McDonnell Douglas / Boeing C-17 Proposed Variants

[Not James Stockdale]

I asked this question in a discord channel, replace the 4 engines with 2 x GE X from the big ass Boeing 777x engines? One of the reasons being future proof for spare parts and my guess it would use less fuel. I know it would take some engineering considering the engine placement and I guess the stol would also get lower ....and ofc the price...but if you would produce enough the amortisation should quite fast
it would look like a big version of the Japabese C-2
It's just me thinking out loud

The C-17's F117s are PW2040s with about 40,000 lbf of static thrust.

1. The USAF already operates 8 C-32As with PW2000 series engines, and large numbers will remain in civilian service with 757s for a very long time. I would expect the last freighter 757s to last until they are 60+ years old in the 2060s, at the earliest.
2. Having four engines gives certain operational benefits, like the ability to use inboard thrust reversers in flight and to use the outboard engines with differential thrust for maneuvering on the ground.
3. The larger engines could also be almost 2 m wider than the PW2000s, so they would come much closer to the ground despite the high-wing configuration. The PW2000s have 2.8 m of ground clearance for the inner pair and 2.4 m of ground clearance for the outer pair. The 777 has between 0.75 and 1 m of ground clearance.
4. Switching from four to two engines would probably require an entirely new wing structure, so I would expect the option to only be used in a very large-scale SLEP. The A330 and A340 initially shared a common wing structure to accommodate two or four engines, but that was heavy compared to purpose-built wings.

An interesting idea.
To add to the conversation: How much more do the 777 engines weigh compared to two current engines?
Does this require a redesign of the wing?

Thinking of the CH-53K logic I would think that a improved technology wing would be in order anyway.

The GE9X weighs 9.6 tons, so the weight of engines would rise from 12.8 tons to 19.2 tons, meaning an additional 6.4 tons. The GE9X is also 4.1 m in diameter, so ground clearance would probably be reduced to something like 0.6 m. Most engines in the 80,000 lbf thrust range weigh about 7 to 7.5 tons, while the PW2040s weigh about 3.2 tons. Overall weight would probably increase by up to 3 tons.

Older engines with around 80,000 lbf of thrust would include the PW4000-112s, Trent 800s, and GE90s from the 300 ton 777 variants and the Trent 900 from the A380. The Trents are the lightest and the GE90s are the heaviest, but none are in civilian use in very large numbers (between 100 and 150 airframes active or stored for all three 777 engine types). The Trent XWB is the newest engine near 80,000 lbf of thrust.