American twins,Brit triple spool engines?

[Vibes]

Hi Guys,

While I was reading up on jet engines used on airliners,I've realised that most of the American built engines like the GE CF6, GE90 and the Pratt and Whitney PW4000 are all twin spool engines whereas those of the Rolls Royce Trent Series are three spool engines.

Thus,is there a reason as to why the Americans tend to favour twin spool engines over triple spool engines?What are the advantages of the twin spool and the triple spool engines?

Would really appreciate if you guys could shed some light on this.Thanks.

[Meikleour]

Vibes: I think you will find it is to do with patent protection.

[tuna hp]

3 spool engine can allow a greater differential between the speed of the high pressure compressor and the fan. This should alllow for higher fuel efficiency.

2 spool engines have fewer parts and are less complicated, so they should have lower maintenance costs.

Currently not all Rolls Royce engines are triple spools, only their biggest ones which are used on the biggest planes for intercontinental flying where they will have a relatively high amount of flight hours and a relatively low number of engine cycles. In other words, where cruise efficiency is relatively more important than engine durability, compared to planes that make several more lower distance flights each day.

Pratt and Whitney is working on their own technological equivalent to the triple spool: the geared fan. Just like the triple spool, it adds complexity in order to allow the speed of the high pressure compressor to be further removed from the speed of the fan.

EDIT: I can color in some more information.

The reason that its advantageous to create a bigger difference between the fan speed and the high pressure compressor speed is because the optimal speed for the fan is tied to the speed that the airplane is flying, while the optimal speed for the high pressure compressor is as high as is possible.

The laws of propulsion are that an airplane will be propelled most efficiently when its exhuast is moving at close to the same speed as the airplane. So if the plane is flying 500 mph, you would want the engines to be pushing a large volume of air at 510mph instead of a smaller volume of air at 1000mph. In the latter scenario, even though your engine may be outputting the same exact amount of energy, a lot of it is lost so it is less efficient. This is the reason why you see those massive super-high-bypass turbofans on large planes, and many of those are the Rolls Royce three spools. They need huge fans in order to push a high enough volume of air. This is also why turbofans have completely replaced turbojet engines, even though the former is theoretically bigger, heavier, and more complex. When you think about it, a turbojet engine is essentially just the core of a turbofan without the big, heavy, drag inducing fan at the front. As far as converting fuel to raw energy output, a turbojet is theoretically more efficient than a turbofan. The problem is that the turbojet thrust might be moving at Mach 2+, so if you're trying to push a subsonic airplane, there's a ton of loss there versus the turbofan pushing a higher volume of air at a slower speed.

Interesting trivia: The Concorde's turbojets had higher propulsive efficiency than any turbojet or fan airliner of its time. This is because the Concorde combined the higher raw efficiency of a turbojet engine with cruise speeds high enough to be relatively close to the exhaust speed. The specific fuel consumption per passenger mile would still be really high though because the Concorde had much higher weight and drag per passenger.

Getting back to 2 spool vs 3 spool... the reason that you want the high pressure compressor to go as fast as feasible is because the faster it spins, the higher compression ratio you'll get, and just like your car, higher compression ratio means better efficiency. Also just like your car, the limiting factors are the technology and materials that you're willing to invest in order to achieve those higher ratios, and the amount of extra maintenance that you're willing to endure. For example, an F1 racing engine has a super high compression ratio, but they more or less have to throw it out after each race.

[Wizofoz]

Bear in mind that the reason Engine manufacturers produce engines is to make money.

The development of the original, 3 spool RB211 sent Rolls Royce broke!

After government intervention, the bailed out company had the technology to build upon, and now produces the very efficient (if a little finicky- ala BA 38!!) Trent.

It is interesting that the US manufacturers have never gone down the triple spool route, but are leaping past it to the geared fan solution for optimizing low-to-high pressure gradient.

[hetfield]

American = Keep it simple
British = Do it different


Ouch
;)

[grounded27]

The RB211 on the 752 has been a huge sucess, it has logged very high on wing hours before overhaul. As FedEx has been the largest 727 operator for years it will probably be the largest 757 operator in the near future as they can not cut the doors fast enough for them to replace the 727 fleet.

[sevenstrokeroll]

KISS

keep it simple stupid

[tuna hp]

KISS

keep it simple stupid

To an extent. But if fuel is 25% of the total cost of your typical 737 flight or 50% of the total cost of your typical 777 flight, then for those long haul international flights it probably makes sense to invest more in more sophisticated engines that might be more expensive to maintain but deliver better fuel economy.

[hetfield]

to invest more in more sophisticated engines that might be more expensive to maintain but deliver better fuel economy.What engine was it with that A380 near crash disaster?

[sooty655]

The three-shaft design separates the fan from the LOW pressure compressor, not the HP. The LP is then often known as the IP (Intermediate Pressure).

Similarly, the geared fan arrangement allows a speed ratio between the fan and the LP(IP) compressor.

[gas path]

That's confusing the issue!
The RB211 always has had the LP compressor (Fan. The 011 module) The IP compressor and the HP compressor.

[chris weston]

Tuna

Good stuff sir.

Not quite so with F1 motors these days. They have to last 3 (!) races.

Forced induction (usually turbo charged) petrol engines when on boost run very high effective compression ratio motors but not too high .....

....or they become diesel!

[tuna hp]

The three-shaft design separates the fan from the LOW pressure compressor, not the HP. The LP is then often known as the IP (Intermediate Pressure).

Similarly, the geared fan arrangement allows a speed ratio between the fan and the LP(IP) compressor.

Semantics. I was thinking about it in terms of wanting to allow the fan and the HP compressor to both spin at closer to their optimal speeds (which for the fan would be slower, the HP compressor faster). Plus not all twin spool engines have a compressor on the LP spool. Plus on a 3 spool, the slowest spool, the one that the fan is on, still gets called the "LP spool".

[sevenstrokeroll]

if you design an engine for efficiency in terms of fuel use...you get that kind of engine.

there are plusses and minuses ...better a few more drops of fuel used than an engine that isn't robust and reliable.

[Cardinal]

Plenty of Pratt & Whitney 3-spools. They just happen to be Turboprops. The PW100 series is a marvelous design with each turbine stage turning a different shaft, Nh, Nl, Np. It manifests the usual 3-spool advantages, impressive Sfc, nimble power response, and easy starting. By the time ones fingers move from the start switch to the fuel control Nh is high enough to introduce fuel, and everything clicks right along. Puts the PT6 to shame.

[Turbine D]

I don't agree that large fan three spool engines are more fuel efficient than two spool designs in the same thrust category. In fact, generally, it is just the opposite. The advantage of a three spool design is a shorter and generally lower weight engine. When coupled with a shorter nacelle, less drag is produced. With these two factors combined (shorter engine/shorter nacelle), parity may be reached with two spool engines. While there may be some advantages of better matching of various compressor section in a three spool design, that is only one part of the total package to gain high efficiency (low fuel burn).

If three spool engines were indeed more fuel efficient, wouldn't we all be flying on three spool engines?

[bearfoil]

The TRENT weighs a ton less than a comparable GE. It gains six hundred extra pounds back because it labors behind a squashed Titanium cylinder array instead of a Carbon Fibre Wheel. Heavy Fan, lightweight Core.

GE, PW, Roller. An engine comes off wing out of plan, and it loses its SFC advantage (if there is one) in perpetuity.

Emirates chose EA engines over Rolls for its A380's. They are unwise, and don't know the value of Fuel??

More than any simple answer to engine selection, the complicated route would fill several books.

[tuna hp]

I don't agree that large fan three spool engines are more fuel efficient than two spool designs in the same thrust category. In fact, generally, it is just the opposite. The advantage of a three spool design is a shorter and generally lower weight engine. When coupled with a shorter nacelle, less drag is produced. With these two factors combined (shorter engine/shorter nacelle), parity may be reached with two spool engines. While there may be some advantages of better matching of various compressor section in a three spool design, that is only one part of the total package to gain high efficiency (low fuel burn).

Its all related. The very reason that they can theoretically be shorter and lighter is because they can remove compressor and turbine stages, and the only reason that they can remove stages while increasing efficiency is because all the spools are spinning at much closer to optimal speeds.

If three spool engines were indeed more fuel efficient, wouldn't we all be flying on three spool engines?

Well come on... ramjets are indeed faster than turbofans, so why aren't we all flying around at Mach 5 [/sarcasm].

I'm no expert, but I would think it has a lot to do with the fact that the 3-spool is an inherently more complicated setup which can induce higher maintenance costs, and so far 3 spools have only made sense for applications where there are relatively many flight hours per engine cycle. However, I have read that Rolls Royce is readying a lower output/ short haul optimized three spool in time to compete for use on the 737 replacement around 2020.

[bearfoil]

The TRENT comes off wing in any combination of six "Modules". 1-5, and eight.

The Modularity was highly touted; wags insisted it was necessary due the need for TRENT's bits to be in the shop. Not too far wrong, v/v the 9.

Modularity saved money, a promise Rolls made to its clients. It saved so much, Rolls took the engines back (on "Total Care"), and advantaged themselves of what they thought would be a profit tool. It was, and it wasn't.

So you are correct in saying the Tri-Spool is more complex, (more parts, more pieces) but it is the separation of twin spool shafts into halves that make it easier to r/r, and more susceptible to service isssues relative to joints, mass, and metallurgy.

imo


(I see you changed Turbine D's qualifier "efficient" to faster. Caught that,)

[twistedenginestarter]

Why only 3 shafts? Presumably 6 shafts would allow even more optimal speeds.

When the RB211 face came out a typical automobile automatic gearbox would have three gears. Now they have up to eight.

I wonder why aero engines have not made corresponding progress.

[bearfoil]

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.

[barit1]

ROFL! And why not a CVT or three?

[unmanned transport]

Twin spool engines are more fuel efficient than three spools.
See ICAO Engine Emissions Databank....Aircraft Engine Emissions | Human and Environmental Issues | Safety Regulation (http://www.caa.co.uk/default.aspx?catid=702)
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 (http://www.youtube.com/watch?v=8DfTX-IAkdg) ..........( 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.

[HarryMann]

The development of the original, 3 spool RB211 sent Rolls Royce broke!It was fundamentally the delay due to problems with the hybrid fan construction (damage tolerance/l.e. erosion) that was responsible, not the choice of a 3-spool configuration..

[Turbine D]

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.

[unmanned transport]

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.

[Jane-DoH]

Wouldn't a geared-fan have torquing issues similar to propellers?

[lomapaseo]

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

[unmanned transport]

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

[Turbine D]

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?

[Turbine D]

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 (http://www.youtube.com/watch?v=7CU0B7VeLFU)

[grounded27]

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.

I have just been exposed to the rb211 on the 752, it is valuable due to it's long on wing time. We have our first pratt powered jet that get's better econemy but has to go out for overhaul in half the time. Just wondering if modern RR/Trent motors are closer to competing with N2 powered aircraft in fuel burn. The company I work for cares more about reliability than fuel cost's as we profit on our flights based on rock solid logistics and carry a high liability over most airlines for late flights.

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..

[sevenstrokeroll]

remember when the Airbus 340 was going to have engines with variable pitch fans?

simple is better...

[bearfoil]

There is a design that locates the Power in the fuselage, with the Fans, freight and fannies in the wings. Drag reduction enormous, but the drawings are proprietary.

How would you do it??

[chris weston]

Bear,

Electrically?
That's the way they went on ships!
I know, lots of Cu wire gets involved and I know the density of it.....

CW

[Turbine D]

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/download?doi=10.1.1.121.8596&rep=rep1&type=pdf

Turbine D

[tuna hp]

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.

[unmanned transport]

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.

[Jane-DoH]

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?

[galaxy flyer]

Jane DOH

The torque is due to the rotation of the propeller, not having a gearbox. A CE-150 has torque, but no gearbox.

GF

[Jane-DoH]

galaxy flyer

Then how come the fans on jet-engines don't cause significant amounts of torque?

[411A]

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.:ok:
NB.
Also operated Conway and Dart-powered airplanes, no problems with those, either.

[galaxy flyer]

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

[bearfoil]

Thrust, Torque, Torsion, Gasoline, JetA. It's all Newton.

[Jane-DoH]

galaxy flyer

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.

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.

[balsa model]

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.

[bearfoil]

I guess wiki trumps 11 thousand hours gf.

(Jane: see, galaxy: C-5. Flyer: Pilot. Our friend has burned enough kerosene to qualify as an expert in any physics. Mostly, I think, burned in massive TurboFans.

bear

[Rosiemoto]

so you do Stats by your own personal experience?

quite a cross section

[Jane-DoH]

I wasn't trying to trivialize galaxy flyer at all. I was just trying to point out that the fan does produce a substantial amount of thrust.

[CliveL]

RR leads the pack of the three engine manufacturers with in-flight uncontained engine failures

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.

[Jane-DoH]

Hasn't the CF6 always had problems with poor resistance to FOD, catastrophic engine failures and so forth?

[barit1]

Jane-DoH:Then how come the fans on jet-engines don't cause significant amounts of torque?

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.

[balsa model]

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.)

[Turbine D]

CliveL

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.

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 (http://web02.aviationweek.com/aw/mstory.do?id=news/avd/2011/02/07/08.xml&channel=mro&headline=AD%20Aimed%20At%20Delinquent%20CF6%20Operators)

Turbine D

[Turbine D]

JaneDoH

Hasn't the CF6 always had problems with poor resistance to FOD, catastrophic engine failures and so forth?

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

[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.OK, I accept that the AD was issued for that reason, but it still remains that the failure mode was identified in the 1970s, and GE did not issue their safety bulletin until 28 August 2009, 14 months after the first noncontainment incident on 07 July 2008, and 5 months after the second on 26 March 2009.

[unmanned transport]

The worst time to get an uncontained engine failure is in flight.

GE - 0.
Rolls Royce - 4.

[Turbine D]

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 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.

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

[Jane-DoH]

barit1

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.

Oh, I thought there was some kind of gyroscopic effect at work from the gear-box.


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.

Why is this so? Didn't they have various things to keep birds away from airports?

[Turbine D]

JaneDoH

Why is this so? Didn't they have various things to keep birds away from airports?

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

[LeadSled]

Emirates chose EA engines over Rolls for its A380's. They are unwise, and don't know the value of Fuel??

Bearfoil,

I don't know where you got this idea.

Compared to the Trent 900 on the A380s, Emirates are way ahead on sfc and block fuel on their aircraft, to the degree that Airbus is producing/has produced a new Performance Manual (by whatever name Airbus uses) to take full advantage of the actually achieved figures.

By comparison, the Trent 900 ( and traditionally since the RB211-22D through the -C,-D and -524) is still well below book figures and contract guarantees.

Incidentally, the "short" cowls of the various RB 211 produce some quite interesting drag problems, particularly above M0.855, not so the CF6-80C2 on many B744 and B767.

In every weight comparison "like for like" the RB 211 is heavier than the GE or PW equivalent, a function of the "three spool" design.

I would check the weight claims of the Trent v the rest very carefully.

All publicly available information.

Tootle pip!!

[bearfoil]

LeadSled

A rhetorical question, and sarcastic in derivation. We agree entirely re: Emirates ea's

bear

[Rj111]

I believe the Trent 800 offers the lowest takeoff consumption on the 777-200A/ER, which is in part due to the triple spool design. This combined with its light weight means it is more efficient than the GE90 for flights under ~3000nm, after this the GE takes over (not sure where Pratts come into this). But then again, if you want a 777 to be efficient under 3000nm you should buy an A330-300.

Another advantage of the triple spool design that an engine family is extremely scalable.

Note that the RB211 has ranged from the -535 at ~37klb to the -T800 with ~94klb. RR also hoped to supply an engine for the 777LR program which demonstrated 114klb in test but were denied a place due to engine exclusivity.

This scalability has proven crucial though as it has allowed RR to not only supply engines for the 787, but exclusively supply them for A350. So even though the 787 order books so far say the GeNX is a better package than the Trent, RR stands to dominate the upcoming generation of widebodies.

[unmanned transport]

For the B777-200ER fitted with the GE - Pratt - RR; here is the ICAO fuel burn data.

GE-94B - Take-off - 3.513 kg/s
Pratt 4090-Take-off - 3.926 kg/s
RR 895 - Take-off - 4.03 kg/s

GE-94B - Climb-out - 2.831 kg/s
Pratt 4090- Climb-out - 2.996 kg/s
RR 895 - Climb-out - 3.19 kg/s.

So from the above data, the RR burns the most fuel during take-off and also in the climb-out.

I have yet to see good data to prove otherwise.

[unmanned transport]

Most engines are scaleable.

I'm interested in the scaleability of the new Pratt GTF series. So far indications are that it will be scaleable all the way from engines powering the Japanese MRJ 100 seat jet to wide bodies. Pratt may even knock GE from number one position on the A320NEO. I predict that Pratt will have a major come-back in wide body frames and will regain number two position in engine sales but it will take some time. This engine will be a 'game changer'. Long live the dependable flying Eagle symbol on engine cowlings.

[FLAPS 10-100]

Someone mentioned P&W doing stuff with geared fans. Rolls Royce did work on a geared fan engine in the late 70's early 80's using a modified M45 engine. called the silent demonstrator. I guess that they never needed the technology the project was scrapped.

[Jane-DoH]

LeadSled

Incidentally, the "short" cowls of the various RB 211 produce some quite interesting drag problems, particularly above M0.855, not so the CF6-80C2 on many B744 and B767.

Doesn't a 747 have a maximum cruise mach of 0.88 and a MMO of 0.92?

In every weight comparison "like for like" the RB 211 is heavier than the GE or PW equivalent, a function of the "three spool" design.

I forgot about that! God those engines were a beast in terms of weight. IIRC, they were planning on using some kind of composite which was to be used on at least the fan-blades if not some of the compressor stages. I do know they wanted to use wide-chord fan-blades (which would be excessively heavy if they used metal, so they instead decided to use composites) to do away with the mid-span shroud. It turned out to handle rain, sand, and FOd poorly, so they replaced it with a more conventional titanium fan which drove up the weight of the fan (possibly some compressor blades), and then required the engine to be strengthened around the extra weight.


FLAPS 10-100

Someone mentioned P&W doing stuff with geared fans. Rolls Royce did work on a geared fan engine in the late 70's early 80's using a modified M45 engine. called the silent demonstrator. I guess that they never needed the technology the project was scrapped.

I assume RR's geared-fan concept worked well...

[gas path]

Not forgetting of course that the weight of the RB211 includes the complete pod. The CF6 and PW4000 the thrust reversers are a boeing part and stay with the airframe.
Reference the fan blades. RR got it wrong as the technology at the time was woefully inadequate. Some 30 years later composite knowledge had come on leaps and bounds and the GE90 composite fan blade is excellent albeit with a titanium leading and trailing edge and titanium in the root BUT it is heavier compared to the Trent Titanium blade and in something of a backward step the -115 blade is susceptible to birdstrike damage. As for maintenance I much prefer the RR (all varieties of the 211)as they are so simple.
One thing the RR motor has always been good at performance retention over its lifetime. The hightime engine achieved over 40k hours on wing. The mount bolts still had the boeing seal on them when it was eventually pulled for overhaul.

[bearfoil]

gas path

An interesting use of the English language for a tech issue. So the RR is superb at retaining its performance whilst it is retaining its performance??

High time leader 40k on wing?? Excellent!! Your statements want data in support of what I think you mean. An anecdote, and an anomalous one at that, I fear.

[K_9]

What factors cause a decrease in performance over the life of the engine?

[unmanned transport]

Sorry Rj111, I should have noted the link for the fuel burn data as it's always good to provide a link to back up ones notation(s).

Document Categories | Human and Environmental Issues | Safety Regulation (http://www.caa.co.uk/default.aspx?catid=702&pagetype=68)

I hope the previously noted data clears up and misunderstanding with regards to fuel burn in the climb stage.

[unmanned transport]

Airbus Payload Range graph for A330-200, A330-200F and A330-300.
http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/Airbus_AC_A330_Jan11.pdf

Note: The GE engined aircraft has the best range as indicated on the Airbus graphs.


ICAO fuel consumption data.
Document Categories | Human and Environmental Issues | Safety Regulation (http://www.caa.co.uk/default.aspx?catid=702&pagetype=68)

Pratt 4164 - Take-off 2.721 kg/s - Climb 2.239 kg/s
GE CF6-80E1 - T-off 2.97 kg/s - Climb 2.337 kg/s
RR Trent 700 - T-off 3.2 kg/s - Climb 2.58 kg/s

Again, the RR triple spool loves her fuel.

[bearfoil]

K 9

Loss of performance is basically just a loosening of the tolerances in the erm....gas path. Tip clearance allows leaks around what must remain a dynamic gas tight seal, or loss of compression occurs, (energy).

I think.

[Turbine D]

K 9

As Bear said, leakage of air around blade tip results in degraded performance. In the LP turbine the blade tip shroud seal teeth wear down creating leakage. Also, compressor blading tends to pick up dust that sticks to the aifoil surfaces and over time builds up changing the aerodynamics from what is desired. In the HP turbine, residue also builds up on the blade airfoils, probably coming from the fuel burn in the combustor that changes performance/efficiency for the worse. Today, some airlines have their engines water washed to restore the intended aerodynamics.

[Turbine D]

unmanned transport

I'm interested in the scaleability of the new Pratt GTF series. So far indications are that it will be scaleable all the way from engines powering the Japanese MRJ 100 seat jet to wide bodies.

I would think the GTF engine would be capable of being scaled larger or smaller than that targeted for the A-320NEO. So far all looks well in the testing phase. Much will depend on the robustness of the gear feature and whether or not required maintenance of this feature is minimal.

Don't forget about the GE "LEAP" engine. It too is going to offer 15% or better fuel utilization verses current engine technology.

[unmanned transport]

For sure Turbine D, this is the prime goal for Pratt, to scale an engine for wide bodies. Hey, maybe a twin decker twin engine monster of a lifter.

(Sorry, I don't know how to copy and paste a previous poster's comments)
Help!

[Turbine D]

unmanned transport

(Sorry, I don't know how to copy and paste a previous poster's comments)
Help!

I have an iMac. What I do to copy & paste is:

1. Pick the spot for the "quote" in your reply and click on the "Wrap(quote)tags" icon which is the third icon tab from the right (toolbar above).

2. Scroll down to the "Topic Review" and copy the comment you want to paste.

3. Scroll back up to your reply box and place your curser between the two quote boxes, click and then click paste.

Hope this works! :)

Turbine D

[Jane-DoH]

Why didn't RR try diffusion bonded titanium fan blades?

The GE-4 which was designed for the failed SST program used wide-chord titanium compressor blades that were formed this way (it's effectively like glass blowing with hot metal) and it was pretty much as light as if it was a honeycomb blade except it wasn't. As far as I know the blades worked fine (the plane simply didn't)

[Turbine D]

JaneDoH

Why didn't RR try diffusion bonded titanium fan blades?

The GE-4 which was designed for the failed SST program used wide-chord titanium compressor blades that were formed this way (it's effectively like glass blowing with hot metal) and it was pretty much as light as if it was a honeycomb blade except it wasn't. As far as I know the blades worked fine (the plane simply didn't)

The question is, how do you know (100% positively sure) the bond has been made? Perhaps today there is adequate inspection technology to survey the bonds and detect abnormalities now, but then inspection technology wasn't as advanced as today. The plane never got a chance to work, the contract (funding) by the US government was cancelled before any planes were built.

Turbine D

[unmanned transport]

Because to my knowledge, the USA holds the patent on diffusion bonded titanium fan blades. I may be wrong and someone please correct me if so.

[unmanned transport]

Thanks for the tutorial re copying, Turbine D but all I have at the top RH corner on my dark blue toolbar is #78(Permalink) underlined.

Not:

"Wrap(quote)tags" icon
which is the third icon tab from the right (toolbar above).

[Turbine D]

unmanned transport

all I have at the top RH corner on my dark blue toolbar is #78(Permalink) underlined.

Sorry, you might try the Forum on "Computer/Internet Issues & Troubleshooting" and go to frequently asked questions. This subject is one of them.

Turbine D

[Rj111]

Sorry Rj111, I should have noted the link for the fuel burn data as it's always good to provide a link to back up ones notation(s).

Document Categories | Human and Environmental Issues | Safety Regulation

I hope the previously noted data clears up and misunderstanding with regards to fuel burn in the climb stage.

Yeah i saw these earlier and was surprised as it's inconsistent with what i've heard.

Though to counter some of the discrepancies it's worth noting that the GE90-94 is much heavier and larger than the T895. This should matter more on the light A-model 777s though.

In addition the figures for the A330 are for a more powerful version of the Trent vs the GE (I CBA to check the Pratts). If you match the rated outputs, the GE and RR at least, are comparable...

http://www.caa.co.uk/docs/702/2RR022_01102004.pdf
http://www.caa.co.uk/docs/702/4GE081_01102004.pdf

RR must be doing something right though as they're the dominant provider on the A330 (by far). And i believe they just snuck the biggest share on the 772ER/772A/773A.

RJ :)

[Turbine D]

gas path

One thing the RR motor has always been good at performance retention over its lifetime. The hightime engine achieved over 40k hours on wing. The mount bolts still had the boeing seal on them when it was eventually pulled for overhaul.

Occasionally, some engines and operators achieve high time on-wing, it depends on lots of factors.

GE Aviation has recognized Kenya Airways for achieving the highest time on wing for a CF6-80C2 engine in Africa. The Kenya Airways' CF6-80C2 engine was installed on a Boeing 767-300ER aircraft in 2001 and has accumulated more than 35,000 flight hours and more than 6,400 cycles without a removal.

American Airlines has set a time on wing record for a GE CF6-80C2 engine - logging more than 40,000 flight hours and nearly 10 years of continuous on-wing operation on a Boeing 767 aircraft.

[unmanned transport]

RJ111, the B744 and B767s GE/Pratt powered craft outsold RR powered ones by a huge margin. In fact BA now have more GE powered 777s than RR powered ones and that is likely to increase with more 773ERs coming into their fleet.

Cathay and Qantas fleet numbers are moving more towards GE power as well.

I bet Qantas and SIA and LH rue the day they ordered Trent engines on their A380s from the huge grounding costs that hit them. I bet Emirates and Air France were smiling every day since they could launch their A380s with EA engines.- no groundings

[Jane-DoH]

Turbine D

The question is, how do you know (100% positively sure) the bond has been made? Perhaps today there is adequate inspection technology to survey the bonds and detect abnormalities now, but then inspection technology wasn't as advanced as today. The plane never got a chance to work, the contract (funding) by the US government was cancelled before any planes were built.

They did test the engine though


unmanned transport

Because to my knowledge, the USA holds the patent on diffusion bonded titanium fan blades. I may be wrong and someone please correct me if so.

I didn't know we did

[K_9]

Bearfoil and Turbine D
Thanks for your explanations. Those both make sense, though now I have another novice question.

When a turbine is windmilling on the ground, you hear a clicking noise. I am given to understand that this is from fan blades having some play (wide tolerances) built into their installation. I thought that design feature was to allow the blades to be flush against the outside circumference of the fan shroud or duct (for want of a better term). What's to keep the fan blade tips from overheating or wearing down at a rapid rate?

[unmanned transport]

K 9, I don't mean to steal Bearfoil or Turbine Ds 'thunder' but here is my take on all that clattering going on from that big 'wheel' in the wind.

During the fan's rotation in the wind, the top blade at the 12 o'clock position
going downhill, falls over towards it's neighboring blade due to the increasing angular separation 'veeing' towards the blade tip. Each blade has what's called a mid-span snubber which is a proturberance (sp?) chordwise across the blade about an inch deep on some engines. This is the first contact point on each blade against which each snubber which makes the clattering noise. When the engine is running the centrifugal force separates each blade equidistant from it's neighbor with a clearance.

[K_9]

Interesting--I always thought it was a radial movement that was happening.

[lomapaseo]

Add in that even the rocking of the blade root in its slot may cause some noise. Curved slots solve that problem. Used to be a problem years ago so I doubt that you hear anything on the newer engines today.

[Rj111]

I was mainly speaking of the Trents. The RB211 was never intended for the 767, it was requested by BA, but its true, it was not great for the 747 and was mainly ordered by the commonwealth.

Of course airlines are now going away from the Trent for the 777, GE bought their way into the LR program. Look at the stink AA, for example, kicked up when that occured. Incidently BA have always had more GE powered 777s than RR.

QF were in part screwed by the amount of sensationalist media coverage they received. How much of world heard about N330AA? Sure they will be angered by the incident and grounding, on the other hand, you shouldn't base a decision on 1 event - the aircraft will be in service for up to 20 years.

I not interested in a pissing contest though, plenty of prestigious airlines have endorsed the Trent, and in numbers. So back to my original point, the design must be doing something right, if that thing isn't fuel consumption.

[Turbine D]

K_9

unmanned transport gave a good explanation of the fan blade clanking heard on a windmilling fan. I think, but not positively sure, this was confined to the early CF6-6 engines on DC-10 aircraft. The fan blades are intentionally not held tightly in the fan disk slots when the fan is at rest (not rotating). Upon spool-up, the centrifugal force moves the blades outward, firmly and evenly seating the fan blade upper dovetail surface to the corresponding disk lobe surface.

Now a little history: When the DC-10 was introduced to revenue service, some airports didn't have either enough jetways or ones they had couldn't be used to board passengers on DC-10s. Also, many terminals were undergoing changes/upgrades. So airlines used mobile stairs for boarding. The stairs were just in front of the engine and if it was windmilling, the clanking noise unnerved boarding passengers. So the airlines asked GE if they could stop the clanking. GE redesigned the fan blade retainer component to stop the clanking but still permit proper seating of the blade upon spool-up. This modification was introduced throughout the DC-10 fleet. This anti-clank modification feature became standard in the CF6-50 & CF6-80A/C engines.

[lomapaseo]

GE redesigned the fan blade retainer component to stop the clanking but still permit proper seating of the blade upon spool-up. This modification was introduced throughout the DC-10 fleet

Redesigned under an AD to prevent another fatal acident like National Airlines N60NA

[Turbine D]

Rj111

There are many reasons why airlines select particular engines, why air-framers offer three, two, or one brand of engines for a given aircraft, or why engine producers choose to participate in a particular aircraft program or not.

Of course airlines are now going away from the Trent for the 777, GE bought their way into the LR program.

GE had an engine (GE90-115) that was already developed and certified by EASA & FAA. Rolls Royce did not. That meant GE could and did offer a better deal to Boeing looking at both timing and total aircraft certification cost which permitted Boeing to get this plane into revenue service sooner at lower cost than other alternatives.

I was mainly speaking of the Trents.

There are various reasons an airline selects a particular engine verses another besides SPF. These reasons include but are not limited to logistics, parts commonality, historical airline/engine manufacturer relationships over time, training costs for both crews and maintenance and so forth. Trent engines will continue to be sold to those operators where it makes total economic sense, relationships continue to be good and service is good.

Engine manufacturers carefully choose which programs to offer engines to or not. For example, GE chose not to participate in the Boeing 757 program because, at the time, they did not see a payback with three engine manufacturers participating, leaving only PW & RR to compete against one another. PW & GE decided not to compete on the A-350 program, leaving RR as the sole supplier. When the final A-350 design was released, the proposed GEnx engine for an earlier A-350 design concept was withdrawn as the final A-350 aircraft competes against the Boeing 777 ER/LR (GE90-115). It is business strategy at play, sometimes you win, sometimes you lose.

How much of world heard about N330AA?

Probably not much of the world knew. It was a ground failure. In fact, it probably shouldn't have happened. On the previous flight, the pilot reported unusual in-flight engine vibration, but to the degree not requiring the engine to be shut down. So instead of removing the engine from service and investigating what the cause might be, the decision was made to take the plane to a more remote area and run the engine up to full TO thrust. The problem was the HPT disk had developed a crack at one of the disk blade posts and the rest is history. The press wasn't there as it wasn't an in-flight uncontained failure during climb-out from the airport as was the Qantas incident. By the way, N330 was written off by the insurers and was dismantled on site at LAX.

[barit1]

By the way, N330 was written off by the insurers and was dismantled on site at LAX.

I was wondering about its final disposition; I had heard at one point that AA was planning to ferry it to the Mojave boneyard. Apparently that was not feasible.

[Turbine D]

barit1

Here is a site that shows the dismantling:

http://www.aircraftrecycling.com/pp%2008-09%20B767%20N330AA%20Airways.pdf

[411A]

Hmmm, much is made (it seems) that Rollers consume more fuel than their GE counterparts.

Nope, not the case, when you compare the L1011 with the DC10, at equal in-flight weights (mass, for our European friends)...

IE: the mad dog consumed 9% more, at the same enroute weight.
Confirmed by IATA data, at the time.
'Tis a fact.
Also, the three-spool Roller design was quieter, by a large measure.
Of the three American original widebody designs, only the L1011's (exclusively Rollers) were stage three compliant...at ALL weights.
(Again, 'mass', for our Euroland friends.:E)

I repeat....RollsRoyce manufactures mighty fine turbine engines.
So says me...with well over twenty thousand hours in RR powered airplanes.
And, at least another year to go....:ok:

NB.
Admitted however...the Rollers are significantly heavier than others, due to the three shaft design.
How much heavier?
Twenty six hundred pounds, in the case of the RR 211 series used on the B747.
But...is saved far more fuel in its years of service.

Another fact.

[Rj111]

GE had an engine (GE90-115) that was already developed and certified by EASA & FAA. Rolls Royce did not. That meant GE could and did offer a better deal to Boeing looking at both timing and total aircraft certification cost which permitted Boeing to get this plane into revenue service sooner at lower cost than other alternatives.


This is true, but RR were willing to go into the 777X program without exclusivity, unlike the other two. GE offered financial incentives to be a risk-sharing partner and that is what went ahead, in hindsight, an extremely good result for GE.

When the final A-350 design was released, the proposed GEnx engine for an earlier A-350 design concept was withdrawn as the final A-350 aircraft competes against the Boeing 777 ER/LR (GE90-115). It is business strategy at play, sometimes you win, sometimes you lose.

Just to add to that, GE were willing to power the smaller 2 A350s in its current incarnation, but Airbus wanted all 3, or nothing.

[bearfoil]

411A

You've lost me. How does comparing disparate airframes with different engines confirm fuel specifics v/v engine mfg.??

Enlighten us??

[411A]

Enlighten us??
Similar airframe configurations (trijets) at the same weight.
Quite reasonable actually, especially for the bean-counter types.

[unmanned transport]

411A, would you please substantiate your notation in the following paragraph with good data to prove your point, and not just loose talk off the top of your noggin:-
Thank you Sir.

"Rollers consume more fuel than their GE counterparts. Nope, not the case, when you compare the L1011 with the DC10, at equal in-flight weights".

(I'm even sceptical about some data that I look at nowadays!!)


Darn it anyway, this copy and paste previous quotes just does not work for me and it is frustrating......sorry folk.

[unmanned transport]

I keep thinking of this old timer engine taking it's time to flash up. Man, this grinding and fan blade clanking and belching of smoke is something else to hear and see. One could almost have gone for a good hearty breakfast and been back in time:)

Not much wonder Stewart and his greenies around LHR banded together to almost shut the works down at this airport, having to see this smoke and noise. Even the current models of Trents are slow dogs during start-up and like to belch out some smoke.
411A, you probably had your hands on the horns of this old frame for some trips. Some of your nervous pax must have just about freaked out listening to this start performance!

Just be patient and listen to all of this video. You'll shake your head at this pathetic performance.

YouTube - L-1011 N700TS Airline History Museum 1 (http://www.youtube.com/watch?v=8DfTX-IAkdg)

[K_9]

So you're suggesting that because the L1011 and the DC-10 are both widebody trijets with comparable weights, that they must have the aerodynamic performance? :ugh:

[gas path]

Even the current models of Trents are slow dogs during start-up and like to belch out some smoke.

What on earth are you on about now?:ugh:

[Turbine D]

unmanned transport

Just take a listen to this old clanker winding up.
That is what you call a "hot start"! ;)

Turbine D

[bearfoil]

411A

The only thing I can fathom from your comments is that you are setting up the Lockheed to garner compliments for its slippery airframe, one that makes a gas pig look lean.

If that is the case, I would agree. Lockheed likes clean, MD likes stout. Airforce Navy thing.

bear

[gas path]

Er no! Actually a hung start. The L1011 apu could be marginal on air delivery at times and that would slow up the start cycle. Looking at the amount of smoke I'd say the engine fuel system was full of inhibiting oil.
If starter air wasn't the issue, from memory I'd pull the plug from the SFFR until the engine was up and running, that would speed up the acceleration.:8

[Turbine D]

gas path

Yes, you are right! hung start is the correct term. :cool:

Turbine D

[unmanned transport]

GE: CF6-80E1
Dry Weight: 5091.62 kg (11225 lb).
Includes all basic engine accessories and optional equipment as listed in the manufacturer’s engine specs.
http://easa.europa.eu/certification/type-certificates/docs/engines/EASA-TCDS-E.007_(IM)_General_Electric_CF6--80E1_series_engines-01-14062004.pdf




RR: T700 series.
Dry Weight: 6160 kg (13580 lb).
(Not including fluids and Nacelle EBU)
http://easa.europa.eu/certification/type-certificates/docs/engines/EASA-TCDS-E.042_Rolls--Royce_plc._RB211_Trent_700_series_engines-01-06032006.pdf

[411A]

411A, would you please substantiate your notation in the following paragraph with good data to prove your point, and not just loose talk off the top of your noggin:-
Thank you Sir.



Air Transport Association
Operating statistics, 1999

DC10-30 fuel consumption 2,693 USG/hr, operating cost $5,972/hr

L1011-200 fuel consumption 2,447 USG/hr, operating cost $4,891/hr.

You're welcome.

NB. Of course, the DC10 might have been dragging a boat anchor...:}

[unmanned transport]

Thank you Sir.

Would you provide an ATA link as I would like to examine this information in more detail.

[411A]

Sorry, no link available from my end, this was info provided at an ATA conference I attended some years ago.
I'm sure you can find a link (although the data ia slightly outdated now, due to not many of these aircraft in service any longer).
I suspect the larger fuel consumption of the DC10 is due in part to the specific location of the number two engine.

[unmanned transport]

This is not a good comparison 411A, as the 10-30 was packing 53 tons more than the L1011. As well, different planform, airfoils and even more differences between the two.

MTOW of the DC10-30 is 572,000lbs.
MTOW of the L1011-200 is 466,000 lbs.

http://www.caa.co.uk/docs/702/3GE069_01102004.pdf

CF6-50A rated at 218.3 kn.
T/off - 2.168 kg/s
C/out - 1.787 kg/s
Idle - 0.163

http://www.caa.co.uk/docs/702/1RR005_01102004.pdf

RB211-524B rated at 218.5 kn.
Take-off - 2.21 kg/s.
Climb-out - 1.79 kg/s.
Idle - 0.24.


So the '10-30 with a CF6-50A engine was burning less fuel in the above noted three flight phases than the the RB211-524B in the L-1011-200.

Mach .04 in favor of the L1011 for cruise speed but 53 tons lighter than the 10.

[unmanned transport]

The 'S' duct for the #2 eng in the L1011 would be 'chocking' off some airflow to the engine in the L1011 resulting in less efficient thrust, a disadvantage when compared to the straight thru airflow in the '10.

[unmanned transport]

Another reason for the RRs being a tad heavier in the CF6 and RB211-524 engines is in the wall thickness of the casings from the LPC all the way back to the HPT. This helps in longtidunal rigidity of the engine. Yet, RR copied GE by using the thrust link arrangement, (aluminum pipe) that ties the aft eng mount to the fwd eng mount to increase stability even some more.......go figure?

Rapid throttle movements aggravates longitudinal bowing of the casing and should be avoided.

Also for the Rolls, the IPC drum and it's associated compressor blades and stator blades including the drive shaft and associated bearings/housing and spoked support struts weigh more than an extra N2 compressor disk/blades and VSV linkages as in the twin spool GE/Pratt designs.

When twin spools can do the job more efficiently why 'over engineer' the engine by adding more spools and it's associated hardware as RR do, making it more complex and costly from a manufacturing and maintenance aspect, yet achieving a similar thrust output.

[411A]

The 'S' duct for the #2 eng in the L1011 would be 'chocking' off some airflow to the engine in the L1011 resulting in less efficient thrust, a disadvantage when compared to the straight thru airflow in the '10.

A careful review of the design will reveal that not to not be the case.

...as the 10-30 was packing 53 tons more than the L1011
Note I specified equal enroute weights, not some 53 tons heavier.

[barit1]

The DC-10/MD-11 #2 engine does create a substantial nose-down moment which must be reacted by the horizontal tail. In this respect it's at some disadvantage compared to the L-1011.

And MD-11 crew have said that a sudden #2 failure in cruise creates a wild ride until they can re-trim.

[TURIN]

There are one or two blinkered views being expressed here.

I have no axe to grind, however one thing that hasn't been mentioned is the line maintenance friendlyness of the different engines. For my part the RB211/Trent has always been easier due to the ancilllary equipment being hung on the outside of the fan case. The GE and PW engines have the equipment hung against the core. It's a hell of a lot quicker on a tight turn round to lift a fan cowl than it is to pump open the T/Rev halves. Admittedly, the PDOS helps with the bigger GE engines but it still has caused delays.


I also remember the first time I saw a CF6 with the cowls off, compared to the '211 it looked incredibly complex with all those VSVs and control linkages. Works very well though and lasts a long time.

Regarding the DC10/Tristar spat. The No.2 engine on both was right royal pain in the backside. But at least the '10 had a platform to work from, in the Tristar one would be sliding around in a pool of oil all night.

Happy days. :ok:

[CliveL]

Note: The GE engined aircraft has the best range as indicated on the Airbus graphs.

I have read and re-read this thread with some interest, but you know it hasn't really addressed the original question.

UT has made a good case for saying that the GE engine has a better fuel consumption than the RR design, but the question was not does GE do better than RR, but what are the advantages of two shaft engines against three shaft designs.

The debate about relative fuel burn at take-off, climb and approach doesn't really address the question since by far the biggest amount of fuel is consumed in cruise and so far as I am aware there is no simple relationship between TO and cruise sfc performance, it depending amongst other things on the BPR (and cruise thrust matters as well). The only truly valid comparison I have seen mentioned in this debate is that given by UT as quoted above. These are estimates by a single manufacturer, for the same airframe and for the same MZFW and TOW, i.e. the same amount of fuel on board and as such should give a coherent assessment of relative performance on real missions.

Sure, the GE aircraft with new engines goes farther, but it isn't all that much of a difference. The graphs are not all that big, but my reading for range taken from the AI graphs is, with 175t MZFW and 233t TOW:


@ Max structural P/L/MTOW PW4000 - 3700 n.mls, RR - 3700 n.mls, GE 90 - 3750 n.mls
@MTOW/Max tankage PW4000 - 5500 n.mls, RR - 5500 n.mls, GE90 - 5550 n.mls
@ Max tankage/zero P/L PW4000 - 6500 n.mls, RR - 6500 n.mls, GE90 - 6600 n.mls

In other words the GE is about 1% better than either the PW4000 or the RR engines when new, but that is a difference that could be easily lost by deterioration.

Some airlines ask for, and are given, performance guarantees to be met after X years in service, so the retention of performance is also very important. Without, as put earlier, wanting to get into a pissing contest, I have to say that when I was in work the RR engines had a good reputation in this respect - certainly there was less heart searching about giving 'in service' guarantees if the airline had chosen RR engines.

What might one deduce from this?

I would say since the PW engines are 2 shaft and identical to the 3 shaft design in aircraft performance terms one cannot conclude superiority of 2 shafts over 3 so far as fuel consumption is concerned, just that one company has better technology than the other two.

Other issues of cost, maintainability and reliability I leave to others who are better informed

[unmanned transport]

Clive and Turin.

Thanks for your contribution which makes this thread interesting and I will admit, I am always learning throughout my lifetime.

Let's try and stay on topic asit's so easy for thread creep by going off on a tangent like Tristar vs DC10 stuff.

[gas path]

@unmanned transport
Exactly which RB211-524 are you refering to?
The -524 does not have a 'thrust link arrangement' as it's not required. The Trent however does have a thrust link as does the 90, that links the aft engine mount to the fancase (NOT the forward mount.).
The rigidity of the base 211 comes from the fact that the engine is complete with all the thrust reverser and cold stream duct. (A tube within a tube if you like, very rigid in its own right!).
The reason that the Trents and the 90 have the thrust links is as you pointed out to increase the rigidity of the engine because the thrust reverser halves are now an airframe part and remain with. The 'tubes' BTW are not aluminium but high grade steel...they need to be as there is a lot of torsional loads on them.

[Turbine D]

gas path

You are correct, it prevent "back bone bending" of the engine that was learned early on to be a serious problem if not addressed.

In the very early days, P&W found out the fan case turned oval on the JT9-3D at high thrust and they had to use a tubular stiffening arrangement to prevent this from happening.

Just a little history from a old guy...

[unmanned transport]

gas path, sorry, I meant the next gen of RRs above the -524.

The thrust link on the CF6s that I was involved with when I was as an inspector was not steel. It's fwd mount area config was a curved and sandwitched plate arrangement that bolted to the fwd LPC flange under the fwd mount and tied in with this floating mount. When you really think about this drag link, it does not prevent all of the bowing of the core casing during what I like to call 'pod nod' during real hard turbulence. What would be a better design for these engines would be longtidunal plate mounted say at the twelve oclock position on the engine 4-6" deep running along the casing and tied into each engine flange.
If they could eliminate minute bowing of the case the mfgs could tighten up blade tip clearances for even more efficency.

That's very true Clive, all this ICAO data excludes the cruise portion.

Turin, so true the GE and PW engines were a nightmare to inspect around the core section and were difficult for the engineers. the only major negative regarding peripheral components mounted on the fancase of the RR would be increased diameter of the cowled up fan case resulting in more flate plate area.

Was the FCOC relocated on the Trent from the fan case to the core for more heat?

Is the ICAO data that I've noted extracted from the manufactures' test cell engine runs? I don't know.

Meanwhile many happy memories I've had of being on 'the hangar floor' playing with these masterpieces of machinery. One must move onwards and upwards for a good future.

Blue skies folks, now off to fly my Cessna....what a great life.

[unmanned transport]

Boeing and GE look to firm third GEnx improvement package (http://www.flightglobal.com/articles/2011/02/14/353150/boeing-and-ge-look-to-firm-third-genx-improvement-package.html)

PIP1 - a revised LPT......wonder which disk.
Man that is a fairly major Product Improvement Program.

Any info on the T1000 is scarce.
Wonder how it is going for pippin.

Fuel burn comparisons between these two big donks will be interesting.

[barit1]

Going back to McDonnell Douglas days - they liked the gearbox under the fan case for maintenance reasons. The CF6-6 and -50 were configured this way, and IIRC the JT9D-59 on DC-10-40s (JAL & NWA) were also.

But Boeing was more performance oriented, and bolting the gearbox up close to the core made the fan cowl a bit slimmer. Thus the CF6-80A and 80C2 have a core-mounted AGB -- as have all P&W Boeing engines.

[unmanned transport]

Since the ICAO data for the previously mentioned engines indicates that the RR hogs more fuel in take-off, climb, descent and idle, she sure ain't going to burn less in cruise than the competition.

[lomapaseo]

Since the ICAO data for the previously mentioned engines indicates that the RR hogs more fuel in take-off, climb, descent and idle, she sure ain't going to burn less in cruise than the competition

How is that so?

[Turbine D]

OK, here is some engine comparison data for all to mull over:
Three spool vs two spool

B-777

Trent882
Engine weight (dry): 12,009 lbs.
Overall length: 172 inches
Fan diameter: 110 inches
Thrust at TO: 80,711 lbs.
Thrust during Cruise: 15,917 lbs.
SFC (cruise): 15.66 mg/N-s

GE90
Engine weight (dry): 18,200 lbs.
Overall length: 187 inches
Fan diameter: 123 inches
Thrust at TO: 85,716 lbs.
Thrust during Cruise: 15,432 lbs.
SFC (cruise): 8.30 mg/N-s

Two spool vs Two spool

Airbus A-320 (assumed)
V2500-A1
Engine weight (bare):
Overall length: 126 inches
Fan diameter: 63 inches
Thrust at TO: 24,526 lbs.
Thrust during Cruise: 4762 lbs.
SFC (cruise): 16.29 mg/N-s

Airbus A-340 (assumed)
CFM56-5C2
Engine weight (bare)
Overall length: 103 inches
Fan diameter: 72 inches
Thrust at TO: 30,600 lbs.
Thrust during Cruise: 6786 lbs.
SFC (cruise): 16.06 mg/N-s

Sorry, couldn't find an apples to apples comparison for the CFM vs V2500 but think they are very close to one another on the Airbus A-320.

This data come from a study done at Stanford University looking at fuel consumption on various engines.

Don't shoot the messenger. :=

Turbine D

[CliveL]

This data come from a study done at Stanford University looking at fuel consumption on various engines.

Don't shoot the messenger.Not trying to shoot the messenger Turbine D, but there is a typo in there - surely somebody at Stanford put in the takeoff sfc for the GE engine by mistake? Otherwise it is twice as efficient as any other turbofan flying.:)

[CliveL]

Since the ICAO data for the previously mentioned engines indicates that the RR hogs more fuel in take-off, climb, descent and idle, she sure ain't going to burn less in cruise than the competition.I hinted at it in a previous post, but I guess I'll have to spell it out - untreated SLS testbed values of sfc. are NOT a valid comparison of installed cruise sfc unless the bypass ratios of the two engines are identical.

Basic engine thermodynamics says that the ratio of SLS to cruise sfc depends on the Bypass Ratio and the cruise Mach Number. The higher the BPR the worse is the ratio (i.e. the worse the cruise sfc for a given SLS sfc.) Comparing engines simply on SLS sfc therefore introduces a systematic bias in favour of the high bypass engine.

In addition, the high BPR engine will have more wetted area (drag) so the installed sfc will be relatively higher and the powerplant will be heavier.

I take the point that one has to be careful about comparing apples with apples, and the engine weights given in the FAA certification fact sheets (which one might have thought free of bias even though one of their functions is to further US civil aviation ;)) do not seem to be consistent definitions from one manufacturer to another. In addition, there is usually a factor of 1.6 or more between the bare dry weight of the engine and the installed powerplant weight, and this factor will obviously depend on what is included in the datum engine weight. For this reason I would prefer to use differences between installed engines derived from the aircraft manufacturers MWE values. For the A330, taking the RR version as datum, the GE aircraft weighed just over 600 lb more and the PW version a whopping 1800 lb more.

To the best of my knowledge, the GE engines have higher BPR than the Trent equivalents, which is probably why the net gain on the A330 was only 1% over the Trent and PW4000 versions rather than the value suggested by ICAO emissions data which is based on SLS measurements.

Don't get me wrong; I hold no brief for one engine manufacturer against another, but I hate to see dodgy comparisons :)

[unmanned transport]

lomapaseo, it's just common logic.

Thanks for the data Turbine D.

Source for data?

No doubt about it, the 90 is a steam engine having chomped down too many hamburgers. I wish they would hurry up and refine it some more and incorporate some GEnx technology into it such as a composite fan case, strain gauge some of the metal in the casing to see if it could go thinner walled. Possibly the disks could go thinner walled as well.

The fan dia on the 90 at 13 more inches will be more drag.

That SFC cruise burn for the Trent at 495lbs more cruise thrust is almost double that of the 90 !

[unmanned transport]

Good points Clive.....we need the BPR numbers.

[Turbine D]

I am having trouble finding the original site tied to Stanford, but here is the the same report that I did find on the internet.

It looks like the cruise thrust is calculated.

B.Tech Seminar (http://www.anirudh.net/seminar/html/)

Turbine D

[KBPsen]

It looks like the cruise thrust is calculated.

It clearly says SLS SFC in the first table for the GE90, while it says SFC (cruise) for the Trent.

Anybody really should be thinking "that can't be right" when presented with numbers that differs by a factor of 2.

The cruise figure for the GE90 is 15.60 mg/N-s versus 15.66 mg/N-s for the Trent.

[CliveL]

Interesting report Turbine D.

I see it does confirm that the 8.3 sfc is indeed SLS, and the (calculated) cruise sfc is 15.6.

I can get the Trent BPRs from the RR website, but I am having difficulty with comparable GE values. Does anyone have any ideas?

CSL

[Turbine D]

CliveL

I put this info out since there was a lot of discussion on SFC. But I am not sure that SFC is really a good measure for comparison purposes. Perhaps the real measure is something like total fuel burn (takes into consideration the total aircraft) or block fuel as was mentioned earlier in this thread.

Turbine D

[unmanned transport]

Thanks for the link Turbine D.

[CliveL]

Turbine D

" I am not sure that SFC is really a good measure for comparison purposes. Perhaps the real measure is something like total fuel burn (takes into consideration the total aircraft) or block fuel as was mentioned earlier in this thread."

I'd go along with that all the way

CSL

[unmanned transport]

Clive, I think it is for a bare engine not attached to the airframe.

When attached to the airframe, pylon/strut sidethrust, downthrust/upthrust angles will be the same for a GE/RR/Pratt. Wetted area will be different for each engine which will make a difference. There are a few more variables.

[CliveL]

Clive, I think it is for a bare engine not attached to the airframe.

Yeah, but when you read the small print it ain't so obvious what you have:

GE engines "includes basic engine, basic engine accessories and optional equipment as listed in manufacturer's engine specifications including condition monitoring instrumentation sensors"

PW engines "includes all essential accessories but excludes starter, exhaust nozzles and power source for ignition system" [but the PW4164 weight includes the starter apparently]

RR Trent 768 gives Basic Engine and Dry Powerplant weights

That's why I think you need to try to find something that includes the all-in values.

Following up on Turbine D's remarks on total fuel burn and your earlier reference to the A330 performance data extracted from the AI Airfield Planning document, Boeing publish similar planning guides for all their aircraft (AI seem very coy about it for some reason - I did find a URL but you need to be registered in their Airbus World). Some of the Boeing planning includes P/L / range diagrams for several engines. Taking the zero P/L / Max.Tankage range is going to be as near as one can get to a "pure" comparison between engines as the fuel on board will be identical and the TOW will be OWE plus fuel so that powerplant weight effects are also included.

This gives:

B757-300:- PW 2040 4250 n.mls: RB211-535E4 4150 n.mls

B767 300ER:- CF6-80C2B7F1 7100 n.mls: PW4062 6950 n.mls

That is all the comparative data I have been able to locate so far

[unmanned transport]

There are four prime factors to consider when comparing engines.

1. Purchase price.
2. Fuel burn.
3. Weight: lower weight means lower Air Traffic Control (ATC) fees if maximum Take-Off Weight (MTOW) is reduced or more revenue from a higher payload.
4. Maintenance cost.




Fuel Burn Comparisons.
ICAO Engine Emissions Databank.
Document Categories | Human and Environmental Issues | Safety Regulation (http://www.caa.co.uk/default.aspx?catid=702&pagetype=68)


A380 with EA or RR engines.
http://www.caa.co.uk/docs/702/9EA001_10122010.pdf

EA 7270 - Rated Output - 332.39 kns.
Take-off - 2.637 kg/s.
Climb-out - 2.169 kg/s.
Approach - 0.711 kg/s.
Idle - 0.234 kg/s.

http://www.caa.co.uk/docs/702/9RR047_10122010.pdf
RR T972-84 - Rated Output - 345.9 kns.

Take-off - 2.69 kg/s.
Climb-out - 2.230 kg/s.
Approach - 0.750 kg/s.
Idle - 0.270 kg/s.

A380-800 Payload/Range charts.http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/AC_A380_20101101.pdf
GP 7200 engine - maximum structural payload range - 9625 nm.
Trent 900 engine - maximum structural payload range - 9525 nm.


B747-400 with GE or Pratt or RR engines.
http://www.caa.co.uk/docs/702/3GE057_01102004.pdf

CF6-80C2B5F- Rated Output - 272.53 kns.
Take-off - 2.685 kg/s.
Climb-out - 2.162 kg/s.
Approach - 0.697 kg/s.
Idle - 0.206 kg/s.

http://www.caa.co.uk/docs/702/1PW043_01102004.pdf
Pratt 4060 - Rated Output - 266.9 kns.

Take-off - 2.647 kg/s.
Climb-out - 2.085 kg/s.
Approach - 0.703 kg/s.
Idle - 0.213 kg/s.

http://www.caa.co.uk/docs/702/1RR011_01102004.pdf
RB211-524H - Rated Output - 264.4 kns.

Take-off - 2.73 kg/s.
Climb-out - 2.17 kg/s.
Approach - 0.71 kg/s.
Idle - 0.26 kg/s.


B777-200ER with GE or Pratt or RR.
http://www.caa.co.uk/docs/702/9GE128_10122010.pdf
GE-94B - Rated Output - 431 kns.

Take-off - 3.513 kg/s.
Climb-out - 2.831kg/s.
Approach - 0.876 kg/s.
Idle - 0.285 kg/s.

http://www.caa.co.uk/docs/702/10PW099_10122010.pdf
Pratt 4090- Rated Output - 408 kns.

Take-off - 3.926 kg/s.
Climb-out - 2.996 kg/s.
Approach - 0.979 kg/s.
Idle - 0.338 kg/s.

http://www.caa.co.uk/docs/702/5RR040_01102004.pdf
RR T895 - Rated Output - 413 kns.

Take-off - 4.03 kg/s.
Climb-out - 3.19 kg/s.
Approach - 1.05 kg/s.
Idle - 0.33 kg/s.


A330-200/300 with GE or Pratt or RR.
http://www.caa.co.uk/docs/702/4GE081_01102004.pdf
GE CF6-80E1A4 - Rated Output - 297 kns.

Take-off - 2.904 kg/s.
Climb-out - 2.337 kg/s.
Approach - 0.744kg/s.
Idle - 0.227kg/s.

http://www.caa.co.uk/docs/702/9PW092_10122010.pdf
Pratt 4164 - Rated Output - 287 kns.

Take-off - 2.721 kg/s.
Climb-out - 2.239 kg/s.
Approach - 0.775 kg/s.
Idle - 0.243 kg/s.

http://www.caa.co.uk/docs/702/3RR030_01102004.pdf
RR T772 - Rated Output - 316 kns.

Take-off - 3.2 kg/s.
Climb-out - 2.58 kg/s.
Approach - 0.85 kg/s.
Idle - 0.28 kg/s.


B767-300ER with with GE or Pratt or RR.
http://www.caa.co.uk/docs/702/8GE101_04102007.pdf
CF6-80C2B8F - Rated Output - 267 kns.

Take-off - 2.583 kg/s.
Climb-out - 2.106 kg/s.
Approach - 0.685 kg/s.
Idle - 0.205 kg/s.

http://www.caa.co.uk/docs/702/1PW043_01102004.pdf
Pratt 4060 - Rated Output - 266.9 kns.

Take-off - 2.647 kg/s.
Climb-out - 2.085 kg/s.
Approach - 0.703 kg/s.
Idle - 0.213 kg/s.

http://www.caa.co.uk/docs/702/4RR037_01102004.pdf
RB211-524H-T - Rated Output - 264 kns.

Take-off - 2.81 kg/s.
Climb-out - 2.22 kg/s.
Approach - 0.77 kg/s.
Idle - 0.26 kg/s.



http://theaviationspecialist.com/350-550_mission_table.gif
Note: The GE has a higher cruise thrust than the Trent, but has a lower SFC than the Trent.

GE90-115B
Cruise Thrust - 19,000 lbs. - 84.6 kns. - Cruise SFC. - 0.530 lb/lbth.
Trent 970
Cruise Thrust - 12,700 lbs. - 56.5 kns. - Cruise SFC - 0.561 lb/lbth.


http://theaviationspecialist.com/777-200lr_a340-500s_dmission.gif

GE90-110B1L
Cruise Thrust - 19,000 lbs. - 84.6 kns. - Cruise SFC. - 0.530 lb/lbth.
Trent 553
Cruise Thrust - 10,700 lbs. - 47.6 kns. - Cruise SFC. - 0.568 lb/lbth.



For the 777 with the GE90, the sea level SFC is 0.324 lb/lbth.
For the 777 with the Trent 800, the sea level SFC is 0.35 lb/lbth.

GE90 SFC (SLS) 8.30 mg/N-s. (cruise)
Trent 882 SFC (SLS) 15.66 mg/N-s. (cruise)

Airbus Payload / Range graphs.http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/Airbus_AC_A330_Jan11.pdf

A330-200.
Trent 700 - 9,100nm
PW4000 - 9,200 nm
CF6-80E1 - 9,450nm


( Source for Data required )
A CF6-80 A330 burns 4,700kgs./hour and a Trent 700 closer to 5,000kgs./hour during cruise.

Range Comparisons.
Airbus graphs, with 175t MZFW and 233t TOW:

@ Max structural P/L/MTOW PW4000 - 3,700 n.mls, RR - 3,700 n.mls, GE 90 - 3,750 n.mls.
@MTOW/Max tankage PW4000 - 5,500 n.mls, RR - 5,500 n.mls, GE90 - 5,550 n.mls.
@ Max tankage/zero P/L PW4000 - 6,500 n.mls, RR - 6,500 n.mls, GE90 - 6,600 n.mls.



B777-200ER GE/RR range comparisons.http://www.boeing.com/commercial/startup/pdf/777_perf.pdf
The GE90-94B has a fuel consumption of 284.8 lbs/seat for a 3000 nautical mile trip while the RR Trent 895 consumes.......... 291.7 lbs/seat for the same distance.

So the Trent 895 burns 6.9 lbs more of fuel than the GE90-94B for each seat every 3000 nautical miles.
With a seat configuration of 300 seats, that equals 2070 lbs or just over a ton more fuel for each 3000nm.


EASA - European Aviation Safety Agency (http://easa.europa.eu/certification/...0E1_series_engines-01-14062004.pdf)
Engine Weight Comparisons.
EASA - European Aviation Safety Agency (http://easa.europa.eu/certification/...700_series_engines-01-06032006.pdf)

GE: CF6-80E1
Dry Weight: 5,091.62 kgs. (11,225 lbs).
Includes all basic engine accessories and optional equipment as listed in the manufacturer’s engine specs.
EASA - European Aviation Safety Agency (http://easa.europa.eu/certification/...1-14062004.pdf)


RR: T700 series.
Dry Weight: 6,160 kgs. (13,580 lbs).
(Not including fluids and Nacelle EBU)
EASA - European Aviation Safety Agency (http://easa.europa.eu/certification/...1-06032006.pdf)



A330-200 O.E.W. weights for each applicable engine http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/Airbus_AC_A330_Jan11.pdf
GE powered O.E.W. - 119,831kgs.
RR powered O.E.W. - 119,931kgs.


Engines applicable to the A330-300http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/3c27fd7504a36b648625760e0046cb5a/$FILE/E36NE.pdf

PW 4168 weighs 12,900 lbs.- 5,863 kgs.

Weight of basic engine includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/d69e8a472455be9286257495006282e5/$FILE/E39NE.pdf

RR Trent 772B-60 dry powerplant weighs 14,360 lbs.- 6,527 kgs.



Engines applicable to the B747-400http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a54a5cdbed477da18625753c004dd282/$FILE/E24NE.pdf
PW 4062 weighs 9,420 lbs. - 4,273 kgs.
Weight of basic engine includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system.

http://rgl.faa.gov/Regulatory_and_Guidance_library/rgMakeModel.nsf/0/706579a7e83efab48625727b00751aff/$FILE/E13NE.pdf
CF6-80C2B5F weighs 9,790 lbs. - 4,441 kgs.
Weight includes basic engine accessories & optional equipment as listed in the engine manufacturer's specifications, including condition monitoring instrumentation sensors.

http://www.caa.co.uk/docs/1419/SRG_PRO_1048%20iss11.pdf
RB211-524H2-T-19 weighs 12,573 lbs. - 5,703 kgs.
Dry powerplant weight less intake, intake systems, cowl doors and cowl door support structure.


Engines applicable to the B767-300ERhttp://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a54a5cdbed477da18625753c004dd282/$FILE/E24NE.pdf
PW 4056 weighs 9420 lbs. - 4,273 kgs.
Weight of basic engine includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/b015c4c8fa2760a18625765c0053b800/$FILE/E13NE.pdf
CF6-80C2B2 weighs 9670 lbs.- 4,395 kgs.
Weight includes basic engine accessories & optional equipment as listed in the manufacturer's engine specifications, including condition monitoring instrumentation sensors.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/78635932a4cb7e7b862572a70057e006/$FILE/E30NE.pdf
RB211-524H-T-36 weighs 12,540 lbs.- 5,700 kgs.
Dry powerplant weight less intake, intake systems, cowl doors, and cowl door support structure.


Engines applicable to the B757-200 / -300http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/4e1d135907e0ce8686256df1005b1233/$FILE/E17NE.pdf
PW 2043 weighs 7,300 lbs. - 3,318kgs.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/1aaba05dd1012e30862574950062f87e/$FILE/E12EU.pdf
RB211-535E4-B-37 weighs 7,603 lbs. - 3,456 kgs.


//www.airbus.com/fileadmin/medi...h_data/AC/Airbus_AC_A330_Jan11.pdf
Twin spool engines have a more stable airflow pattern since the airflow is being compressed all the way to the last stage of the High Pressure Compressor (HPC) before it enters the diffuser section.
This makes the engine less surge prone in comparison to a three spool design. In a three spool engine, there is a sudden interruption (slowing down) of the airflow in the void between the Intermediate Compressor (IP) 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.

The distance between the High Pressure Turbine (HPT) and the Intermediate Pressure Turbine (IPT) also hurts the triple spool's efficency. This distance is required to locate the disks around an extra pair of 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 adding another turbine disk would increase the weight of the engine even more.

In a 3-spool engine, there is quite a bit of extra fuel burn due to the fan being oversped and the turbine powering it spinning below its optimal mach number.

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 twin 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.
They have had to combat oil system problems with the RB211 / L1011; Trent 500 / A340-500/600’s; Trent 700 / A330 and Trent 900 / A380.


Oil Temperature comparisons.

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 in a three spool engine.
For this reason triple spool engines emit more smoke during start-up.


Twin spools engines (non contrarotating) have lower gyroscopic moments than triple spool engines, resulting in less side loading of the pod/strut.


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


Most fighter aicraft engines use a twin spool design for faster throttle response.

Twin spool turbofans have the basic two spool configuration where both the fan and LP turbine (i.e. LP spool) are mounted on a second (LP) shaft, running concentrically with the HP spool (i.e. HP compressor driven by HP turbine). Twin spool engines have lower maunfacturing costs due to a lower parts count than three spool engines. Twin spools are less expensive to overhaul due to the fact that they have only two concentric drive shafts and support bearings.

Rolls-Royce chose a three spool configuration for their large civil turbofans, where the Intermediate Pressure (IP) compressor is mounted on a separate (IP) drive shaft, running concentrically with the LP and HP drive shafts, and is driven by a separate IP Turbine. However, three spool engines are more labor intensive to both build and maintain.

The Rolls Royce single stage High Pressure Turbine (HPT) is at a disadvantage to the competition due to the turbine blades being 30% heavier since they are shrouded at their tips. These heavier blades result in a longer time to reach optimum rotational speed for the HPT with it's coupled HP compressor. Shrouded blades decrease airflow leakage past the turbine blade tips but the unshrouded blades in GE and Pratt & Whitney engines are lighter which promotes faster engine acceleration. In twin spool engines manufactured by GE and Pratt, turbine blade tip airflow loss is reduced and controlled with a design known as Active Clearance Control (ACC) which also improves fuel efficency and lowers emissions. This clearance control design uses an ACC valve which captures cool ambient by pass airflow and routes this air to pipes with exit holes directed at the exterior surface of the turbine casing surrounding the turbine. This airflow reduces the thermal expansion of the turbine case and maintains the critical clearance between the turbine case and the blade tips. In other words, it shrinks the diameter of the turbine case and also allows it to expand when required.

Since three spool engines use three concentric shafts and more support bearings are than are required in twin spool engines. A three spool engine requires three compressors, a low pressure compressor, an intermediate compressor and a high pressure compressor, a high pressure turbine, an intermediate pressure turbine and a low pressure turbine. Twin spool engines have just two compressors, a low pressure and a high pressure compressor, a low pressure turbine and a high pressure turbine.

The RR three spool is more difficult and more labor intensive to manufacture because of the nature of the concentricity of the three drive shafts, support struts/bearings and the fact that is has three distinct compression and turbine stages.

Three spool engines are more labor intensive to balance and are more prone to vibration than twin spool engines.

An Oxford University/Rolls Study from 4/9/02 - 9/30/03 document notes that 10% or more of RR engines failed the final passing out test due to imbalance.
Eleven 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 also detected when the engines are overhauled at the RR appointed agents than twin spool engines during overhaul.

[lomapaseo]

Someday we gotta ask a RR Development engineer why they stick with that lousy design seeing that it's at such a disadvantage :}

[barit1]

u.t.:There are four prime factors to consider when comparing engines.

1. Purchase price.
2. Fuel burn.
3. Weight: lower weight means lower Air Traffic Control (ATC) fees if maximum Take-Off Weight (MTOW) is reduced or more revenue from a higher payload.
4. Maintenance cost.

Item 3 is likely a no-brainer. If an aircraft receives original cert at xx MTOW with a heavy engine, and later a lighter engine is installed and cert, it will probably be at the same MTOW - i.e. greater useful load.

Then, assuming it's not ZFW-limited, the later version carries more payload, more $$$ income, more than making up for higher fees.

[unmanned transport]

A higher bypass pressure ratio (BPR) improves thermodynamic efficiency and also propulsive efficiency.

B777-200ER Engine comparisons:

GE GE90-94B
FAN DIAMETER: 123 Inches
COMPRESSOR LAYOUT: 1 Fan/3LP+10HP
TURBINE LAYOUT: 2HP+6LP
BPR: 8.40
MASS FLOW: 3398lb/s
TO THRUST: 93,700lbt

PRATT-WHITNEY PW4090
FAN DIAMETER: 112 Inches
COMPRESSOR LAYOUT: 1 Fan/6LP+11HP
TURBINE LAYOUT: 2HP+6LP
BPR: 6.41
MASS FLOW: 2948lb/s
TO THRUST: 90,100lbt


ROLLS-ROYCE TRENT 895
FAN DIAMETER: 110 Inches
COMPRESSOR LAYOUT: 1 Fan+8IP+7HP
TURBINE LAYOUT: 1HP+1IP+5LP
BPR: 5.74
MASS FLOW: 3123lb/s
TO THRUST: 93,100lbt


Engine Noise Comparisons:

GE90-94B
http://noisedb.stac.aviation-civile.gouv.fr/pdf.php?id=8091

Lateral Full Power - 96.5 EPNdB.
Approach - 98
Flyover - 90.7


PW 4090
http://noisedb.stac.aviation-civile.gouv.fr/pdf.php?id=8110

Lateral Full Power - 96.9 EPNdB.
Approach - 99.2
Flyover - 95.2


RR T895
http://noisedb.stac.aviation-civile.gouv.fr/pdf.php?id=8129

Lateral Full Power - 98.3 EPNdB.
Approach - 99.4
Flyover 93.4

[Turbine D]

unmanned transport

I hadn't looked at this thread for a while. You assembled a lot of good and interesting information in your most recent post as well as your #139 post.
One other advantage of a two spool engine is its more rapid air start time verses a three spool engine. There was an incident years ago involving a Delta Boeing 767-200 (GE CF6-80A engines) departing LAX for CVG where this advantage became very important.

30 June 1987; Delta Air Lines 767-200; Los Angeles, CA: The engines were inadvertently shut off during climb at about 2,000 feet. The crew was able to restart the engines at about 500 feet and continued to their original destination of Cincinnati.

I recall seeing data (think it was in Aviation Weekly) regarding the time to start GE, Pratt and RR engines after a flameout and both GE and Pratt engines had the shortest restart times by quite a bit verses the RR three spool engine (RB211).

TD

[unmanned transport]

Thanks again Turbine D.

It's my understanding that a triple spool engine requires a higher volume of air to start than a twin spool engine.

A twin spool engine produces more power from two High Pressure Turbines (HPT) driving it's coupled High Pressure Compressor (HPC) than one HPT as in a triple spool engine driving it's respective HPC. That's the main reason that RR will be adding an extra HPT disk in it's XWB series engines for improved efficency. This will add quite a bit more extra weight to this engine series and one could say that they are copying some of the twin spool advantages in turbine architecture.


A330-300 Estimated Maximum Payload.http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/Airbus_AC_A330_Jan11.pdf
Chapter 2-1-1 - page 1 - Revision Jan 01/11

CF6-80E1 - 52,169 kgs.- 115,012 lbs.
Trent 700 - 52,069 kgs. - 114,792 lbs.



A330-300 Airbus Payload / Range graphs.http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/Airbus_AC_A330_Jan11.pdf
Chapter 3-2-1 pages 6 & 7 Rev. Jan 01/11

CF6-80E1 - 6,625 nm.
Trent 700 - 6,500 nm.

[unmanned transport]

Sorry my mistake in the previous post.

Not an extra stage for the HPT but an extra stage for the IPT in the XWB engine.

HP turbine: single-stage, aircooled
IP turbine: two-stage, aircooled
LP turbine: 6-stage, uncooled

[lomapaseo]

The time it takes to restart is governed by the core inertia (HPT/HPC) being able to presurize the combustor to hold a flame. After that it is accel time limited.

I don't see the relationship in this thread of bringing in the Delta B767 since the core (HPT) hadn't spun down very much.

It's kind of subjective to argue good-better-best for products that all meet the same regulation and customer satisfaction levels as-installed.

[unmanned transport]

From all the data provided, we are just proving that twin spool engines have the 'edge' over the triple spool design. Less fuel burn and lower weight being the two big advantages for the twin spool. There are many misinformed people out there that think the triple spool is superior. This is not true but the reverse is true.

[sooty655]

From all the data provided, we are just proving that twin spool engines have the 'edge' over the triple spool design. Less fuel burn and lower weight being the two big advantages for the twin spool. There are many misinformed people out there that think the triple spool is superior. This is not true but the reverse is true.
That's why no-one is buying or operating triples any more. :rolleyes:

[unmanned transport]

LOL sooty655:)

RR must have given those T900s free to Asiana for their A380s.
On another note,
PW seem to be on a roll with 1,200 orders so far for their GTF mill. Just wait until they scale this design up for wide body airframe use. I can very well see them becoming #2 again.

[ITman]

We should also remember that Boeing only offer US engines on there 737, 747-8 and later 777's as a direct move to reduce certification costs. The 787 is the first new Boeing to offer the RR engine as well as a US engine.

[TURIN]

It's my understanding that a triple spool engine requires a higher volume of air to start than a twin spool engine.


I understood that the Trent 777-200 could start both engines simultanously, whereas the GE model could not due to the APU not supplying enough puff.

Does that contradict your statement? :confused:

[AerialNinja]

Triple-spooled turbofans are just too damned heavy for their own good

[ITman]

From the data provided by Turbine_D at post #126 the Trent is lighter than the GE..?

Trent882
Engine weight (dry): 12,009 lbs.
Overall length: 172 inches
Fan diameter: 110 inches
Thrust at TO: 80,711 lbs.
Thrust during Cruise: 15,917 lbs.
SFC (cruise): 15.66 mg/N-s

GE90
Engine weight (dry): 18,200 lbs.
Overall length: 187 inches
Fan diameter: 123 inches
Thrust at TO: 85,716 lbs.
Thrust during Cruise: 15,432 lbs.
SFC (cruise): 8.30 mg/N-s

[barit1]

Assuming these weights are accurate, one could cruise a good while longer when fuel is consumed at half the rate -- readily making up the engine weight difference.

[unmanned transport]

This link does not include the Trent 882 but I would expect it to weigh the same as the other 800 series weight.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/b443906400b2f413862572a4006eb74e/$FILE/E00050EN.pdf

RB211-TRENT 892-17, RB211-TRENT 875-17
RB211-TRENT 884-17, RB211-TRENT 884B-17
RB211-TRENT-892B-17, RB211-TRENT 895-17
RB211-TRENT 877-17

This engine approval includes bare engine plus engine mounting feet, core engine cowlings, and engine accessories, coolers, filters, harness, and instrumentation transmitters as defined in the appropriate RR DIS.
Hydraulic pump, VSCF and IDG are aircraft supply.

Dry powerplant weight less intake, intake systems, cowl doors, and cowl door support structure.

An inlet cowl is quite heavy.


GE90-76B thru 90B link:

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/8cf409747c1d7b1b86257823007a1b25/$FILE/E00049EN.pdf

WEIGHT (DRY) Includes basic engine, basic engine accessories, and optional equipment as listed in the manufacturer's engine specifications.
17,400 lbs.

[ITman]

Have a look at post 125 onwards where the difference in SFC is discussed in depth.

[gas path]

An inlet cowl is quite heavy
No it isn't!
Inlet Cowl: 315kgs GE 355kgs Trent
Fan cowls: 140kgs GE 115kgs Trent
T/Rev halves: 800kgs GE 650kgs Trent


Trent 895 95k lbs of thrust (BET will be lower*)
The Trent weighs in at 7136kgs as an EBU (that includes all the boeing fit
components, so thats the nose cowl, IDG and hyd. pump).
The GE90 weighs in at 8500kgs as an EBU.
The base engine ranges from 76k to 94k*

*Boeing equivalent thrust (BET) is a calculated number. It is equivalent to
the thrust at 165 knots at sea level. BET is defined so that engines with the same BET will have the same TO perf. at sea level.

As TURIN says. The Triple spool needs a lot less air to start than the '90. A dual engine start is easily achieved on the Trent (I always do dual starts).
An inop APU can be a real PITA down route as you also need three ASU's for the GE90:8

[SeenItAll]

I am an economist, and the way we would evaluate which engine is superior is which airplane sells for a higher price. The all-in price of the plane should incorporate all of the engine considerations mentioned (initial cost, fuel cost, maintenance cost, thrust, etc.). One would only pay for plane equipped with XX engine versus YY engine if on net, XX engine is more economical.

While I am certainly not an expert on this, but it is my understanding that RR-equipped 757s sell at a higher price than PW-ones. While this is not definitive as to whether 2-spools are better/worse than 3-spools, it does suggest there are aspects of initial cost, fuel cost, maintenance cost, thrust, etc. in which the Roller must be better than the Pratt (unless the airline CEO just likes the look of interlocked Rs on cowling better than an eagle) :O

Of course it is also possible that different airlines' demands (lots of short hops and high cycles vs. long haul) could make Airline A find engine XX to be most economical while Airline B finds engine YY to be most economical.

Since both 2-spool and 3-spool models have been successful, it seems the latter explanation is likely.

[Dalex64]

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.

[unmanned transport]

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.

[unmanned transport]

Here are some more fuel burn comparisons.

Source:
http://www.boeing.com/commercial/startup/pdf/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.

[unmanned transport]

IATA Jet Fuel Price MonitorJet Fuel Price Monitor (http://www.iata.org/whatwedo/economics/fuel_monitor/Pages/index.aspx)

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.

[bearfoil]

I get a bit under 600k US$. That pays for 12 pilots!! (At least at UAL).

[unmanned transport]

Good to have you back with us bearfoil as I wondered where you had been.

[3holelover]

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.

...only if the GE kept running. :cool:

[bearfoil]

With the TRENT, the issue is the AD'd fuel supply, not the sfc.... Perhaps no longer.....

[gas path]

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.

[unmanned transport]

@ 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?

[barit1]

gas path:Time on wing and performance retention over the lifetime of the engine is a good measure.

Absolutely. These are major cost drivers.

I've yet to pull a roller for loss of EGT margin.

Then you weren't at RJ 25 years ago when R-R techs were scurrying to keep open holes from developing in the 1011s.

[unmanned transport]

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.

[Castle Don]

Not quite sure what that means......? Can you elaborate

(And the single HP turbine drives the HP compressor not the fan)

[unmanned transport]

Sorry CD, it should read, the LP turbine.

[lomapaseo]

Is it really a single stage??

[barit1]

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.

[Turbine D]

barit1,

The PW1000G (geared fan engine) has a 2 stage HPT and 3 stage LPT, one LPT stage less than what would normally be expected.

TD