Originally Posted by
tdracer
Once you make the decision to put the gearbox on the fan case (and as I noted in a post early in this thread, on a CFM sized engine there simply isn't room to mount it on the core as is done on some bigger engines such as the PW4000 and GE90), part of it has to go at the six o'clock position. The reasons is quite simple - the gearbox drive shaft comes through the lower bifurcation. Putting the gearbox drive anyplace else would require a radical redesign of the entire engine nacelle - throwing away billions of hours of operational experience with the current design practices - and would probably create far more problems than it might solve.
No matter where you hide the gear box you are still stuck with the most exposed point on the engine the bottom of the fan case. One of the kill mechansms on such an engine are distorted cases and the resulting change in blade tip clearance. Any damage there and the engine cycle goes to hell and you start surging or toasting the turbine.