Qantas A380 uncontained #2 engine failure
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Bearfoil
Using your location methodology, we are in agreement as to the location of the rigid coupling for the IP shaft.
I take it that your belief of the location of the failed stub pipe is different than what Ferpe's Post#1647 suggests? Where would the resulting fire occur, in the area of the radial drive arm? I had been thinking more along the lines of what Ferpe suggested. The ATSB isn't real specific but says in part: It has been identified that the leakage of oil into the HP/IP bearing structure buffer space (and a subsequent oil fire within that area) was central to the engine failure and IP turbine disc liberation event.
Turbine D
Using your location methodology, we are in agreement as to the location of the rigid coupling for the IP shaft.
I take it that your belief of the location of the failed stub pipe is different than what Ferpe's Post#1647 suggests? Where would the resulting fire occur, in the area of the radial drive arm? I had been thinking more along the lines of what Ferpe suggested. The ATSB isn't real specific but says in part: It has been identified that the leakage of oil into the HP/IP bearing structure buffer space (and a subsequent oil fire within that area) was central to the engine failure and IP turbine disc liberation event.
Turbine D
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Turbine D
A quick read of the Patent referenced by Diversification explains that the scavenge pipes penetrate from the bearing collection area through the Gas Path, and even if cracked, or broken, there is a positive pressure (!) that prevents oil spill into the combusted gases. This may not have worked in this case? The scavenge pipes lead to an oil collection tray and thence to the Oil Tank., and a de-aerating chamber. I see the cross section of the delivery tube as approx. five eigths an inch, and at 70psi, that is a fair amount of oil.
What confuses. It is the Spline wear addressed by the AD that allows "aft migration" of the IP Disc, and I cannot visualize splines at the roller bearing case. The Drive Arm seems a solid "Coupling" without allowance for movement, so other than a plasticized wheel, what would allow the drift back into the Stator? I had thought it was a compromised ball bearing at #2 that let slip the wheel.
For the record, and to address a poster's PM:
I consider the RB 211 a work of art, no less, and if anyone thinks differently, you are not reading my posts. My disagreement is with the Stewards of this engine, who allow a reputation to suffer because of bumbling greed, and Pride.
bearfoil
A quick read of the Patent referenced by Diversification explains that the scavenge pipes penetrate from the bearing collection area through the Gas Path, and even if cracked, or broken, there is a positive pressure (!) that prevents oil spill into the combusted gases. This may not have worked in this case? The scavenge pipes lead to an oil collection tray and thence to the Oil Tank., and a de-aerating chamber. I see the cross section of the delivery tube as approx. five eigths an inch, and at 70psi, that is a fair amount of oil.
What confuses. It is the Spline wear addressed by the AD that allows "aft migration" of the IP Disc, and I cannot visualize splines at the roller bearing case. The Drive Arm seems a solid "Coupling" without allowance for movement, so other than a plasticized wheel, what would allow the drift back into the Stator? I had thought it was a compromised ball bearing at #2 that let slip the wheel.
For the record, and to address a poster's PM:
I consider the RB 211 a work of art, no less, and if anyone thinks differently, you are not reading my posts. My disagreement is with the Stewards of this engine, who allow a reputation to suffer because of bumbling greed, and Pride.
bearfoil
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Bearfoil
I looked at the patent, and read about the feature described to preclude a fire. I can only think it didn't work if this was the system used.
The problem though is in the turbine area as quoted in the corrective action section of the ATSB report: These investigations have led Rolls-Royce to draw two key conclusions. First, as previously announced, the issue is specific to the Trent 900. Second, the failure was confined to a specific component in the turbine area of the engine. This caused an oil fire, which led to the release of the intermediate pressure turbine disc.
On 18 November 2010, Rolls-Royce plc issued a further NMSB 72-AG590 Revision 2, detailing further Trent 900 engine inspections, including for defects in a number of turbine area oil and air feed pipes.
Perhaps the shaft didn't move aft at the rigid coupling spline, but failed at the IPT rotor area?
Turbine D
I looked at the patent, and read about the feature described to preclude a fire. I can only think it didn't work if this was the system used.
The problem though is in the turbine area as quoted in the corrective action section of the ATSB report: These investigations have led Rolls-Royce to draw two key conclusions. First, as previously announced, the issue is specific to the Trent 900. Second, the failure was confined to a specific component in the turbine area of the engine. This caused an oil fire, which led to the release of the intermediate pressure turbine disc.
On 18 November 2010, Rolls-Royce plc issued a further NMSB 72-AG590 Revision 2, detailing further Trent 900 engine inspections, including for defects in a number of turbine area oil and air feed pipes.
Perhaps the shaft didn't move aft at the rigid coupling spline, but failed at the IPT rotor area?
Turbine D
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Notes on Couplings and Bearings - 1
I've been away, except for a little comic relief over an AD, but not idle. Since Bearfoil appears to be digging up reference material day and night into the wee hours, I'll post an outline of what might be useful things to look into. Turning serious for a moment:
1. I've been led astray by the term "rigid coupling", which may have first cropped up in the official communiques. At least one of these so-called splined couplings-- it would have to be the one joining the long innermost shaft from the entry fan disc (LPC) to its counterpart from its driver, the LPT--is not rigid. This in American terminology would be called a "geared coupling", and is a flexible coupling which will accommodate both axial misalignment of the 2 joined shafts, and axial offsets. The term is more often seen in a self-contained separate coupling, but the function here is the same.
The clue is in the term "crown" applied to the spline tooth. It isn't a crown of the top of the tooth in cross-section, but a crown along the length of the so-called spline. It is better to think of this spline as a gear tooth lying on something akin to a spherical surface. It's like a ball joint in action, except more like a section out of the middle of an American football --and it's geared.
2. Being a set (really two sets in this coupling) of gears, continuous lubrication is essential into these "splines".
3. The "gears" rotate back and forward through mesh as the shaft turns. The teeth can have other geometry overlaid, such as being made slightly helical (I think, and don't yet know about substantially helical, although I would think yes to this also).
4. It's possible the other splined couplings are more rigid.
5. Ball and roller bearings need continuous lubrication. They should never be turned when dry, as this will lead to rapid, although not necessarily instantaneous, failure. (Explanation later)
6. Ball thrust bearings may be available with opposing sides open on the inner and outer races, such that thrust is resisted in only one direction. This would be the major thrust. Minor transient thrust might be resisted by a small plain flat bearing elsewhere. The arrangement might faciliate assembling/disassembling the engine.
7. Inner races need to be clamped to their shafts, otherwise the shaft will turn inside the inner race. This is because smooth bearings have less friction than roller or ball bearings. The effect is less seen on outer races. This suggests hand holes; it maybe possible to preinstall some races with a press fit. Press fits can alter bearing clearances-- well, they will, so this must be designed for.
8. Tapered roller bearings also exist, for thrust. Spherical outer race outer surfaces exist (don't see any application of these here yet).
Footnote: I used to specify geared couplings. Odd it took me so long to realize that that's what was on the innermost, longest shaft. Any coupling covered by the AD mentioning a "crowned spline" is such a coupling.
Have at it... I'm going to key in "geared coupling" to the search engine just for fun, now. My remarks are mostly from my own experience, although I admit that until seeing pictures of these coupling teeth ground to powder
, I had little interest in the tooth forms of geared couplings.
OE
1. I've been led astray by the term "rigid coupling", which may have first cropped up in the official communiques. At least one of these so-called splined couplings-- it would have to be the one joining the long innermost shaft from the entry fan disc (LPC) to its counterpart from its driver, the LPT--is not rigid. This in American terminology would be called a "geared coupling", and is a flexible coupling which will accommodate both axial misalignment of the 2 joined shafts, and axial offsets. The term is more often seen in a self-contained separate coupling, but the function here is the same.
The clue is in the term "crown" applied to the spline tooth. It isn't a crown of the top of the tooth in cross-section, but a crown along the length of the so-called spline. It is better to think of this spline as a gear tooth lying on something akin to a spherical surface. It's like a ball joint in action, except more like a section out of the middle of an American football --and it's geared.
2. Being a set (really two sets in this coupling) of gears, continuous lubrication is essential into these "splines".
3. The "gears" rotate back and forward through mesh as the shaft turns. The teeth can have other geometry overlaid, such as being made slightly helical (I think, and don't yet know about substantially helical, although I would think yes to this also).
4. It's possible the other splined couplings are more rigid.
5. Ball and roller bearings need continuous lubrication. They should never be turned when dry, as this will lead to rapid, although not necessarily instantaneous, failure. (Explanation later)
6. Ball thrust bearings may be available with opposing sides open on the inner and outer races, such that thrust is resisted in only one direction. This would be the major thrust. Minor transient thrust might be resisted by a small plain flat bearing elsewhere. The arrangement might faciliate assembling/disassembling the engine.
7. Inner races need to be clamped to their shafts, otherwise the shaft will turn inside the inner race. This is because smooth bearings have less friction than roller or ball bearings. The effect is less seen on outer races. This suggests hand holes; it maybe possible to preinstall some races with a press fit. Press fits can alter bearing clearances-- well, they will, so this must be designed for.
8. Tapered roller bearings also exist, for thrust. Spherical outer race outer surfaces exist (don't see any application of these here yet).
Footnote: I used to specify geared couplings. Odd it took me so long to realize that that's what was on the innermost, longest shaft. Any coupling covered by the AD mentioning a "crowned spline" is such a coupling.
Have at it... I'm going to key in "geared coupling" to the search engine just for fun, now. My remarks are mostly from my own experience, although I admit that until seeing pictures of these coupling teeth ground to powder
, I had little interest in the tooth forms of geared couplings.OE
Last edited by Old Engineer; 7th Dec 2010 at 05:42. Reason: Fix incomplete sentence in #1.
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In case this helps.
The Rolls Royce publication of January 2000 – the Modern Gas Turbine, how it works and how it’s built – is a simplified description of the Trent 800 modular construction with line drawings of the various modules.
http://aircraftengineering.webs.com/gasturbines%5B1%5D.pdf
Module 01, LP compressor, “At the rear end of the shaft is a helical spline which transmits the drive from the LP turbine shaft.”
Module 02, IP compressor, “A stub-shaft at the front of the drum locates in the IP roller bearing, and a curvic coupling extends from the stage 6 disc to connect to the IP shaft.”
Module 05, IP turbine, “Bolted to the turbine disc is the turbine shaft which has helical splines at its forward end. These connect to the IP compressor stub-shaft via the thrust bearings in the intermediate case.
Module 07, LP compressor (fan) case, “At their inner ends, the fan OGVs are secured to the torsion ring which locates the IP compressor module,whilst the outer ends are bolted to the front mounting ring.This assembly is welded to the titanium rear casing and bolted to the front casing.”
Module 08, LP turbine, “The turbine shaft is bolted to the rotor via a curvic coupling and connects to the LP compressor shaft through helical splines at its forward end. The shaft extends rearwards into the roller bearing.”
What is still unclear is the method by which the spline joint is kept tight (my money still on torque). I have to say that I do not agree with Old Engineer about his geared coupling description.
The Rolls Royce publication of January 2000 – the Modern Gas Turbine, how it works and how it’s built – is a simplified description of the Trent 800 modular construction with line drawings of the various modules.
http://aircraftengineering.webs.com/gasturbines%5B1%5D.pdf
Module 01, LP compressor, “At the rear end of the shaft is a helical spline which transmits the drive from the LP turbine shaft.”
Module 02, IP compressor, “A stub-shaft at the front of the drum locates in the IP roller bearing, and a curvic coupling extends from the stage 6 disc to connect to the IP shaft.”
Module 05, IP turbine, “Bolted to the turbine disc is the turbine shaft which has helical splines at its forward end. These connect to the IP compressor stub-shaft via the thrust bearings in the intermediate case.
Module 07, LP compressor (fan) case, “At their inner ends, the fan OGVs are secured to the torsion ring which locates the IP compressor module,whilst the outer ends are bolted to the front mounting ring.This assembly is welded to the titanium rear casing and bolted to the front casing.”
Module 08, LP turbine, “The turbine shaft is bolted to the rotor via a curvic coupling and connects to the LP compressor shaft through helical splines at its forward end. The shaft extends rearwards into the roller bearing.”
What is still unclear is the method by which the spline joint is kept tight (my money still on torque). I have to say that I do not agree with Old Engineer about his geared coupling description.
Last edited by firstfloor; 7th Dec 2010 at 10:10.
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Regarding my earlier post why the engine management systems can not detect irregularities:
Translated: Short term an updated software will ensure that an overheated engine is turned off faster (read earlier).
Automatic or not?
Read in German Manager Magazin online just now.
Kurzfristig soll eine neue Software dafür sorgen, dass die Triebwerke bei Überhitzung schneller abgestellt werden.
Automatic or not?
Read in German Manager Magazin online just now.
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Turbine D
Good morning. From the outset, I took the "aft migration" of the IPT to imply involvement of the Thrust Bearings. There are two HP/IP cavities, fore and aft. I can't explain why I have been focused on the one forward all this time. I took 6,7 to be radial take up only, so axial slop seemed unlikely to be located here. If its dedicated oiling supply tube failed, either location would be prime candidate for disaster?
The more I "get" of the mechanism of this powerplant, the more impressed I become. Borders on awe, really, and the more I also become convinced that poor stewardship of this fine machine has caused damage to its market. That is inexcusable. The fault is most certainly not with her engineers, but her Step-parents, focused on profit, secrecy, and deception.
bearfoil
Good morning. From the outset, I took the "aft migration" of the IPT to imply involvement of the Thrust Bearings. There are two HP/IP cavities, fore and aft. I can't explain why I have been focused on the one forward all this time. I took 6,7 to be radial take up only, so axial slop seemed unlikely to be located here. If its dedicated oiling supply tube failed, either location would be prime candidate for disaster?
The more I "get" of the mechanism of this powerplant, the more impressed I become. Borders on awe, really, and the more I also become convinced that poor stewardship of this fine machine has caused damage to its market. That is inexcusable. The fault is most certainly not with her engineers, but her Step-parents, focused on profit, secrecy, and deception.
bearfoil
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Bearfoil
I agree completely with you post this morning, I am impressed as well with this powerplant. As was suggested in a poster's PM I received last night, I did indeed "Google" to search for a patent I recalled, dealing with the advantages of helical spline shaft couplings and the advantages offered over conventional splines. You can see this patent by going to: Parabolically helical spline shaft coupling - US 5533825 - IP.com
In the background of the invention, it mentions an older reference patent as to how the coupling to a disk is made. This is actually a Rolls Royce patent (US patent #4,292,001) and you can view it by Googling the #. I was curious to see if the IPT disc could be liberated from the shaft at this connection point. Take a look and see what you think.
Regards,
Turbine D
I agree completely with you post this morning, I am impressed as well with this powerplant. As was suggested in a poster's PM I received last night, I did indeed "Google" to search for a patent I recalled, dealing with the advantages of helical spline shaft couplings and the advantages offered over conventional splines. You can see this patent by going to: Parabolically helical spline shaft coupling - US 5533825 - IP.com
In the background of the invention, it mentions an older reference patent as to how the coupling to a disk is made. This is actually a Rolls Royce patent (US patent #4,292,001) and you can view it by Googling the #. I was curious to see if the IPT disc could be liberated from the shaft at this connection point. Take a look and see what you think.
Regards,
Turbine D
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Ball thrust bearings may be available with opposing sides open on the inner and outer races, such that thrust is resisted in only one direction. This would be the major thrust.
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@HarryMann:
Thanks-- I could not remember the term used.
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@Bearfoil:
Bear, roller bearings make line contact, while ball bearings make point contact, so the rollers will take a bigger load (in theory). The contact pressure flattens both the line and the point to a line of some width and a point of some diameter. This effect can be readily calculated, and the repetitive flattening eventually fatigues the surface, so the life is limited even though long.
Oil can actually bear this pressure, to a point which depends on its viscosity (which in turn depends on temperature). The small clearances act as a pump to retain the even greater pressures at the exact otherwise point of contact. The oil pressure (not the supply pressure, but the much greater pressure due to the rolling action) can widen the effective width of line contact, or area of point contact. The oil film must not become thinner than required to keep the asperities of the two metal surfaces apart, hence the need for a very fine finish.
Nice calculation goes pear-shaped in two or three areas: a) the oil film is obvious; b) fatigue life varies about four to one among the same bearing, recorded over several engines-- and in service you can't get past the point of shortest life, so you get no in-service data in quantity; and c) these bearings are really susceptable to mishandling in the field during disassembly and re-assembly, compared to say a smooth-bore bearing. Mishandling ruins the fine finish or brinnells the races, results in too much or too little clamping force; wrong or conterfeit oil...
The use of ball bearings as thrust bearings has puzzled me, given the front fan thrust. My working hypothesis at the moment is that there is room at the aft end of the LP shaft for a more adequate thrust bearing to hold the tension of the shaft. This would be a bearing more like a tapered-roller bearing-- this is usual for high thrust loads. Then this tension would be passed through the helical splines of the separable coupling by the torque of the shaft. The helical angle would be chosen to create the required tension, with some margin. Helical gears (or splines with gear tooth profiles, as one prefers) always create an end thrust along their shaft, you see.
To borrow a phrase from you, I don't actually know yet if this is so. I just think it is worth exploring. I admit to being a little concerned about a tapered-roller bearing turning at 11000 rpm. But there is a lot of radial room back there, together with a couple of lines on the drawing that could be interpreted as one of several (3?) very substantial radial fins supporting this area. There is a largish nook there where a curved-flaring cone appear to divert the hot blast into mixing with the cooler, slower bypass air. I have more thoughts, but I leave it there.
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@ Turbine D:
It's commendable that you took the time and effort to look all this up. I haven't even read your reference yet, but I will.
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@ firstfloor:
I was rushing the post out the door and have no objection to standing corrected. "Geared coupling" is a term I was used to, and that would lead to a lot of pictures and reference material making the principle easy to follow by others. It may be an American term; not sure about "curvic" coupling usage here. But I could agree that curvic coupling is what we are looking for. I don't understand curvic coupling with helical splines on the end; in my view this would be combined into the shape of one set of teeth, but I just don't know and could well be wrong.
I too am working on the assumption that torque is holding the joint together. It reduces the part count. I'm also getting a glimmer that the axial (lengthwise of shaft) force that is generated is in part applied to hold in location the IPT that migrated aft in the event (have I got that part right?). That would also simplify assembly and disassembly, and again reduce part count. I just can't as yet see the boss or whatever (on the isometric engine cutaway) that would do this.
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@ mike-wsm:
Your comment has made me re-think. If only angular shaft displacement is allowed for, the joint collar need not depart from the engine axis (locally, as I assume that the engine axis bends under heavy load). In "geared couplings", one can mate a rigid half with a flexible half, requiring the shaft centerlines to intersect-- this intersection could be maintained by flexing of the long, slender shafts, perhaps. Perhaps this particular "curvic coupling" is built in that manner. Perhaps the reaction boss for the IPT can then be on the collar of the curvic coupling.
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I'm wondering if there is a plain-surfaced ball thrust bearing between the ends of the two shaft sections. This incurs more lubrication needs; but the compression force (generated by the screwing-together action of the helical splines) would only be that amount needed for any non-linear relation between torque input at the front fan, and the thrust output there. That would be plus a margin for uncertainty and for various excursions from normal operations, and the IPT load, but could be manageable. It's worth being a working hypothesis.
I'm seeing a lot of potential problems here that don't involve oil fire, given the pictures of damaged splines in RB211-form engines I've seen. I do know something about forces on, and wear and breakage of, gear-tooth section [read spline] elements, if nothing else about this situation.
Footnote: "Rigid coupling", in the King's English, appears to mean a coupling that is rigid in transmitting torque. This is in contrast to say an automotive clutch coupling, which is fitted with torque springs to cushion the application of torque. Anyway, in the official communiques, this regrettably (IMO) seems to have implied this coupling is so simple a device that the required safety margin in the face of spline wear and chipping could easily be determined. Maybe it's just my inference.
OE
Known as angular-contact ball bearings
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@Bearfoil:
Lost train, still uncertain how "Splines" would obtain at the Disc? Also, I am thinking the Ball Bearings were chosen for this location due to the need for far greater contact area than Roller? Most of the mechanicals bear on this location?
Oil can actually bear this pressure, to a point which depends on its viscosity (which in turn depends on temperature). The small clearances act as a pump to retain the even greater pressures at the exact otherwise point of contact. The oil pressure (not the supply pressure, but the much greater pressure due to the rolling action) can widen the effective width of line contact, or area of point contact. The oil film must not become thinner than required to keep the asperities of the two metal surfaces apart, hence the need for a very fine finish.
Nice calculation goes pear-shaped in two or three areas: a) the oil film is obvious; b) fatigue life varies about four to one among the same bearing, recorded over several engines-- and in service you can't get past the point of shortest life, so you get no in-service data in quantity; and c) these bearings are really susceptable to mishandling in the field during disassembly and re-assembly, compared to say a smooth-bore bearing. Mishandling ruins the fine finish or brinnells the races, results in too much or too little clamping force; wrong or conterfeit oil...
The use of ball bearings as thrust bearings has puzzled me, given the front fan thrust. My working hypothesis at the moment is that there is room at the aft end of the LP shaft for a more adequate thrust bearing to hold the tension of the shaft. This would be a bearing more like a tapered-roller bearing-- this is usual for high thrust loads. Then this tension would be passed through the helical splines of the separable coupling by the torque of the shaft. The helical angle would be chosen to create the required tension, with some margin. Helical gears (or splines with gear tooth profiles, as one prefers) always create an end thrust along their shaft, you see.
To borrow a phrase from you, I don't actually know yet if this is so. I just think it is worth exploring. I admit to being a little concerned about a tapered-roller bearing turning at 11000 rpm. But there is a lot of radial room back there, together with a couple of lines on the drawing that could be interpreted as one of several (3?) very substantial radial fins supporting this area. There is a largish nook there where a curved-flaring cone appear to divert the hot blast into mixing with the cooler, slower bypass air. I have more thoughts, but I leave it there.
---------
@ Turbine D:
Bearfoil
I agree completely with you post this morning, I am impressed as well with this powerplant. As was suggested in a poster's PM I received last night, I did indeed "Google" to search for a patent I recalled, dealing with the advantages of helical spline shaft couplings and the advantages offered over conventional splines. You can see this patent...
I agree completely with you post this morning, I am impressed as well with this powerplant. As was suggested in a poster's PM I received last night, I did indeed "Google" to search for a patent I recalled, dealing with the advantages of helical spline shaft couplings and the advantages offered over conventional splines. You can see this patent...
---------
@ firstfloor:
What is still unclear is the method by which the spline joint is kept tight (my money still on torque). I have to say that I do not agree with Old Engineer about his geared coupling description.
I too am working on the assumption that torque is holding the joint together. It reduces the part count. I'm also getting a glimmer that the axial (lengthwise of shaft) force that is generated is in part applied to hold in location the IPT that migrated aft in the event (have I got that part right?). That would also simplify assembly and disassembly, and again reduce part count. I just can't as yet see the boss or whatever (on the isometric engine cutaway) that would do this.
---------
@ mike-wsm:
Old Engineer - Oh wow, a waggly joint carrying how much torque at how many rpm?
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I'm wondering if there is a plain-surfaced ball thrust bearing between the ends of the two shaft sections. This incurs more lubrication needs; but the compression force (generated by the screwing-together action of the helical splines) would only be that amount needed for any non-linear relation between torque input at the front fan, and the thrust output there. That would be plus a margin for uncertainty and for various excursions from normal operations, and the IPT load, but could be manageable. It's worth being a working hypothesis.
I'm seeing a lot of potential problems here that don't involve oil fire, given the pictures of damaged splines in RB211-form engines I've seen. I do know something about forces on, and wear and breakage of, gear-tooth section [read spline] elements, if nothing else about this situation.
Footnote: "Rigid coupling", in the King's English, appears to mean a coupling that is rigid in transmitting torque. This is in contrast to say an automotive clutch coupling, which is fitted with torque springs to cushion the application of torque. Anyway, in the official communiques, this regrettably (IMO) seems to have implied this coupling is so simple a device that the required safety margin in the face of spline wear and chipping could easily be determined. Maybe it's just my inference.
OE
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balls vs. rollers
Tapered roller bearings have too much sliding and skidding going on, I believe it is impossible to eliminate 100 percent. It is hard to trust them at high rpm for long period. They also have roller edge stresses. Balls run so nice and smooth. Cylindrical rollers run nice too. I don't understand why they use so many rollers in the engines, when the bearing that carries all the engine trust is a ball bearing. I would think the thrust bearing would need replacement before the radial load bearings, which will have a far greater life both from reduced load. Balls have a little sliding going on too under high loads. My gut feeling is the lube is mostly working on this area, adjacent to the high stress contact area. Contact area is left with microscopically thin lubrication thickness.
What amazes me the most is how small the main thrust bearings are, how few balls it takes to transmit 80,000 horsepower. I once had a 5-axis 15 horsepower Matsuura machining center spindle apart. That seemed to use bearings about 1/3 the diameter of the Trent 900, and about the same quantity. This machine could make a barrel of Hastelloy or Waspaloy chips in a few hours, so enough power to cut anything fast. (Machine not for high speed high horsepower easy cutting aluminum however).
What amazes me the most is how small the main thrust bearings are, how few balls it takes to transmit 80,000 horsepower. I once had a 5-axis 15 horsepower Matsuura machining center spindle apart. That seemed to use bearings about 1/3 the diameter of the Trent 900, and about the same quantity. This machine could make a barrel of Hastelloy or Waspaloy chips in a few hours, so enough power to cut anything fast. (Machine not for high speed high horsepower easy cutting aluminum however).
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Aerodynamic transfer of thrust
@Blade Master
as stated before in this thread 95% or more of the thurst is transfered via aerodynamic pressure differences between rotor discs and the casing walls in the different cavities in the engine, the thrust ball bearing is thus just balancing out the residue thrust that remains. Clever method to keep the ball bearings small and to make them last longer.
as stated before in this thread 95% or more of the thurst is transfered via aerodynamic pressure differences between rotor discs and the casing walls in the different cavities in the engine, the thrust ball bearing is thus just balancing out the residue thrust that remains. Clever method to keep the ball bearings small and to make them last longer.
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Ferpe - All very true, in fact it's very important to keep the ball bearings properly loaded at all times.
I seem to remember RB 211-22B problems with lightly loaded bearings at some phases of flight.
But why are we discussing bearings? Has bearing failure been identified as a possible cause of the incident?
I seem to remember RB 211-22B problems with lightly loaded bearings at some phases of flight.
But why are we discussing bearings? Has bearing failure been identified as a possible cause of the incident?
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According to ABC News this morning regarding Qantas RR court hearing....
I wonder if we will look back on this and view Qantas response as hysterical overreaction. The press always overreact and are therefore excused criticism.
RR meanwhile maintaining a cool aloofness just as they should.
And no, the initial failure has nothing to do with bearings, splines, etc. It was a fatigue fractured oil pipe of faulty manufacture according to latest information. And so far only one reported example in the whole Trent 900 fleet as far as I know.
The airline's fleet has been plagued with problems over the past few months, with engine failures and mass groundings.
RR meanwhile maintaining a cool aloofness just as they should.
And no, the initial failure has nothing to do with bearings, splines, etc. It was a fatigue fractured oil pipe of faulty manufacture according to latest information. And so far only one reported example in the whole Trent 900 fleet as far as I know.
Last edited by firstfloor; 8th Dec 2010 at 09:01.
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Originally Posted by Turbine D
You can see this patent by going to: Parabolically helical spline shaft coupling - US 5533825 - IP.com
Thanks, TD, that makes sense.The patent describes a set of splines that are longditudinal and join two shafts, inner and outer.
But when torque is transmitted the shafts twist and the load becomes unevenly distributed along the length of the splines.
The patent says the way to compensate for this is to machine the splines so that they will match when torque is applied.
I guess assembling the pre-reverse-distorted splines to each other requires a certain amount of torque and persuasion.
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Fascinating interview on the Royal Aeronautical Society's site with one of the QF32 flight crew - including in-flight pics of the cockpit displays...
EXCLUSIVE - Qantas QF32 flight from the cockpit | Aerospace Insight | The Royal Aeronautical Society
Great advert for Qantas crew training and CRM...
EXCLUSIVE - Qantas QF32 flight from the cockpit | Aerospace Insight | The Royal Aeronautical Society
Great advert for Qantas crew training and CRM...
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The AD's are specific in identifying Spline wear as the salient concern. It is logical to conclude from this (I did not find in the AD) that slop in the splines can result in, and therefore cause additional thrust loading on the bearing. Rather than attenuating low levels of thrust (from Shaft), there may be enhanced levels; along with this, perhaps more rapid cycling (therefore damage to spline faces) of Thrust orientation (both directions?). More slop, more energy when each opposite face arrests the other component.
If Oil loss is patent, and addressed (AD?), the possibilities were known. A finely machined set of effacing surfaces, once worn, will wear faster, then faster. Failure point accelerates as wear continues.
I think it is illogical to point at an oiler, identify its failures, but then leave unaddressed the target (and the reasons) for the lubrication. The AD id's an aftward drift of the IP Shaft, this can be bearing wear, or spline wear, or both. Other? The isometric shows that the IP Shaft is made up of two separate Shafts.
Oil Fire. Fine. And???
From the patent, I think one of the reasonings behind its elegance is the accomplishment of constant contact spline to spline, as the torque is transferred, rather than a clash, thus attenuating wear, extending its service life. IMO
bear
If Oil loss is patent, and addressed (AD?), the possibilities were known. A finely machined set of effacing surfaces, once worn, will wear faster, then faster. Failure point accelerates as wear continues.
I think it is illogical to point at an oiler, identify its failures, but then leave unaddressed the target (and the reasons) for the lubrication. The AD id's an aftward drift of the IP Shaft, this can be bearing wear, or spline wear, or both. Other? The isometric shows that the IP Shaft is made up of two separate Shafts.
Oil Fire. Fine. And???
From the patent, I think one of the reasonings behind its elegance is the accomplishment of constant contact spline to spline, as the torque is transferred, rather than a clash, thus attenuating wear, extending its service life. IMO
bear
Last edited by bearfoil; 8th Dec 2010 at 12:34.