How much of the nacelle struts are structural? I'm asking because you show the struts as one continuous volume reaching down into the secondary hull that seems to include the outer skin. I can imagine their interior containing structural components that support the attachment of the nacelles along with engineering components for cooling, power transfer, etc. woven between them. If the forward and aft parts of the struts aren't structural, but coverings over engineering bits, might you save yourself a couple of meters here and there? Only the structural support elements need to meet at the axis of the secondary hull. The sheathing stops at the secondary hull's skin, and the engineering bits fan out and get where they're going by whatever route necessary.
Yeah, that's something like what I was thinking, too... the real question is "what do the structural elements look like?"
What you see below is my "first pass" on this.
My initial take on the nacelle pylons is that they've got a largish "box beam" in the center, with a pair of "C-channels" on the leading and trailing edges, all linked together with only intermittant drilled-out regions for pass-throughs of various types.
Note that, unlike MOST of what you've seen from me, what you see here as "solid" is intended to be just that... solid. Imagine these as extruded steel (or "duranium" or whatever) shapes, welded together and given a heavy coat of paint.
There's plenty of room inside the channels for running power and utilities and so forth, as well as having a "jefferies tube" (or more than one?) for access to hardware. Maybe even a lift of sorts for maintenance access to the nacelle?
Now, I plan to use something similar to that, but I'm not convinced I've got it "right" yet. Perhaps I go with three identical "box beams," or a single extrusion, or two boxes with a structural linkage between them?
The reason I want box-beams is that they're very effective at resisting torsion, something that more conventional open beams (like I-beams) aren't nearly so effective with. I see the nacelles as being under tremendous torsional force, so the nacelle pylon needs to be designed to resist that. Tensile force isn't nearly so much of a concern... the majority of force seen by this structure will always be torsion, around any of the three principle vectors.
I'm actually thinking about doing a little FEA problem to determine the best practical construction for this structure. Maybe even doing it with the "strongback" and dorsal included as well?
The one weak point in the TOS design which I can't see a practical way around is the interface between the primary hull and the dorsal. It's fine in any of the three major translational vectors (forward-aft, port-starboard, up-down) and for torsion in two of the vectors (yaw and pitch) but it's inevitably going to be fairly weak in roll. Unfortunately, there's nothing to be done about that other than adding additional structure to the dorsal (not in the way that was done for ST-09, by the way, which really doesn't help in roll, does it?). The Galaxy class "flair" (or a triangle with two dorsals at angles, perpendicular from the secondary hull axis) would be the best solution... but that's a different design, not the TOS Enterprise. Oh well...