Introduction -- Symbols -- Fundamental theoretical considerations -- The principle of vorticity attenuation -- The effective aspect ratio of nonplanar lifting systems -- Determination of the span loading distribution for minimum induced drag -- Solutions for the effective aspect ratio of optimally loaded arcs -- Solutions for more complex systems -- The induced lift of nonplanar systems -- Practical application considerations -- Concluding remarks -- References.

The basic theory of the induced lift and drag of nonplanar, circulation lifting systems is investigated, and conformal transformation and electrical-analog techniques are developed for determining the minimum induced drag of arbitrary systems. Several complex systems are analyzed to illustrate the procedures. Problems attending the practical application of the results to airfoil design are discussed and possible solutions suggested.