American twins,Brit triple spool engines?
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The reliability of the RR three-spool design is very good, at least with my experience on the TriStar.
In sixteen thousand hours of flying the type, I have experienced one engine failure (flameout on descent due to a HS gearbox failure...repairable on wing in 6 hours) and two inflight shutdowns, due to high vibs.
Otherwise, no further problems.
RR builds mighty fine engines.
NB.
Also operated Conway and Dart-powered airplanes, no problems with those, either.
In sixteen thousand hours of flying the type, I have experienced one engine failure (flameout on descent due to a HS gearbox failure...repairable on wing in 6 hours) and two inflight shutdowns, due to high vibs.
Otherwise, no further problems.
RR builds mighty fine engines.
NB.
Also operated Conway and Dart-powered airplanes, no problems with those, either.
Not sure of the physics, but 11,000 hours of flying tells me the observation is true. A jet powered aircraft is thrust forward by the reaction in the engine, while a propeller aircraft action of the prop.
GF
GF
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galaxy flyer
A turbojet derives all of it's thrust through the combustion of compressed air and fuel going out the back of the engine; a high bypass turbofan (such as the TF39, which had a bypass ratio of 8:1) derives a sizable portion of it's thrust from a fan at the front of the engine, with a smaller portion from the combustion of compressed air and fuel going out the back of the engine; a turboprop derives almost all of it's thrust via the propeller with a small amount produced by the thrust of the jet driving the propeller; a piston driven prop derives all of it's thrust via the propeller.
Not sure of the physics, but 11,000 hours of flying tells me the observation is true. A jet powered aircraft is thrust forward by the reaction in the engine, while a propeller aircraft action of the prop.
Just for completeness: At least later models of Merlin derived a substantial amount of thrust from their exhaust stacks as well. And Mustangs got some thrust out of their cooling duct arrangement.
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RR leads the pack of the three engine manufacturers with in-flight uncontained engine failures
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Jane-DoH:
The torque resulting in a prop aircraft is because the slipstream leaving the plane of the prop is rotating - a vortex, the result of the action of the blades' airfoils. The air is accelerated both aft and in the direction of prop rotation. This vortex represents lost propulsion energy.
The fan module of a turbofan includes both the rotating airfoils AND a stage of stator airfoils. These stators capture the vortex, and straighten the flow so it is directed straight aft. Since the flow passage between adjacent vanes is divergent - a diffuser - the flow is slowed, and static pressure is increased.
And since the flow leaves in a straight, non-vortex manner, there is no torque to be reacted by the airplane.
Then how come the fans on jet-engines don't cause significant amounts of torque?
The fan module of a turbofan includes both the rotating airfoils AND a stage of stator airfoils. These stators capture the vortex, and straighten the flow so it is directed straight aft. Since the flow passage between adjacent vanes is divergent - a diffuser - the flow is slowed, and static pressure is increased.
And since the flow leaves in a straight, non-vortex manner, there is no torque to be reacted by the airplane.
Except for spool-up/down torque. This one is mitigated in some designs by using contra-rotating spools. F119 is one example. And honestly, I don't have an idea whether this torque is of relevance in reality. Does anyone here?
I am aware that in fighter jets, the motivation behind contra-rotating spools is to reduce their gyroscopic moment, and perhaps increase efficiency.
(Reference: avid reading and my crappy memory.)
I am aware that in fighter jets, the motivation behind contra-rotating spools is to reduce their gyroscopic moment, and perhaps increase efficiency.
(Reference: avid reading and my crappy memory.)
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CliveL
To complete your quote, you may want to read this Aviation Week story. It seems that some operators ignored service safety bulletins from GE and GE then requested the NTSB and the FAA to issue these directives. Certain freight operators are the delinquent ones that have not responded.
AVIATION WEEK
Turbine D
The National Transportation Safety Board issued two urgent safety recommendations to the Federal Aviation Administration (FAA) following four recent events in which the aircraft experienced an uncontained engine failure of its GE CF6-45/50 series engine.
AVIATION WEEK
Turbine D
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JaneDoH
This isn't the case at all. CF6 engines are no better or no worse in resistance to FOD damage than other engines.
You are going to see more and more FOD damage to engines, all sizes and all makes and models. The reason is birds. There were 150 severe bird strikes reported in 2009, up 40% from the average 2000 through 2008. The increasing trend applied to 2010. More birds are hanging out around airports than ever before. Recently, I was waiting for a flight from Palm Springs to SLC. When the plane came in to Palm Springs, it hit a flock of birds causing some damage to one engine and lots of dents to the right wing LE slats. Its not unususal these days.
As far as uncontained failures go, these are pretty much spread around among the engine manufacturers and are the result of various causes. See the Qantas Airbus A-380 uncontained failure thread for the most serious recent event.
Turbine D
Hasn't the CF6 always had problems with poor resistance to FOD, catastrophic engine failures and so forth?
You are going to see more and more FOD damage to engines, all sizes and all makes and models. The reason is birds. There were 150 severe bird strikes reported in 2009, up 40% from the average 2000 through 2008. The increasing trend applied to 2010. More birds are hanging out around airports than ever before. Recently, I was waiting for a flight from Palm Springs to SLC. When the plane came in to Palm Springs, it hit a flock of birds causing some damage to one engine and lots of dents to the right wing LE slats. Its not unususal these days.
As far as uncontained failures go, these are pretty much spread around among the engine manufacturers and are the result of various causes. See the Qantas Airbus A-380 uncontained failure thread for the most serious recent event.
Turbine D
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To complete your quote, you may want to read this Aviation Week story. It seems that some operators ignored service safety bulletins from GE and GE then requested the NTSB and the FAA to issue these directives.
Last edited by CliveL; 11th Mar 2011 at 16:59.
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CliveL
The problem was identified in the early 1970s, but on the CF6-6 engine. The LPT on this engine is different, different airfoils and disks. It is a 5 stage turbine, whereas the CF6-50 engine has a 4 stage LPT.
The rotor unbalance condition leading to the excitation of the stage 3 disk and the subsequent fatigue cracking of the forward arm is not sensed by the vibration detectors that are used. You have to remember these engines are between 30 to approaching 40 years old. Servicing of these engines is somewhat unclear as to procedures used. For instance, it is required to not only balance and test individual rotor stages, but the completed rotor assemblies. It is known this was not happening. So another FAA AD was issued this year requiring a complete vibratory assessment of the core engine to assure at specific set engine cycles to assure undetected vibration does not cause future disk failures.
A similar FAA AD has been issued for JT8-D engines that are also aged and are widely distributed throughout the world.
Hope you find this informative.
Turbine D
The problem was identified in the early 1970s, but on the CF6-6 engine. The LPT on this engine is different, different airfoils and disks. It is a 5 stage turbine, whereas the CF6-50 engine has a 4 stage LPT.
The CF6 LPT S3 disk resonance response to HP rotor unbalance was first identified in the GE CF6-6 engine, which shares the CF6-45/-50 type certificate. The CF6-6 experienced four uncontained LPT S3 disk forward spacer arm separations between 1975 and 1978 due to HP rotor unbalance.
As a result, GE redesigned the CF6-6 LPT S3 disk so that an HP rotor unbalance condition would not excite the LPT S3 disk and result in disk failure. The CF6-50 engine has experienced 12 instances of LPT S3 disk forward spacer arm cracking since 1973. Eight of the cracked CF6-50 disk forward spacer arms were discovered during shop-level inspections when LPTs were disassembled for unrelated reasons, such as engine model conversion or the replacement of life-limited parts. In the remaining cases, all of which are cited above, disk cracks progressed to failure, leading to in-service uncontained engine failures.
As a result, GE redesigned the CF6-6 LPT S3 disk so that an HP rotor unbalance condition would not excite the LPT S3 disk and result in disk failure. The CF6-50 engine has experienced 12 instances of LPT S3 disk forward spacer arm cracking since 1973. Eight of the cracked CF6-50 disk forward spacer arms were discovered during shop-level inspections when LPTs were disassembled for unrelated reasons, such as engine model conversion or the replacement of life-limited parts. In the remaining cases, all of which are cited above, disk cracks progressed to failure, leading to in-service uncontained engine failures.
A similar FAA AD has been issued for JT8-D engines that are also aged and are widely distributed throughout the world.
Hope you find this informative.
Turbine D
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barit1
Oh, I thought there was some kind of gyroscopic effect at work from the gear-box.
Turbine D
Why is this so? Didn't they have various things to keep birds away from airports?
The torque resulting in a prop aircraft is because the slipstream leaving the plane of the prop is rotating - a vortex, the result of the action of the blades' airfoils. The air is accelerated both aft and in the direction of prop rotation. This vortex represents lost propulsion energy.
Turbine D
You are going to see more and more FOD damage to engines, all sizes and all makes and models. The reason is birds. There were 150 severe bird strikes reported in 2009, up 40% from the average 2000 through 2008. The increasing trend applied to 2010. More birds are hanging out around airports than ever before. Recently, I was waiting for a flight from Palm Springs to SLC. When the plane came in to Palm Springs, it hit a flock of birds causing some damage to one engine and lots of dents to the right wing LE slats. Its not unususal these days.
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JaneDoH
That is what I thought, but apparently the controls at airports have a limited effect once an aircraft lifts off. The bird strikes seemingly more often occur outside the airfield property limits. I am thinking that in some cases, migratory birds are not migrating like they use to do. For example, Canadian geese stay around mid-America all winter rather than migrating to the southern wet-lands. Presently, there is no government policy in dealing with or preventing off-airport strikes. Supposedly, the FAA is investigating potential technology to keep birds away from aircraft.
Turbine D
Why is this so? Didn't they have various things to keep birds away from airports?
Turbine D