|Quoting parapente (Thread starter):|
If so they must be enjoying some significant improvements in economy and reliability over the past few years - and indeed the next couple.Or are they in some way "too different"
While the CFM56-5B on the 320 and the CFM56-7B on the 737NG are not very different (apart from the fan), then the CFM56-5C on the 340 is a rather different animal.
It is for instance some 66% heavier - 8,800 lbs vs 5,250 lbs for the -5B and -7B. It also has by far the biggest fan of all CFM56 versions.
While some -5B and -5C versions are rated at rather similar takeoff thrust, the the -5C has much higher thrust rating for climb and cruise at altitude.
The few dozen CFM56 variants can be grouped into three groups:
1. The old ones, -2, -3 and -5A
2. The much reworked and improved ones (first certification 1994), -5B and -7B
3. The bigger, heavier and more powerful one (first certification 1991), -5C.
At the end of the day hardware updates on the -5B and -7B will hardly be directly transferable to the -5C. But since all CFM56 engines share the same basic design philosophy, then improvements may over time find their way to all versions the same way as RR Trent 1000 (B787) design details are these days planned to be implimented on Trent 700 and 900 engines on A330 and A380, also as update kits.
Creation of the -5C in 1987-1991 was in fact the major "revolution" in CFMI engine design. The smaller -5B and -7B owes a lot of design details to the several years earlier -5C. But no more than that, they are very different animals.