Qantas A380 uncontained #2 engine failure
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From another chemists point of view I can't see how the Gibbs free energy rule will work in this situation.
As the temperature rises, as will the pressure, pV=nRT and what not.
As the temperature rises, as will the pressure, pV=nRT and what not.
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bear:
I think what you mean is that the fan doesn't unwind as fast as the core.
In this condition, yes, there is a mismatch between what the fan is delivering vs.
what the core (IPC) swallows. Not so much a problem, I think, for the three-spool machine, since the extra air can easily "dump" out the fan exhaust duct.
It's definitely more an issue when the IPC / LPC / booster (whatever it's called) is hard-coupled to the fan rotor per P&W or GE / CFMI designs. In their case, bleeds must be provided to get rid of the extra air. They pop open during decels and low power ops to vent inter-compressor air into the fan duct. GE & P&W differ in location, operating logic etc. but the principle is similar.
My guess is a too rapid decel would subject the Fan to Windmill, and an uncomfortable disparity in Fan LP might ensue?
In this condition, yes, there is a mismatch between what the fan is delivering vs.
what the core (IPC) swallows. Not so much a problem, I think, for the three-spool machine, since the extra air can easily "dump" out the fan exhaust duct.
It's definitely more an issue when the IPC / LPC / booster (whatever it's called) is hard-coupled to the fan rotor per P&W or GE / CFMI designs. In their case, bleeds must be provided to get rid of the extra air. They pop open during decels and low power ops to vent inter-compressor air into the fan duct. GE & P&W differ in location, operating logic etc. but the principle is similar.
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Brilliant!
Telltale lights for when something goes wrong, hardwired switches to mitigate the situation, and a gaggle of steam gauges with which a trained, experienced human being can interpret the outcome(s).
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A grizzled old FE once told me that Pilots and FEs were taught to think different.
"A Pilot would look through the telescope, an Eng would look at it!..........then make sure the Pilot is looking through the right end!"
"A Pilot would look through the telescope, an Eng would look at it!..........then make sure the Pilot is looking through the right end!"
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Thanks for that pix of the panel. I remember it, although now I couldn't say if that's the one in the super Connie. The engines had two plugs in each cylinder, and on that panel you could scope the voltage trace to each one in turn, to see if it was firing. I made several trips across the big pond in those, on the Africa run. Brings back memories.
MATS (and its sucessors) never lost a plane of their own until the Secy Brown incident-- altho I recall two incidents where the mail had to be thrown overboard to lighten ship.
To get back on topic, I've been reflecting that computers have never been very good at pattern recognition; that is a human capability that is unusually sharp, little understood, and only crudely reproducible by programmers. Of course steam gages excelled at showing patterns. Something to be said for FE's and that approach in AC on the cutting edge.
OE
MATS (and its sucessors) never lost a plane of their own until the Secy Brown incident-- altho I recall two incidents where the mail had to be thrown overboard to lighten ship.
To get back on topic, I've been reflecting that computers have never been very good at pattern recognition; that is a human capability that is unusually sharp, little understood, and only crudely reproducible by programmers. Of course steam gages excelled at showing patterns. Something to be said for FE's and that approach in AC on the cutting edge.
OE
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First in the interest of full disclosure, I'm am not a pilot, but an EE (not even an ME), but I've been thinking about it and would like to put in my 2¢ worth (and that may be all it's worth) on the thrust bearing loads.
For the purposes of explaining my thinking and keeping this short, I'm not going to include the intermediate stages (pressure compressor, turbine, etc.) as this system doesn’t directly affect the net bearing thrust loads (for the same reasons below). I’m also going to assume that fans/turbines/compressors are 100% efficient.
Start first by thinking of the engine as a simple rocket engine. Thrust is produced by the expulsion of gases rearward out the nozzle causing a counter force (good old Newton) to be distributed onto the inside surfaces of the engine combustion chamber and any nozzles and other surfaces there. The same thing happens on a turbine engine with the counter force from the expanding burnt fuel gases pushing against the combustor/hot section areas. Fortunately most of that available surface area is part of the engine housing, etc. which we hope is firmly attached to the pylon. Let's say that thrust is 70K pounds and let's say that there is ~2K sq. in. of surface area (just a guess from the drawing). This gives a pressure of about 35 psi of pressure on the engine housing which seems quite reasonable.
If the Trent were a simple turbojet, this would be all the forward push you would get. But in the turbofan, a portion of this thrust is intercepted by the LPT and turned into rotational energy so only about 10-20% of the direct thrust exists out the back. The portion of the energy that is intercepted produces a rearward force on the LPT and the LP shaft (the thrust from the force pushing against the engine housing wants to blow the LPT out the back). The LP shaft rotational energy drives the fan producing rearward airflow and aft thrust but also producing a forward counter force (the fan wants to pull forward) that cancels the net fore/aft thrust on the thrust bearing. So, in effect, all of the fans/turbines/shafts act as a coupling system (much like a transformer matches voltages/currents/impedances in an electrical system) that allows the rearward thrust to push forward against the engine casing and not the thrust bearing in order to move the a/c forward.
Obviously a thrust bearing is still needed because nothing is 100% efficient so the forces don’t exactly cancel. I’m sure there are additional forces like thrust differentials during spool up/down due to the rotational inertia of the rotating components, G loads not perpendicular to the axis of rotation, etc. But the net fore/aft bearing forces are substantially less than full thrust.
I think this is a reasonable assessment, but please let me know if it is not.
For the purposes of explaining my thinking and keeping this short, I'm not going to include the intermediate stages (pressure compressor, turbine, etc.) as this system doesn’t directly affect the net bearing thrust loads (for the same reasons below). I’m also going to assume that fans/turbines/compressors are 100% efficient.
Start first by thinking of the engine as a simple rocket engine. Thrust is produced by the expulsion of gases rearward out the nozzle causing a counter force (good old Newton) to be distributed onto the inside surfaces of the engine combustion chamber and any nozzles and other surfaces there. The same thing happens on a turbine engine with the counter force from the expanding burnt fuel gases pushing against the combustor/hot section areas. Fortunately most of that available surface area is part of the engine housing, etc. which we hope is firmly attached to the pylon. Let's say that thrust is 70K pounds and let's say that there is ~2K sq. in. of surface area (just a guess from the drawing). This gives a pressure of about 35 psi of pressure on the engine housing which seems quite reasonable.
If the Trent were a simple turbojet, this would be all the forward push you would get. But in the turbofan, a portion of this thrust is intercepted by the LPT and turned into rotational energy so only about 10-20% of the direct thrust exists out the back. The portion of the energy that is intercepted produces a rearward force on the LPT and the LP shaft (the thrust from the force pushing against the engine housing wants to blow the LPT out the back). The LP shaft rotational energy drives the fan producing rearward airflow and aft thrust but also producing a forward counter force (the fan wants to pull forward) that cancels the net fore/aft thrust on the thrust bearing. So, in effect, all of the fans/turbines/shafts act as a coupling system (much like a transformer matches voltages/currents/impedances in an electrical system) that allows the rearward thrust to push forward against the engine casing and not the thrust bearing in order to move the a/c forward.
Obviously a thrust bearing is still needed because nothing is 100% efficient so the forces don’t exactly cancel. I’m sure there are additional forces like thrust differentials during spool up/down due to the rotational inertia of the rotating components, G loads not perpendicular to the axis of rotation, etc. But the net fore/aft bearing forces are substantially less than full thrust.
I think this is a reasonable assessment, but please let me know if it is not.
Of course steam gages excelled at showing patterns.
For the same reason I don't wear a digital watch - I don't "read" my watch, I look at the "picture"
I blame Bill Gates.
and yes, bring back the Flt. Eng. maybe call him what the RAF created years ago, Flight Electronics Officer - whatever the name, someone who knows what the f**k is going wrong, leaving others to continue " flying the aeroplane " always the priority.
but then I started on a 5 man flight deck. ( and I mean 'man' )
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Back on topic ever so slightly...
Should be up on here possibly early hours of tomorrow morning at the following link
ATSB site
Media Briefing
On Friday 3 December 2010, the ATSB will hold a media briefing to accompany the release of its preliminary factual investigation report into the 4 November 2010 engine failure onboard Qantas Flight QF32 over Batam Island, Indonesia.
On Friday 3 December 2010, the ATSB will hold a media briefing to accompany the release of its preliminary factual investigation report into the 4 November 2010 engine failure onboard Qantas Flight QF32 over Batam Island, Indonesia.
ATSB site
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> If so, with his statement that apparently 3 more experienced pilots in the CP just have nothing to offer
There's a polish proverb which goes more or less along the lines of 'where there are 6 cooks there is nothing to eat'.
Having additional persons in the cockpit at a time like this - no matter what their experience - without clearly defined roles and knowing 'who does what' could equally well contribute to a bad outcome.
GS
There's a polish proverb which goes more or less along the lines of 'where there are 6 cooks there is nothing to eat'.
Having additional persons in the cockpit at a time like this - no matter what their experience - without clearly defined roles and knowing 'who does what' could equally well contribute to a bad outcome.
GS
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Just going back to the thrust loads on bearings for a second.
Some old turbojet engines had a 'balance disc' with high pressure air on one side&
ambient air on the other. The purpose was to reduce thrust on the shaft & to transfer
it to piston areas.
Maybe the geometry of modern engines obviates the need for balance discs?
If RR were to release details of all the forward & rearward gas loads, it would make it
all easier to understand, but I doubt if they will do that
Some old turbojet engines had a 'balance disc' with high pressure air on one side&
ambient air on the other. The purpose was to reduce thrust on the shaft & to transfer
it to piston areas.
Maybe the geometry of modern engines obviates the need for balance discs?
If RR were to release details of all the forward & rearward gas loads, it would make it
all easier to understand, but I doubt if they will do that
Maybe the geometry of modern engines obviates the need for balance discs?
If RR were to release details of all the forward & rearward gas loads, it would make it
all easier to understand, but I doubt if they will do that
If RR were to release details of all the forward & rearward gas loads, it would make it
all easier to understand, but I doubt if they will do that
Some poster is still going to offer up a redesign for an obtuse reason other than it's different
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Dear mods
I find it strange that posts including:
'Balance discs', forward & rearward gas loads, 'axial bearing thrust control' among other more obscure topics are tolerated on Rumours & News.
Whereas, mention of a composite fuselage (the future of aviation, no kidding) suffering fire damage and not complying with FAA requirements, is sent to Tech Log.
What is happening now to the 787 affects us ALL. Please don't hide it away.
.
'Balance discs', forward & rearward gas loads, 'axial bearing thrust control' among other more obscure topics are tolerated on Rumours & News.
Whereas, mention of a composite fuselage (the future of aviation, no kidding) suffering fire damage and not complying with FAA requirements, is sent to Tech Log.
What is happening now to the 787 affects us ALL. Please don't hide it away.
.
Last edited by oldchina; 1st Dec 2010 at 19:24.
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Internal Air Load summations for determining net shaft axial loading
For "Flight Idle"
Jet Engines and Propulsion Systems For Engineers
Chapter 8-26
(pages 319-323 of pdf)
Jet Engines Engine
AXIAL BEARING THRUST CONTROL
Balancing the.axial thrust loads which develop in the flowpath and internal cavities of jet engines is critical to obtaining acceptable thrust bearing lives. Since the secondary systems air model includes all major cavities, a simple summation of pressure times projected area for all pertinent cavities will give the resultant load on all rotating hardware. Factoring in the compressor and turbine aerodynamic blade loads yields the axial forces on the engine thrust bearings.
HP Rotor Thrust Table 8.1 shows a schematic and tabulation of pressures, areas, and forces involved in obtaining me resultant loads on the high pressure rotor bearings of the CF6-80C engine at takeoff. Note that the resultant load (-4561 lb.) is small relative to the major cavity loads. This is typical of HP rotor bearing axial loads. Also, note that maximum cavity loads are substantially higher than either compressor or turbine total airfoil aerodynamic loads. Compare forces 104 and 114 with force 113 on Table 8.1. The accuracy of predicting these cavity pressures is a critical factor in predicting bearing loads.
Once the bearing load is predicted and determined to be too high for acceptable bearing life it can usually be adjusted to required levels by moving a critical seal to a larger or smaller diameter thus changing its projected area.. For instance, in Table 8.1, changing the diameter of the seal which affects forces 105 and 106 would be used to balance the load on the HP thrust bearing. In drastic cases if more adjustment is necessary, several seals or even turbine airfoil changes may be required to obtain desired bearing loads. Figure 8.24 shows a comparison of four different engines axial HP load and how they change with engine speed.
LP Rotor Thrust Prediction of the low pressure rotor thrust bearing load is generally much easier mainly due to the lower pressure levels involved. The principles remain the same. Figure 8.25 shows the low pressure rotor thrust for the same CF6-80C engine. Note that the predicted load is very close to the measured data presented in the figure.
Table 8.1 Variables Affecting Loads On High Pressure Rotor Bearings
NO Rt RO CHAM AREA PRESS FORCE
101 3.19 3.845 30 14.48 19.69 -285
102 3.845 4.840 33 27.16 33.07 -898
103 4.840 6.944 5 77.89 24.71 -1925
104 1 1 — — — +5783
105 7.640 11.825 7 253.92 364.65 +9332
106 6.375 7.650 36 55.70 102.82 +5727
107 4.650 6.375 59 59.75 22.75 +1359
108 4.000 4.650 41 17.66 26.65 +471
109 4.000 4.075 58 1,90 20.93 +40
110 4.325 5.050 62 21.35 21.32 -451
111 5.050 6.200 39 40.64 105.14 -4273
112 6.200 7.470 40 54.34 316.95 -1130£
113 7.470 4.040 10 448.39 253.99 -118879
114 1 1 — — — -31856
115 12.89 1.825 11 85.04 186.08 -17448
116 12.89 14.00 12 93.77 128.76 -8282
117 6.830 13.660 51 64.23 76.22 +41339
118 4.425 3.543 54 429.66 83.70 +7118
119 2.925 6.830 50 85.04 25.09 + 869
Jet Engines and Propulsion Systems For Engineers
Chapter 8-26
(pages 319-323 of pdf)
Jet Engines Engine
AXIAL BEARING THRUST CONTROL
Balancing the.axial thrust loads which develop in the flowpath and internal cavities of jet engines is critical to obtaining acceptable thrust bearing lives. Since the secondary systems air model includes all major cavities, a simple summation of pressure times projected area for all pertinent cavities will give the resultant load on all rotating hardware. Factoring in the compressor and turbine aerodynamic blade loads yields the axial forces on the engine thrust bearings.
HP Rotor Thrust Table 8.1 shows a schematic and tabulation of pressures, areas, and forces involved in obtaining me resultant loads on the high pressure rotor bearings of the CF6-80C engine at takeoff. Note that the resultant load (-4561 lb.) is small relative to the major cavity loads. This is typical of HP rotor bearing axial loads. Also, note that maximum cavity loads are substantially higher than either compressor or turbine total airfoil aerodynamic loads. Compare forces 104 and 114 with force 113 on Table 8.1. The accuracy of predicting these cavity pressures is a critical factor in predicting bearing loads.
Once the bearing load is predicted and determined to be too high for acceptable bearing life it can usually be adjusted to required levels by moving a critical seal to a larger or smaller diameter thus changing its projected area.. For instance, in Table 8.1, changing the diameter of the seal which affects forces 105 and 106 would be used to balance the load on the HP thrust bearing. In drastic cases if more adjustment is necessary, several seals or even turbine airfoil changes may be required to obtain desired bearing loads. Figure 8.24 shows a comparison of four different engines axial HP load and how they change with engine speed.
LP Rotor Thrust Prediction of the low pressure rotor thrust bearing load is generally much easier mainly due to the lower pressure levels involved. The principles remain the same. Figure 8.25 shows the low pressure rotor thrust for the same CF6-80C engine. Note that the predicted load is very close to the measured data presented in the figure.
Table 8.1 Variables Affecting Loads On High Pressure Rotor Bearings
NO Rt RO CHAM AREA PRESS FORCE
101 3.19 3.845 30 14.48 19.69 -285
102 3.845 4.840 33 27.16 33.07 -898
103 4.840 6.944 5 77.89 24.71 -1925
104 1 1 — — — +5783
105 7.640 11.825 7 253.92 364.65 +9332
106 6.375 7.650 36 55.70 102.82 +5727
107 4.650 6.375 59 59.75 22.75 +1359
108 4.000 4.650 41 17.66 26.65 +471
109 4.000 4.075 58 1,90 20.93 +40
110 4.325 5.050 62 21.35 21.32 -451
111 5.050 6.200 39 40.64 105.14 -4273
112 6.200 7.470 40 54.34 316.95 -1130£
113 7.470 4.040 10 448.39 253.99 -118879
114 1 1 — — — -31856
115 12.89 1.825 11 85.04 186.08 -17448
116 12.89 14.00 12 93.77 128.76 -8282
117 6.830 13.660 51 64.23 76.22 +41339
118 4.425 3.543 54 429.66 83.70 +7118
119 2.925 6.830 50 85.04 25.09 + 869
Flight idle: I learned something for you having asked the question, so please don't be shy about speaking up again.