American twins,Brit triple spool engines?
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You should also consider what engines the airline has in the rest of their fleet. Commonality of tools, parts, suppliers, technology, and training for maintenance is no doubt also a factor.
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In the triple spool's hot end, the distance between the High Pressure Turbine (HPT) and the Intermediate Pressure Turbine (IPT) also hurts the engine's efficency. This distance is required to locate the disks around an extra pair of shaft bearings.The hot gas flowing at a high subsonic speed in this void requires a lot of cooling air to be introduced which results in a considerable airflow loss that could be used for turning another turbine disk which would mean a lower fuel burn but increase the engine's weight considerably. As well, this void between the two turbine disks allows the hot subsonic airflow to lose some of it's speed and efficency before it hits the IPT blades for more energy extraction. This contributes to the triple spool design having a higher fuel burn than a twin spool disign.
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Here are some more fuel burn comparisons.
Source:
http://www.boeing.com/commercial/sta...f/777_perf.pdf
B777-200
GE90-77B fuel burn/seat over 3,000 nmi 124.5 kg - 274.5 lb.
Trent 877 fuel burn/seat over 3,000 nmi 127.6 kg - 281.4 lb.
B777-200ER
GE90-94B fuel burn/seat over 6,000 nmi 274.5 kg - 605.3 lb.
Trent 895 fuel burn/seat over 6,000 nmi 283.9 kg - 626.1 lb.
B777-300
GE90-94B fuel burn/seat over 3,000 nmi 118.9 kg - 262.2 lb.
Trent 892 fuel burn/seat over 3,000 nmi 122.2 kg - 269.5 lb.
Source:
http://www.boeing.com/commercial/sta...f/777_perf.pdf
B777-200
GE90-77B fuel burn/seat over 3,000 nmi 124.5 kg - 274.5 lb.
Trent 877 fuel burn/seat over 3,000 nmi 127.6 kg - 281.4 lb.
B777-200ER
GE90-94B fuel burn/seat over 6,000 nmi 274.5 kg - 605.3 lb.
Trent 895 fuel burn/seat over 6,000 nmi 283.9 kg - 626.1 lb.
B777-300
GE90-94B fuel burn/seat over 3,000 nmi 118.9 kg - 262.2 lb.
Trent 892 fuel burn/seat over 3,000 nmi 122.2 kg - 269.5 lb.
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IATA Jet Fuel Price MonitorJet Fuel Price Monitor
A B777-200ER powered by GE90-94B engines flying a 6,000nmi leg would consume 888 less US gallons of fuel than one powered by Trent 895 engines. That's in a three class aircraft configuration with 300 seats.
This year (2011) with average cost of fuel at 334c/gal this flight would cost US $2966 less with a GE than with a Trent engine. This would be a considerable cost saving spread over one year of flying.
A B777-200ER powered by GE90-94B engines flying a 6,000nmi leg would consume 888 less US gallons of fuel than one powered by Trent 895 engines. That's in a three class aircraft configuration with 300 seats.
This year (2011) with average cost of fuel at 334c/gal this flight would cost US $2966 less with a GE than with a Trent engine. This would be a considerable cost saving spread over one year of flying.
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A B777-200ER powered by GE90-94B engines flying a 6,000nmi leg would consume 888 less US gallons of fuel than one powered by Trent 895 engines. That's in a three class aircraft configuration with 300 seats.
This year (2011) with average cost of fuel at 334c/gal this flight would cost US $2966 less with a GE than with a Trent engine. This would be a considerable cost saving spread over one year of flying.
This year (2011) with average cost of fuel at 334c/gal this flight would cost US $2966 less with a GE than with a Trent engine. This would be a considerable cost saving spread over one year of flying.
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@ Concorde Rules.
They are not my figures, they are Boeing Data.
RR would like to go to the twin spool design for their big fan engines as they have done for their smaller engines. The triple spool design has given RR a lot of headaches in the past.
Are you saying that all of the IATA data and airframe manufacturer's data that has been previously noted in past threads is wrong and that your 'calculations' are correct?
They are not my figures, they are Boeing Data.
RR would like to go to the twin spool design for their big fan engines as they have done for their smaller engines. The triple spool design has given RR a lot of headaches in the past.
Are you saying that all of the IATA data and airframe manufacturer's data that has been previously noted in past threads is wrong and that your 'calculations' are correct?
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gas path:
Absolutely. These are major cost drivers.
Then you weren't at RJ 25 years ago when R-R techs were scurrying to keep open holes from developing in the 1011s.
Time on wing and performance retention over the lifetime of the engine is a good measure.
I've yet to pull a roller for loss of EGT margin.
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The single hp turbine powering the fan in a triple spool is not very efficient due to its Mach number being about 22% of its optimal RPM which makes it more difficult to increase the pressure ratio.
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Every high-bypass turbofan I know has 4-5-6 stages in the LP turbine, necessary because of the low rotational speed of the fan rotor system.
That said, I haven't taken a good look at P&W's geared turbofan; since the LPT turns 3:1 or more compared to the fan, they may use fewer LPT stages.
That said, I haven't taken a good look at P&W's geared turbofan; since the LPT turns 3:1 or more compared to the fan, they may use fewer LPT stages.
