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.
Totally agree
tdracer. I guess the point I was making (probably badly!!!!) to
AGBagb was the reason the ancillaries are still down at 6 o'clock is, historically, for a number of reasons - accessibility, using gravity returns to sumps, pylon and aero considerations at the engine/wing interface, ...... etc, etc, etc - even taking a legacy core as your start point in the new higher by-pass design - all of which were was probably re-considered but retained with the advent of the engines which started to replace the earlier JT8D class of engine in the late '70's/early 80's.
That necessitates deciding to retain a drive out the bottom of the engine which, as you say, now has many hours of safe useage/history behind it. Clearly, when the new higher by-pass CFM56's engines came along, initially they were aimed at the DC8/707/KC-135 and so ground clearance was not an issue - but accessibility for maintenance on the line must have been. When ported to the 737, the increased fan diameter on the -56, IIR, led to some head-scratching and several things were pushed out to either side (and fan downsized against the earlier -56's) when fitted to the 737's (here we go with re-using an old design airframe - done to death in the Max threads!), hence the semi-elliptical/"squidged" shape of the CFM56 on the 737.
Interestingly, with better ground clearance, everything is retained (I assume - I stand to be corrected) closer to the 6 o'clock position on the A319/320. The Pan Am "incident" noted by
Airbuba must have been a 737-200 so that's JT8D's which also had the accessories at 6 o'clock so they were very fortunate to make it round in their roulette game. Regarding the larger engines, as
lomapaseo notes, even if you protect the ancillaries moving them towards the core, distortion of the fan casing due to ground contact will then be an issue. Thinking about it, there have (as illustrated by
megan) been cases of turboprops and pistons brushing props on the runway during landing/go-around incidents/accidents - but it all goes back to Statistics in the end - rare in the jets.
All in all, it points to the simple fact that landing on your engines (for whatever reason) is definitely something that comes under the "that's a rather bad idea" category - and then re-aviating after such an event is even worse!!!!! Megan has it summed up perfectly -
"You can't completely design out human failures, or stupid."! Mmmmm, you ever flown with me
megan? - I relate well to your quip - particularly the latter bit of it!
Cheers,
H 'n' H