The „war of words“ on the GLG website

The GLG website is a big fairground for those who wish to tell the audience what they think about the two engines currently in development for the new or re-engined narrowbodies. I found the most of the claims that are being made in the recent “expert contributions” as just plain wrong or as misunderstandings.


Take the contribution “CFM International LEAP-X Engine Anything But A Derivative” as an example. This article is nothing as plain anti-rhetoric against P&W’s GTF and pure PR for the LEAP-X, but has nothing to do with an objective analysis.

Both engines feature (or will feature) a complete new core, both will have a 2 stage HPT.

One can guess that the HPC of the LEAP-X is a scaled-down and advanced version of the GEnx HPC and the same is true for the HPT. New materials further improve the performance of the core, as less cooling is needed as with conventional materials. What we don’t know is if the HPT would basically need more cooling air than the GEnx HPT as it probably runs even a little hotter. This is unusually for a narrowbody engine, as maintenance costs play a significant role here in the equation.
The core of the GTF is all new and was already tested successfully (if you want to believe the PR from P&W).
Now take a look at the comparison the author makes:

He states that the baseline thrust of the GTF starts at 21,000lbs – wrong as the MRJ engine starts at about 15,000lbs for the MRJ70. The engine for the CSeries starts at 21,000lbs and the proposed engine for the A320NEO covers the full range of the thrust needed for the Airbus narrowbody family up to 33,000lbs. This engine would have an up-scaled core from the CSeries engine, as the NG34 (or TECH-X) from GE would get a scaled-down core from LEAP-X.

If the author would be right when he writes that the baseline thrust for LEAP-X would be 30,000lbs (for the C919), CFM would have a hard time to sell that engine to Boeing, as the B737 does not need more than 27,300lbs today and a downrated engine would be sub-optimal for the B737. So CFM might have to come up with a separate engine (maybe with a smaller core) to cover Boeing’s thrust needs.

If one claims that the GTF architecture is forty years old as the author does, he has to call the architecture of the LEAP-X at least forty years either, as it is nothing less but nothing more than a 2 spool turbofan.

SFC reduction for both is in the same range. CFM gives a certain number, P&W gives something like a range, but in the end they will end in the same area – it’s coming down to physics.

Please, bloggers, experts and who-else-writes-about engines: let’s do not just play CFM vs. P&W, just as others always play A. vs. B. on the aircraft side. It might be fun when you start but soon turns boring.