“Supplant the C17 for the B-52 ... [replace engines] ... redesign so it has a weapons bay underneath, not out the back. ...”
Assuming that with the word “supplant,” taildragger means “replace B-52s with C-17s”:
Modifying airlifters to launch weapons has been proposed over and over. The projects are dropped when someone figures out the costs of modification usually end up higher than what a new aircraft would cost.
Redesigning airframes from the cargo-carrying role to the bomb-cropping role isn’t trivial. Actually modifying them might cost more than buying a new fleet - a constraint often encountered in the aviation world, even if we’re not talking about warplanes.
Uprated engines may not work: as utahb52 pointed out in post 26, added thrust might be welcome, but the pylons and wing structural components might not be able to stand the additional stresses and torque moments. If we’re thinking of the high-bypass-ratio turbofans that have graced many airliners in recent years, they may not even fit under a B-52’s wings ... current TF-33 powerplants are easy to access from the ground. And airframe manufacturing is a bit more complex that hot rods or monster trucks: one doesn’t just “beef up” an airplane.
Even if newer, bigger engines can be mounted without breaking anything, the control surfaces may not be large enough to assure the aircraft can be safely taken off, operated inflight, and landed.
Launching munitions from an aircraft in flight is somewhat more complex than kicking oil drums off the bed of a moving pickup truck. Not only does each separate munition have to be compatible in dimension and weight and connectivity to the airframe’s electrical/ hydraulic/ air systems, it must be capable of safe separation. Tests must be performed in flight over a properly safed and controlled range. And the testing must go beyond individual munitions, to explore every possible combination and loadout configuration. The B-52H already has its “book of approved munitions” partially written; any envisioned C-17 arsenal plane would necessarily start from zero.
A bomber requires different sensors and avionics, compared to an airlifter. Refitting them to a C-17 is a little more complicated than simply pulling out the airlifter’s black boxes and plugging in those from a bomber. Entirely different antennas would be needed, and most of the cabling (waveguides, for radar signals) would have to be replaced.
The current thinking is to replace the TF33 with eight CF34s, a civilian airliner version of the the TF34 engine used on the A-10, and on the long retired S-3 Viking.
With a 30% fuel savings, the B-52 would get an instant 30% increase in range.