Hey gang, don't get too far ahead of yourselves...
All the inlet/engine combinations you're talking about here are dependent on the design of the wing/fuselage. As pointed out up above that's not the premise here.
What you need is something evolutionary. If you're going to just slap a new engine and pod on a 757 wing and hope for it to go supersonic everything that engine needs from an aerodynamic standpoint is going to have to be on that pod. You can't count on the airframe (at least if you want to have it resemble a 757 in any shape or form).
So this pod is going to have to do several things: 1. House the massive GE90 engine. 2. Allow for the mass flow of the engine. 3. Compress the airflow down to subsonic speed. Just off the top of my head I'd say this pod is going to be about the size of 737 fuselage.
so it's probably not going to fit under our unredesigned 757 wing......
Would probably be smarter to start with an engine that's designed for non-augmented supersonic cruise, say the F22 engine. Hard to say how many we're going to need since our 757 wing is so supersonic unfriendly, but lets go with 6 for starters. Since this engine is considerably smaller than the GE90, we can pod up the engines in a side by side fashion ala B-52 only with 3 to a pod vs 2.
To get the mass flow slowed down before it enters the engine we're going to need a pod say 2.5 times the engine length. I envision the actual engine section being underneath the wing with the inlet section protruding out front.
Ok, now what's this massive flat topped pod going to do when we go to rotate? It's going to blank out a good amount of wing acreage that's what.
Folks you can't take a subsonic optimized airframe and make it supersonic cruise simply by putting a supersonic engine on it. The airframe needs to be optimized for the supersonic cruise condition. Has anyone seen a supersonic airframe where the engine/inlet were not integral to the airframe design? I'm not aware of one, although it's commonplace in subsonic airliner designs.
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