Nonplanar wings include configurations such as biplanes, box-planes, ring-wings, joined wings, and wings with winglets. Apart from configuration differences related to stability and trim, variations in nonplanar geometry represent one of the few major differences in aircraft conceptual design.

Such designs may be of interest because of their potential for lower vortex drag at a fixed span, a key constraint for many aircraft, including very large commercial transport concepts. However, several non-aerodynamic features are of interest as well including effects on stability and control, characteristics of wake vortices, and structural implications of the nonplanar design.

This paper reviews some of the concepts that have been pursued and discusses some of their possible advantages or disadvantages. We consider the potential of some of the concepts to improve performance incrementally or to change the configuration significantly.

Nonplanar wing concepts may be divided into a few categories based on their primary geometric or aerodynamic characteristics. These include: