Ba777 engine fire Las Vegas
Discussion
Seight_Returns said:
Please could someone please clarify the meaning of the phrase "uncontained engine failure" that I'm reading repeatedly on the Pprune thread and elsewhere ?
Does it mean a fire and/or engine components not being contained within the engine cowling ?
As mentioned by others "uncontained" simply refers to components of the engine exiting the engine!Does it mean a fire and/or engine components not being contained within the engine cowling ?
The spinning components of a jet engine, whilst highly reliable normally, have a LOT of energy contained in their spinning mass. Typically, a Fan or Compressor stage (blade/rotor) failure would be expected to be contained by the engine cowling (the cowlings on modern engines have a "ballistic" cover, made of kevlar to do just this). Unfortunately, a failure in the turbine section is much much harder, in fact virtually impossible to contain. This is because the turbine blades and support "disc" must withstand high loadings at high temperatures, and as such they must be made of very dense / strong metals (unlike the Fan / compressor, that can be made of composites and aluminium). Pretty much any turbine failure, especially one that occurs at high power (and hence high shaft rpm) settings (like on takeoff!), is going to result in parts leaving the engine, exiting via the cowling, and flying off at high speed. The results are generally pretty catastrophic, and can only really be negated by multiple system redundancy, and sometimes, just luck.
ie this happened in 2010 to a A380:
And this is the bit of turbine disc:
It's also worth noting that a jet engine is, for packaging reasons, pretty much entirely surrounded by a maze of plumbing and wiring:
Damage to these systems can lead to a fuel leak and fire.
In this case, the footage recorded suggest the majority of the hull damage was from the ground burning phase, where fuel pooled under the aircraft and burnt upwards
onyx39 said:
Out of interest, is there any chance / danger in an uncontainable failure of parts editing the engine, penetrating the cabin and injuring passengers?
If so, won't be sitting over the wing again!
Worth noting that in the 777 short "landing" incident at Heathrow, a passenger was injured by the undercarriage penetrating the pressure hull and ramming up through the passenger cabin floor.........If so, won't be sitting over the wing again!
Max_Torque said:
As mentioned by others "uncontained" simply refers to components of the engine exiting the engine!
The spinning components of a jet engine, whilst highly reliable normally, have a LOT of energy contained in their spinning mass. Typically, a Fan or Compressor stage (blade/rotor) failure would be expected to be contained by the engine cowling (the cowlings on modern engines have a "ballistic" cover, made of kevlar to do just this). Unfortunately, a failure in the turbine section is much much harder, in fact virtually impossible to contain. This is because the turbine blades and support "disc" must withstand high loadings at high temperatures, and as such they must be made of very dense / strong metals (unlike the Fan / compressor, that can be made of composites and aluminium). Pretty much any turbine failure, especially one that occurs at high power (and hence high shaft rpm) settings (like on takeoff!), is going to result in parts leaving the engine, exiting via the cowling, and flying off at high speed. The results are generally pretty catastrophic, and can only really be negated by multiple system redundancy, and sometimes, just luck.
A minor comment if I may, it's not so much the difference between fan / compressor vs turbine that tends to determine whether something is contained or not - it's blades versus discs. Fan, compressor, or turbine blades are all normally contained. Fan, compressor, or turbine discs, if they actually fail, are rarely if ever contained.The spinning components of a jet engine, whilst highly reliable normally, have a LOT of energy contained in their spinning mass. Typically, a Fan or Compressor stage (blade/rotor) failure would be expected to be contained by the engine cowling (the cowlings on modern engines have a "ballistic" cover, made of kevlar to do just this). Unfortunately, a failure in the turbine section is much much harder, in fact virtually impossible to contain. This is because the turbine blades and support "disc" must withstand high loadings at high temperatures, and as such they must be made of very dense / strong metals (unlike the Fan / compressor, that can be made of composites and aluminium). Pretty much any turbine failure, especially one that occurs at high power (and hence high shaft rpm) settings (like on takeoff!), is going to result in parts leaving the engine, exiting via the cowling, and flying off at high speed. The results are generally pretty catastrophic, and can only really be negated by multiple system redundancy, and sometimes, just luck.
Edited by Mave on Wednesday 9th September 22:57
onyx39 said:
to quote someone on PPRUNE "Already declared a hull loss". No idea if he is just stating what was said on another post, or has inside knowledge.
How do they deal with the plane now? They need to crawl all over it, I assume to investigate what happened then break it up. Is it just dragged to the far end of the airport for this? Willy Nilly said:
onyx39 said:
to quote someone on PPRUNE "Already declared a hull loss". No idea if he is just stating what was said on another post, or has inside knowledge.
How do they deal with the plane now? They need to crawl all over it, I assume to investigate what happened then break it up. Is it just dragged to the far end of the airport for this? Mave said:
A minor comment if I may, it's not so much the difference between fan / compressor vs turbine that tends to determine whether something is contained or not - it's blades versus discs. Fan, compressor, or turbine blades are all normally contained. Fan, compressor, or turbine discs, if they actually fail, are rarely if ever contained.
You are correct. Tbh there aren't really any "discs" in the compressor section these days, more support rotors, because the fan drive shafting / bearing arrangements sit in the middle axially, and i've never heard of a fan hub failing? (too big / slow to come apart itself)Edited by Mave on Wednesday 9th September 22:57
Fan blade shedding makes for an exciting test:
FanBladeSheddingtestvideo
Blade contained by shroud! Bit of a mess mind.......
That's part of a TV documentary, more footage of it here: https://www.youtube.com/watch?v=j973645y5AA
When the engine is spooling up to full power it always raises the hairs on the back of my neck!
When the engine is spooling up to full power it always raises the hairs on the back of my neck!
Max_Torque said:
You are correct. Tbh there aren't really any "discs" in the compressor section these days, more support rotors, because the fan drive shafting / bearing arrangements sit in the middle axially, and i've never heard of a fan hub failing? (too big / slow to come apart itself)
Fan blade shedding makes for an exciting test:
FanBladeSheddingtestvideo
Blade contained by shroud! Bit of a mess mind.......
Pretty much every disc these days is more a support rotor - the disc in the photos you posted is an IP turbine support disc by your definition, as it has the LP shaft going down the centre.Fan blade shedding makes for an exciting test:
FanBladeSheddingtestvideo
Blade contained by shroud! Bit of a mess mind.......
I think the CF6 has had uncontained fan disc failures, as did the F119 in an F35 last year; even though the speeds in a fan are lower, the stresses are still very high; if they weren't then it would be slimmed down to make it lighter ;-)
Mave said:
Pretty much every disc these days is more a support rotor - the disc in the photos you posted is an IP turbine support disc by your definition, as it has the LP shaft going down the centre.
I think the CF6 has had uncontained fan disc failures, as did the F119 in an F35 last year; even though the speeds in a fan are lower, the stresses are still very high; if they weren't then it would be slimmed down to make it lighter ;-)
Interesting point! In the quest for more power in a smaller, lighter engine, then rotational speeds are always going to have to go upwards. Once you reach the load limit of a single blade, then the only way to get more power is to have more of them (bigger, heavier engine) or spin the ones you have faster (same torque at higher speed = more power)I think the CF6 has had uncontained fan disc failures, as did the F119 in an F35 last year; even though the speeds in a fan are lower, the stresses are still very high; if they weren't then it would be slimmed down to make it lighter ;-)
It would be interesting to see a chart of maximum turbine shaft speeds vs engine design date to see the trend?
Max_Torque said:
Mave said:
Pretty much every disc these days is more a support rotor - the disc in the photos you posted is an IP turbine support disc by your definition, as it has the LP shaft going down the centre.
I think the CF6 has had uncontained fan disc failures, as did the F119 in an F35 last year; even though the speeds in a fan are lower, the stresses are still very high; if they weren't then it would be slimmed down to make it lighter ;-)
Interesting point! In the quest for more power in a smaller, lighter engine, then rotational speeds are always going to have to go upwards. Once you reach the load limit of a single blade, then the only way to get more power is to have more of them (bigger, heavier engine) or spin the ones you have faster (same torque at higher speed = more power)I think the CF6 has had uncontained fan disc failures, as did the F119 in an F35 last year; even though the speeds in a fan are lower, the stresses are still very high; if they weren't then it would be slimmed down to make it lighter ;-)
It would be interesting to see a chart of maximum turbine shaft speeds vs engine design date to see the trend?
Max_Torque said:
Interesting point! In the quest for more power in a smaller, lighter engine, then rotational speeds are always going to have to go upwards. Once you reach the load limit of a single blade, then the only way to get more power is to have more of them (bigger, heavier engine) or spin the ones you have faster (same torque at higher speed = more power)
It would be interesting to see a chart of maximum turbine shaft speeds vs engine design date to see the trend?
Rotational speeds don't neccesarily go up over time per se - you've normally got a compromise between turbine speed and compressor speed. You want a large fan to get the bypass ratio up to improve propulsive efficiency - but then the tip speed is limited by compressibility (hence the GE90 swept fan) so there is a limit to rotational speed before the tip losses become excessive. By comparison you want a high rotational velocity (velocity in m/s rather than rad/s) on the turbines to keep the stage loading (change in enthalpy divided by absolute tangential velocity squared) reasonable; alternatively you need extra turbine stages for the same amount of work, adding length and cooling flow requirement. This is the reason for P&W introducing geared fans; trying to change the trade between fan speed and turbine speed (at the expense of size, weight, and thermal load on the oil system).It would be interesting to see a chart of maximum turbine shaft speeds vs engine design date to see the trend?
Spinning rotor systems faster doesn't make more power, it just trades the aerodynamic and mechanical optimisations in making the power.
Mave said:
Max_Torque said:
Interesting point! In the quest for more power in a smaller, lighter engine, then rotational speeds are always going to have to go upwards. Once you reach the load limit of a single blade, then the only way to get more power is to have more of them (bigger, heavier engine) or spin the ones you have faster (same torque at higher speed = more power)
It would be interesting to see a chart of maximum turbine shaft speeds vs engine design date to see the trend?
Rotational speeds don't neccesarily go up over time per se - you've normally got a compromise between turbine speed and compressor speed. You want a large fan to get the bypass ratio up to improve propulsive efficiency - but then the tip speed is limited by compressibility (hence the GE90 swept fan) so there is a limit to rotational speed before the tip losses become excessive. By comparison you want a high rotational velocity (velocity in m/s rather than rad/s) on the turbines to keep the stage loading (change in enthalpy divided by absolute tangential velocity squared) reasonable; alternatively you need extra turbine stages for the same amount of work, adding length and cooling flow requirement. This is the reason for P&W introducing geared fans; trying to change the trade between fan speed and turbine speed (at the expense of size, weight, and thermal load on the oil system).It would be interesting to see a chart of maximum turbine shaft speeds vs engine design date to see the trend?
Spinning rotor systems faster doesn't make more power, it just trades the aerodynamic and mechanical optimisations in making the power.
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