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Faro
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Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 10:23 am

The GTF and LeapX exploit substantially different technologies to each achieve double-digit fuel burn reductions. Reasoning from a energy security/ecological perspective, could PW and CFM be forced to collaborate on one engine incorporating all planned technologies? Would the US government presently have any legal means of forcing this "merger" short of enacting new energy legislation? Would any such new legislation have a chance of being constitutional?

Seems a pity not to profit from both technologies combined...

Faro
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 11:49 am

Simple answer is, if you try to "force" something like this you'll get nothing. I doubt that there is any remotely legal pretext for doing so, and I can't imagine key engineers and project leaders sticking around to be told what they have to do or not do.

One can hope for a combo or equivalent to happen naturally, but attempting to force it would certainly be a massive blunder.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 12:45 pm

You're talking about technology from two fierce competitors being used in the same engine. There's no way they would ever go for it. Especially Pratt if GTFs turn out to deliver the improvements they promise.
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 12:53 pm

Quoting faro (Thread starter):
Should GTF & LeapX Be Forced Into One Engine?  

Aside from the "it's wrong to put a gun to someone's head and tell them what to do" argument, you are combining not just technology potentials, but risks. Getting an engine designed right already appears to be quite tricky, imagine not just one big technology leap, but two.

If both turn out successful, I am sure they will each pursue each other's technologies to improve their product.

[Edited 2010-09-03 05:55:38]
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 1:00 pm

Quoting PITingres (Reply 1):
One can hope for a combo or equivalent to happen naturally, but attempting to force it would certainly be a massive blunde
Quoting Delimit (Reply 2):
There's no way they would ever go for it.

The question is whether there can be a *legal* justification to make PW and CFM "collaborate" on a single engine from a public law perspective. Commercially we agree it's impossible.

IMO it would boil down to consideration of whether there is a greater, overriding public interest in securing the fruit of the collaboration (energy security/ecology) than the alternative public interest in maintaining free enterprise in this particular industry segment. Maybe free enterprise has a stronger case today but will that always be the case? What if the single engine would have near to double the fuel efficiency gains of either GTF or LeapX? After all, it powers the most numerous mainliner fleet category today. Is there or is there not a public interest in having an engine powering the most numerous fleet segment which is doublymore efficient than either competitor designs? One for the jurists I guess...

PS: Free enterprise is a wonderful thing but does have its limits. Imagine where the world economy would be today if the US government and the Fed did not intervene in the recent financial crisis and just let things be like in 1929...

Faro

[Edited 2010-09-03 06:06:28]

[Edited 2010-09-03 06:49:59]

[Edited 2010-09-03 06:54:21]
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 1:14 pm

I believe we need to wait for Lightsaber to wake up and kill this idea, but I have a distant memory it's been discussed before. Then, it was concluded that the LeapX technology wouldn't bring that much to the table if it was combined with GTF technology. It's two different methods of attacking the same problem, and doing it "twice" in one engine won't make it twice as effective.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 1:23 pm

There is absolutely no way the US governments could force GE and Pratt to do it without completely demolishing the law. My guess is you would see GE and Pratt both threaten to shut down their respective US operations if this was tried. You'd also have a lot of other businesses become very concerned about doing business in the US.

There is no way any engine, no matter how fantastic, would be worth the cost.
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 1:25 pm

Quoting EBGARN (Reply 5):
I believe we need to wait for Lightsaber to wake up and kill this idea, but I have a distant memory it's been discussed before. Then, it was concluded that the LeapX technology wouldn't bring that much to the table if it was combined with GTF technology. It's two different methods of attacking the same problem, and doing it "twice" in one engine won't make it twice as effective.

I strongly suspect that this is the case. And any government action would be not only illegal, it would be foolish in the extreme. The only thing government can do in industrial development is screw it up. It would be one thing if the government was sponsoring something, like the space program, that results in private industry spin-offs; but for the government to interfere in competition between two private entities and force them to collaborate would be the worst abuse of power I can imagine, and totally contrary to the letter and spirit of our constitution. Be assured that both GE and PW will be looking at what the other is doing, and if they can incorporate the ideas of the other (barring patent issues) they will. There is nothing that spurs innovation more than competition, and forcing collaboration will kill that on the spot.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 3:38 pm

Quoting faro (Thread starter):
Reasoning from a energy security/ecological perspective, could PW and CFM be forced to collaborate on one engine incorporating all planned technologies?

No.

Quoting faro (Thread starter):
Would the US government presently have any legal means of forcing this "merger" short of enacting new energy legislation?

No. For starters, CFM is partly Snecma, which isn't under jurisdiction of the US government. Even enacting new energy legislation wouldn't provide the legal means to force the collaboration.

Quoting faro (Thread starter):
Would any such new legislation have a chance of being constitutional?

No. The federal government would probably try to shoehorn it under the "regulation of interstate commerce" part of the constitution, but that would pretty obviously be against the intent.

Quoting faro (Reply 4):
Imagine where the world economy would be today if the US government and the Fed did not intervene in the recent financial crisis and just let things be like in 1929...

Way off topic, but we'd be much better off *now* if they hadn't intervened. The bottom would have been deeper, but the recover would have been much faster. The Great Depression in 1929 was greatly extended due to government action.

Quoting EBGARN (Reply 5):
Then, it was concluded that the LeapX technology wouldn't bring that much to the table if it was combined with GTF technology. It's two different methods of attacking the same problem, and doing it "twice" in one engine won't make it twice as effective.

They're not purely additive, but they are complimentary. LeapX is tackling thermodynamic efficiency, GTF is tackling propulsive efficiency. They're not mutually exclusive.

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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 5:49 pm

Quoting faro (Thread starter):
Should GTF & LeapX Be Forced Into One Engine?

That's like Boeing and Airbus being forced into one combined next/generation NB. Seems extremely unlikely either way.

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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 10:30 pm

Forcing them would be difficult.

Airbus tried to pull RR into the GTF via IAE. It didn't work.

In theory Airbus could say they want 20% better sfc and prefer 1 extra engine option a GE/PW GTF.

A GE/PW engine is flying on the A380.. an optimized GP1000 engine for the NEO, a nice thought.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 03, 2010 10:50 pm

Quoting faro (Thread starter):
...could PW and CFM be forced to collaborate on one engine incorporating all planned technologies? Would the US government presently have any legal means of forcing this "merger" short of enacting new energy legislation?

I would be surprised if French Snecma is prepared to take orders from the US government.

Maybe one day if France becomes the 51st state in the union, but that's something which I don't see come pretty soon.  Wow!

Maybe I am wrong? Maybe we can have an oppinion from some French a.netters.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Sat Sep 04, 2010 6:17 pm

Quoting EBGARN (Reply 5):
I believe we need to wait for Lightsaber to wake up and kill this idea,

  

I'm going to go into a technical discussion by component on why some of the LEAP-X technologies would help the GTF and for some not so much. The first thing to remember is engine blades have optimum mach numbers. Due to NDA's, I'll talk RPM instead of Mach number, but the proper technical operating range of a blade is Mach #, not RPM.

1. First, the fan. For this size of engine, about 3,000 to 2,500RPM is optimal.

Per this link that really doesn't understand the GTF, the low spool on the LEAP-X is about 4,200RPM!
http://www.flightglobal.com/articles...ter-as-engine-makers-take-aim.html

Thus GE is doing an *incredibly* advanced fan to run it that quick (high Mach number at the blade tips). This is a technological boost.

Pratt's fan is spining at the optimal Mach number/RPM (set the gear ratio to ensure this), so the technological advantage of the GE fan adds little to *nothing* for fuel burn advantage.

For GE, this fan itself adds 0.5% or so of fuel burn improvement. If the fan were put into a GTF? 0.05% (or less)

2. 2nd, the low pressure tubine (LPT). For this size of engine, the optimal RPM is 7,500 to 9,000 RPM.   

GE is having to go all out with LPT advances due to the poor Mach number through their LPT. These advances would help the Pratt, but the diameter of the LPT is matched with the gearbox to ensure the LPT is at the optimal Mach #. Thus (which makes me laugh at the link I found) since Pratt's LPT is at the optimal Mach number, GE's more advanced LPT,

Now a good chunk of the LEAP-X's improvement in fuel burn is due to the higher RPM of the LPT allowed by its adavanced fan! (They technologies are 'synergous.')

Putting a LEAP-X LPT into the GTF would probaby cut fuel burn 2%. But Pratt, for cost, schedule, and risk chose to *not* go with their latest LPT in the PW1000 family of GTF's. I think Pratt could match or *beat* GE on the LPT. So the advantage is little.

Unless GE goes with the CMC turbine...   
http://www.cfm56.com/pdf/leap-brochure.pdf

I'll talk about CMC turbine blades later.

3. High Turbine.

Any advanced technology for the high turbine would directly apply to the Pratt GTF from the LEAP-X. It looks like GE has figured out the direct bonding of the termal barrier coating to the turbine blades ahead of Pratt. (Both have worked on this since at least 1995.) This is a 2% advantage in fuel burn adapting LEAP-X technology to a GTF.

4. Low pressure compressor (LPC).

The optimal RPM for this engine size is 7,000 to 8,500 RPM (slightly lower than the turbine). The LEAP-X compressor benefits *more* from the advanced technology (due to the sub-optimal Mach #) than the GTF would.

Say about 0.5% drop in fuel burn adapting it to the GTF. (Much more for the LEAP-X, possibly as much as a 2.0% drop in fuel burn.)


5. High Pressure compressor (HPC)

GE is a bit ahead of the tech curve here vs. Pratt. Any technological advantage would be just as usefull in either engine as both have high spools running at their optimum Mach # compromise (turbine vs. compressor) or optimal RPM.

GE also does more work on the pre-diffuser.

GE also does lean-burn combustors which sacrifice in flight relight but have a lower heat load on the combustor walls. This lower heat allows less pressure drop across the combustor liner, so that is another 0.1% pick up in fuel burn. I personally prefer the Pratt approach (keep the engines turning). No... the in flight shutdown rate doesn't support my bias... I still have that bias.  

6. Oil delivery to the core bearings:

GE has the tubine in the TURBINE fixed stators vs. Pratt in the COMPRESSOR fixed stators. This cuts fuel burn about 0.3%. Pratt's have longer oil life for a reason... This is trading fuel burn for a trivial maintenance costs (hot oil needs more attention in the form of additive replenishment).

Quoting tdscanuck (Reply 8):
LeapX is tackling thermodynamic efficiency, GTF is tackling propulsive efficiency. They're not mutually exclusive.

In an oversimplified sense... yes. But both are improvements in thermodynamic and propulsive efficiency. The speeding up of the low spool on the GTF really helps the thermodynamic efficiency of the GTF.

This article has a nice optimization graph by CFM and is well worth the read to compare the two techological approaches:
http://www.flightglobal.com/articles...s-divergent-paths-to-a-common.html

If you use that graph, the 'propulsion system weight' curve drops compared to the one drawn. The slope at larger fan diameters would be *much* lower than a non-GTF. Why? Fewer LPC and LPT stages at *smaller diameters* (far less weight).    The difference isn't huge, but it does shift the optimization curves toward a larger fan for a given thrust target for a given mission.

Also the engine cruise TSFC drops more with larger fan diameter for a GTF (asymptotes at a lower value) due to better match between fan Mach # and LPT Mach #. Again, this drives the optimal optimization to a larger bypass ratio than a non-GTF.

Hence the physics forces the two engines to be optimized very differently! Both GE and Pratt went for the simplist engine (for each vendor) that acheived a major improvement in fuel burn.

Note: The article mentions the low spool only adds 7% to the maintenance costs... Wow... I'd swear there were a lot more labor hours in the LPC and LPT than that. The HPT (or HPC) does drive when the over-haul occurs, but is not 90% of the cost of the overhaul. Pratt is also engineering for longer maintenance intervals. I like how GE tries to claim higher gas temperatures into a turbine is low risk... Tell that to any PW2000 customer.  

In summary:
I see LEAP-X technology improving the fuel burn of the GTF only about 3%.

That is unless CFM goes forward with CMC turbine blades.   
In that case I would expect the LEAP-X to *beat* the current promised fuel burn and have a 7% benefit retrofiting the technology into a GTF. The first engine to market with CMC turbine blades is going to be a tough engine to compete against. I say this as a *huge* GTF enthusiast. CMC turbine blades have been the 'technology of the future' for 30 years. If GE/SNECMA is ready...   

Pratt has newer coating technologies and LPT technologies they *chose* not to impliment for risk/cost/schedule reasons. But GE is ahead in certain areas. But as already noted, not everything is additive when you fix the poor Mach # of the conventional low spool. There is a reason RR goes with Triple spools *other* than 'rebalancing.' That reason is supperior efficiency for the booster compressor (LPC in Triple spool talk) and 'intermediate turbine.' The issue for the triple spool is that the Low turbine is at a very poor mach number and the turbine at optimum mach # (you can think RPM for layman's discussion) is more important than the compressor. But RR puts *one* (two with the XWB) 'low' turbine stages at optimal mach #.    And yes... having *every* turbine stage at its own optimal Mach # (RPM) would be the most aerodynamically advantagous, but that is a maintenance and weight nightmare. Hence why turbine stages are ganged together into 2 or 3 'spools.'

Neither GE nor Pratt wants to teach the other their tricks. Both learned too much off of each other in the GP7200 for either to want to repeat a joint venture. From a technical perspective, the combined engine would be a little more efficient. But...

Quoting PPVRA (Reply 3):
Aside from the "it's wrong to put a gun to someone's head and tell them what to do" argument, you are combining not just technology potentials, but risks.

  

Pratt didn't do their most advanced fan nor their most advanced LPT due to the risks. Heck, the HPC is also not 100% 'leading edge' due to maintenance and surge risks. The LEAP-X doesn't have everything GE could do either (my contacts consider it quite the 'rushed engine' for the level of technology in it). Risk management is always part of engine design.

Quoting SEPilot (Reply 7):
There is nothing that spurs innovation more than competition

   Some joint ventures work well. But that is usually because there is some competition. (e.g., EA GP7200 vs. T900). Both Pratt and GE are looking over their shoulders at some future Chinese engine. The V2500 produced a better engine than RR or Pratt could have done solo back then. Today the cost of a joint venture to either Pratt or GE is more than the value in further reduced fuel burn.

Quoting keesje (Reply 10):
Airbus tried to pull RR into the GTF via IAE. It didn't work.

Pratt's only hope to return into the civil engine market strong is the GTF. Neither GE nor RR is ready to deliver an engine (heck, not even launch one) soon. In about 5 years, RR will be ready (they've been working on GTF's quietly per my rumor mill). GE would be a few years behind if they chose to start investing the billions required to catch up.

So unless Pratt was *guaranteed* a partnership on every engine for the next 20 years, they will not give up their intellectual nor patent rights. Please ask further questions.

Lightsaber

ps
I'm almost glad this thread was moved to tech ops. Posts like this do not 'read well' in Civ-aviation. Alas, fewer will see the details.  
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RE: Should GTF & LeapX Be Forced Into One Engine?

Sat Sep 04, 2010 8:17 pm

Quoting lightsaber (Reply 12):
CMC turbine blades have been the 'technology of the future' for 30 years.

Thanx for the detailed reply Lightsaber. IIRC however, doesn't the EJ200 already have CMC turbine blades? In that case, what is the impediment to having them on civil engines? Not reliable enough maybe?

Also, IIRC LEAPX has a CFRP fan and fan casing vs the GTF's metallic components. I recall having read in a neighbouring thread that fan momentum and casing size are big drivers of an engine's overall size and sturdiness. Wouldn't the GTF derive some % fuel burn benefit from these too, if only in reducing overall engine weight?

Faro

[Edited 2010-09-04 13:24:31]

[Edited 2010-09-04 13:28:58]
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RE: Should GTF & LeapX Be Forced Into One Engine?

Sat Sep 04, 2010 10:43 pm

Typo above:
The fan should have an optimal RPM of 3,000 to 3,500 RPM.

Quoting faro (Reply 13):
Thanx for the detailed reply Lightsaber. IIRC however, doesn't the EJ200 already have CMC turbine blades? In that case, what is the impediment to having them on civil engines? Not reliable enough maybe?

There have been several engines with CMC blades adapted to them... PR releases touting the technology and then a quiet replacement of the blades (and rotors) with conventional materials.

Also recall the cycle life difference between a military engine and a civilian engine.

Wide body civilian engines go for 2,500 to 4,000 cycles between overhauls.
Narrowbody civilian engines go for 6,000 to 10,000 cycles between overhauls.

The US military does the most training, so they demand a cycle life near a widebody engine.

Most other Air Forces demand a far shorter life. The shortest I'm aware of was a cycle life of 200 for many of the cold war Russian designs. (The war was won or lost by the 20th cycle per their theory.)

I do not know the Eurofighter engine cycle life, but I know it at most 1/3rd of what Pratt is promising with the GTF. The high turbine is the most expensive part to service... its cycle life sets the overhaul interval. Hence why CMC's will have to be mature for the LEAP-X. I missed they were in the Eurofighter. If SNECMA was the vendor... then they can help do the LEAP-X turbines...

The issue with CMC's is fatigue life. In particular thermal stress crack propagation. This is a NASA paper for a different application, but it does a good job of explaining the fatigue and stress on vanes. Civil aviation turbine blades would be designed with less stress (far longer cycle lives), but the design methodology is the same:
http://ntrs.nasa.gov/archive/nasa/ca...asa.gov/20060013345_2006014311.pdf

High cycle fatigue, low cycle fatigue, and creep as still and issue with CMC vanes. Thermal stress is far more of an issue with CMC vanes than nickel vanes (where it is still a major issue!). Hence, why it has been the technology of the future for a long time...

Quoting faro (Reply 13):
Wouldn't the GTF derive some % fuel burn benefit from these too, if only in reducing overall engine weight?

Yes, but due to the lower fan RPM (in this case RPM is the appropriate engineering term), the reduced centrifugal force on each fan blade makes the weight penalty *far* less in a GTF than in the high RPM LEAP-X.

Lightsaber
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RE: Should GTF & LeapX Be Forced Into One Engine?

Sun Sep 05, 2010 1:19 am

Quoting faro (Reply 4):
IMO it would boil down to consideration of whether there is a greater, overriding public interest in securing the fruit of the collaboration (energy security/ecology) than the alternative public interest in maintaining free enterprise in this particular industry segment. Maybe free enterprise has a stronger case today but will that always be the case?

"Overriding public interest"? Who makes that decision? Capitalism is not perfect, but history has repeatedly shown that in the long run competition is better than government dictate. Governments are typically short-sighted and have little profit motive to drive rational decisions, while corporations at least care about remaining viable in the marketplace.

For an example of how the government can really screw things up read on this wonderful site about UK military aircraft starting here: http://www.thunder-and-lightnings.co.uk/tsr2/history.php

Quoting tdscanuck (Reply 8):
The Great Depression in 1929 was greatly extended due to government action.

Quite. And here we are again in 2010...  
Quoting SEPilot (Reply 7):
There is nothing that spurs innovation more than competition

Indeed. For a good aviation example, just look at WWII. 20-30 years of technological progress packed into 5-6.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Sun Sep 05, 2010 5:35 pm

Hi,

This is an exract from CFM 56 website:
"The CFM56-5C, the most powerful engine in the CFM56 family, is the sole cost-effective propulsion system perfectly tailored for the long-range Airbus A340-200 and A340-300 aircraft.

The CFM56-5B is the engine of choice for the A320 family."

Lightsaber,
If I am not mistaken CFM-5C and CFM-565B are fitted with the same core engine. How each engine is optimized to each use: one for short/medium range aircraft and the other for long range aircraft.

I apologize if this post is out of the subject

Feedback appreciated
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RE: Should GTF & LeapX Be Forced Into One Engine?

Mon Sep 06, 2010 7:20 am

Quoting aerotech777 (Reply 16):
If I am not mistaken CFM-5C and CFM-565B are fitted with the same core engine. How each engine is optimized to each use: one for short/medium range aircraft and the other for long range aircraft.

I apologize if this post is out of the subject

Its on subject enough to talk how optimizing the same components ends up with different results.

First, let's understand the background of the core of the CFM-56. The F101 engine for the F-15. It is a core designed to take rapid transients and a decent number of cycles (IIRC, contract target for the F100/F101 was 3,000 cycles). By pushing the cores a little less, one gets excellent narrow body cycle life.

But this is a high cycle core. In other words, it is lacking a 2nd stage HPT and associated compressor stages. So it is a core that is 'sub-optimal' for long stage lengths. Why? Overall pressure in the engine is lower as a twin stage high turbine (HPT) is the most efficient way in a twin spool to achieve thermodynamic efficiency.

So how does one get more thrust and better long haul TSFC? It is possible to put on additional low pressure turbine stages. Thus powering a larger fan.

By taking a cycle durability hit, the core is being 'pushed harder' (higher temperatures rotate the core faster producing a higher pressure ratio). The combination of enlarging the fan and pushing the core harder (dumping in more fuel into otherwise the same engine) produces the added thrust required on the A343 at a lower TSFC. (Running a core harder always produces better efficiency.)

Due to the extra low turbine stage, the exhaust pressures of the fan and turbine are compatible to be 'mixed.' This improves propulsion efficiency (the core air is still exiting faster than the fan air, so 'mixing' creates a more homogeneous exit velocity profile which is always more efficient).

The cost? Weight. Thus not an optimal engine for short hops. Also, by pushing the core so hard, the ratio of climb thrust to max takeoff thrust is less. (The harshest wear and tear on the turbine is at the end of climb and so a core that has more fuel dumped into it will wear far more than the -5B variation of the engine with its smaller fan.) So a -5C on the A320 wouldn't be economical just do to the low cycle life. But on the A343, which was intended to do far longer missions than the A333 (its stable mate for a long time), is unlikely to see 'high cycle utilization.'

The cost benefit is one reason widebody engines almost always have half the cycle life of narrow body engines. For long missions, the cost savings are greater cutting fuel burn versus how many takeoffs to the next shop visit. (More hours of fuel burn per takeoff is another way of looking at it.)

Quoting Starlionblue (Reply 15):
Indeed. For a good aviation example, just look at WWII. 20-30 years of technological progress packed into 5-6.

While true, the cost was high in 'upheaval.' Just talking about the aerospace industry, let's talk winners and losers.

Curtis: Went from being a *major* global aerospace provider to a component vendor.
Boeing: Blew Consolidated out of the water, which gave them a profitable franchise (707 tanker was helped)
Douglas: The C-47 (military DC-3) made them the defunct global propeller transport supplier.
Pratt: Became the dominant transport engine vendor.

Now, I only mentioned US companies as WWII made aerospace a 'mass produced' industry instead of a 'craft industry.' For example, Merlin engines made by RR had higher horsepower and reliability than Packard produced engines (team built versus assembly line engines). But the assembly line allowed Pratt to out-produce everyone.

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RE: Should GTF & LeapX Be Forced Into One Engine?

Mon Sep 06, 2010 8:48 am

From reading Lightsaber and Tdscanuck's posts, I'm starting to wonder why not a triple spool narrow body engine? I could waffle on about the advantages, but those that would reply would already know. Is the problem a weight penalty?
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Mon Sep 06, 2010 10:07 am

Quoting lightsaber (Reply 14):
Hence why CMC's will have to be mature for the LEAP-X. I missed they were in the Eurofighter.

From the following (rather good) reference: http://typhoon.starstreak.net/Eurofighter/engines.html some information re the EJ200's use of ceramic composites in the HPT. Fair use extract:

"...the HPT uses air cooled single crystal blades. However there is a limit to what can be achieved using air cooling. In fact it eventually becomes detrimental to use cooling because it adversely effects the achievable combustion temperature and thus reduces efficiency. To overcome this the EJ200's HP turbine blades also utilise a special Thermal Barrier Coating, or TBC. This barrier is comprised of two plasma deposited layers, a special bonding coat over which a top layer of a Nickel-Chromium-Yttrium ceramic material is applied."

Funny that with all the fancy technologies used in the EJ200, it achieves a thrust-to-weight ratio of over 10:1 which I believe is pretty much the same ratio achieved by the most powerful version of the J85 which first ran in the 1950's. That was one exceptional engine back then...

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RE: Should GTF & LeapX Be Forced Into One Engine?

Mon Sep 06, 2010 1:34 pm

Quoting thegeek (Reply 18):
From reading Lightsaber and Tdscanuck's posts, I'm starting to wonder why not a triple spool narrow body engine?

I wonder too. All indications were that RR was ready for a competitive triple spool down to 25k of thrust. Airbus rejecting their proposals on fuel burn implies that the weight penalty for the bearings and such is too much for this low thrust level.

I need to be clear. A triple spool, due to the inherently more efficient RPM of the intermediate turbine (and booster compressor) is lighter than a double spool at high thrust (> 90k lbf). Why? Component efficiency (more optimum Mach number on the turbrine and compressor blades) allows for fewer parts (fewer rows of compressor or turbine blades). But for a small engine, the added weight of the shafts, bearings, and rotors (having two rotors is much heavier than one for the 'low spool' of a double spool becomes the 'low spool' and 'intermediate spool' on a triple spool).

I expected RR to counter with an effective triple spool on the A320 re-engine. I'm enthusiastic as to the theoretically excellent costs of a narrow-body triple spool. I would have to have someone from RR break their non-disclosure for me to understand why their projected fuel burn wasn't good enough.

Note: I expect cruise fuel burn to be less than the GTF or LEAP-X. But climb fuel burn and maintenance would be so much better that most narrow body missions would benefit. I really thought the greatest threat to the GTF would be a small triple-spool and not the LEAP-X. So if anyone has any good links, I'd like to learn more as to why Airbus rejected the triple spool (Yea, I read cruise fuel burn, but there is more to it than that...The climb fuel burn should have offset that issue.).

Lightsaber
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RE: Should GTF & LeapX Be Forced Into One Engine?

Mon Sep 06, 2010 1:35 pm

Quoting faro (Reply 19):
EJ200's use of ceramic composites in the HPT

I think CMC stands for ceramics; Ceramic Matrix Composites. Only small smaller applications are used sofar I think (rings etc. CMCs are made from silicon carbide ceramic fibers and ceramic resin. GE will use turbine blades on the F136 I think, if it works out well..
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RE: Should GTF & LeapX Be Forced Into One Engine?

Tue Sep 07, 2010 5:41 pm

The kind of technology merger being discussed here cannot happen without some sort of mutually collaborative development project, if competing companies just start copying each other's good ideas, either intentionally or independantly, this is what happens:

http://www.rolls-royce.com/investors...s/2010/100826_patent_complaint.jsp
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RE: Should GTF & LeapX Be Forced Into One Engine?

Tue Sep 07, 2010 7:27 pm

Quoting faro (Thread starter):
The GTF and LeapX exploit substantially different technologies to each achieve double-digit fuel burn reductions. Reasoning from a energy security/ecological perspective, could PW and CFM be forced to collaborate on one engine incorporating all planned technologies? Would the US government presently have any legal means of forcing this "merger" short of enacting new energy legislation? Would any such new legislation have a chance of being constitutional?

Seems a pity not to profit from both technologies combined...

Faro

This is a free market. No one is going to be forced to do anything. Companies will build engines and there will be winners and losers.
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Tue Sep 07, 2010 10:24 pm

Quoting Boeing1970 (Reply 23):
Companies will build engines and there will be winners and losers.

Or two looser, but that's also in the free market system.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Wed Sep 08, 2010 6:43 am

Quoting Wingscrubber (Reply 22):
this is what happens:

RR and Pratt have been in a building patent war for 15 years (maybe 20). This isn't something that will be settled tomorrow.

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RE: Should GTF & LeapX Be Forced Into One Engine?

Wed Sep 08, 2010 3:59 pm

Lightsaber, your posts are both instructive and enjoyable. I hope you teach, somehow, in your profession.

What about a triple-spool GTF? Would the added weight kill it? Would the difference in shaft Mach# (RPM) make it useless?
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RE: Should GTF & LeapX Be Forced Into One Engine?

Wed Sep 08, 2010 10:09 pm

Quoting aircellist (Reply 26):
What about a triple-spool GTF? Would the added weight kill it? Would the difference in shaft Mach# (RPM) make it useless?

You have the right idea. There must be enough of a benefit to justify a triple shaft GTF. It would take an engine of 100K+ of thrust to justify the concept.

Why? With a GTF the low compressor would be at their optimal RPM. However, with a triple spool, one could put one (maybe two) compressor stages with the fan. Why would one do this after I just pointed out the advantages of getting the compressor going at a higher Mach #?

Spool optimization. By having a low compressor on the fan, the air into the 'booster' compressor would be warmer. Thus, the optimal RPM of the booster would be higher. Wait... the optimal RPM of earlier turbine stages is higher than later turbine stages... So there is some merit to a triple GTF. But only if the weight of the added compressor stage (or two), shaft and bearings is paid for by a clear efficiency advantage. It could happen, but only at *very* high thrust engines.

Y3 would be the smallest design to consider this concept. Alas, it is too early to have such a complicated design launched with a GTF.

Now let me point out what will eventually kill off the GTF: A fuel cell powering an electric fan (most likely ducted). But that is a few decades off... But there are some very natural places to put the fuel cells in a BWB.    But I'm getting about 30 years ahead of myself.   One thing I like about Aerospace R&D, those in the know always know what technology will replace (or technologies that have a chance) what they're developing.

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RE: Should GTF & LeapX Be Forced Into One Engine?

Wed Sep 08, 2010 10:39 pm

Quoting aircellist (Reply 26):
What about a triple-spool GTF?

GTF already has much of the advantages offered by triple spool.

One major disadvantage with two spool non-GTF is that the LP compressor is locked to the same low rotation speed of the fan. It means that it must have plenty of LPC stages, each of them doing little work.

On GTF you choose a gear ratio which gives the LPC an optimal rpm, much like the IPC on a triple spool engine. It wouldn't be totally unfair to call a GTF a 2½ spool engine.

Also the LP turbine takes advantage of the higher rpm. On non-geared turbofans (also triple spool) the LPT has a diameter much, much wider than the HPT (and IPT). That gives the HPT blades a workable tip speed, even if it is locked at the low fan rpm. But it also gives an S-bend of the core exhaust which is an aerodynamic disadvantage to the core gas flow.

On a GTF the LPT diameter can be reduced, giving a more straight core gas flow. Less energy is wasted on drag between the HPT and the LPT, and the energy which isn't wasted can be put to work on the LPT to pull the fan.

I wouldn't rule out triple spool GTF completely, but its advantages compared to non-GTF is very much reduced, while the disadvantages (complexity and weight) are the same. And the major disadvantage of GTF is already weight - the addition of a high loaded gearbox including its lubricating system, oil pumps, oil coolers, and oil.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Thu Sep 09, 2010 7:45 am

Quoting lightsaber (Reply 27):
However, with a triple spool, one could put one (maybe two) compressor stages with the fan.

Oh, Congrats on Tail 2. Forgot to say before.

I expect that a further advantage of doing such a thing is that you don't have pressure to have a 2 stage IPT like RR have done on the TXWB. Single stage would have enough power, unless pressure ratios rise a lot.
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Thu Sep 09, 2010 1:50 pm

Lightsaber, Preben, thanks again for taking the time to answer. I find it fascinating that, somehow, even though all of it is about "physics" and "science", there is always a philosophical aspect to the choices taken.

Quoting lightsaber (Reply 27):
A fuel cell powering an electric fan (most likely ducted).

I like it! Hopefully something quite quiet?

Now, one more question: how about the variable pitch? I still have the ADP bochure from a Paris Air Show about 20 years ago. Really looked like a brilliant idea. And, looking at the incredible complexity of today's fan blades, could variable pitch mean a simpler blade shape? The ADP's reverse seemed interesting as well... What happened?
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RE: Should GTF & LeapX Be Forced Into One Engine?

Thu Sep 09, 2010 2:14 pm

Confused here: just read that the ALF 502 powering the BAe 146 is also a GTF. How then is the PW1000 GTF different from the ALF 502 which is 30 year old? Why is it a breakthrough?

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RE: Should GTF & LeapX Be Forced Into One Engine?

Thu Sep 09, 2010 3:24 pm

Quoting faro (Reply 31):
How then is the PW1000 GTF different from the ALF 502 which is 30 year old? Why is it a breakthrough?

Much much larger. The AFL502's thrust gives its gearbox a horsepower equivalent to a medium-sized turbo-prop engine...turboprops have been running around with geared "fans" for way more than 30 years.

What's unique about P&W's GTF is the *much* higher power density in their gearbox, and the concurrent huge jump in thrust capability. The PW1000 gearbox can carry more horsepower than the largest turboprops ever built.

Tom.
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 10, 2010 12:10 am

Quoting lightsaber (Reply 27):
A fuel cell powering an electric fan (most likely ducted). But that is a few decades off...

While that's an attractive idea, large electric motors are unfortunately quite heavy compared to turbines, even the ones based on superconductors.

For example, there's a prototype 39MW (49kHP - about 93% efficient) motor intended to drive a ship, that's only 75 tons. It's not quite directed at aviation, as it's got a 120rpm output.

http://www.amsc.com/products/motorsgenerators/shipPropulsion.html

But that's pretty heavy (it's actually not physically that big - just dense – by eyeball it looks similar in size to a GE-90). For comparison, a GE-90-115 generates about 110,000HP, and weighs about 9 tons, vs. 170t for a scaled up version of the above.

If you scaled that down to the cruise power requirements, you're a lot closer - about 30t for the GE-90-115 equivalent, but that leaves you with the need for some other source of thrust for takeoff and climb.

Obviously, a motor intended for an aircraft would be somewhat lighter, but probably not all that much - a substantial portion of the mass is in the magnetics, which are hard to shrink.

Nor is this an area that's seen more than slow progress over a considerable period of time, with superconducting magnetics being the only the second really big breakthrough in power density in the last century (wound stators being the first). I'm not saying that there isn't room for improvement, especially with a big focus on light weight designs, but it not really an area that's been neglected, and there isn't any real evidence that any big improvements are plausible in the short term.
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 10, 2010 12:53 am

Quoting prebennorholm (Reply 28):
I wouldn't rule out triple spool GTF completely, but its advantages compared to non-GTF is very much reduced
Quoting faro (Reply 31):
Confused here: just read that the ALF 502 powering the BAe 146 is also a GTF. How then is the PW1000 GTF different from the ALF 502 which is 30 year old? Why is it a breakthrough?

he ALF502 proved a geared ducted fan would dramatically improve the efficiency of a core. Look at that TSFC. For that thrust class... impressive (with a very low bypass ratio!).  http://en.wikipedia.org/wiki/Honeywell_ALF_502

Notes electronics overheating issue:
http://en.wikipedia.org/wiki/BAe_146


Bummer it was known for maintenance issues...

Quoting rwessel (Reply 33):
While that's an attractive idea, large electric motors are unfortunately quite heavy compared to turbines, even the ones based on superconductors.

Work is in progress. Please recall ship based motors have extra weight to deal with salt-water corrosion margins. There is a reason I do not think it will happen this decade. But long term, that is what I think will replace gas turbines.   

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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 10, 2010 12:55 am

Quoting faro (Reply 31):
the ALF 502 powering the BAe 146 is also a GTF. How then is the PW1000 GTF different from the ALF 502 which is 30 year old?

As tdscanuck already told us, it's the scale - the larger PW1000 variants are 5-6 times more powerful.

In principle GTF is nothing new. You could call it a ducted turboprop.

High power gear boxes are also nothing new. They are used on every RR Trent when they power a cruise ship or navy ship. But on a ship, the size and weight of the gearbox is not all that important.

The more powerful PW1000 variant will have a reduction gear which shall convert something like 30,000 HP (+/- 5,000) at take-off power. The new thing is to make such a thing small and lightweight enough. And to get a significant fuel efficiency gain to make it all worthwile. If it is too bulky, then the fan hub will be thick, and it will add drag and kill the fuel efficiency gain.

The ALF 502 is a slightly different story. It was created as a "simple and cheap engine with ultra low noise". The low speed fan was the main thing to reach that goal. But compromises were made, and one of them was that the ALF 502 never became an especially fuel efficient engine by today's standard. Another compromise is that it isn't good at high speed - Mach 0.70 is fast for an ALF 502.

Its somewhat older sister engine, from which it was developed, is the Lycoming T55 helicopter engine which is used on the Boeing CH-47 Chinook helicopter. It has of course also a gear box, but with a much different gear ratio.

Also PW has made many such gear boxes. For instance such gear boxes on PW1830 engines on Douglas DC-3 have now been running for almost 80 years. The difference is that the PW1000 gear box shall spin a lot faster and convert 25 times more power.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 10, 2010 4:51 am

Quoting lightsaber (Reply 34):
Work is in progress. Please recall ship based motors have extra weight to deal with salt-water corrosion margins.

Not to mention that the low rpm increases the torque and therefore the component strength required.
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Fri Sep 10, 2010 10:09 pm

Quoting prebennorholm (Reply 35):

High power gear boxes are also nothing new. They are used on every RR Trent when they power a cruise ship or navy ship. But on a ship, the size and weight of the gearbox is not all that important.

Also, the degree of reduction is higher (ship props turn at a few hundred RPM max) and it isn't necessary that the gearbox be completely coaxial with the engine. And there just isn't as much inertia in a ship propeller as there is in a fan. The ship propeller may be more massive, but it turns far slower and it also is turning in a much more viscous medium. Finally, if the gearbox should seize up, the ship will be dead in the water, but it won't sink. So reliability isn't quite as critical.

Quoting lightsaber (Reply 34):

Work is in progress. Please recall ship based motors have extra weight to deal with salt-water corrosion margins. There is a reason I do not think it will happen this decade. But long term, that is what I think will replace gas turbines.

I doubt it. I think that we will switch to biofuels, but I don't think we're going to stop using hydrocarbons until there's a way to actually generate the electricity safely aboard. There are a few advantages to hydrocarbons. First, the energy density is about as high as you can get for energy stored by the electromagnetic force (in chemical bonds, as opposed to other forces, like the nuclear forces, which store a lot more energy but have certain technical barriers to being used in aviation). Second, a hydrocarbon-driven plane gets lighter as it flies, which it would not do if it were full of supercapacitors. Third, most of the benefit that electric motors offer are simply not that advantageous in the aviation setting. For example, electric motors have a very fast response time, which is not really needed in the aviation setting. They also can run backwards as quickly as they run forward, which is also not needed in the aviation setting. They also don't use air, which is very useful for submarines, but again not so much for planes.

If we ever figure out a way to negate the effects of gravity, I think that electric motors will be great. But as long as we're flying fixed-wing, heavier-than-air craft, they aren't going to be the way to go.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Sat Sep 11, 2010 1:37 am

Quoting DocLightning (Reply 37):
I don't think we're going to stop using hydrocarbons

Agreed.   Hydrocarbon fueled fuel cells powering the fans.   
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RE: Should GTF & LeapX Be Forced Into One Engine?

Tue Sep 14, 2010 9:08 am

RR and Pratt have been in a building patent war for 15 years (maybe 20). This isn't something that will be settled tomorrow.

Lightsaber


Well according to the article thats not exactly true "late 1990's". It perhaps sheds some light why they are unable to co-operate any more.Why would you co-operate with a company (upheld in the USA) that steals your patented ideas.

Not impressed.
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Tue Sep 14, 2010 5:34 pm

Quoting parapente (Reply 39):
Why would you co-operate with a company (upheld in the USA) that steals your patented ideas.

A patent war is two ways and RR has patented some ideas Pratt came up with (Pratt used to not patent and keep proprietary). So do not think this is one way. Do not get me wrong, I really respect RR's technical talent. But they have patented some ideas where the patent will be easy to defeat in court. Also, I worked on research (years ago) to find Pratt patents RR was violating (hint, there are some, but Pratt chose not to go to court).

And this 'patent war' was going on 'behind the scenes' much earlier than the article notes.

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RE: Should GTF & LeapX Be Forced Into One Engine?

Tue Sep 14, 2010 5:38 pm

In my industry (IT) the patent wars make this look like a song and dance! I have no doubt that there are many takes on this.I raise it only as this one appears to have flown over the wall into the public domain.As such the feelings may be strong enough to hinder coloboration issues.
 
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RE: Should GTF & LeapX Be Forced Into One Engine?

Tue Sep 14, 2010 6:22 pm

Quoting parapente (Reply 41):
In my industry (IT) the patent wars make this look like a song and dance! I have no doubt that there are many takes on this.I raise it only as this one appears to have flown over the wall into the public domain.As such the feelings may be strong enough to hinder coloboration issues.

Good point.

The first ten years of this 'patent war,' it was unusually gentalmanly. RR would notify Prat they were violating patent X. Pratt would notify RR that they were either protected by patent Y (two similar but different patents are often issued as you know) or that RR was violating patent Z and wouldn't it be best if some small payment was made between the two to keep 'playing nice.'

Neither will stop delivering engines. There might be some payments between the two. I have a feeling this is like AMD vs. Intel. While AMD was paid some cash, the big deal was the 'patent sharing' between the two. I expect a similar solution. Who pays who? That is more dependent on the lawyer quality than the technology, so I do not feel qualified to comment.

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RE: Should GTF & LeapX Be Forced Into One Engine?

Tue Sep 21, 2010 9:19 pm

Quoting lightsaber (Reply 17):
First, let's understand the background of the core of the CFM-56. The F101 engine for the F-15. It is a core designed to take rapid transients and a decent number of cycles

Hey 'saber, first, congrats on that recent big EIS.

Regarding CFM56 background, you may have typo'd. The F101 was indeed the parent, but it was the 320+ pound per second engine for the B-1 bomber. The F-14, F-15, and F-16 received the F110, which debuted as the F101DFE (Derivative Fighter Engine). It has the circa-270 pps three stage fan. Sound right?
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RE: Should GTF & LeapX Be Forced Into One Engine?

Wed Sep 22, 2010 12:08 am

Quoting F14D4ever (Reply 43):
Sound right?

Yes that is correct. Would love to say more but, can't.
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RE: Should GTF & LeapX Be Forced Into One Engine?

Wed Sep 22, 2010 5:58 pm

Quoting lightsaber (Reply 14):
I do not know the Eurofighter engine cycle life, but I know it at most 1/3rd of what Pratt is promising with the GTF.

The EJ2000 has a engine cycle life of 6000h some parts 4.500h. AFAIK they want achieve 8000h in T3.
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