I'm wondering if it's practical to design and build a small composite aircraft that's as light as a metal one. It would seem possible given the very good strength to weight properties of foam sandwich construction, but I'm not seeing it in the weights of aircraft now being designed and built. Example: A Sonex has an empty weight of about 650 lbs with the VW engine. A composite Personal Cruiser weighs 650-750 lbs empty. The heavier cruisers do tend to have a heavier engine (Corvair) that accounts for about 50 lbs of the difference, but still . . . . The Sonex is longer, seats 2 instead of just one, and has a wing with 98 sq feet of area, vs just 76 sq feet for the Cruiser. The Sonex is bigger in every respect, yet weighs less. To build a Personal Cruiser with the Sonex's wider fuselage, extra seat and controls, and 20 more sq feet of wing and required additional tail volume--the empty weight would be at least 75-100 lbs more than the Sonex. That's a lot. The folks who market the Vision have suggested that aircraft could be built to LSA specs (meeting stall speed by adding LE slots, building with with graphite spar caps for reduced weight, etc), but the slots are a big aerodynamic price to pay when the Sonex achieves the same result simply by using more wing area (and possibly a more appropriate airfoil). Are the aircraft designs I've cited outliers, or are they good representative cases of glass and metal construction? Would it be practical to design and build a "plastic Sonex? of comparable size, weight, design load factor, and performance?