have a look at the RR 524g/h engines as used onboard some 747-400s. have a loot at the fan diameter. It is much smaller than PW or GE engines. i went to the RR web site and the P&W web site, and, found the PW engines to have a diameter of 94 inches, while the roller engine has just 86 inches. Don't know what the GE engine is but my bet would be it would be very close to the PW one.
So, then i had a look at bypass ratios, thinking that perhaps the RR engine bypassed less air. Not so, it was about the same as the PW. It puts out about the same thrust too. So, just how does RR achieve all of this in a smaller engine? Is it the 3 stage shaft design? Does it simplify things so less room is needed in the high stage compressor, thus less room is needed to bypass air? This got me thinking, so i had a look around at other RR engines - the trents, and, the story is the same their. In each Case, the RR engine is smaller than its competitors while offering the same thrust and efficiency, and roughly the same bypass ratios (with the eception of the Trent800 and the GE90 - we won't go there, the rest of the family seems to obay this though) Is there anybody out there who knows the engine well and can explain?