More on the changes to the CFM LEAP-1B

As we reported earlier today, Boeing and CFM didn’t stop with the previously announced 68.4 inch fan for the LEAP-1B engine on the 737 MAX.

Buckingham Research, citing Boeing at the investors’ day, wrote that Boeing talked about a 70 inch fan.  Jon Ostrower–now at the Wall Street Journal–confirmed the larger fan, but at 69.4 inches (70 inches apparently was a rounded number) as well as pursuit of a smaller core.

The smaller core is important for two reasons: a larger fan and a smaller core provide for a higher by-pass ratio, increasing fuel burn reduction performance. The smaller core also enabled the engine to be mounted closer to the wing, which in turn means the previously announced 8 inch nose gear extension remains valid.

46 comments on “More on the changes to the CFM LEAP-1B

    • The A320neo requires too much thrust to use the 737 MAX engine. The LEAP-1A must be capable of 33K thrust to power the A321, while the 737-9 only requires 28K from the LEAP-1B.

      • I expected my post to be interpreted as “proportionally” bigger fan and “proportionally” smaller core. I’m not interested in defying physics or logic.

        Why shouldn’t airbus request an enhancement on the same lines effectively yielding and even greater bpr? I sources are true, it would only even out the performance battle between the gft and the leap.

      • The A320 requires more thrust per cert for takeoff.
        In cruise thrust requirements should be nearly equal.
        Otherwise sfc differences on the very low % range would
        not be possible. IMU the -5 and -7 engines swap a bit between propulsive and thermodynamic efficiency. ( this prob. gives the hreadroom for the A321 engine )

    • Because they don’t have to. The smaller core will probably have to be run at higher temperatures with the help of cutting edge technology. Like ceramic coating for example. The smaller core, hence the higher temperatures, will affect the efficiency, reliability and durability of the core parts.

      The above qualities will be easily implemented on the neo engines. Both the LEAP-1A and the PW1100G. But for the LEAP-1B all kinds of compromised solutions will have to be devised before the engine can meet the desired specifications at the maximum fan diameter that will have been imposed by the physical dimensions of the 737 airframe.

      • Quoting: Normand Hamel

        “Because they don’t have to. The smaller core will probably have to be run at higher temperatures with the help of cutting edge technology. Like ceramic coating for example. The smaller core, hence the higher temperatures, will affect the efficiency, reliability and durability of the core parts.”

        Did you not bother to read CM’s comment above? That 5k of extra thrust is not Free…

        • That extra 5k thrust is required on the engine with the much better propulsive efficiency which should have more headroom for running the core slightly hotter.

      • The problem with that point of view is that it depends on the future credibiliy of the engine oem.
        If CFM gets it right and these modifications do not affect reliabiity, then it would be a great idea for Airbus to demand to have their neo engines at the same technology level.
        On the other hand, if reliability will be affected, then Boeing would be crazy to request these changes and Airbus should restrain from following the suicide path.

        CFM gained its prestige by showcasing an exemplar reliability in both families of narrowbodies. However, their past track record may not me a good guidance on their abilities to deliver on a new family of engines. Gecas finance also plays a great role in cfm’s market traction, although that alone will not sell engines. Take as an example the a321, where the tendency is to order the slightly less reliable pw only due to perfomance advantages. That showcases that there is a fine line to what extent reliability can be acceptedly lower as a tradeoff for perfomance.

        Where is my crystal ball when I need it? Will cfm deliver on their promises?

    • CFM will do the improvements by themselves if it is needed.
      They did it before, when they where loosing all the engine competitions against PW, that is the good thing about the competition ;-)

  1. Observer :
    Did you not bother to read CM’s comment above?

    I never miss an opportunity to read CM because he is one of my all time favourite blogger. But it’s not me who did not understand what CM said. I believe it is CM who failed to grasp the essence of the question hardwaremister was asking. So I tried to answer it to the best of my knowledge and understanding. And I am still satisfied with what I said.

    But if you are not happy with my answer to hardwaremister please explain your viewpoint, if you have any. But please try to avoid the nasty remarks.

  2. My viewpoint… Ok

    Quote: “The smaller core is important for two reasons: a larger fan and a smaller core provide for a higher by-pass ratio, increasing fuel burn reduction performance. The smaller core also enabled the engine to be mounted closer to the wing,”

    hardwaremister asked?

    Quote: “Why wouldn’t airbus request an even-bigger derivated fan and smaller core too?”

    CM Replied..

    Quote: “The A320neo requires too much thrust to use the 737 MAX engine. The LEAP-1A must be capable of 33K thrust to power the A321, while the 737-9 only requires 28K from the LEAP-1B.”

    Now, what part of the additional 5k of thrust that the NEO family requires vs the Max would make you believe that the Max would require special cutting edge technologies? Point: The lower thrust requirement = smaller core.

    I believe that is what CM was pointing out. If not, I’m sure he will weigh in on it.

    • “Smaller Core” acutally is the alleged GTF forte, right?
      Interesting:
      Just a couple of weeks before Boeing announced its BATW wingtips we read this fascinating article bashing the established API winglets.
      Just before Boeing announces another potential increase in fan diameter the GTF for MAX is paraded across the stage.

      • It’s funny, you make it sound like if Air Insight was biased in favour of Boeing, whereas yesterday CRJ was trying to convey the opposite impression. I think that one opinion neutralizes the other and make Air Insight come out clean.

  3. The point is the Leap-1A engine is a much more mature design than the Leap-1B is. CFMI has a lot more they can do with the -1B at this point in developement than they have with the -1A. The Leap-1A engine is more closely designed to the certified Leap-1C engine than it is to the -1B. The -1A and -1C are the actual LEAP-X engines, with the -1B more or less a follow on engine in the family, as defined in its place as the 3rd engine in the series. That means the -1B does not have to have as much in common with its two bigger sister engines. It is more of a cousin engine than a sister engine.

    • I think the differences between the different Leap versions will be kept to a minimum. Just like the different CFM56s with their various applications on NBs and quads. It seems some variants have a bit more space to optimize everything, e.g more earodymic inlets.

      • Sorry KEESJE, i do not understand!
        It is now obvious that LEAP1B will have a smaller core and run hotter, meaning cveramics…
        This means HUGE differences!
        NEARLY A COMPLETELY REDESIGNED ENGINE
        And probably (nobody mentioned that in this blog) a delayed EIS for the 737 MAX

        • keesje :
          I think the differences between the different Leap versions will be kept to a minimum. Just like the different CFM56s with their various applications on NBs and quads. It seems some variants have a bit more space to optimize everything, e.g more earodymic inlets.

          No keesje, the CFM-56-5C2/3/4 on the A-342/3 are very different from the CFM-5A/5B engines on the A-32X airplanes. They have more LPT stages and a much different fan section, among other changes. The differences between the -5C engine and the -5A/-5B engines, though, are not as numerous as the differences between the Leap-1A/-1C engines and the Leap-1B engine.

          flying frog :
          Sorry KEESJE, i do not understand!
          It is now obvious that LEAP1B will have a smaller core and run hotter, meaning cveramics…
          This means HUGE differences!
          NEARLY A COMPLETELY REDESIGNED ENGINE
          And probably (nobody mentioned that in this blog) a delayed EIS for the 737 MAX

          Correct, it is nearly a new engine, rather than a new derivitive engine. But at this point, I don’t see any delays in the engine or airframe portions of the B-737MAX program. The program is still very young and almost nothing is written in stone yet and that is why no one is talking about any delays in the program.

          Could the B-737MAX have a delayed EIS? Of course it can.

          Could the A-320NEO have a delayed EIS? Of course it can.

      • My estimate, new fan, with higher rpm, means new low pressure turbine,
        higher temperature means ceramics in high pressure turbine
        What is kept from existing LEAP?
        Maybe high pressure compressor, a big maybe, because smaller core may mean downsized…
        Remember that the new TRENT XWB for 350 1000 contributed to a 2 years delay, and differences with other TRENT was minimal compared
        we can now expect MAX EIS: 2019 instead of 2017

        • The problems that created the 2 year delay in the A-3510 were not really engine related. RR only had to increase thrust while maintaning the same FSC. The main reason for the delay was the shift of engineers from the A-3510 to the A-359. So, at this point, I don’t see a two year delay in the MAX program, nor do I see any relationship of the MAX program and the problems with bringing the A-350 program to EIS.

  4. Observer :
    What part of the additional 5k of thrust that the NEO family requires vs the Max would make you believe that the Max would require special cutting edge technologies?

    My understanding is that CFMI is trying to make the core as small as possible so that Boeing would be able to hang the engine from a higher position on the pylon. Which would automatically provide additional ground clearance, regardless of the fan diameter. If that is the case I think it is a brilliant idea because it should also provide a higher BPR for a given fan diameter.

    But if you make the core smaller, for a given thrust, there is a penalty associated with it. In other words there is a price to pay for making the core smaller while keeping the thrust at the same level. A smaller core will have to work harder for a given thrust, which means it will have to run hotter. And if the core has to run hotter, this will have an impact on the reliability and durability of the core parts. Unless they use exceptionally reliable and durable parts, that only cutting edge technology like ceramic coating can provide.

    The whole concept is not transferable to the LEAP-1A because of the penalty associated with a smaller core. And the neo does not need to have a smaller core because the A320 airframe provides ample ground clearance to play with. That is what I meant when I said “because they don’t have to”.

    • Fan and LPT diameter are rather hardlinked via tipspeed on the fan and machnumber
      in the LPT, the reason why these engines show a pronounced Betty Page profile.
      ( That is what the GTF tries to fix: allow a large slowturning fan and a compact LPT with higher rpm and machnumber.

      • Yes the GTF provides an elegant solution to this problem. Your friends at MTU did a beautiful job on the LPT of that engine. It turns at 2.5 times the speed of the CFM56 LPT. But thanks to the gear system the fan speed is correspondingly lowered by a factor of 3 to 1. The lower fan speed will allow the GTF to run much quieter, even at take-off power. A feat that is totally out of reach for a conventional engine like the LEAP, or less conventional one like the RR three-spool.

  5. Normand Hamel :
    It’s funny, you make it sound like if Air Insight was biased in favour of Boeing, whereas yesterday CRJ was trying to convey the opposite impression. I think that one opinion neutralizes the other and make Air Insight come out clean.

    In a game the ball tends to not be partisan ;-)

    The word “meme” tries to link ideas, thoughts, feelings to virii and bacteria and model the growth and spreading accordingly.

    My impression is that interested parties regularly launch meme-attacks.
    This may come in the form of helpfull cheat-sheets for articles or in the
    timely release of some old or new research document or even only a dropped hint.

    The first infectors are certainly partisan. The second generation may already be
    nonpartisan, unthinkingly spreading the “infection”.

    I have followed some of these bashfests. They tend to show an early and wide distribution different from most other rumors/news i.e. they resemble a concious distributed infection
    “meme warfare” and not the regular exponential growth from single source.
    Just like two of the known gospel that are linked by a common but invisible/inaccessible ancestor these seem linked not in hierarchical/tree order but all to one common but not visible source.
    Historically and in this context there seems to be only one potential benefactor ( who need/may not be the source).

      • Yes when it first came out it generated a mass hysteria of a magnitude rarely seen on that particular blog. But that is to be expected when someone launch an all-out assault on a well established conception (or misconception). Is this not another example of the paradigm phenomenon first described by Thomas Kuhn in “The Structure of Scientific Revolutions”?

        I have read the Arvai article attentively when it came out. It was so shocking that I thought I would be better to study it carefully. And then I read the comments. The majority of the posts were emotional reactions from readers who had obviously not paid much attention to the basic arguments of the author.

        It’s too bad because I would have liked to hear what other well informed readers or observers had to say on the subject. But nothing of any practical value came out of the infantile reactions. And because of that I am still unable to make myself a definitive opinion.

        • If you read the Arvai article closely and listen closely to what Airbus and Boeing say about winglets, including the recently announced BATW, the conclusions are pretty close.

          Arvai said the winglets are more effective the longer the routes. Airbus and Boeing say the same thing. Airbus and Boeing are very careful (and clear) in saying winglets provide “up to” X% gains. It is common knowledge that fuel savings are less the shorter the range.

          So, frankly, we were surprised by and still don’t understand the screaming and shouting (and personal attacks) that resulted from Arvai’s commentary.

          What Arvai did not mention was the increased take-off performance that is a benefit of winglets. He did mention the landing characteristic challenges.

    • An interesting philosophical essay. But that is to be expected from a guy who lives in the land of Leibniz, Kant, Hegel, Schopenhauer, Marx, Nietzsche, Heidegger and Wittgenstein. :)

        • Yes OV, you are right. Wittgenstein is indeed from Austria. But like Søren Kierkegaard who is Danish, Wittgenstein is often classified as a german philosopher.

      • Normand, as you probably know, there were very strong scholarly and culturally ties between Scandinavian and Germany right up until the start of WWII. It looks as if these ties once again are being strengthened after more than half a century of global anglo-saxon-american cultural, technical and scientific dominance helped lead Scandinavia to look west, rather than looking south to Germany.

        As for German cultural dominance, at least in one area this is not true; popular music export which seems to be a one-way street, from Scandinavia (Sweden in particular) to Germany. ;-)

  6. And the list could go on and on, ad vitam aeternam. And eternity is very long, especially towards the end. But that shows the extent of the intellectual heritage of the German people.

  7. leehamnet :
    If you read the Arvai article closely and listen closely to what Airbus and Boeing say about winglets, including the recently announced BATW, the conclusions are pretty close.
    Arvai said the winglets are more effective the longer the routes. Airbus and Boeing say the same thing. Airbus and Boeing are very careful (and clear) in saying winglets provide “up to” X% gains. It is common knowledge that fuel savings are less the shorter the range.
    So, frankly, we were surprised by and still don’t understand the screaming and shouting (and personal attacks) that resulted from Arvai’s commentary.
    What Arvai did not mention was the increased take-off performance that is a benefit of winglets. He did mention the landing characteristic challenges.

    The Arvai essay did not bring much new information to the discussion. But it placed its reiteration in a rather disruptive fashion. Just like the recent deconstruction of our Head of State it is not a question about the how but about the why ( why this article, why just weeks ahead of Boeing presenting their own wingtip device. ).
    IMHO this was placed for taking down the API winglets to make room for that small bit
    of improvement BATW will provide. ( I would not be surprised if the BATW advantages are limited to a still more restricted part of the flight envelope )

    Also:
    Bashing API in this way indicates imho that their patent is toast. It won’t survive the coming legal assault. ( again imho not unsurprising as it seems to describe a generic optimisation process and not a distinct solution. Problem with bright lawyers is that they are blinded by their own light on occasion. )

    • You forgot Bach, Telemann, Mozart (I know OV, he came from Austria), Beethoven, Brahms, Bruckner, Wagner. Just to name a few (who happen to be my favourites). :)

    • vergessen sie nicht Herbert! http://www.youtube.com/watch?v=UC81i2M30Bc

      back on topic, I still feel GE will keep differences between LEAP variants to a minimum.

      The core is not the issue, nor does a new core promise some unforeseen miracles..

      If GE introducing ceramics on the MAX LEAP, if they’ve reached the right TRL, they be used on other LEAPs too..

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