Minimum Induced Drag

IT is fairly well known that for any given wing arrangement—monoplane, biplane, monoplane with end‐plates corresponding with an increasingly popular type of tail unit, etc.—there is a definite lift distribution associated with the minimum value of induced drag of which a particular span is capable. The theory giving the appropriate lift distribution and, what is perhaps of more general practical interest, the resulting induced drag coefficient, is perhaps not so well known and while numerical results for arrangements in common use have been published, novel arrangements require a knowledge of the underlying theory for their evaluation, and this is in any case useful as giving a clear grasp and understanding of the problem.