The Princeton Sailwing

Double-cloth sailwing supported by trailing edge cable with lift an drag coefficients right.

From A Comparison of the Aerodynamic Characteristics of Eight Sailwing Airfoil Sections by M. Maughmer (1979):

• The Princeton sailwing, which has been under development since 1948, is a unique, semiflexible wing intended to provide the practical ultimate in a light-weight, low-cost lifting surface suitable for a number of low- speed applications. 
• Basically, the structural configuration of the sailwing consists of a leading-edge spar with attached ribs which ideally form a rigid framework supporting a trailing-edge cable in tension. 
• A non-porous, non-stretchable cloth membrane, usually dacron, is then wrapped around the leading-edge and attached to the trailing-edge forming the upper and lower sail surfaces....it has been found that the aerodynamic efficiency of the sailwing can indeed approach that of a hard wing.

Compare with Chapter 5 From Circular Cylinder to Wing in The Secret of Flight.

Note that with a single cloth membrane, like an ordinary sail, the lift-to-drag ratio decreases from about 15 to 10 because of the effect of a one-sided leading edge (mast) to increase drag and decrease lift.