An aircraft subassembly that comprises a fuselage structure, comprising a first side, which comprises a first plurality of frame members, and a second side, which comprises a second plurality of frame members, the aircraft subassembly further comprising a pair of wings, attached to the fuselage structure, and a main-landing-gear system, having a single pair of wheels, consisting of a first wheel, having a first-wheel azimuthal-rotational-symmetry axis and a first-wheel mid-plane, perpendicular to the first-wheel azimuthal-rotational-symmetry axis, and a second wheel, having a second-wheel azimuthal-rotational-symmetry axis and a second-wheel mid-plane, perpendicular to the second-wheel azimuthal-rotational-symmetry axis, the main-landing-gear system additionally comprising: a sponson, connected to and extending outward from the fuselage structure and comprising: a central portion; a first main-landing-gear door, moveable relative to the central portion between, inclusively, a closed position and an open position; and a second main-landing-gear door, moveable relative to the central portion between, inclusively, a closed position and an open position; a first main-landing-gear assembly, connected to the first wheel; and a second main-landing-gear assembly, connected to the second wheel, wherein the fuselage structure further comprises a cargo-bay portion, having a cargo-bay-portion cross-sectional area CSA1, and a gear-bay portion accommodating at least part of the first and part of the second main-landing-gear assemblies (106,112) and at least part of the first and part of the second wheels (110, 116) the retracted state of the landing gear, the gear-bay portion having a gear-bay-portion cross-sectional area CSA2; the cargo-bay portion and the gear-bay portion are separated by a cargo-bay floor; the sponson has a sponson cross-sectional area CSA3; the sponson cross-sectional area CSA3, the cargo-bay-portion cross-sectional area CSA1 and the gear-bay-portion cross-sectional area CSA2 collectively form an aircraft cross-sectional area CSA4, and the sponson cross-sectional area CSA3 is 25% to 35% of aircraft cross-sectional area CSA4. a sponson, connected to and extending outward from the fuselage structure and comprising: a central portion; a first main-landing-gear door, moveable relative to the central portion between, inclusively, a closed position and an open position; and a second main-landing-gear door, moveable relative to the central portion between, inclusively, a closed position and an open position; a central portion; a first main-landing-gear door, moveable relative to the central portion between, inclusively, a closed position and an open position; and a second main-landing-gear door, moveable relative to the central portion between, inclusively, a closed position and an open position; a first main-landing-gear assembly, connected to the first wheel; and a second main-landing-gear assembly, connected to the second wheel, wherein the fuselage structure further comprises a cargo-bay portion, having a cargo-bay-portion cross-sectional area CSA1, and a gear-bay portion accommodating at least part of the first and part of the second main-landing-gear assemblies (106,112) and at least part of the first and part of the second wheels (110, 116) the retracted state of the landing gear, the gear-bay portion having a gear-bay-portion cross-sectional area CSA2; a cargo-bay portion, having a cargo-bay-portion cross-sectional area CSA1, and a gear-bay portion accommodating at least part of the first and part of the second main-landing-gear assemblies (106,112) and at least part of the first and part of the second wheels (110, 116) the retracted state of the landing gear, the gear-bay portion having a gear-bay-portion cross-sectional area CSA2; the cargo-bay portion and the gear-bay portion are separated by a cargo-bay floor; the sponson has a sponson cross-sectional area CSA3; the sponson cross-sectional area CSA3, the cargo-bay-portion cross-sectional area CSA1 and the gear-bay-portion cross-sectional area CSA2 collectively form an aircraft cross-sectional area CSA4, and the sponson cross-sectional area CSA3 is 25% to 35% of aircraft cross-sectional area CSA4.