Lightsaber From United States, joined Jan 2005, 3926 posts, RR: 71 Posted (2 years 7 months 2 weeks 18 hours ago) and read 2711 times:
This theread, at the end became a discussion on aircraft engines.
Since a new thread was started, I'll let that one go back to the original topic, PIA Claims B777-200LR Not Upto Specifications... (by Blrsea May 22 2006 in Civil Aviation)#259 (old)
A geared turbo fan has a fixed gearbox between the turbine that powers the fan and the fan? Now, that same turbine powers the first half of the compressor (called the low compressor). All airfoils operate at their peak efficiency at the same mach number. Rather than explain the speed of sound, think of it as RPM times diameter with a temperature correction. ok?
Now the fan is a really big diameter, so it needs to spin at a low RPM. Overspeeding the fan quickly has huge noise and fuel efficiency penalties. But... fans are usually run 7% to 10% overspeed! About 1400 RPM when you might really want 1300 RPM for the fan.
The fan must be powered by the relatively small diameter turbine (low turbine). That turbine is powered by hot gases coming out the high turbine.
So hot gases mean the turbine needs a higher RPM to be efficient. The smaller diameter and hot gasses mean that the optimum RPM for the turbine is about 4,500 RPM.
The low compressor is most efficient in the 3,500 to 4,000 RPM range.
Ok, so you have one part that is most efficient at 4,500 RPM powering a part that would do best at 1,300 RPM. Simple solution, put in a gear box! Now, since the low compressor is happiest at 4,000 RPM (or less), that's the speed you run the low turbine. Because the fan is slowed down, you gain about 3% improvement in fuel efficiency. Because the turbine is sped up, you gain about 5% in fuel efficiency. We engineers say TSFC rather than fuel efficiency as its a number we can put into our equations. spin
Now TSFC is "Thrust Specific Fuel Consumption."
It the amount of fuel burned per hour (in lbm) divided by the engines thrust (at that setting). Values are dropping (better fuel efficiency) toward a TSFC of 0.510 for cruise. The harder you run a jet engine, the more thrust you get for each pound of fuel (about 7.8 lbm per gallon) so engine makers prefer to quote takeoff TSFC, but for long haul planes cruise is what we discuss. Climb is important too... but one actually looks at dozens of design points... so on a.net we usually just talk cruise to simplify things. spin
Now, if you haven't realized, there is concern over the gearbox durability and reliability. Thus, Rolls Royce has chose another alternative. Their fan is powered by its own turbine, but the fan still runs at the inefficient 1,300 ish RPM.
But, their fix is instead of running the low compressor and its turbine at a very inefficient 1,300 RPM, they put those two on their own shaft and bearings at about 4,000 RPM. This improves fuel efficiency by about 2% (or lowers TSFC by 2%, a good thing).
What it also does is reduce engine weight! By about a ton per engine! Why? Engines are made from lots of nickel and titanium (some other stuff too). Nickel is rather heavy. Well, a more efficient compressor means that less compressor is needed as well as less turbine. This makes the engine shorter. That shorter engine, called a "triple spool" has quite a bit fewer parts in it. Really, the only downside is the extra set of bearings added which can be a bear to service. We call this new shaft the "intermediate spool" even though it has the low compressor on it. RR calls the "low compressor" the "intermediate compressor" so have fun calling it what you want. Smile
Why aren't triple spools the only engines offered? There very heavy for *small* engines. But at 60,000 lbf and above ... they're very light. Thus why the only narrow body with a triple spool is the 757. All the other triple spool engines go on widebodies.
Also, GE and RR have been able to make their double spools as efficient or even more efficient than RR's triple spools by spending money on optimizing the other parts of an engine. On a Boeing 777, if you're flying > 4,000nm get the GE-90. For flights less than 4,000nm get the Trent triple spool. I'm ex-Pratt, but since Pratt blew the Pw4098's fuel efficiency... they're out of the game effectively. cry And the pw4168 is the most efficient engine on the Airbus A330... but one needs 72k of thrust for the latest A330's and its a bit of a story why the Pratt's are stuck at 68k thrust... cry (68k is 68,000 lbf of thrust)
Since engines have to be started, takeoff, climb, cruise, land, be restarted in flight (rare, but important), produce minimum emissions, burn minimum fuel, weigh as little as possible, survive for thousands of takeoffs and hours of operation, not spit out fireballs (awwww...) etc. they are very complicated. Some added cooling to increase cruise fuel efficiency must be turned down or off for large changes in engine thrust. I alluded to that earlier. Some engines are more sensitive to wear and tear, etc.
Please take all RPM's as approximate. I was too lazy to look up exact numbers.
My background: I designed gas turbine engines for almost 5 years at Pratt. I also have some experience at Solar gas turbines. My current job is propulsion related, but my employer strickly forbids me from discussing my job in online forums. What I can say is I'm much more involved on the fuel aircraft system side than before, so I'm getting a different perspective. spin
This thread has been discussing a situation where the better climb durability and increased climb thrust of a triple spool compared to a double spool has been important. Also, all airplanes must fly safely such that if they suddenly lose an engine's thrust everyone is ok. Smile That means you do not fly a 777 or any other two engine plane directly over K2 or everest (unless they're "light") but you're allowed to fly a four engine plane. It happens that the A340 does very well in an engine out situation. Your seeing a bit of argument over how much of a diversion is required by the 777 due to those tall mountains... And some argument on the weights PIA is flying their 777's at and if they're light enough or not to safely fly near K2/Everest. But I know the kind of work Oldaeroguy and Widebodyphotog do, so I'm going to believe them.
Unfortunately, you will find a lot of A vs. B on these forums. I will vouch that neither OldAeroguy nor Widebodyphotog take sides; they both will present their data and tell you the conclusions they make. Most of the time we're making assumptions off incomplete data... so expect some small errors. But this is discussion. I'm certainly not in the market for a 777 or an A340. duck
I hope this helps,
Lightsaber
[quote]
and...
[quote] Oh, I missed a few definitions:
Oh, if it helps, engines work by "Squeeze-bang-blow" You squeeze the air, "bang" fuel (add heat energy) and then "blow" the air/fuel through the turbine to extract work (more work out due to volumetric expansion)
Engine terms:
GTF=geared turbo fan
LPC=Low pressure compressor
LPT=Low pressure turbine, usually drives the LPC and fan
HPC=High pressure compressor
HPT=High pressure turbine (only drives the HPC, on the GeNx also a generator)
IPC=Intermediate Pressure compressor. An RR term for the LPC on its own turbine
IPT=In a Triple spool, the turbine that drives the LPC (aka IPC).
RPM=Revolutions per minute (in my posts, there are other uses for this)
Cassing=the pressure vessal that holds the engine together.
Quoting Lumberton (Reply 242):
But doesn't the gear box itself add weight? Are you saying that the weight savings elsewhere compensate for the gearbox weight?
IIRC you posted elsewhere that many crashes win WWII were from gearbox failures? How will the OEM's sell gearbox reliability?
The gearbox more than compensates. By having a slow turning (or more precisely, low mach #) LPC, extra stages must be added to it and the LPT (since it too is turning too slowly for the optimal blade shapes). This stretches out the engine. The pressure vessal (aka casing) of the engine must be made from Inconel 715 (ok, in low pressure designs Inconel 625 is possible, but 715 casts easier in spin casting). That's a really heavy nickel alloy. The longer the engine, the thicker the nickel must be to keep the engine "stiff" (adding weight) *and* the longer the casing must be (adding weight). The gearbox adds a few hundred pounds yet in total on a 60k engine would weigh in like a triple spool. (or net 2,000 lbm weight savings).
You recall correctly on the WWII engines. About half of the engine failures were due to gearbox failures. Why?
1. No temperature sensors. We now have cheap reliable temperature sensors.
2. No synthetic oil. This makes a huge difference!
3. New gear tooth designs (this really helps)
4. Testing, testing, and more testing.
To my knowlege, only Pratt has taken the time to characterize high horsepower gearboxes into the detail required to predict (via oil pressure and temperature) a gearbox failure 100+ cycles before the failure.
...snip of some comment...
IAE is gearing up to launch a GTF for their next engine. (Finally, the "superfan!"). Due to contracts, that locks both RR and Pratt into IAE for the A320NG and 737RS. Thus, that keeps the triple spool out of the < 35k market for a generation. I do belive Boeing will allow IAE to offer an engine on the 737RS. Why? Its either that or Airbus will be the only one with a GTF and you know GE will get its engine on the Airbus too... Lets put it this way, a GTF offers the same drop in fuel burn as composites and bleedless combined! I expect a solution like the 787 where IAE and CFM (or will it be GE solo sans SNECMA) share a nacelle. With bleedless designs, that's quite possible.
ok, I was asked to say if the 787 truly shares a nacelle or not... I cannot answer that. However, Boeing tried to keep control the nacelle to keep it a common part... does anyone know if they did?
Also, the thread ended on why the triple spool doesn't have better efficiency:
my start at my speculation:
It could also be the turbine technology. While shrouded turbines have theoretical advantages (blade tip sealing) its a bit wasted with the required added cooling for the added metal. I know one reason GE and Pratt avoid shrouded turbines is that with optical measurements minimizing turbine blade tip clearences via active cooling, the real world benifit of shrouded turbines is believed to be negative by their numbers. But then again, by GE's numbers every Pratt PW4090 would have snapped its low spool shaft by now and every GE-90 by Pratt design methodology would have fan surges. So each engine maker has a few tricks they just don't share with *anyone*. Smile
I also think its because RR just doesn't put on a 2nd row of high turbine blades. This can dramatically help the engine efficiency (if paired with one or two more HPC rows of blades) by increasing the engine pressure ratio (higher pressure=more efficient energy extraction of the fuel's heating value). But ohh... it would add weight big time and cost... a lot of cost. Sad
I see two issues:
1. A very old design pre-diffuser concept (design of the exit of the HPC). This adds 1/2% to fuel burn. Since RR now owns Allison and they have the sweetest pre-diffuser designs I've ever seen... I bet the Trent 1000 fixes this (I can't help but notice this part of the engine is missing on the RR online pages for the future trents... scratchchin so something is changing that they don't want GE to know about...)
2. That long distance between the high turbine and intermediate turbine. That's a killer for engine efficiency. Unfortunately, this distance is to get around the extra set of bearings and this seems to be still a long stretch in the Trent 1000 (but not as extreme). Well... thats *really* hot gas flowing at an high subsonic mach number. So a bunch of added cooling air must be dumped in and the pressure that should be turning a turbine is thrown away to the considerable losses always present in high mach # flow environments. This could increase fuel burn by 2%!!!
But I think the fact that RR tends to go for lower pressure ratios than GE or Pratt is a real part of what is hurting their TSFC. But adding that 2nd row of high turbine blades will add 1,500+ lbm to each engine... so their goes RR's weight advantage. So my guess is that the system engineering folks just went for a design better optimized for the shot hops and lower manufacturing costs. But note, we're in the speculation zone as to why RR made decisions. I've never worked for RR, so I cannot tell you for certain.
Oh, just in case you weren't familiar, the higher the pressure ratio in an engine, the more efficient it is. But with Pratt and GE, they're getting up to the temperature limits of Inconel 715 at the exit of the HPC. wideeyed As Oldaeroguy noted, its a conservative industry. No one is quite ready to make the main casting out of anything more exotic... yet. But the engine after the GenX will have to be made from something new. Are their materials out there? Sure! But they aren't proven to case as nicely as Inconel 715 in *large* spin casting applications. Sad So its possible a 2nd row in the high turbine of the trents would increase the HPC exit temperature beyound what Inconel 715 can handle. But I haven't done the math... I admit this would be a very interesting design study to look into. spin
***Exiting speculation zone***
Then one final unanswered question by Baroque:
Quote:
Hmm, that had not occurred to me, although the inverse is clearly going to be true - good TSFC will be rather useful on long range aircraft. Can we soon have a thread on high BPR high thrust engines, or are they getting taken out as collateral damage in other threads?
I was intending to have this more of a give and take thread on engines.
Oh, just to be clear, when talking about the weight added to a triple spool to increase its overall pressure ratio, its not just the added row of turbine blades that adds the weight (or its rotor). Its the added HPC rows, added length and required thickness of 3 rotor shafts (all three must get stiffer if they are longer), and the weight of the engine casing (also, this must get stiffer as it gets longer). That is why I *speculate* RR has only gone for a single row high turbine.
So if there are any more questions, I'll answer.
What I would request is more input on the engine selection's impact from OldAeroguy or Widebodyphotog. Most of my career has been "oh, you need more thrust here... WILCO!. At better TSFC? Yep!" In particular, any information on how the Trent 1000's climb performance versus the GenX is effecting customer selection.
Baroque From Australia, joined Apr 2006, 8202 posts, RR: 29 Reply 1, posted (2 years 7 months 2 weeks 17 hours ago) and read 2662 times:
Thank you Lightsaber. The combination of the effects of various aspects of engine design and the realities of flight with them should be fascinating.
At least it is clear there IS a reason for all these things, even if the details turn out to be complex.
I guess the weight problem of adding a few blades is much like the problem of weight growth in structures. I seem to remember Barnes Wallis had a few things to say on that account. Just as Frank Whittle had a few to say about RRs early efforts at making jet engines. Still they were better than Rover it seems.
Rheinbote From Germany, joined May 2006, 1253 posts, RR: 21 Reply 2, posted (2 years 7 months 2 weeks 16 hours ago) and read 2620 times:
Okay, so let's fill this new thread with life
Lightsaber, I'd like to get back to that 150,000hp gearbox. What's the concept for heat dissipation? What can we expect in terms of design life (or what's the current target)?
SunriseValley From Canada, joined Jul 2004, 1870 posts, RR: 0 Reply 3, posted (2 years 7 months 2 weeks 13 hours ago) and read 2561 times:
Quoting Rheinbote (Reply 2): Okay, so let's fill this new thread with life Smile
I have some qoestions..
1. can this gearbox be changed on the wing? If so about how many manhours?
2. you stated that PW had got the reliability prediction down to about 100 cycles. Are PW still working on this device ,if so I wonder what new materials and manufacturing methods have been developed for it.
2. Is it something a specialty gearbox manufacturer could customise for different engine manufacturers? Seems to me Sundstrand was in this field some years ago.
Geo772 From United Kingdom, joined Jul 2004, 449 posts, RR: 0 Reply 5, posted (2 years 7 months 2 weeks 12 hours ago) and read 2480 times:
Quoting SunriseValley (Reply 4): I have a question; what are the indicators that tell an operator under ETOPS that they should be changing an engine.
Magnetic Chip detectors, vibration monitoring, engine parameter moniotring, eg EGT variation, Oil pressure and temp, boroscope inspections, life.
Point of note RR Trents have Low, intermediate and high pressure sections. The actual weight difference between the trent 800 and the GE90 is nearer 2 tonnes each than 1 tonne.
The trent 1000 will have the following major differences over previous trent engines: Bleedless and the accessory gearbox will be driven by the Intermediate stage turbine.
Flown on A300B4/600,A319/20/21,A332/3,A343,B727,B732/3/4/7/8,B741/2/4,B752,B762/3,B772/3,DC10,L1011-200,VC10,MD80,1-11
ClassicLover From Ireland, joined Mar 2004, 3506 posts, RR: 14 Reply 6, posted (2 years 7 months 2 weeks 12 hours ago) and read 2468 times:
For me, regardless, Rolls Royce have the best engines.
GE sell by exclusivity, which they are entitled to due to the amount of money they have from other businesses. If i had to choose between GE or RR, it would be RR all the way. It's a shame P&W aren't so much in the running now...
I choose to fly oneworld, as a member of Qantas Frequent Flyer.
ContnlEliteCMH From United States, joined Mar 2005, 1299 posts, RR: 41 Reply 7, posted (2 years 7 months 2 weeks 9 hours ago) and read 2416 times:
Quoting Rheinbote (Reply 2): Okay, so let's fill this new thread with life
Lightsaber, I'd like to get back to that 150,000hp gearbox. What's the concept for heat dissipation? What can we expect in terms of design life (or what's the current target)?
I don't know what to expect in terms of design life. However, I've been able to run a few figures for the heat dissipation question.
Assumptions:
1 hp = 0.746 kW
specific heat of water = 4.160 J/g-K (or 4.16 kJ/Kg-K)
specific heat of oil = ~2 J/g-k (or 2 kJ/Kg-K)
Assuming a 90% transmission efficiency, the losses through the transmission at full load would be approximately 11,190 kW, or about 11 mW. I don't know what the transmission efficiency would actually be, but I expect it would be at least this high. I hope it would be much higher, and some cursory research tells me to expect at least a 95% efficiency, and possibly 98%. Let's take 98% efficiency. That gives a dissipation requirement of 2238 kW.
I did some quick math. (If any of you find errors, please correct it.) If you used 100 Kg of oil as coolant, one minute at 150,000 SHP and 98% efficiency would result in a temperature rise of 671 K. That value assumes absolutely no heat transfer *out* of the oil. Obviously, you'd use a heat exchanger and some mass flow rate to effect a heat transfer rate. Furthermore, the altitudes at which this kind of heat transfer is required are also the altitudes at which heat transfer in an oil-to-air exchanger is most efficient. Perhaps an oil-to-fuel cooler would be a better choice, as the capability of liquid-to-liquid heat transfer tends be quite good.
Consider as well that it is not difficult to pump 100 Kg of oil in one minute. There is no exact correlation between the 100 Kg figure I picked as a heat sink, and the 100 Kg of mass I cite in the circulation figure. I picked them only as examples, but if you consider a working temperature in the oil of 100 to 150 C, I don't think cooling out of the gearbox will be problematic -- even if the efficiency isn't 98%.
I would also assume two additional items. First, the system will surely be designed to cool the gearbox at indefinite maximum thrust. Second, such a cooling requirement would only be required at takeoff thrust. If climb thrust is only 20% to 40% that of maximum thrust, then cooling will surely not be an issue.
Perhaps Lightsaber or somebody else can provide figures on the working temperatures, volumes, and flow rates of the oil in a modern turbofan. Will the engine oil also be used for the gearbox?
Christianity. Islam. Hinduism. Anthropogenic Global Warming. All are matters of faith!
98% is a better starting point for gear efficiency.
Quoting ContnlEliteCMH (Reply 7): Obviously, you'd use a heat exchanger and some mass flow rate to effect a heat transfer rate. Furthermore, the altitudes at which this kind of heat transfer is required are also the altitudes at which heat transfer in an oil-to-air exchanger is most efficient. Perhaps an oil-to-fuel cooler would be a better choice, as the capability of liquid-to-liquid heat transfer tends be quite good.
Actually, you do an oil to air cooler with the cooler in the *fan duct*. Yes, there is a tremendous propulsion loss due to the drag of having an oil cooler in that fast of an airstream. Also, realize that the oil would be completely recirculted within seconds as is engine oil. So yes, the oil heats up a bunch, but then its cooled by an incredibly fast blast of air (near sonic speed). Convienient... the harder the engine is working, the faster the cooling air.
Quoting ClassicLover (Reply 6): For me, regardless, Rolls Royce have the best engines.
GE sell by exclusivity, which they are entitled to due to the amount of money they have from other businesses. If i had to choose between GE or RR, it would be RR all the way. It's a shame P&W aren't so much in the running now...
??? GE right now has the lowest fuel burn. The JT8D remains the lowest cost engine to maintain (and cheapest to operate when oil < $25/bbl). Yes, RR makes good engines, but realize all engine decisions are economic. Each engine family is a compromise tailored toward their primary customer base.
The GE-90 easily has the lowest fuel burn on the 777, The Trent has by far the highest! But... the trent is far lighter and thus in < 4000nm missions ends up with the best efficiency. I've already gone over why a triple spool has a climb advantage. The Pw4090 is the least expensive 777 engine to manufacture. IF the Pw4098 has met promise (which it missed on TSFC by 4%!), it would be besting the GE-90A on fuel burn. The Pw4168 is the most fuel efficient A330 engine. IF Pratt hadn't been hamstrung by a darn nacelle contract or had realized the compressor bleeds would fry the 68k nacelle when the engine is pushed to 72k... Pratt would still rule the A330...
Yes, couda, shouda woulda... but understand that no engine maker is invulnerable. RR is a bit weak in the single isle market as is Pratt. Only GE is strong there (CFM-56 on the 737/A320 and the CF-34 family con the CR7/CR9/E-jets). Yes, I disount the Allisons and CR2... sorry, but I don't think they have much of a future sales life. Pratt somehow has remained very strong on business jets (thanks to the parent company letting P&W Canada have a bit more say in their strategy). Yes,the BR 710 is the high end business jet engine...
The point is that the engine market is a very fractured market. For example, I bet that Honda/GE will do very well in the VLJ market. Why? Honda has a passion for mass production that the other engine companies are tyring to copy, but haven't acheived.
Quoting Geo772 (Reply 5):
The trent 1000 will have the following major differences over previous trent engines: Bleedless and the accessory gearbox will be driven by the Intermediate stage turbine.
Taking all of the power off of the intermediate turbine will help the Trent 1000 have nice climb and cruise stall characteristics. This will allow the engine to push the LPC and HPC stall margins. Why is this good? This allows for a more efficient compressor without having the engine risk hocking out a fireball out the front.
But again, that long legth between the high and intermediate turbine has got to be killing the Trent's efficiency. Don't get me wrong, I think the Trent 1000 is a great concept. Just always understand every design is a compromise, even whichever is your favorite.
Quoting SunriseValley (Reply 3): 1. can this gearbox be changed on the wing? If so about how many manhours?
2. you stated that PW had got the reliability prediction down to about 100 cycles. Are PW still working on this device ,if so I wonder what new materials and manufacturing methods have been developed for it.
2. Is it something a specialty gearbox manufacturer could customise for different engine manufacturers? Seems to me Sundstrand was in this field some years ago.
Good questions.
1. The gearbox is a shop change. The engine would be pulled and the gearbox would require 4+ shop hours to change out.
2. The reliability is more in mapping out the gearbox cooling, etc. As a conservative industry, I'm not aware of the exact materials... so I will avoid speaking where I don't know enough.
3. A gearbox manufacturer could customize for the different manufacturers if they bothered to know their failure modes that well. FYI, Sunstrand is now merged into Hamulton-Sunstrand (ex Hamulton-Standard), a division of United Technologies, the parent company of Pratt. Note: I believe Textron did work too on GTF gearboxes.
Quoting ContnlEliteCMH (Reply 7):
I would also assume two additional items. First, the system will surely be designed to cool the gearbox at indefinite maximum thrust. Second, such a cooling requirement would only be required at takeoff thrust. If climb thrust is only 20% to 40% that of maximum thrust, then cooling will surely not be an issue.
Normally good assumptions. However:
1. Maximum thrust has a time limit. Usually just a few minutes, so the answer is that you might overheat the oil a bit at the end of this interval.
2. Takeoff must be possible in 125F weather (Pratt's standard maximum temperature takeoff, but that's *Not* at maximum thrust.) However, once you start climbing, the temperature in the fan case drops toward -55F or maybe a little warmer (yes, the air outside is -70F in the stratosphere, but the recovery of pressure and the fan will heat the air a tiny amount.) So its easy to cool the gearbox for cruise. For climb... after the first few minutes the air is much cooler than the assumed 125F, so again, cooling is easier. Also remember how fast the air is hitting the oil cooler. Imagine your car radiator being hit with 500mph+ air. I bet it would cool a bit better. Hint: your cars fan probably accelerates the air to Mach 0.1 (at best). Not mach 0.8+. Recall again, the oil coolers are put *inside* the fan duct for FOD reasons. (on the inner diameter so that the fan centerfuges any water/birds/stones/whatever away from the vulnerable oil coolers including the current engine oil coolers.)
Quoting ContnlEliteCMH (Reply 7): Perhaps Lightsaber or somebody else can provide figures on the working temperatures, volumes, and flow rates of the oil in a modern turbofan. Will the engine oil also be used for the gearbox?
Pratt keeps this information tight to the chest. Or at least, I do not know. I do know the gear oil and engine oil would be seperate systems.
I'm excited where engines are going. We're seeing contra-rotation go from being a fantasy to a reality. I know all three major engine makers are working hard to replace nickel in their high turbine blades. Each has their own solution... the first to get it to market has a definative advantage. However, recall the pw2000 was the first commercial engine with single crystal turbine blades... it took a decade+ of service to get the durability right. I'm also excited about integrade blade/hub rotors. As simple as it sounds, this saves a lot of weight in an engine and that's always good. I'm not as certain about the high RPM high spools (instead of 15,000 RPM, how about 30,000+?!?) I think it will happen in military engines; there will almost certainly be a noise issue in civil aircraft. I also believe we are at a breakthrough in composites. All composite& titanium nacelles will probably be the future. And CFD (which used to be my bread and butter) is only getting better.
Beaucaire From Syria, joined Sep 2003, 5051 posts, RR: 23 Reply 9, posted (2 years 7 months 2 weeks 1 hour ago) and read 2285 times:
I'm no expert in engine design or not even remotely familiar with the constraints -but Lightsaber's posts gives an excellent introduction in the complexities of engine -design.
Thanks for sharing your expertise with "greenhorns" and allow us to understand a little better ,why those dam engines are so expensive !!!!
Welcome on my RUL....
Can you say what sort of range of solutions are being looked at there? Will there be an end to the nickel era? Ceramics must be tempting, but they are still brittle? Presumably there is quite a way to go with the working temperature range that the combustors can give. Any estimates of how much additional efficiency is out there to be achieved - just from basic thermodynamics?
A question that might be more for Geo772, is there much in the Trents that can be traced back to the acquisition by RR of Bristol and Armstrong Siddeley, not to mention Vickers Met, I guess?
Quoting Baroque (Reply 10):
Eeek! must be about the right comment there. Presumably this is to get more work out of smaller and therefore lighter blades?
Actually, its to do the work with 1/2 the number of blades. This shortens the engine, gets rid of parts, and lightens the engine that way. In actuality, each blade is bigger and heavier than the current designs. But the weight savings is still tremendous if it can be pulled off. I know just enough to say its going to be a tough design to get to work. I expect the first one to be in a military engine.
Quoting Baroque (Reply 10):
Surprising that these improvements are so late in the curve.
Not really. Believe it or not, its a very conservative industry. But... there is no reason an aluminum aircraft cannot have a composite nacelle.
As to the materials in a turbine, I have to tiptoes around an NDA So I must speculate in general and not talk specifics.
Ceramics still have hope, but it is not the focus of GE or Pratt. Both of those companies are looking more at refractory metals due to their incredibly high temperature resistance. This should suprise no one. If you know what refractory metals are, you know that they have incredible temperature capabilities. But, Tungston, Moly, Tantalium, Niobium, Rhenium, and maybe I'm forgetting a few. Platinum works well too, but is a wee bit pricey.
ContnlEliteCMH From United States, joined Mar 2005, 1299 posts, RR: 41 Reply 12, posted (2 years 7 months 1 week 6 days 13 hours ago) and read 2201 times:
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Note: I believe Textron did work too on GTF gearboxes. 
I'm also excited about integrade blade/hub rotors. As simple as it sounds, this saves a lot of weight in an engine and that's always good. I'm not as certain about the high RPM high spools (instead of 15,000 RPM, how about 30,000+?!?) I think it will happen in military engines; there will almost certainly be a noise issue in civil aircraft. 
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