Optimum Transverse Span Loading for Subsonic Transport Category Aircraft

This study considers the overall system impact of the design transverse aerodynamic load distribution on future subsonic, transport category aircraft. The fundamental question revisited here concerns wing design ground rules. Should the wing be designed to favor an aerodynamically optimal, "elliptical" transverse span load that minimizes induced drag? Or, should the wing be tailored to have a reduced root bending moment in order to save structural weight at some expense of increased drag? The problem is examined at three levels of technical scrutiny: from a qualitative, rational basis perspective; from a quantitative, intermediate-fidelity parametric performance perspective; and from the results of a quantitative, coupled multidisciplinary optimization trade. The quantitative trades indicate that tailoring of the design transverse load distribution to favor a reduced wing root bending moment results in some structural weight savings, but at the expense of higher drag, increased fuel consumption, and reduced mission performance. These trades substantiate a different rational basis argument: a balancing test that will typically recommend the aerodynamically optimal design for all but the shortest-range aircraft.