Contrary to what I read on this site IMO the advantages of the new generation of the new bigger turbo fans (GP7200, Genx, Trent1000) is not in the fact they do/don´t give bleed air, work only in combination with an advanced wing or whatever.
You can see the fanblades are more complex then the existing straight ones, like used in the GE90. http://www.klm-engineering-maintenance.com/media_relations/image_library/images/21_rel3_LM_777_H11.jpg
GE-90 blades are cabonfibre, but still have the conventional shape, the best compromise for the different fan speeds/functions. (the newer -115´s have new ones)
New engine fan blades´ are shaped by 3 functions (from hub to tip)
- providing sufficient pressure for the compressor close behind
- providing maximum efficiency in the middle (most of the ´thrust´)
- close to the tip it is bended to minimize supersonic interference with the cowling
These more "ideal" shapes of the fan blades are known for a long time but blades with these complex shapes could not withstand the enormous forces. Now they can be made of carbonfibre (GE) or hollow titanium (RR) they can.
Where the traditional fanblades had to be heavy close to the hub to absorb the forces, the new blade are more smaller at the root, enabling a smaller hub and thereby increasing the available airflow& bypass ratio within the same overall engine cross section.
Apart from this they have better fuel mixing, contra rotating shafts etc. But I believe the biggest gains come from the new fan, more specifically from the materials that make them possible.
so IMO : it´s mainly the fans ! anybody know if this is right?