In joined-wing designs (below) the horizontal tail sweeps forward and joins the main wing, forming a strut. The tail is then in compression, reducing wing bending moments. If the tail is large enough to be positively loaded, some induced drag savings is achieved, while if it is carrying a down-load, the closed loop feature of the system minimizes trim drag. The concept was proposed by Dr. Julian Wolkovitch, who conducted numerous system studies, wind tunnel, and flight tests of the concept. (See references.) He envisioned applications for general aviation (see figure below), UAV's, and commercial aircraft. It has been studied by Boeing as a radar platform and by NASA for application to medium range transports.
Pfenninger's laminar designs with lifting struts exploit the nonplanar strut geometry primarily for structural weight and stiffness, although some induced drag reduction may be achieved.