A flight-operable, truly modular aircraft has an aircraft core to which one or more of outer wings members, fuselage, cockpit, leading and trailing edge couplings, and empennage and tail sections can be removably coupled and/or replaced during the operating life span of the aircraft. In preferred embodiments the aircraft core houses the propulsive engines, avionics, at least 80% of the fuel, and all of the landing gear. The aircraft core is preferably constructed with curved forward and aft composite spars, that transfer loads across the center section, while accommodating a mid-wing configuration. The aircraft core preferably has a large central cavity dimensioned to interchangeably carry an ordnance launcher, a surveillance payload, electronic countermeasures, and other types of cargo. Contemplated aircraft can be quite large, for example having a wing span of at least 80 ft.