Bolty McBolt
In my previous post, I erred on the clipped fan and re-balancing scenario. Actually, I should have been referring to the GE90, not the Trent 800. The core of the GP7200 engine comes via the GE90 core. So when the fan diameter was reduced to 116" from the normal ~123" diameter fan used on the GE90, some other things had to be adjusted. The GE90 core evolved out of the "Energy Efficient Engine". A scaled GE90 engine was built to test the concept from which the true GE90 emerged. So GE had good knowledge as to how to scale downward the core to match fan diameter. In fact, the GEnx engine basically uses the scaled GE90 core.
I just think the drive for both the Trent 900 and GP7200 engines was to improve specific fuel consumption (SFC). If you look at the CF6-80C2, the model used on the B-747-400, The sea level SFC is 0.316, at cruise it is 0.605.
If you look at the Trent 800 on the B-777, the sea level SFC is 0.35, at cruise it is 0.56.
If you look at the GE90 on the B-777, the sea level SFC is 0.324, at cruise it is 0.52.
It is estimated the GEnx on the B-747-8, the sea level SFC is 0.27, no figures yet for cruise.
Theere are no SFC published figures out yet for the Trent 900 or the GP7200 engines, except for the comments from the Emirates CEO.
So with the trend of less fuel usage (improved engine efficiency), IMO, the Trent 900 and GP7200 fits somewhere nearer to the GEnx.