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Topic: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-17 17:34:49 and read 14832 times.

Pointing out that CFM’s Leap-1A engine for the Airbus A320NEO will not run until the fall, P&W President David Hess says “our NEO engine is flying and, in the most recent configuration, the fuel-burn numbers are half a percent better than predictions.”

http://www.aviationweek.com/Article....e-xml/awx_06_17_2013_p0-588704.xml

Ok, a half percent isn't much, but usually from now until EIS fuel burn is improved 2.5% or so...



I'm facinated that GE is promising 1% lower fuel burn than the PW1100G and better fuel burn retention... Its a match!   

Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: tortugamon
Posted 2013-06-17 18:06:51 and read 14665 times.

Rooting for the GTF. Its great to see them take a bold step in a new direction. Hope they are rewarded.


tortugamon

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: Asiaflyer
Posted 2013-06-17 18:33:33 and read 14518 times.

Quoting lightsaber (Thread starter):
Ok, a half percent isn't much, but usually from now until EIS fuel burn is improved 2.5% or so...

Interesting article! For sure a real battle,
It depends if he compares to the expected final fuel burn or where they expected themselves to be at this stage of the project.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: Klaus
Posted 2013-06-17 18:38:03 and read 14482 times.

Quoting tortugamon (Reply 1):
Rooting for the GTF. Its great to see them take a bold step in a new direction. Hope they are rewarded.

Indeed. It shouldn't have taken the industry that long to take this major step ahead.

Guaranteeing reliability is probably a necessity at this point, but I hope that it won't bite them too hard, if at all.

But exceeding fuel burn sounds like a great start already. That should relax the overall risk equation both for them and for their customers, even if some initial issues should in fact crop up (knock on wood).

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: tugger
Posted 2013-06-17 19:38:44 and read 14239 times.

Quoting Klaus (Reply 3):
Guaranteeing reliability is probably a necessity at this point, but I hope that it won't bite them too hard, if at all.

At this point I think it all comes down to reliability and maintenance costs. Along as reality meets projections then it will be good for PW. Of course if they exceed then that's just gravy and I suspect they have been trying to remain conservative just to hedge bets.

Tugg

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: francoflier
Posted 2013-06-17 20:49:51 and read 13968 times.

Quoting tortugamon (Reply 1):
Rooting for the GTF.

+1.

They're the only ones who have boldly gone for a radical engine design instead of incremental improvement. They should be rewarded.

As Tugger said, they have likely been conservative due to the risk of introducing a new technology. The room for improvement on the GTF is, IMO, huge. Much larger than for the LEAP.

Of course, all of that won't mean much if the reliability, time on wing and cost of maintenance don't follow suit...

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-17 21:12:51 and read 13874 times.

Quoting Asiaflyer (Reply 2):
Interesting article! For sure a real battle,

For sure. But its not just a technology battle (as much as I wish that was the case). It is also going to be a case of financing and there GE has a leg up.

Quoting Asiaflyer (Reply 2):
It depends if he compares to the expected final fuel burn or where they expected themselves to be at this stage of the project.

A fair question. I believe the former, but it could very well be the later.

Quoting Klaus (Reply 3):
Indeed. It shouldn't have taken the industry that long to take this major step ahead.

Have the billions to invest.  

However, I was frustrated. I was working the PW8000 for a circa 2001 launch and that certainly didn't happen...

But these things take time...

Quoting francoflier (Reply 5):
They're the only ones who have boldly gone for a radical engine design instead of incremental improvement. They should be rewarded.

I'm a Pratt fan, so I'm going to put my bias aside. Pratt with the C-series forced the NEO. The GTF on the NEO has forced GE and partners to counter with a whole set of new technologies that sum up, at least per promise, will match the GTF. It is interesting to see the forward movement through two parallel paths. So its good to have competition.

Besides, I work for a vendor with product on *both* engines now.  

Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: faro
Posted 2013-06-18 02:47:15 and read 13131 times.

Go Pratt go!

Will be happy to see their once-ubiquitous eagle logo ply the skies the world over again.


Faro

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: cuban8
Posted 2013-06-18 04:35:25 and read 12148 times.

Quoting lightsaber (Reply 6):
It is interesting to see the forward movement through two parallel paths. So its good to have competition.

Besides, I work for a vendor with product on *both* engines now.  

Definitely interesting and rewarding for future Airbus customers!!!! If you don't mind, I will ask for your opinion in the future in regards of engine options.

My boss is pushing me for the A319 CJ NEO, but we still haven't received the performance data for the ACJ NEO and it's is still not officially announced (I'm hoping for some news at Le Bourget, but so far no news). Rumours says they are working on a new wing and engine option to be able to provide a 6000nm range for the ACJ NEO (which would make Dubai-New York non-stop possible), so I believe these small fractions of percentages on engine efficiency are going to be very important for us at the end of the day...

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: parapente
Posted 2013-06-18 05:30:35 and read 11447 times.

I hope GE/Cfm have not put their (performance) words into contracts - 'cos if they have they will go bust!

RR correctly decided to bow out. They could see the writing on the wall with the GTF. Cfm feel that by incorporatig fighter jet temps and pressures they can match it. I do not believe they can and certainly not on mantainance.

I bet RR are working away on Planitary GTF technology to prevent a similar move into the big jets where they enjoy a duopoly (or merge?)

BTW I bet the GTF is quiet too.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: RussianJet
Posted 2013-06-18 05:44:17 and read 11246 times.

I don't think half a percent "isn't much". Over time it's a hell of a lot really, and on a machine that was already predicted to be very efficient.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: A380900
Posted 2013-06-18 05:54:19 and read 11112 times.

What I don't get in this kind of competition is that as soon as the numbers are out, why would anybody buy the engine that performs less well? If I remember well most A320 fly with the same engine even thought there are two available. And the A321 with another.

Or is it always a question of trade-offs? One engine is better but not in every aspect so there is room for both in the market? Or some companies like Air France always stay with one brand.

In this case. What will happen if the Pratt burns 1.5% less than the Leap? Is it winner takes all? HOw about the A380 two options? Isn't the EA a better engine?

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-18 06:04:16 and read 10972 times.

Quoting cuban8 (Reply 8):
If you don't mind, I will ask for your opinion in the future in regards of engine options.

Feel free. There are a mix of people here who know the different aspects. I know the theory/design. Others here are more an expert on the operations.

Quoting cuban8 (Reply 8):
My boss is pushing me for the A319 CJ NEO, but we still haven't received the performance data for the ACJ NEO and it's is still not officially announced (I'm hoping for some news at Le Bourget, but so far no news).

I'm not a fan of the A319NEO for commercial airlines. IMHO, it is the next A318 (if built). The leasing companies won't touch it until it sells well which means it won't sell... Only F9 has bought the A319NEO and with their impending sale, I fully expect the order to be up-gauged.

Quoting cuban8 (Reply 8):
Rumours says they are working on a new wing and engine option to be able to provide a 6000nm range for the ACJ NEO

I've heard rumors of the A321 wing... but for the A320 CJ NEO...

Quoting RussianJet (Reply 10):
I don't think half a percent "isn't much". Over time it's a hell of a lot really, and on a machine that was already predicted to be very efficient.

Fair enough. But 1/2% is only a 0.15% reduction in total costs for a typical narrowbody mission. So while it is an advantage, it takes more fuel burn reduction to drive sales from the LEAPx. And the LEAPx is promising 1% lower fuel burn than Pratt, so closing that gap (if any really exists) is critical to sell the new concept.


Now for some related news for everyone.
First, I'm amused IAE just hit a peak production rate of 500 engines/year:
http://www.ainonline.com/aviation-ne...e-brazilian-kc-390-transport-tests

However that doesn't compare to GE's plans of 1,700 LEAPx per year!   
http://www.ainonline.com/aviation-ne...ies-drive-engine-makers-their-game


Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-18 07:11:01 and read 10147 times.

Quoting A380900 (Reply 11):

What I don't get in this kind of competition is that as soon as the numbers are out, why would anybody buy the engine that performs less well? If I remember well most A320 fly with the same engine even thought there are two available. And the A321 with another.

Or is it always a question of trade-offs? One engine is better but not in every aspect so there is room for both in the market?

It is a matter of trade offs. Almost always the engine with less fuel burn has higher maintenance costs. Then there is financing. Each engine manufacturer can only afford to loan out so much money each year (in this economy, that helps move engines).

But remember for narrowbodies, fuel costs are up to 30% to 50% of total costs. So a 0.5% reduction in fuel burn is only 0.15% of total costs. Since spare parts are ~4% to 5% of costs, a little discounting there does more. Then there are maintenance plans where a better maintenance plan will save more. Then there is warrantee, spare engines, spare buying schedule/location, and production rates.

For example, for the A321, the V2500 is the better engine. But IAE is only able to make 500 engines per year. Why the better engine? Lower fuel burn. But on the A319, the CFM-56 is the better engine due to lower maintenance costs (shorter typical mission).

Its also tooling. If an airline owns all the custom stuff to service a GE engine, the 0.5% difference in fuel burn could be less than the equipment. Now if it were 1.5%, the airline would switch as that is a notable range difference.

Now if an engine is clearly superior, then it sells very well. e.g, the T700 on the A330. But on the 787, the GEnX is promising better fuel burn, so its sold better. But wait, the T1000 has less fuel burn during climb. So its only past 2500nm the GEnX is burning less fuel.

And what of reliability. The inital Pratt PW2000 burned 7% less fuel than the RR Trents. But the Pratt's were so trouble prone that it gave RR time to redesign and replace the existing engines to the point they were competitive. While the Pratt's still burn less fuel, until a few years ago the RR lasted 4X as long between overhauls! Pratt improved just in time to watch the 757 line shut down...

Its all tradeoffs and negotiations expressed as dollars for each airline.

Quoting parapente (Reply 9):
I hope GE/Cfm have not put their (performance) words into contracts - 'cos if they have they will go bust!

They had to. They won't go bust. But oh boy... We received a rather gleeful e-mail from the Paris Air show from our 'mucky muck' there as GE is YELLING at their vendors trying to meet promise and the majority of them can't do it. We are delivering.  

Look at the 787. Both RR and GE missed promise by quite a bit. RR has improved fuel burn since EIS by 3.5% and GE has improved too (I forgot where they are... I know... need to wake up). Yet neither is at promise yet both are selling product.   

Now my rumor mill insists the PW1500G has margin. They don't talk the PW1100G (too far into the NDAs).

Quoting parapente (Reply 9):
BTW I bet the GTF is quiet too.

The LEAP-X might be quieter. Pratt avoided the Chevrons due to the fuel burn penalty and fatigue risk. Yes, the PW1100 has a higher bypass ratio, but the Chevrons really help reduce noise at a 0.25% fuel burn penalty and some weight.

Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: dynkrisolo
Posted 2013-06-18 08:44:26 and read 9128 times.

Quoting francoflier (Reply 5):
They're the only ones who have boldly gone for a radical engine design instead of incremental improvement. They should be rewarded.

Geared turbofans have been in service for more than three decades. The Lycoming/Honeywell LF502 was first certified in 1980. Pratt's PW1000G will have much higher thrust than LF502. So, the gear technology would be more challenging than LF502. But it definitely is not a radical engine design.

Quoting parapente (Reply 9):
I hope GE/Cfm have not put their (performance) words into contracts - 'cos if they have they will go bust!

RR correctly decided to bow out. They could see the writing on the wall with the GTF. Cfm feel that by incorporatig fighter jet temps and pressures they can match it. I do not believe they can and certainly not on mantainance

I don't mean history will repeat itself, but we need to be aware of the history. When Pratt launched PW2000 for 757, it had ~10% better fuel burn than RB211-535C2 and CF6-32. GE bowed out. Rolls improved the offer with -535E4, but it was still ~5% worse on fuel burn on paper than PW2000. Pratt did deliver the fuel burn promise, but under-delivered on many other aspects. RB211 was the eventual market winner.

So, let's see how P&W executes on PW1000G this time around.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: N757ST
Posted 2013-06-18 11:00:54 and read 7657 times.

Quoting lightsaber (Reply 12):

There is no difference between an a321 wing and an A319/320 wing except for the double slotted flap. The intent of the double slot it to reduce pitch on landing by 1 degree to help with potential tail strike issues.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-18 11:33:11 and read 7253 times.

Quoting N757ST (Reply 15):
There is no difference between an a321 wing and an A319/320 wing except for the double slotted flap. The intent of the double slot it to reduce pitch on landing by 1 degree to help with potential tail strike issues.

You're right. For some reason I was thinking there was more than the 0.8m^2 difference in wing area... Its the fuel system that is quite different. But that is already on the CJs...

Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: N757ST
Posted 2013-06-18 11:50:13 and read 7024 times.

Fuel system is a bit different. Fuel cannot pump directly from the center fuel tanks to the engines like on the a320, instead scavenge pumps are used to pump fuel from the center tank to the wing tanks to the engines. Also, unlike the a320, the a321 doesn't have outer wing tanks, just main wing fuel tanks.

Not to rattle on, I just went though differences training in the last week in anticipation of our first a321s coming online this fall, so the info is fresh in my head.

[Edited 2013-06-18 11:51:35]

[Edited 2013-06-18 11:52:23]

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: r2rho
Posted 2013-06-18 12:46:03 and read 6422 times.

Quoting A380900 (Reply 11):
why would anybody buy the engine that performs less well? [...] Or is it always a question of trade-offs? One engine is better but not in every aspect so there is room for both in the market? Or some companies like Air France always stay with one brand.

Definitely a matter of trade-offs. Lighsaber has given some good examples. Also, look at large airlines like LH or AA. They have large enough fleets that they generate enough economies of scale to buy both CFM and IAE depending on the mission. AF is quite close to GE and Snecma (which remember makes 50% of the CFM56 & LeapX and 24% of the GE90), and likely have good deals running with them in terms of maintenance and financing.

Basically, if Pratt & CFM can replicate today's situation with the IAE and CFM56 where each engine has small advantages/disadvantages over the other (IAE lower fuel burn but higher maintenance, CFM higher fuel burn but better on maintenance), there will be a market for both.

Quoting lightsaber (Reply 13):
Almost always the engine with less fuel burn has higher maintenance costs.

That rule has applied when comparing similar architectures (CFM vs IAE, etc), but I wonder what will happen with the different GTF vs classic architectures. One would think the gear would need higher maintenance, but CFM will have to run their engine at higher temperatures to match it, which means higher maintenance costs as well.   

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: cuban8
Posted 2013-06-18 14:46:39 and read 5227 times.

Quoting r2rho (Reply 18):
Basically, if Pratt & CFM can replicate today's situation with the IAE and CFM56 where each engine has small advantages/disadvantages over the other (IAE lower fuel burn but higher maintenance, CFM higher fuel burn but better on maintenance), there will be a market for both.

As far as I know, the CFM engine has been the most popular engine for the A320 family. Hearing from engineers, the IAE engine is very complicated when it comes to maintenance (too many parts to remove for simple adjustments). As you mentioned, the IAE engine burns less fuel in flight while I believe the CFM engine is supposed to have better efficiency at lower altitude and to a certain extent better climb performance than the IAE engine. All in all, I guess they are quite equal when everything is summed up.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: cornutt
Posted 2013-06-18 17:43:15 and read 4143 times.

Quoting r2rho (Reply 18):
That rule has applied when comparing similar architectures (CFM vs IAE, etc), but I wonder what will happen with the different GTF vs classic architectures. One would think the gear would need higher maintenance, but CFM will have to run their engine at higher temperatures to match it, which means higher maintenance costs as well

And presumably the Pratt engine will be running the fan at a lower speed, so there should be a reliability advantage there. How does the GTF drive the accessories? Does it come off the fan gearbox?

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-18 22:36:40 and read 3859 times.

Quoting r2rho (Reply 18):
I wonder what will happen with the different GTF vs classic architectures.

I should have been more specific. Normally the way to cut fuel burn is by upping pressure. Yes, the GTF sidesteps that. In fact, the PW1000G family is *very* simple and low temperature (by today's standards). I fully expect it to have a third lower maintenance cost than the LEAP-X. (I'm still amazed by the LEAP-X stage counts.)




Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: francoflier
Posted 2013-06-19 08:16:34 and read 3555 times.

Quoting parapente (Reply 9):
I hope GE/Cfm have not put their (performance) words into contracts - 'cos if they have they will go bust!

The LEAP-X certainly has to wow the same crowd with a smaller bag of tricks, but I'm not worried for them.

Even if they lost every single NEO client, the MAX would bring them 50-ish % market share anyhow.
As it stands now, the LEAP-X is bound to represent roughly 75% of the next gen narrow bodies powerplants worldwide. Soon, it will be just as ubiquitous as the CFM-56 is today.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: dynkrisolo
Posted 2013-06-19 09:42:34 and read 3380 times.

Quoting lightsaber (Reply 21):
I should have been more specific. Normally the way to cut fuel burn is by upping pressure. Yes, the GTF sidesteps that. In fact, the PW1000G family is *very* simple and low temperature (by today's standards). I fully expect it to have a third lower maintenance cost than the LEAP-X. (I'm still amazed by the LEAP-X stage counts.)

For the GTF to have better fuel burn than LEAP-X, the GTF will need to have similar thermal efficiency as LEAP-X, because on the NEO application, the bypass difference of the two engine offerings is relatively small. Hence, the propulsive efficiency advantage is relatively small. If GTF has low temperature, then it means it has lower thermal efficiency. I doubt the small propulsive efficiency can make up for the thermal efficiency difficency, let alone to maintain a fuel burn advantage. You can't have both low temperature AND better fuel burn. Simple physics! And Pratt's commercial experience on high pressure ratio compressor is lagging.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: Revelation
Posted 2013-06-19 09:59:16 and read 3315 times.

Related article at AvWeek: Pratt Begins Talking Next-Generation GTF

Quote:

Hess says P&W has a roadmap to increase the GTF fuel savings to 20-30% from 15% by the middle of the next decade. Some of that will come from bigger fans that increase bypass ratio to 15-18 from around 12 on the PW1000G, but P&W also plans to improve the core.

This will involve increasing the overall temperature of the engine and require new materials, says Adams. “We will drive thermal efficiency. Core technology will push overall pressure ratio beyond 60, which is the next threshold for this size of engine.”

“Temperature is a value trade with cash operating cost. We will not arbitrarily drive temperatures too high to gain performance but lose on maintenance cost,” he says. “We are in a good place with the current GTF.”

So we'll be seeing bigger fans and better cores.

We also read:

Momentum Building To Bring PW1100G GTF Under IAE:

Quote:

Sales and marketing for both engine programs have been combined since November 2012, to present “a single face to the customer,” says Beatty. “With the same shareholders in both programs, it is an opportunity to look at more collaboration.”

Hess agrees that IAE is the appropriate brand for the PW1100G on the A320NEO, while Pratt’s own PurePower brand for the GTF family is now firmly established with engines on the Bombardier CSeries, Embraer E-Jet E2, Mitusbishi MRJ and Irkut MC-21.

I like the idea: put the IAE name on the ones going on the NEOs and keep the good ol' Pratt name on the new applications.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-19 10:04:04 and read 3428 times.

Quoting dynkrisolo (Reply 23):
the GTF will need to have similar thermal efficiency as LEAP-X,

The GTF has a much higher propulsion efficiency thanks to the lower fan Mach #. The GTF also has a *far* higher low turbine efficiency thanks to the higher Mach # there (most of the GTF gain, actually).

Quoting dynkrisolo (Reply 23):
If GTF has low temperature, then it means it has lower thermal efficiency.

   and?

Quoting dynkrisolo (Reply 23):
Simple physics!

Yes, the GTF is. Simply improving the fan, low compressor, and low turbine component inefficiencies. A 10% efficiency improvement over a standard engine.

Quoting Revelation (Reply 24):
So we'll be seeing bigger fans and better cores.

   After everyone else has debugged their issues and Pratt hires a few engineers from their competitors...  
Quoting Revelation (Reply 24):
I like the idea: put the IAE name on the ones going on the NEOs and keep the good ol' Pratt name on the new applications.

I do too. It also lets IAE customers know the transition will be managed by many of the faces they know.

Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-19 10:54:11 and read 3296 times.

I personally like this link for comparing the two engines:
http://airinsight.com/2011/11/09/com...nes-gtf-vs-leap-maintenance-costs/


CFM’s parts would need to be twice as durable as PWs to maintain maintenance cost parity.

Our preliminary estimates indicate that the PW1000G should have an advantage in maintenance costs over LEAP, and could reach the 10-20% level, based on the latest configuration data we have obtained from each manufacturer and other industry sources.

I still estimate 30%...


As to fuel burn, the two engines have the same pressure ratio (within 2%). The GE needs to run 60F to 130F hotter to have the same efficiency thanks to Pratt's more efficient low compressor and low turbine. Yes, GE has a better high compressor, but Pratt as far better fan efficiency (per article, worth 2-3% on its own).

My math says the PW1100G should be a few percent more efficient then the LEAP-X. Let's see how it goes...

Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: dynkrisolo
Posted 2013-06-19 11:39:54 and read 3217 times.

Quoting lightsaber (Reply 25):
The GTF has a much higher propulsion efficiency thanks to the lower fan Mach #. The GTF also has a *far* higher low turbine efficiency thanks to the higher Mach # there (most of the GTF gain, actually).

You're talking about component efficiencies. Propulsive efficiency is only a function of bypass ratio.

Quoting lightsaber (Reply 25):
Yes, the GTF is. Simply improving the fan, low compressor, and low turbine component inefficiencies. A 10% efficiency improvement over a standard engine.

Are you saying component efficiencies can swing overall efficiency, which is a product of propulsive efficiency and thermal/cycle efficiency, by 10%? Then maybe your physics is different from mine.   You know, Rolls-Royce's three shaft design uses the same principles as the GTF. That is, better matching the speeds of fan and low speed compressor. Except Rolls is using three shafts while the GTF is using a gear to achieve similar goals. Rolls certainly hasn't demonstrated the kind of component efficiency gains that you are asserting!

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: dynkrisolo
Posted 2013-06-19 11:56:56 and read 3136 times.

Quoting lightsaber (Reply 26):
I still estimate 30%...

Go ask an engine MRO: what part of the engine makes up most of the engine maintenance cost. You'll get the answer: hot section. The GTF advantage on fewer stages and fewer parts are mostly in the cold section. But because the GTF cold section is operating at a much higher RPM, it means some of the reduced parts advantage will likely be eroded by the higher operating speed. It's highly unlikely PW1000G can get 30% maintenance cost advantage.

[Edited 2013-06-19 11:58:31]

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-19 12:24:03 and read 3071 times.

Quoting dynkrisolo (Reply 27):
You're talking about component efficiencies. Propulsive efficiency is only a function of bypass ratio.

Its also a function of the profile factor of the fan in the real world.   The high mach # fan of the LEAP-X is not producing a plug flow by any means... The GTF will be far closer to the ideal. Technically component efficiency is expressed in total pressure, but that doesn't fully explain the thrust difference, hence propulsion efficiency. Component efficiency is impacted by the high blade tip mach # creating shock waves in the LEAP-X, but that is mitigated to a high degree by GE's latest fan blades. But I've seen better fan blades back in 2000 at Pratt.  

I live in the world where I have to go beyond the text books, so we mix the terms a bit. I can talk in either set of Jargon. But for discussing these fans, we end up having to break down the terminology as while the school book physics is still accurate, it must be integrated across the engine diameter which produces some interesting numbers. To make things more interesting, there are East Coast US, West Coast US (highly influenced by old German conventions), and British conventions on how to do this properly and each group 100% believes it is correct.

Quoting dynkrisolo (Reply 27):
Are you saying component efficiencies can swing overall efficiency, which is a product of propulsive efficiency and thermal/cycle efficiency, by 10%? Then maybe your physics is different from mine.

Pratt claims 11%.    But the range is 7% to 15% depending on how agreesing the gearing is. Look at the links in post # 24 to see where Pratt is taking the GTF for widebodies (further up the curve).

What are you assuming for compressor efficiency? Its really poor in low compressors. Even the ground breaking ones in the LEAP-X (Scalloped compressors). So I'll break it down in the answer to your next statement. But I ask you, how has Pratt demonstrated 0.5% better than promise fuel burn, which is within 1% of what the LEAP-X is promising, if they do not have some gain from the GTF? Doing so with 1,000 to 3,000 fewer blades!!!

And Pratt is keeping some of the gain 'in reserve' fully expecting the first GTFs to miss target.    GE is having to push the limit...

Do remember, some of the thermal efficiency must be given back with cooling... Pratt is using advanced materials to reduce cooling required. Cooling wastes air that does little (if any) work where injected that has already 'sucked up' horsepower from the compressors. While GE has the CMCs, they are still having to use a large amount of cooling air to maintain durability.

And GE has intentionally sacrificed 0.5% fuel burn for the Chevrons to cut noise. Noise that doesn't happen thanks to the slower fan of the GTF and thus no mitigation required.

Quoting dynkrisolo (Reply 27):
You know, Rolls-Royce's three shaft design uses the same principles as the GTF. That is, better matching the speeds of fan and low speed compressor. Except Rolls is using three shafts while the GTF is using a gear to achieve similar goals.

   Except go back to the two most important components: low pressure turbine and the fan. Neither of those are helped by RR's triple spool. While the triple spool is at an advantage over a double spool for component efficiency, the components that are furthest away from ideal are not being helped!

*Most* of the advantage is getting the low turbine up to a good mach number to power the fan. The low turbine powering the Trents is at a low Mach # and thus sacrificing several percent in fuel efficiency (about 6% to 8%). GE is trying to use a HUGE number of stages. The fan at proper Mach # gives another 2% to 4%. Another 2% is the low compressor that is already reached its benefit in the triple spool. The ranges are due to 'mission optimization' of the design and thus the difference between a short haul engine and a long haul engine.

Yes, RR has a far more efficient "booster compressor" and turbine powering that compressor on the "intermediate shaft." That means combustor inlet air temperature is quite a bit lower than Pratt or GE's older engines and part of the reason RR has such an excellent reputation for durability (every 70 degrees F hotter the metal gets cuts part life in half).

RR has also been overcoming a 'less than optimal' high turbine/intermediate design in prior Trents. Their shrouded turbines were at a less than optimal Mach # due to the weight of the shroud (stress induced into the blade). They are now going to unshrouded turbines with better active case cooling. Part of the reason RR went with Shrouded turbines is the triple spool is the difficulty in actively cooling the high turbine and intermediate turbine separately. RR has finally gone to a more conventional high turbine in the Trent XWB. I'm very curious how RR will cool their turbine casing in that engine as that is key for un-shrouded turbine efficiency. But having the case contract to maintain blade tip clearances for three turbines shall be a 'unique challenge.' A challenge RR avoided with their shrouded turbine blades on the high and intermediate turbines.

Quoting dynkrisolo (Reply 27):
That is, better matching the speeds of fan and low speed compressor.

Fan speed is *not* matched on the triple spools at all with its turbine. The fan mach # is the exact same as a idential bypass ratio twin spool and the same is true of the low turbine powering the fan (mach # too low). On a widebody, the needed RPM ratio is 'out of whack' by a factor of 3.5. One is forced to slightly overspeed the fan (but only by 10% or so) and thus run the low turbine at a mere 30% of its ideal RPM.

Lightsaber
Oh, its not low speed compressor. Its low PRESSURE compressor. And just to be clear, I agree the GTF has zero advantage over a triple spool's booster (low) compressor. In fact, the booster compressor will achieve a much better efficiency during climb as its spool is not slowed by the fan during the slower climb mach numbers. Hence why Trents, which all have higher fuel burn at cruise than the competing GE/Pratt engines, do well. For the fuel burn 'equality' doesn't usually happen until 4000nm. (Further for the latest Trents: A380, 787, and XWB.)

Did you ever wonder why the T1000 sold when the GEnX-1B promised 2% lower cruise fuel burn? The answer is the triple spool burns much less fuel during climb. IIRC, equality in fuel burn happens at about 5500nm which is longer than most 787 missions will be. So airlines with shorter missions (e.g, mid-east to Europe or TATL) will favor RR. Airlines with longer missions (Asia to Europe or TPAC) should favor GE.

Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: PW100
Posted 2013-06-19 13:49:54 and read 2852 times.

Quoting lightsaber (Reply 29):
Lightsaber's tutorial

Be careful, next thing we know this thread end up in TechOps!
Anyway, thank you greatly for taking the time for this very thorough insight! And I do share your GTF enthusiasm. I also agree that GE is taking significantly more risk than Pratt, not only in their compressor and turbine efficiencies, but almost certainly in the durability field. Which ironically was one of their major selling points on the CFM56. 100% HP turbine blade and vane replacement every 5k – 10k cycles or so is going to be very very expensive . . . for the time being.

Quoting lightsaber (Reply 29):
(every 70 degrees F hotter the metal gets cuts part life in half

Is that number normally associated with large wide body engines (5-10 hr mission average), or does this also apply to the 2-3 hr mission profile of your average narrow body?
Reason I ask, is that in my field of experience (see my username), where we usually use cycle/hr ratio of 1:1, I tend to see a considerably lower number of 30-50 R/F.

PW100

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-19 14:35:30 and read 2780 times.

Quoting PW100 (Reply 30):
Quoting lightsaber (Reply 29):
(every 70 degrees F hotter the metal gets cuts part life in half

Is that number normally associated with large wide body engines (5-10 hr mission average), or does this also apply to the 2-3 hr mission profile of your average narrow body?

Both. Now the peak temperature is at end of initial climb, so it happens once per cycle. Thus the hours for a widebody aren't really aging the engine at cruise as the time at climb did the 'wear and tear.'

Quoting PW100 (Reply 30):
Anyway, thank you greatly for taking the time for this very thorough insight!

Your're welcome.

Quoting PW100 (Reply 30):
I ask, is that in my field of experience (see my username), where we usually use cycle/hr ratio of 1:1, I tend to see a considerably lower number of 30-50 R/F.

Well that gets into coatings and which metal... We would have to pound down a few to have a proper discussion.   
For example, your numbers work better with the old thermal barrier coatings with a sublayer while my numbers are for the metals that if they have a TBC, the TBC is directly bonded to the metal.

There isn't quite 'one number.'  
Quoting PW100 (Reply 30):
but almost certainly in the durability field. Which ironically was one of their major selling points on the CFM56. 100% HP turbine blade and vane replacement every 5k – 10k cycles or so is going to be very very expensive . . . for the time being.

Hey, the V2500 has the same overhaul interval as the CFMs now.    The V2500 just cost more to overhaul as when the majority of the overhaul cost is the high turbine and you double the number of blades... the cost of the overhaul goes way up! The V2500 also has some oil leak issues... hence its 20% higher maintenance costs vs. the CFM-56-5. But it has lower fuel burn, so at a certain mission length it is break even and longer missions, such as those flown by B6, the V2500 is cheaper to fly.

Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: Revelation
Posted 2013-06-20 05:37:50 and read 2468 times.

Another interesting point from Pratt Dismisses CFM Leap's Superiority Claims Regarding GTF:

Quote:

Flight-testing, first on the CSeries and then of the A320NEO engines, has resulted in deletion of the variable-area fan nozzle (VAFN), which Pratt had thought would be needed to provide enough flutter margin for the large-diameter fan.

But Hess says the latest hybrid-metallic fan blade has much better flutter characteristics than expected and sufficient margin to eliminate the VAFN “and get rid of the complexity and weight.” NEO test engines are now flying with the nozzle locked, but design changes will delete that feature from production engines.

Google brings me to https://www.flightglobal.com/news/articles/farnborough-cseries-gtf-to-feature-variable-area-fan-nozzle-373956/ which says:

Quote:

The fan nozzle expands on take-off to increase the flow of air bypassing the core of the engine, thus reducing noise and increasing velocity, with greater fuel efficiency.

SS White also says the nozzle helps protect the engine against dangerous conditions such as fan resonance or flutter.

I'm not quite getting its use. The counter of the above statement is that it'd contract after takeoff (in cruise phase?) and decrease the flow of air bypassing the core, but that to me seems counter-intuitive, unless the flutter they are concerned about is happening mostly during cruise.

I do see how such a thing would be heavy and complex, so I can see why they are glad they are getting rid of it.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: lightsaber
Posted 2013-06-20 06:01:40 and read 2410 times.

Quoting Revelation (Reply 32):
Flight-testing, first on the CSeries and then of the A320NEO engines, has resulted in deletion of the variable-area fan nozzle (VAFN), which Pratt had thought would be needed to provide enough flutter margin for the large-diameter fan.

It wasn't just for flutter margin. It was to provide a 2% drop in fuel burn. Its being eliminated to ensure the engines meet maintenance promises. It doesn't really reduce the air flow as the backpressure on the fan would be low. What it did was optimize the fan air nozzle for cruise *and* takeoff, a normally impossible feat.

Technically, what needs to be done versus a fixed nozzle is expand the nozzle area during high thrust and low mach # operations. At cruise, a smaller nozzle area is optimal due to the higher flight mach # and lower fan pressure ratio (due to burning less fuel than takeoff).

I've always heard of reducing fan flutter/surge margins as a bonus, but not the main reason for the fan nozzle. I'm sad they're not going forward. That was one technology I considered a given due to the cheap and easy way to cut fuel burn 2%.

What it means is Pratt is confident enough in their fuel burn to give up 2% in fuel burn to reduce maintenance costs.

Quoting Revelation (Reply 32):
I do see how such a thing would be heavy and complex, so I can see why they are glad they are getting rid of it.

Its a cold air variable nozzle which makes it *very* simple for Pratt nozzles to design a simple device.

A core variable nozzle would be heavy and complex due to the heat. But nothing as complex as the military nozzles post augmentor (laymen call them an afterburner).

Lightsaber

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: Revelation
Posted 2013-06-20 06:48:15 and read 2297 times.

Quoting lightsaber (Reply 33):
At cruise, a smaller nozzle area is optimal due to the higher flight mach # and lower fan pressure ratio (due to burning less fuel than takeoff).

Thanks, your explanation makes sense to me. Seems to be yet another tradeoff for bigger fans to deal with.

Of course if anyone has a diagram lying around, it'd be interesting to see too.

Quoting lightsaber (Reply 33):
I've always heard of reducing fan flutter/surge margins as a bonus, but not the main reason for the fan nozzle. I'm sad they're not going forward. That was one technology I considered a given due to the cheap and easy way to cut fuel burn 2%.

Maybe they are dissembling a bit - customers might get mad if the explanation was that more fuel savings weren't needed.

Quoting lightsaber (Reply 33):
Its a cold air variable nozzle which makes it *very* simple for Pratt nozzles to design a simple device.

Seems that simple to design is in conflict with the statements that they are complex, heavy and costly to maintain.

We know the world is happy with PIPs that provide 0.5% fuel burn gains, so leaving 2% on the table is hard to fathom, especially after you already have a design flying on two different test engine families.

Something is not quite adding up here.

Topic: RE: Pratt Beating Fuel Burn On NEO
Username: Sharktail
Posted 2013-06-20 07:09:27 and read 2207 times.

When we say a 2% fuel savings, what mission profile are we talking about?

Since this adds weight, it probably does not improve fuel savings in shorter missions, but only is an advantage on longer missions. So keeping it increases the advantage CFM has on shorter mission profiles. CFM is not going to match the Pratt on longer missions anyway.


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