showthread.php?threadid=105978

Cheers

ATN

[Jack Carson]

An As-350 B-3 recently experienced an engine failure during takeoff in Sierra Vista, AZ. Has anyone experienced similar difficulties with this model machiine? We are currently operating a B-2 and are due to get a new B-3. Our pilots are expressing concern with opering this new aircraft in the mountains at night.

[helmet fire]

None that i have heard of in Oz, BUT

flying any single engine helicopter over mountains at night is something you SHOULD be concerned about. At least tell me you will be using NVG?

Statistics can be bent anywhich way, but engine failures are not a rare occurence, and rarely are failure statistics recorded where the failure does not result in damage or injury. For the pro single engine mob that are bound to be wound up by this statement: when it all goes quiet at night, out to sea, IFR, over inhospitable terrain or day care centres, console your selves in the statistics of how safe single engines can be.

And how much money was saved by the operator to put you there. Who knows, maybe they put it all into accident insurance for the sake of your loved ones!
:8

[Jack Carson]

We have a very solid track record with tens of thousands of single engine flight hours. Good maintenance and professional pilots. We do have a few intermediate twins but they are not capable of operating even duel engine at the altitudes and temps we experience. OEI capabilities are even more limited. No we are not presently NVG's but we are working on it. Any knowledge or increased understanding of the machines we operate goes along way toward keeping our operation safe. Thanks you for your input.:ok:

[3fittydriver]

Great machine, great engine. ****ing computer. I'm flying one of the first B3's to come off the line. We're within (knock on wood) 150 hours of engine overhaul with no problems. Unscientific observations point to Texas built machines having problems, Canadian built not so much. Please Eurocopter, lose the DECU, or FADEC, or whatever you're calling it now. That would make it the near perfect machine.

[paco]

They're probably using a 386 :yuk:

Phil

[SASless]

This term "jack stall" is a new one on me....anyone out there that can enlighten me? Was used in disussing a recent 350 accident and was related to large agressive control movements and the inability of the controls to function as expected or demanded.

[NickLappos]

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.

[Disguise Delimit]

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.

[Collective Bias]

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

[NickLappos]

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?

[SASless]

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)?

[A10 Thundybox]

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

[Dynamic Component]

'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.:}

[Thomas coupling]

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:\

[Pub User]

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.

[Lu Zuckerman]

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

[407 Driver]

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.

[A10 Thundybox]

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?

[212man]

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.

[Aesir]

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" :)

[Head Turner]

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.

[oldbeefer]

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.

[leemind]

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!

[NickLappos]

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.

[SASless]

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.

[Firepilot]

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.

[2beers]

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

[Devil 49]

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.

[NickLappos]

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!

[inditrees]

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'

[Collective Bias]

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:{

[ATN]

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

[SASless]

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.

[Nigel Osborn]

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.

[NickLappos]

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.

[Gomer Pylot]

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.

[b.borg]

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

[JimL]

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

[SASless]

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!

[Collective Bias]

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

[Homer_Jay]

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.

[407 Driver]

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.

[Nigel Osborn]

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:

[ShyTorque]

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:

[Jack Carson]

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.

[Devil 49]

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.

[NickLappos]

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

[SASless]

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.

[4dogs]

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,

[NickLappos]

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.

[407 Driver]

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.....

[Flingwing207]

"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.

[SASless]

Again Nick hits the nail squarely upon the head!

[Warren Buffett]

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

[twinstar_ca]

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...

[ATN]

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