EC225 crash near Bergen, Norway April 2016
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in any case as long as there is a rigid fit between rotor
mast and 2nd stage planet carrier it will take up radial load.
the bearing in the bottom of the conical housing will take up some load.
that was the principle of the load distribution that we just talked about!
even if you say there is enough radial play in the planetary bearing/gear to completely unload the 2nd carrier of any radial load from the rotor mast
it will be taking up the load as long as it is driven
That is not what I am saying.
Picture yourself, the AC with rotor mast and MRA, but without the MGB.
Is it a rigid construction that could carry the load of the AC? No.
That is what I am talking about. If the MGB is a rigid part of the MRA
and MGB fails shattering the housing, the Rotor will detach.
In order to do this, you need to make a gearbox with a stiff housing.
Possibly add 7-10 susp bars.
The stiff housing is increasing load on individual gears and reducing lifetime of them, but if it could allow a total break-up of MGB without sacrificing the rigidity of the rotor assembly, in my view that would be a life-saving solution because it would allow to autorotate without the MGB
In the same way as twin-engine, emergency lubrication etc are needed.
There is no saying against a multiple failing MGB cannot be a rigid part of the AC airworthy capability.
So I dont say that either susp bars, conical housing or gears broke first.
I am saying the should never break together.
mast and 2nd stage planet carrier it will take up radial load.
the bearing in the bottom of the conical housing will take up some load.
that was the principle of the load distribution that we just talked about!
even if you say there is enough radial play in the planetary bearing/gear to completely unload the 2nd carrier of any radial load from the rotor mast
it will be taking up the load as long as it is driven
Also the suspension bars locating the upper mast bearing are unlikely to have contributed in any way to the fatigue crack in the planet gear that propagated to failure. Three bars is determinate and an ideal way of locating something with predictable distribution of loads. On this aircraft they failed as a consequence of gearbox breakup, they were not a cause of it. Once the lower location is lost, no number of bars at the upper bearing will prevent the mast pivoting. The bars can take axial loads only (i.e. in their own axis), normally tensile.
Picture yourself, the AC with rotor mast and MRA, but without the MGB.
Is it a rigid construction that could carry the load of the AC? No.
That is what I am talking about. If the MGB is a rigid part of the MRA
and MGB fails shattering the housing, the Rotor will detach.
In order to do this, you need to make a gearbox with a stiff housing.
Possibly add 7-10 susp bars.
The stiff housing is increasing load on individual gears and reducing lifetime of them, but if it could allow a total break-up of MGB without sacrificing the rigidity of the rotor assembly, in my view that would be a life-saving solution because it would allow to autorotate without the MGB
In the same way as twin-engine, emergency lubrication etc are needed.
There is no saying against a multiple failing MGB cannot be a rigid part of the AC airworthy capability.
So I dont say that either susp bars, conical housing or gears broke first.
I am saying the should never break together.
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Btw,
in the Nasa report and Bell report that I linked to (earlier in this thread)
there was even a test showing the rigidity of the conical housing with respect to
the gear failure.
The next thing about only 3 susp bars would also possible be ground resonance dampening.
Any thoughts on that?
in the Nasa report and Bell report that I linked to (earlier in this thread)
there was even a test showing the rigidity of the conical housing with respect to
the gear failure.
The next thing about only 3 susp bars would also possible be ground resonance dampening.
Any thoughts on that?
A redesign as suggested by 'turboshafts' would not be inexpensive either structurally or financially.
AH would very likely rather accept reduced performance placards rather than spending a lot to get the same end performance.
Seen that the major operators for the type going forward are governments and the military, such a rerating would also be less disruptive.
AH would very likely rather accept reduced performance placards rather than spending a lot to get the same end performance.
Seen that the major operators for the type going forward are governments and the military, such a rerating would also be less disruptive.
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in any case as long as there is a rigid fit between rotor mast and 2nd stage planet carrier it will take up radial load.
the bearing in the bottom of the conical housing will take up some load.
that was the principle of the load distribution that we just talked about!
even if you say there is enough radial play in the planetary bearing/gear to completely unload the 2nd carrier of any radial load from the rotor mast
it will be taking up the load as long as it is driven
That is not what I am saying. Picture yourself, the AC with rotor mast and MRA, but without the MGB. Is it a rigid construction that could carry the load of the AC? No. That is what I am talking about. If the MGB is a rigid part of the MRA and MGB fails shattering the housing, the Rotor will detach. In order to do this, you need to make a gearbox with a stiff housing. Possibly add 7-10 susp bars. The stiff housing is increasing load on individual gears and reducing lifetime of them, but if it could allow a total break-up of MGB without sacrificing the rigidity of the rotor assembly, in my view that would be a life-saving solution because it would allow to autorotate without the MGB. In the same way as twin-engine, emergency lubrication etc are needed.
There is no saying against a multiple failing MGB cannot be a rigid part of the AC airworthy capability.
So I dont say that either susp bars, conical housing or gears broke first. I am saying the should never break together.
the bearing in the bottom of the conical housing will take up some load.
that was the principle of the load distribution that we just talked about!
even if you say there is enough radial play in the planetary bearing/gear to completely unload the 2nd carrier of any radial load from the rotor mast
it will be taking up the load as long as it is driven
That is not what I am saying. Picture yourself, the AC with rotor mast and MRA, but without the MGB. Is it a rigid construction that could carry the load of the AC? No. That is what I am talking about. If the MGB is a rigid part of the MRA and MGB fails shattering the housing, the Rotor will detach. In order to do this, you need to make a gearbox with a stiff housing. Possibly add 7-10 susp bars. The stiff housing is increasing load on individual gears and reducing lifetime of them, but if it could allow a total break-up of MGB without sacrificing the rigidity of the rotor assembly, in my view that would be a life-saving solution because it would allow to autorotate without the MGB. In the same way as twin-engine, emergency lubrication etc are needed.
There is no saying against a multiple failing MGB cannot be a rigid part of the AC airworthy capability.
So I dont say that either susp bars, conical housing or gears broke first. I am saying the should never break together.
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Turboshafts
A redesign as you suggest with a stiff casing could, to describe it in a term you will understand better than most, result in a 'schlimmbesserung'. Not only would the stiffness increase be counter to load sharing among planet gears but by containing fragments in a space designed only for gears' running clearances you could jam up the gearbox with equally catastrophic consequences.
You are getting there, recognising the need to secure the bottom of the mast after epicyclic failure, but there are more practical ways of achieving this than an array of up to 10 suspension bars.
I can think of 2 practical solutions, one of which is particularly elegant. It would not surprise me if AH are already working on one, or even both.
It is probably too late for the offshore market but it can be made safe again. Probably in a similar timescale to the bevel gear shaft redesign and replacement.
A redesign as you suggest with a stiff casing could, to describe it in a term you will understand better than most, result in a 'schlimmbesserung'. Not only would the stiffness increase be counter to load sharing among planet gears but by containing fragments in a space designed only for gears' running clearances you could jam up the gearbox with equally catastrophic consequences.
You are getting there, recognising the need to secure the bottom of the mast after epicyclic failure, but there are more practical ways of achieving this than an array of up to 10 suspension bars.
I can think of 2 practical solutions, one of which is particularly elegant. It would not surprise me if AH are already working on one, or even both.
It is probably too late for the offshore market but it can be made safe again. Probably in a similar timescale to the bevel gear shaft redesign and replacement.
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Load distribution between epicyclic planet gears has also been a chronic problem with large wind turbine transmissions. Here is an interesting tech paper from Timken that describes their flexible planet pin concept.
That IFB looks much superior to the AH planetary arrangement, on so many levels:
- Enabling use of taper roller bearings,
- Preloading the bearings,
- Reversing the angle of the bearings from dihedral to anhedral,
- Increasing material in the rim, giving a stronger ring in bending.
It is a great pity that technology was not around when the L2/225 epicyclic module was designed.
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Turboshafts
A redesign as you suggest with a stiff casing could, to describe it in a term you will understand better than most, result in a 'schlimmbesserung'. Not only would the stiffness increase be counter to load sharing among planet gears but by containing fragments in a space designed only for gears' running clearances you could jam up the gearbox with equally catastrophic consequences.
You are getting there, recognising the need to secure the bottom of the mast after epicyclic failure, but there are more practical ways of achieving this than an array of up to 10 suspension bars.
I can think of 2 practical solutions, one of which is particularly elegant. It would not surprise me if AH are already working on one, or even both.
It is probably too late for the offshore market but it can be made safe again. Probably in a similar timescale to the bevel gear shaft redesign and replacement.
A redesign as you suggest with a stiff casing could, to describe it in a term you will understand better than most, result in a 'schlimmbesserung'. Not only would the stiffness increase be counter to load sharing among planet gears but by containing fragments in a space designed only for gears' running clearances you could jam up the gearbox with equally catastrophic consequences.
You are getting there, recognising the need to secure the bottom of the mast after epicyclic failure, but there are more practical ways of achieving this than an array of up to 10 suspension bars.
I can think of 2 practical solutions, one of which is particularly elegant. It would not surprise me if AH are already working on one, or even both.
It is probably too late for the offshore market but it can be made safe again. Probably in a similar timescale to the bevel gear shaft redesign and replacement.
but the same problems is apparent in all automatic gearboxes.
They do not have the same amount of planetary gears,
but they do have "stiff" housings. The same accounts for automotive differentials.
I will go back in citate the Nasa conical housing test that I referred to.
Yes I agree there could probably be more solutions to this that is smarter than my suggestions, I was not trying to come up with a final solution, but rather to prove my point. And I realize as well, making the mast completely stiff to the AC would probably allow for much more frequent ground resonance problems as long as the AC has stiff landing gears and not a flexible undercarriage.
Riff_raff
If the planet carrier is unloaded, what is actually
contributing to the load-sharing? Only the input torque?
I donŽt agree to that the splines are not a rigid fit.
it is probably a very rigid fit. otherwise it may suffer from
severe failure due to the nature of the vibrations acting directly on the shaft.
loose fit, normally leads to small spot weldings on the shaft and finally overheating. in this case the splines are running completely in oil.
but to say that the splines are a loose fit that unloads the ring carrier I have problems to understand. How are they preloaded? How do you see that the lower bearing is tapered? In any case i would say that the bearing of this size would not be able to take any axial load at all. given the size of it
Statoil had reviewed it's own organisation and response procedures.
Statoil investigation
The pdf link at the bottom of the article is missing. Should be possible to find in on the web but in Norwegian anyway.
SLB
Statoil investigation
The pdf link at the bottom of the article is missing. Should be possible to find in on the web but in Norwegian anyway.
SLB
Last edited by jimf671; 24th Sep 2016 at 16:53.
Care to enlighten us to which you refer?
Seems you are always a bit light on facts,data, and evidence to back up your posts!
Seems you are always a bit light on facts,data, and evidence to back up your posts!
"The Turøy helicopter accident investigation report will be made available as soon as possible."
Watch this site:
http://www.statoil.com/en/NewsAndMed...3Sept2016.aspx
SLB
Watch this site:
http://www.statoil.com/en/NewsAndMed...3Sept2016.aspx
SLB
It's a Statoil report produced to make sure they don't come out with too much **** stuck to them. Nothing much to do with the technical issues relating to the failure. Ignore it; its for PR purposes only.
As to following SAI, I wouldn't rely on them for a good lead.
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Originally Posted by 212man
I assume you know of their role in the introduction of HUMS, HFDM
Si
I thought Bristow did that off their own back way back when and prior to anyone else?
