Wow, this thread really blew up! Based on the last simple glider design I posted, I didn't expect anything like this response.
I did a preliminary loft of the fuselage and a side and top view based on the loft and a guess at the wing:
Some notes and comments:
* The span and length are the same as the Mini Max, but the wing area is a bit less; 89 versus 112.5. However, on the Mini Max a lot of that area is out at the tip and isn't working very hard because of inherent tip losses. So I'm not particularly worried about the takeoff and landing speeds.
* Observe that the wing spar carrythrough takes up considerable cockpit volume. This is just one of the packaging realities of a cantilever single-seater. To place the spar under the pilot's knees I had to move the wing about 7" further forward than on the Mini Max. To compensate, the engine is moved forward a little, and the aft fuselage would have to be a bit lighter than on the Mini Max. I think that there is enough flexibility in the design of the engine mount and the location of ancillary components to make the CG come out in a reasonable spot. This might also make the airframe more amenable to a heavier powerplant like one of the B&S clones with a redrive.
* The pilot is the standard Darryl Stinton model scaled to 6'2". For a tiny airplane like this, I wouldn't want to try to design it for any larger pilot.
* The fuselage encloses a lot more volume than the Mini Max. However, there will be a lot less parasitic drag from struts, wires, and other protuberances. So the overall cruise drag is probably a lot lower.
* As sleek as this thing looks, it would be very lightly built, basically a carbon fiber bubble in the shape of an airplane. When the engine is running you'd see the lighter parts of it shimmer like a soap bubble in the wind. The VNE would not be very high, probably 100 - 115 mph. Rule zero is never let epoxy resin touch your bare skin. Rule one is, don't crash.
* As I proposed earlier, the wing is a combination of moldless foam core (MFC) D-tube and fabric covered ribs. My reasoning is that air is lighter than styrofoam even if it is partitioned by the occasional web of carbon fiber. However, you'd have to be careful about fully encapsulating the foam core of the D-tube to protect it from attack by chemicals used in later finishing processes. Plenty of LongEZs survive being painted, so it's probably not that much a problem.
* The aileron/flaperon is MFC and goes pretty much full span. It is driven at the inboard end and hinged on four sections of extruded piano hinge. The hinge pop-rivets to inclusions of Garolite under the composite skin. The aileron is constant section for simplicity.
* The wing section is an RIFPIB (round in front, pointy in back) loosely based on the 23000 series, and jiggered as necessary to accommodate the constant section aileron and drag spar. It probably sets a real aero engineer's teeth on edge, but it's not nearly as bad as what passes for a wing on many ultralights.
* The tail surfaces are MFC, and probably semi-permanently attached. The tail span is 90" which is probably okay to trailer if you're careful.
* No, this isn't a real FAR 103 ultralight. You could probably bring it in near the Mini Max's 280 lbs, but I doubt you could make it lighter. But you could probably get it within range of a strategic game of liar's dice. The FAA would probably only check if you crashed it, and it's doubtful they'd bother even then if they weren't certain they'd found all the pieces.
* If you squint your eyes a bit, you see that one wing is about 7/8" further forward of the other. That lets the wings be mirror images of each other but still allows the wing spars to overlap inside the fuselage. Do not confuse symmetry for balance.
* The configuration I've drawn is a razorback, but a lower fuselage top and a bubble canopy would not be beyond reason.
* If you really wanted to make this thing into a subscale warbird replica, it wouldn't be that hard to customize the wingtips and flaperon trailing edges to achieve something like the desired effect. P40, Hellcat, and Spitfire would take only minor tweaks. For a P51 you could put a little scoop and oil cooler under the belly, but a real engine coolant radiator is probably out of the question.