Subsonic VSTOL Aircraft Configurations with Tandem Wings

The Prandtl-Munk theory predicts that tandem-wing configurations with large (vertical) gap have substantially lower induced drag than conventional wing-tail configurations of similar span, total lift, and dynamic pressure. Wind-tunnel tests were performed to check the theory for a configuration with equal-span tandem wings with gap/span = 0.25, and a stagger/span = 0.44. The tests show that the tandem-wing induced drag is even lower than theoretically predicted values. The application of tandem wings to VSTOL subsonic aircraft is discussed, and a new type of tandem-wing configuration is described. This employs extreme gull-type dihedral and anhedral on the rear wing. This feature reduces induced drag, and also reduces wetted area by eliminating the need for a separate vertical tail. Nomenclature