AS350 Astar / AS355 Twinstar [Archive Copy]
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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.
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.
Anything to do with the relative conventions of piston engine direction of rotation in the early days?
AS 350 B-3 Engine Failures
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.
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!
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!
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.
Join Date: Jun 2004
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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.
A-Star "Jack Stall"???
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.
Join Date: Apr 2003
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It is the term to describe when the blades overpower the hydraulic servos, causing the controls to whip around, and usually causing control loss.
It is the product of having servo hydraulics that are too small for the helicopter in question, because the servos should be able to muscle the blade without feedback. No modern US Military aircraft is allowed to experience servo stall or jack stall, as the hydraulics are designed to have enough force to overcome the most extreme blade forces without being back driven.
The forces produced by the blade are generally the stall forces due to the strong pitching moment changes produced when the stall occurs, usually due to extreme maneuvering.
It 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.
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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.
When i did this, the controls moved a bit, but the cyclic then locked solid, and the aircraft, which had started to turn right and nose up, suddenly flipped back to a level attitude. When I stopped trying to fight the controls, and the aircraft stopped reacting, all returned to normal, though my heart rate took a little longer.
Lucky it flipped back to the left and not further to the right, as I would have been upside down.
Agrees with DD, it does not have to be that violent. On a straight B model at max gross and MCP, a dive up to 135 kts and just a bit aft stick will give this symptom. Lessen the collective or aft stick and it goes away. Not any diffrent load than servo off in cruise. IMHO I think it is vital to have felt this during initial training, to recognize it and act accordingly.
I think the idea with this is to limit the load being fed into the swashplate, the pilot will feel the "jack stall" and lessen the load. On the first 355 with dual servos they did not have any limit switch, and to much load was feed into the swashplate with permanet deformation seen as a result. After that the limit switch was installed on top of one of the servos.
CB
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
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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?
What altitude, OAT, Indicated Air Speed and gross weight were you when this occurred?
Collective Bias,
I think your description is quite correct, but let me translate the logic just a bit:
The swashplate is too weak for the rotor blades, because the rotor forces generated can create high enough stresses to bend the swash plate. As a result, the manufacturer reduced the strength of the hydraulic servos, so that the servos would back-drive before these high stresses could be generated. This safety feature prevents over stressing the helicopter, but also reduces the pilot\'s ability to control the aircraft during relatively mild maneuvers within the flight envelope.
Is this reasonably correct?
Errrr...Nick...guys....let me get this straight.....the 350 is designed and certified with this "capability" or as I see it....built in lack of control or questionable handling ability?
What you guys are describing are somewhat "normal" situations that easily result in the loss of control of the helicopter....frozen controls....feedback during cruise flight maneuvering?
Am I getting timid in my old age or is this a desirable situation? Has this a bearing on some recent crashes due to hydraulic failures....feedback forces that preclude safe landing of the helicopter?
For Nick...have you encountered...or know of other aircraft that have similar characteristics....or is this like unique to Euro-choppers? (of the French variety)?
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)?
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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
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
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'hydraulic jack stall' as everyone refers to it is something that can be avoided.
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.
I agree with what everyone else says,but here's some more info.
When this accurs, the aircraft will normaly roll to the left with slight back pitch. The correct action to take is to not fight the controlls and the aircraft will fly itself out of this situation.
All of the accidents I have read about have been low level with high speeds and aggresive control inputs.
We used to demonstrate (nearly said 'teach' then!) Jackstall to ab initio students in the gazelle during basic trng.
If memory serves me right:
Dive the helo to close to Vne (160 in Gaz piece),
pull like f**k on the cyclic (aft) and follow me through bloggs
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
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
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
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
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
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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.
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.
Iconoclast
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Jack stall?
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.
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.