727EMflyer From United States of America, joined Mar 2005, 547 posts, RR: 1 Reply 1, posted (4 years 7 months 3 weeks 3 days 2 hours ago) and read 12549 times:
They offered it for the 787 program but Boeing passed it over. Who knows, it could have a shot on the A350, but not likely. There are no other probable applications in the works, so this one looks pretty dead. PW could keep up the R&D and have it READY for the next big thing, but I doubt they have the revenue to spend the money.
ArmitageShanks From United Kingdom, joined Dec 2003, 3123 posts, RR: 19 Reply 2, posted (4 years 7 months 3 weeks 2 days 21 hours ago) and read 12484 times:
What is a geared turbofan? Anywhere I can read details about it?
DfwRevolution From United States of America, joined Jan 2010, 39 posts, RR: 54 Reply 3, posted (4 years 7 months 3 weeks 2 days 20 hours ago) and read 12472 times:
>> What is a geared turbofan? Anywhere I can read details about it?
It's a turbofan engine with something akin to an automatic transmission in the turbine core. This allows different portions of the engine to opperate at variable speed so the various components always opperate at their optimal speed.
MrChips From Canada, joined Mar 2005, 706 posts, RR: 0 Reply 4, posted (4 years 7 months 3 weeks 2 days 18 hours ago) and read 12447 times:
Quoting DfwRevolution (Reply 3): It's a turbofan engine with something akin to an automatic transmission in the turbine core.
Not quite...a geared turbofan has a fixed gear ratio. Having a "shift" system would be too heavy and expensive.
Think of it this way...on a scale ranging from pure turbojet to turboprop, a geared turbofan is closer to a turboprop than a conventional engine is, in that the fan would be geared much the same way a propeller is.
And it's hardly new technology either. The Lycoming ALF500-series engine is a geared turbofan as well...found on the AvroRJ/BAe-146 and early Canadair Challenger 600s. The only thing new about the PW8000 is the larger scale.
Beowulf From Singapore, joined Jul 2003, 679 posts, RR: 25 Reply 5, posted (4 years 7 months 3 weeks 2 days 14 hours ago) and read 12409 times:
Quoting MrChips (Reply 4): Think of it this way...on a scale ranging from pure turbojet to turboprop, a geared turbofan is closer to a turboprop than a conventional engine is, in that the fan would be geared much the same way a propeller is.
And why is this better or an innovation? I don't understand where the benefit lies.
Brons2 From United States of America, joined Sep 2001, 2672 posts, RR: 6 Reply 6, posted (4 years 7 months 3 weeks 2 days 13 hours ago) and read 12401 times:
Quoting Beowulf (Reply 5): And why is this better or an innovation? I don't understand where the benefit lies.
Nick
Higher bypass ratio and greater efficency.
Firings, if well done, are good for employee morale.
MrChips From Canada, joined Mar 2005, 706 posts, RR: 0 Reply 7, posted (4 years 7 months 3 weeks 2 days 13 hours ago) and read 12402 times:
A geared turbofan offers much a much better SFC (specific fuel consumption) than just about any other engine offered. Again, the major disadvantages of this engine (such as huge maintenance cost for the gearbox...could double overhaul costs over current or bleedless engines) could outweigh the advantages.
Not only that, but a lower fan rotation speed allows for less noise, allowing for a larger fan without violating any noise restrictions. A larger fan makes for a lerger bypass ratio, which in turn allows for either a substantially reduced noise footprint, or more power for a comparable noise footprint (compared with previous generation engines). Essentially, it allows the fan to run at a greater blade pitch than a conventional fan.
Now, correct me if I'm wrong, but I am under the impression that the P&W entry into the 787 engine selection was based upon a geared, HBP version of the F119?
727EMflyer From United States of America, joined Mar 2005, 547 posts, RR: 1 Reply 8, posted (4 years 7 months 3 weeks 1 day 22 hours ago) and read 12287 times:
Quoting Beowulf (Reply 5): And why is this better or an innovation? I don't understand where the benefit lies.
A larger fan running at a slower speed is more efficient than a smaller fan running at a faster speed. In addition to the noise benefits described above, the great amount of torque that is created when you gear the speed down will let a smaller turbine (read: less fuel consumption) provide the same power output to the fan. Propeller power has been doing this for decades, I believe the first major example being the F4U Corsair flown by the US Marines and Navy in WWII. The same concept is applied in nearly every field mechanical engineering gets involved with. Look at your car... if you have a standard transmission, yes you CAN start from a dead stop in third gear but the gas pedal will be floored to get you to even 5 mph! If PW, or the others, can get fuel efficiency with a concept like this, and with further advances in technology along the lines of GEnx it would be VERY attractive to the likes of 787 and A350, but the technology isn't ready to perform in a turbofan engine.
Areopagus From United States of America, joined Sep 2001, 1288 posts, RR: 1 Reply 9, posted (4 years 7 months 3 weeks 1 day 22 hours ago) and read 12279 times:
In a 2-spool engine, one turbine turns the high pressure compressor, and the other turns the low pressure compressor and the fan. But the fan, being bigger, is most efficiently driven at a lower speed than is most efficient for the LP compressor. Hence the gearbox.
Rolls-Royce has long used an alternative approach: a 3-spool engine, wherein the fan and LP compressor are driven at different speeds by different turbines.
It weighs more, but then, so does a gearbox. In the past, gearboxes have had particular problems with wear, and big fans take a lot of power. AW&ST estimated that it takes 25,000 shaft horsepower to drive the fan on a 787.
F14D4ever From United States of America, joined May 2005, 316 posts, RR: 4 Reply 10, posted (4 years 7 months 3 weeks 1 day 3 hours ago) and read 12214 times:
Quoting Areopagus (Reply 9): ... big fans take a lot of power. AW&ST estimated that it takes 25,000 shaft horsepower to drive the fan on a 787.
Strictly speaking the AvWeek number is 'thrust horsepower', not shaft power. They're slightly different.
What they didn't tell you is power transmission requirements at takeoff. For comparison, the GE90-115 fan is absorbing over 100k shaft horsepower to put out ~115k pounds thrust. On the 747-400, the CF6-80C2B fan transfers approximately 50,000 shaft horsepower generating ~60000 pounds thrust. If we dare to interpolate transfer efficiency, thrust, and power linearly, the GEnx-75 fan ought to be transferring roughly 65000 hp shaft-to-gaspath at takeoff. This number would seem to be the operative number for hypothetical gearbox design.
Efohdee From United States of America, joined Oct 2004, 214 posts, RR: 0 Reply 11, posted (4 years 7 months 3 weeks 16 hours ago) and read 12151 times:
The Honeywell/Garrett TFE-731 has a gear driven fan.
TwinCommander From United States of America, joined Apr 2005, 114 posts, RR: 0 Reply 12, posted (4 years 7 months 2 weeks 22 hours ago) and read 11956 times:
Same as the Honeywell 331. Though it is meant to have a prop on the end of it.
Dive and maintain 2500, cleared runway 10r approch, Fedex 3603 Heavy
Lightsaber From United States of America, joined Jan 2005, 5509 posts, RR: 87 Reply 13, posted (4 years 7 months 2 weeks 2 hours ago) and read 11916 times:
Folks, Since I worked on several "paper" geared turbofans I feel *very* qualified to answer this question.
Background: I had worked on the pw8163, pw8133 (737NNG/320NG concept) and other concept engines for years on the fluids side.
First a technical background probably more appropriate for tech-ops, but I'll post it here.
1. The fan has its highest efficiency with a tip speed of about mach 1.1. Yes, curved blade fans to change the optimum tip blade speed (or you can think of it as RPM, but engines are designed to Mach number and RPM falls out). One needs to keep a significant portion of the fan, most of the fan area, just subsonic to keep high compression efficiency.
2. The efficiency of the engine drops off *dramatically* at even slightly higher mach numbers due to shockwave propagation. Again, curved blade technology helps mitigate this a bit, but it doesn't eliminate it.
3. The turbine has its best efficiency at about the same mach number. But... Its operating in a *much* hotter environment (read lower mach number) on a much smaller diameter (read lower mach number). So... The turbine *must* be sped up for best efficiency.
4. The low compressor also has about the same Mach=1.1 blade peak efficiency point. But its a smaller diameter than the fan... (read its RPM is way too low) RR gets around this by putting the low compressor on its own turbine.
5. An exposed propeller has high tip losses;a shroud really helps keep the air on the blades and mitigate shock losses. Not to mention the significant noise reduction. One cannot get the average mach number at the most efficiency levels without the shroud (nacelle).
Most turbofans run on a N1 (low spool RPM) of about 1300 RPM. Ideal for the fan would be about 1,150 to 1,200 RPM (slightly higher for a smaller engine). Ideal for the turbine would be about 3,600 RPM. But... the low compressor starts having problems that fast as its optimum RPM is about 2,800 or so. Thus run the turbine at 3,000 RPM, overspeed the low compressor a little as the turbine is a little underspeed (peak efficiency compromise), and gear the fan down to its optimum or ~ a 3:1 gear ratio. Note: The gear ratio is going to be a function of engine size. Note: peak fan RPM does go up a little with curved blades, I'm doing straight blade fan Mach numbers (I must respect NDA's.) As to horsepower... I'm also still under NDA on that aspect. The rest Pratt published at one time or another so is in the public domain.
Pratt did propose the geared turbo fan for the sonic cruiser and Boeing was loud and clear that they weren't going to be the geared turbofan launch customer. When Pratt proposed it again for the 787, they entered the room with another proposal that was a conventional shaft arrangement as Boeing dismissed the geared turbofan very quickly. Why? Recall that half of the propeller plane crashes in WWII were due to engine failures and half of those were due to the reduction gearbox failing. Ok, modern lubricants and more importantly temperature sensors eliminate the "surprise catastrophic" failure mode, but aerospace is a conservative industry.
Quoting MrChips (Reply 7): A geared turbofan offers much a much better SFC (specific fuel consumption) than just about any other engine offered.
~10% better. At higher thrust levels, a greater efficiency gain is possible (as with a tripple spool too). The weight difference is smaller as the weight of the gearbox is about the same as the weight saved by fewer compressor stages due to operating the low compressor at a more efficiency RPM (mach #).
Quoting MrChips (Reply 7): Not only that, but a lower fan rotation speed allows for less noise,
Much less. A geared turbofan is an instant drop of 2 noise categories (Far 36 Cat 3 down to a cat 5). Forget the chevroned nacelles, they don't do much once you've dropped the noise that much.
DfwRevolution From United States of America, joined Jan 2010, 39 posts, RR: 54 Reply 14, posted (4 years 7 months 2 weeks 2 hours ago) and read 11908 times:
>> When Pratt proposed it again for the 787, they entered the room with another proposal that was a conventional shaft arrangement as Boeing dismissed the geared turbofan very quickly. Why?
Wasn't the IAE Superfan a geared turbofan? In that event, Boeing was trying to avoid being the second customer burned by the geared turbo...
Lightsaber From United States of America, joined Jan 2005, 5509 posts, RR: 87 Reply 15, posted (4 years 7 months 2 weeks 2 hours ago) and read 11904 times:
Quoting DfwRevolution (Reply 14): Wasn't the IAE Superfan a geared turbofan? In that event, Boeing was trying to avoid being the second customer burned by the geared turbo...
Yes, the IAE was supposed to initially be a geared turbofan. Airbus was very unhappy as the A342/343 business case was partially built on the higher engine efficiency. Obviously the airframes did well in the end. And yes, the A320 would have benefited from a GTF too.
BTW, if you didn't notice from my post, engine design is a *very* iterative process due to different groups "duking it out" while the sytems group makes sure the overall product is the best it can be.
This does make me wonder, since the 787 has a common mechanical & electrical mounting for the engines, what would it hurt to let P&W develop their engine for that interface and certificate it at their own expense? I can think of a couple of possible reasons:
1. It still takes some Boeing employees' time to communicate the interface. But Pratt could pay compensation.
2. Boeing is really distrustful, and thinks there is a good chance of unreliability that would reflect on their airplane. But, when Boeing did the downselection, they did say they were pleased by all 3 engines. Just PR?
Lightsaber From United States of America, joined Jan 2005, 5509 posts, RR: 87 Reply 17, posted (4 years 7 months 1 week 6 days 21 hours ago) and read 11881 times:
Quoting Areopagus (Reply 16): This does make me wonder, since the 787 has a common mechanical & electrical mounting for the engines, what would it hurt to let P&W develop their engine for that interface and certificate it at their own expense?
RR & GE were promised a "2 way exclusive." As risk sharing partners in the 787 they will have that provision in writing. There is a lot more than this, but it doesn't belong on tech/ops.
What does belong on this topic is that *any* engine that Pratt would design that would be "better enough" than the Trent 1000 or GenX would require a GTF. It could be made to fit in the common nacelle of the 787. It could be done technically, but not contractually. (e.g., Boeing would have to immediately pay back the "risk sharing loans" paid by RR and GE.)
Ferroviarius From Norway, joined Mar 2007, 71 posts, RR: 0 Reply 18, posted (2 years 8 months 2 weeks 6 days 6 hours ago) and read 9934 times:
Good evening.
I should like to re-activate this old thread and allow myself to post two questions.
First, however, I should like to thank Lightsaber for the very informative contribution, which I quote completely:
Quoting Lightsaber (Reply 13): Folks, Since I worked on several "paper" geared turbofans I feel *very* qualified to answer this question.
Background: I had worked on the pw8163, pw8133 (737NNG/320NG concept) and other concept engines for years on the fluids side.
First a technical background probably more appropriate for tech-ops, but I'll post it here.
1. The fan has its highest efficiency with a tip speed of about mach 1.1. Yes, curved blade fans to change the optimum tip blade speed (or you can think of it as RPM, but engines are designed to Mach number and RPM falls out). One needs to keep a significant portion of the fan, most of the fan area, just subsonic to keep high compression efficiency.
2. The efficiency of the engine drops off *dramatically* at even slightly higher mach numbers due to shockwave propagation. Again, curved blade technology helps mitigate this a bit, but it doesn't eliminate it.
3. The turbine has its best efficiency at about the same mach number. But... Its operating in a *much* hotter environment (read lower mach number) on a much smaller diameter (read lower mach number). So... The turbine *must* be sped up for best efficiency.
4. The low compressor also has about the same Mach=1.1 blade peak efficiency point. But its a smaller diameter than the fan... (read its RPM is way too low) RR gets around this by putting the low compressor on its own turbine.
5. An exposed propeller has high tip losses;a shroud really helps keep the air on the blades and mitigate shock losses. Not to mention the significant noise reduction. One cannot get the average mach number at the most efficiency levels without the shroud (nacelle).
Most turbofans run on a N1 (low spool RPM) of about 1300 RPM. Ideal for the fan would be about 1,150 to 1,200 RPM (slightly higher for a smaller engine). Ideal for the turbine would be about 3,600 RPM. But... the low compressor starts having problems that fast as its optimum RPM is about 2,800 or so. Thus run the turbine at 3,000 RPM, overspeed the low compressor a little as the turbine is a little underspeed (peak efficiency compromise), and gear the fan down to its optimum or ~ a 3:1 gear ratio. Note: The gear ratio is going to be a function of engine size. Note: peak fan RPM does go up a little with curved blades, I'm doing straight blade fan Mach numbers (I must respect NDA's.) As to horsepower... I'm also still under NDA on that aspect. The rest Pratt published at one time or another so is in the public domain.
Pratt did propose the geared turbo fan for the sonic cruiser and Boeing was loud and clear that they weren't going to be the geared turbofan launch customer. When Pratt proposed it again for the 787, they entered the room with another proposal that was a conventional shaft arrangement as Boeing dismissed the geared turbofan very quickly. Why? Recall that half of the propeller plane crashes in WWII were due to engine failures and half of those were due to the reduction gearbox failing. Ok, modern lubricants and more importantly temperature sensors eliminate the "surprise catastrophic" failure mode, but aerospace is a conservative industry.
Quoting MrChips (Reply 7):
A geared turbofan offers much a much better SFC (specific fuel consumption) than just about any other engine offered.
~10% better. At higher thrust levels, a greater efficiency gain is possible (as with a tripple spool too). The weight difference is smaller as the weight of the gearbox is about the same as the weight saved by fewer compressor stages due to operating the low compressor at a more efficiency RPM (mach #).
Quoting MrChips (Reply 7):
Not only that, but a lower fan rotation speed allows for less noise,
Much less. A geared turbofan is an instant drop of 2 noise categories (Far 36 Cat 3 down to a cat 5). Forget the chevroned nacelles, they don't do much once you've dropped the noise that much.
I hope this helps,
Lightsaber
Now my questions:
a)
Would it have been possible to avoid a gear wheel based gear box and use a hydraulic gear box (à la Voith, see e.g. http://www.voithturbo.de/index_e.htm or )?
b)
Would it make sense to optimize the angular velocity of not just the fan but also the other elements in the compressor? While it would be extremely hard to make this efficiently using gear boxes with wheels - since one would need an individual gear box for each element, making everything extremely heavy -, one could use one hydraulic shaft for individually gearing all driven rotating elements. (I hope I could make it clear what I mean.)
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From Canada, joined Jul 2004, 2359 posts, 
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From Singapore, joined Jul 2003, 679 posts, 
It could be made to fit in the common nacelle of the 787. It could be done technically, but not contractually. (e.g., Boeing would have to immediately pay back the "risk sharing loans" paid by RR and GE.)
From Norway, joined Mar 2007, 71 posts, 
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