AS350 Astar / AS355 Twinstar [Archive Copy]
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George, I don't know if you will be flying corporate, EMS, or offshore. But if the 355 you're flying is an F1, a little advice. If you are at max gross, it will not fly on one engine. Did you take the corporate job in New Jersey? Or if this is the EMS job with a certain operator, be careful
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I'm driving one of these at the moment, and came from over 2000 hours 206, so I was in the same position as you, except I had a little gazelle time to help with the rotors going the other way. The F1 has the same engines as the jetranger, so there's part of the learning curve out of the way, except you switch the generators on as you start (haven't found out why yet). It's also a noticeably heavier machine and it is twitchy in the hover, but I got it subdued after a while. It comes down like a greased manhole cover with both throttles back, and you don't level the machine in autos - it does that by itself.
I don't know what job you're doing, but ours is an F1 and lifts a 150 gallon water bucket with no problem, plus 40 foot electricity poles. It's pretty good for passengers too.
You will find an excel/Psion spreadsheet for the CG on my website, that gives you weight and balance every half hour
hope that helps
Phil
I don't know what job you're doing, but ours is an F1 and lifts a 150 gallon water bucket with no problem, plus 40 foot electricity poles. It's pretty good for passengers too.
You will find an excel/Psion spreadsheet for the CG on my website, that gives you weight and balance every half hour
hope that helps
Phil
Avoid imitations
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I was told by my previous company's chief engineer that starter/generators for the F1 /F2 should be switched off for engine start because of a possible weakness in the genny driveshafts. There may be a recent mod; I'm not sure as I haven't flown them for a while.
When in starter mode, the drive quill is stressed in one direction (driving engine). When in generator mode, it is stressed in the opposite sense (being driven by engine).
Going immediately from one to the other can overload the genny driveshaft quill in torsion and cause a failure. If the generator is not selected on for start, it gives the drive quill chance to unload when the starter mode drops off line, before being driven under electrical load by the engine. Obviously, the drive stays engaged with the genny off but isn't stressed as highly.
The 355N can be started with gennies on because it has a stronger drive system (Arrius engines). That model has very pilot friendly engines, because of its DECUs. Booster pump on, switch on engine, watch it accelerate the rotor to fly all by itself. Start second engine. No need to move ECLs at all, they stay in FLY position. Much rated by police pilots as it enables a very rapid departure and a good OEI performance to boot! They don't leak oil either.
A possible "gotcha!" with the 'N' is that the collective MUST be locked down for start, for obvious reasons...so that the single engine hover performance isn't explored inadvertently..Yes, it has been done!
[ 10 November 2001: Message edited by: ShyTorque ]
When in starter mode, the drive quill is stressed in one direction (driving engine). When in generator mode, it is stressed in the opposite sense (being driven by engine).
Going immediately from one to the other can overload the genny driveshaft quill in torsion and cause a failure. If the generator is not selected on for start, it gives the drive quill chance to unload when the starter mode drops off line, before being driven under electrical load by the engine. Obviously, the drive stays engaged with the genny off but isn't stressed as highly.
The 355N can be started with gennies on because it has a stronger drive system (Arrius engines). That model has very pilot friendly engines, because of its DECUs. Booster pump on, switch on engine, watch it accelerate the rotor to fly all by itself. Start second engine. No need to move ECLs at all, they stay in FLY position. Much rated by police pilots as it enables a very rapid departure and a good OEI performance to boot! They don't leak oil either.
A possible "gotcha!" with the 'N' is that the collective MUST be locked down for start, for obvious reasons...so that the single engine hover performance isn't explored inadvertently..Yes, it has been done!
[ 10 November 2001: Message edited by: ShyTorque ]
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I know that on the 206 the reason for the 1 minute wait is so the battery can recover and not require so much charge that the genny will work too hard. I was trying to develop a quicker method of starting and I was told by Eurocopter that you could treat the engines like a 206 in that you could start the first engine with generator off, then start the other during the minute's warmup and while the second is warming up, wind up the first one to 70%, switch on gennies, etc, then complete the process. We found that the battery can stand it OK, but the second generator had a tendency not to cycle on, so we reverted to plan A, that is wind up the first one completely, switch the generator off then do the second.
A very slow way of doing it!
There's only one leak on our F1, though
Phil
[ 10 November 2001: Message edited by: paco ]
A very slow way of doing it!
There's only one leak on our F1, though
Phil
[ 10 November 2001: Message edited by: paco ]
Paco, the 1 minute wait on the 206 has nothing to do with the battery, it is a thermal restriction on the engine before you wind it up past idle to 70%. That impression has been floating around for years because it 'feels' right, but it is not the case.
In the 407, for example, the genererator is switched on at idle, and can be done immediately. However, if the ship has been shut down for more than 15 minutes you still have to wait the minute to wind it up.
Sorry to stray off topic.......
In the 407, for example, the genererator is switched on at idle, and can be done immediately. However, if the ship has been shut down for more than 15 minutes you still have to wait the minute to wind it up.
Sorry to stray off topic.......
Iconoclast
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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.
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.
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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.
PS Lu, thanks for the input, I'm sure the Eurocopter Bureau D'Etudes will jump for joy.
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?
My understanding is the huge feedback forces generated by a high 'G' manouver cause the controls to lock.
Correct?
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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.
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.
Iconoclast
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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 ]
“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 ]
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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?
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?
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.
It is also unfair to the Astar/squirell/AS350 to be mentioned in the same context as a Robinson. A far superior aircraft.
Iconoclast
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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?
“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?
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?
As for "design flaw", I assume you were joking.
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.
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?
As for "design flaw", I assume you were joking.
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.
Iconoclast
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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).
“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).
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?
Again: The AS350 is an outstanding aircraft. Enjoy it's huge capability and dont fly it against the POH - like EVERY OTHER AIRCRAFT.
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?
Again: The AS350 is an outstanding aircraft. Enjoy it's huge capability and dont fly it against the POH - like EVERY OTHER AIRCRAFT.
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!
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!
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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.
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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.
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Of course, I haven't flown or touched either aircraft so what the hell do I know?
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.
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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.
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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.
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Of course, I haven't flown or touched either aircraft so what the hell do I know?