American twins,Brit triple spool engines?
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Well, the TRENT does actually have five shafts. A geared Fan arrangement allows an actual shaft "addition", and if instead of rigid couplings, the TRENT had a gearbox twixt each stub shaft, now you are talking plenty of flexible ratios. Talk about complex. Maybe Rolls' Affiliate, Allison, could get some of the Gearbox business.
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Twin spool engines are more fuel efficient than three spools.
See ICAO Engine Emissions Databank....Aircraft Engine Emissions | Human and Environmental Issues | Safety Regulation
Note: Compare engines with similar thrusts.
For the 777 with the GE90, the sea level SFC is 0.324, at cruise it is 0.52.
For the 777 with the Trent 800, the sea level SFC is 0.35, at cruise it is 0.56.
For the 747-8 with the GEnx, the sea level SFC is 0.27, no figures yet for cruise.
GE90 SFC (SLS) 8.30 mg/N-s (cruise)
Trent 882 SFC (SLS) 15.66 mg/N-s (cruise)
Twin spool engines have a more stable airflow pattern since the airflow is being compessed all the way to the last stage of the HP compressor before it enters the diffuser section.
This makes the engine less surge prone than a three spool design.
In a three spool engine, there is a sudden interruption (slowing down) of the airflow in the void between the IP Compressor and the HP Compressor. When the compressed air leaves the last stage of blades of the IP compressor no more compression takes place until the first stage of the HP compressor blades. This airflow interruption between the two compressors in this uncompressed void makes the engine more surge prone.
Twin spool engines, (GE or Pratt) have less heat to dissipate than three spool (Rolls Royce) engines.
Three spool engines operate at a higher oil temperature when compared to two spool engines and the oil distribution is much more complex in three spool engines. This more complex oil distribution has given RR problems over the years, some call it oil hiding.
RB211 Series 335'
Trent 700 374'
Trent 800 375'
Trent 900 385'
Trent 1000 365'
CF6-50 320'
CF6-80C2 320'
PW4000 350'
GE90 270'
Internal engine cooling airflow is less complex in a twin spool engine than a three spool one.
For this reason triple spool engines emit more smoke during start-up.
Twin spools engines have lower gyroscopic moments resulting in less side loading of the pod/strut. (pod nod)
Twin spools light off and accelerate faster than three spools.
Compare the slow spool-up time of a RR Trent compared to a GE or Pratt engine in the following link.
YouTube - L-1011 N700TS Airline History Museum 1 ..........( this almost sounds like a hung start as it takes such a long time to start )
Most fighter aicraft engines use a twin spool design for faster throttle response.
Twin spools have lower maunfacturing costs due to a lower parts count.
Twin spools are less expensive to overhaul due to the face that they have only two concentric shafts, no third (Intermediate) compressor with it's associated compressor and stator blades as in a three spool design.
The RR three spool is more difficult and more labor intensive to manufacture beacuse of the nature of the concentricity of the drive shafts, support bearings and the fact that is has three distinct compression stages.
An Oxford University/Rolls Study from 4/9/02 - 9/30/03 document notes that 10% or more of RR engines fail the final passing out test due to imbalance. 11 Trent 500 production engines failed pass-off testing due
to abnormal vibrations. This indicates that there was a systemic vibration problem. A higher rejection rate due to vibration is detected when the engines are overhauled at the RR appointed agents.
See ICAO Engine Emissions Databank....Aircraft Engine Emissions | Human and Environmental Issues | Safety Regulation
Note: Compare engines with similar thrusts.
For the 777 with the GE90, the sea level SFC is 0.324, at cruise it is 0.52.
For the 777 with the Trent 800, the sea level SFC is 0.35, at cruise it is 0.56.
For the 747-8 with the GEnx, the sea level SFC is 0.27, no figures yet for cruise.
GE90 SFC (SLS) 8.30 mg/N-s (cruise)
Trent 882 SFC (SLS) 15.66 mg/N-s (cruise)
Twin spool engines have a more stable airflow pattern since the airflow is being compessed all the way to the last stage of the HP compressor before it enters the diffuser section.
This makes the engine less surge prone than a three spool design.
In a three spool engine, there is a sudden interruption (slowing down) of the airflow in the void between the IP Compressor and the HP Compressor. When the compressed air leaves the last stage of blades of the IP compressor no more compression takes place until the first stage of the HP compressor blades. This airflow interruption between the two compressors in this uncompressed void makes the engine more surge prone.
Twin spool engines, (GE or Pratt) have less heat to dissipate than three spool (Rolls Royce) engines.
Three spool engines operate at a higher oil temperature when compared to two spool engines and the oil distribution is much more complex in three spool engines. This more complex oil distribution has given RR problems over the years, some call it oil hiding.
RB211 Series 335'
Trent 700 374'
Trent 800 375'
Trent 900 385'
Trent 1000 365'
CF6-50 320'
CF6-80C2 320'
PW4000 350'
GE90 270'
Internal engine cooling airflow is less complex in a twin spool engine than a three spool one.
For this reason triple spool engines emit more smoke during start-up.
Twin spools engines have lower gyroscopic moments resulting in less side loading of the pod/strut. (pod nod)
Twin spools light off and accelerate faster than three spools.
Compare the slow spool-up time of a RR Trent compared to a GE or Pratt engine in the following link.
YouTube - L-1011 N700TS Airline History Museum 1 ..........( this almost sounds like a hung start as it takes such a long time to start )
Most fighter aicraft engines use a twin spool design for faster throttle response.
Twin spools have lower maunfacturing costs due to a lower parts count.
Twin spools are less expensive to overhaul due to the face that they have only two concentric shafts, no third (Intermediate) compressor with it's associated compressor and stator blades as in a three spool design.
The RR three spool is more difficult and more labor intensive to manufacture beacuse of the nature of the concentricity of the drive shafts, support bearings and the fact that is has three distinct compression stages.
An Oxford University/Rolls Study from 4/9/02 - 9/30/03 document notes that 10% or more of RR engines fail the final passing out test due to imbalance. 11 Trent 500 production engines failed pass-off testing due
to abnormal vibrations. This indicates that there was a systemic vibration problem. A higher rejection rate due to vibration is detected when the engines are overhauled at the RR appointed agents.
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The development of the original, 3 spool RB211 sent Rolls Royce broke!
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3 Spool vs 2 Spool
unmanned transport
Thanks for your post, it was very accurate and informative.
tuna hp
The real key is not only the compressor rotational speed, but the aerodynamics that is designed into to both blades and vanes throughout the compressor and for that matter, the turbine. Also, don't forget the combustor efficiency, a big part of good, efficient fuel burn. A 3-D highly swept, light weight fan also helps immensely, as much of the thrust comes from the air passing through the fan which by-passes the core engine.
Faster doesn't = fuel efficient as "Bear" pointed out, except the Concorde with its engines were very good.
As I understand it, Rolls Royce is developing two new engines (concepts): One is an open fan design, not unlike the GE36 and the other is an engine that could compete if Boeing carries through on developing a total new replacement for the B-737. This engine is being designed at Rolls-Royce Deutschland Ltd & Co KG, and is a two spool design. This is where their two spool design expertise resides.
As in everything, you have to think outside the box at times to successfully move forward.
Thanks for your post, it was very accurate and informative.
tuna hp
The real key is not only the compressor rotational speed, but the aerodynamics that is designed into to both blades and vanes throughout the compressor and for that matter, the turbine. Also, don't forget the combustor efficiency, a big part of good, efficient fuel burn. A 3-D highly swept, light weight fan also helps immensely, as much of the thrust comes from the air passing through the fan which by-passes the core engine.
Faster doesn't = fuel efficient as "Bear" pointed out, except the Concorde with its engines were very good.
As I understand it, Rolls Royce is developing two new engines (concepts): One is an open fan design, not unlike the GE36 and the other is an engine that could compete if Boeing carries through on developing a total new replacement for the B-737. This engine is being designed at Rolls-Royce Deutschland Ltd & Co KG, and is a two spool design. This is where their two spool design expertise resides.
As in everything, you have to think outside the box at times to successfully move forward.
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You are welcome Turbine D.
It's my understanding that RR would like to return to twin spooled engines for their big ones as they have had too many problems with three spools especially 'oil hiding' over the years. Historically, Rolls has had to combat oil system issues with the RB211 / L1011; Trent 500 / A340-500/600’s; Trent 700 / A330; Trent 900 / A380.
RR leads the pack of the three engine manufacturers with in-flight uncontained engine failures. That is not something to be proud of.
It's my understanding that RR would like to return to twin spooled engines for their big ones as they have had too many problems with three spools especially 'oil hiding' over the years. Historically, Rolls has had to combat oil system issues with the RB211 / L1011; Trent 500 / A340-500/600’s; Trent 700 / A330; Trent 900 / A380.
RR leads the pack of the three engine manufacturers with in-flight uncontained engine failures. That is not something to be proud of.
Lots of hand waving conclusions and opinions without substantiation suitable for a technical forum.
Every engine design has its advantages and limitations and is well designed to provide value to the cutomer (the installer) and ultimately the operator.
Let's move on and stick with facts only appropriate to narrow subject matter rather than degrade into the A vs B type arguments that clutter most threads
Every engine design has its advantages and limitations and is well designed to provide value to the cutomer (the installer) and ultimately the operator.
Let's move on and stick with facts only appropriate to narrow subject matter rather than degrade into the A vs B type arguments that clutter most threads
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Even though this ICAO data is for emissions, it is also valid for fuel consumption. So far it is the best fuel burn data that I have come across.
Now let us look at a comparison between twin spool and triple spool engine fuel consumption as applicable to a B777-200ER.
GE90-94B
Take-off - 3.513 kg/s
Climb-out - 2.831 kg/s
Approach - 0.876 kg/s
Idle - 0.284 kg/s
Trent 895
Take-off - 4.03 kg/s
Climb-out - 3.19 kg/s
Approach - 1.05 kg/s
Idle - 0.33 kg/s
Pratt 4090
Take-off - 3.898 kg/s
Climb-out - 2.977 kg/s
Approach - 0.957 kg/s
Idle - 0.268 kg/s
Now let us look at a comparison between twin spool and triple spool engine fuel consumption as applicable to a B777-200ER.
GE90-94B
Take-off - 3.513 kg/s
Climb-out - 2.831 kg/s
Approach - 0.876 kg/s
Idle - 0.284 kg/s
Trent 895
Take-off - 4.03 kg/s
Climb-out - 3.19 kg/s
Approach - 1.05 kg/s
Idle - 0.33 kg/s
Pratt 4090
Take-off - 3.898 kg/s
Climb-out - 2.977 kg/s
Approach - 0.957 kg/s
Idle - 0.268 kg/s
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Handwaving Conclusions
lomapaseo
Go back and look at the opening post. Most of the posts are debating the differences between the two engine styles. If you have something to contribute to the discussion or data that is different from that which has been presented, why not post it?
Go back and look at the opening post. Most of the posts are debating the differences between the two engine styles. If you have something to contribute to the discussion or data that is different from that which has been presented, why not post it?
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Jane-DoH
I am not sure what you mean by "torquing issues". Here is a nice simplistic overview of the geared fan engine.
YouTube - Pratt and Whitney PW1000G PurePower Engine How It Works
I am not sure what you mean by "torquing issues". Here is a nice simplistic overview of the geared fan engine.
YouTube - Pratt and Whitney PW1000G PurePower Engine How It Works
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An Oxford University/Rolls Study from 4/9/02 - 9/30/03 document notes that 10% or more of RR engines fail the final passing out test due to imbalance. 11 Trent 500 production engines failed pass-off testing due
to abnormal vibrations. This indicates that there was a systemic vibration problem. A higher rejection rate due to vibration is detected when the engines are overhauled at the RR appointed agents.
to abnormal vibrations. This indicates that there was a systemic vibration problem. A higher rejection rate due to vibration is detected when the engines are overhauled at the RR appointed agents.
Edit or note, ok 3 spool motors burn gas, just wondering if the time between overhaul is worth it? One down aircraft equals millions in revinue lost in a day..
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Bearfoil
Here is an interesting study on engine positioning and wing design for large commercial aircraft. The study was done at Virginia Tech.
http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf
Turbine D
Here is an interesting study on engine positioning and wing design for large commercial aircraft. The study was done at Virginia Tech.
http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf
Turbine D
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I did a little research and while I was surprised to find that as unmanned transport et al have been saying, the Trent gets worse fuel economy compared to other engine options on the 777. But I was even more surprised to find that the Trent is considered the most RELIABLE engine on the 777 and that the GE90 777 engines have actually had more problems and require more maintenance hours per flight hour.
Interesting flip of what I would have thought.
Interesting flip of what I would have thought.
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The early GE90s on the 777-200s had teething problems but they are a bullet proof engine now.
Keep in mind that triple spool engines are more costly to overhaul due to their higher parts count and compressor blades are expensive.
The GE90-115B engine on the 773ER is one great engine and operators love it.
Keep in mind that triple spool engines are more costly to overhaul due to their higher parts count and compressor blades are expensive.
The GE90-115B engine on the 773ER is one great engine and operators love it.
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Turbine D,
As I understand it, the reason propeller planes experienced torque was because of the gear-box. If this engine had a gearbox, wouldn't you get torque?
As I understand it, the reason propeller planes experienced torque was because of the gear-box. If this engine had a gearbox, wouldn't you get torque?