C-Wing Aerodynamics

The optimal loading of this lifting system is shown in the figure below. The circulation of the main wing is carried onto the winglet so that the winglet is loaded inward. When the horizontal extension is added to the winglet, forming the "C" shape, the circulation is extended from the winglet as well, producing a surface that is loaded downward for minimum induced drag at fixed total lift. It is only when the lifting surface is extended to the centerline to form a box plane that the upper wing can efficiently carry an upload. This is because, as mentioned previously in connection with closed systems, we can superimpose a constant circulation ring on the closed system to redistribute the lift without changing the wake.

This download on the C-wing horizontal surfaces affects structural weight and trim and the implications for aircraft configuration concepts was intriguing.

This configuration was independently "discovered" by a genetic algorithm that was asked to find a wing of fixed lift, span, and height with minimum drag. The system was allowed to build wings of many individual elements with arbitrary dihedral and optimal twist distributions. The figure below depicts front views of the population of candidate designs as the system evolves. On the right, the best individual from a given generation is shown.

Ilan Kroo (kroo@leland.stanford.edu)