Basic Induced Drag Study of the Joined-Wing Aircraft

Abstract

J OINED-WING configuration was considered for the first time by Prandtl in 1924 [1]. The first attempt to build a joinedwing airplane was undertaken by the Moscow Institute of Aviation in the 1940s, when they redesigned a classic biplane called the Polikarpow Po-2 to create the joined-wing airplane [2]. More recently, the configuration was studied by Wolkovitch [3] and Kroo and Gallman [4] in the 1980s. A project described in [5] was inspired by these works. It consisted of a series of wind-tunnel tests with models of a small transport airplane (see Fig. 1). The most interesting result obtained in this project was that a greater L=Dwas achieved for negative angles of attack than for positive ones (see Fig. 2). This observation suggests that the front wing of the aircraft in a joined-wing configuration should be located on top of the fuselage and the rear wing at the bottom to obtain greater aerodynamic efficiency. This complicates the design because it is not possible to use the fin as a pylon for the rear wing and fuselages usually are not particularly high. Anyway, this front-high-joinedwing configuration can be considered in cases of small 2–4 seat general aircraft, small transport aircraft, and very large commercial double-deckers. Later, in the 1990s, a few papers on the joinedwing configuration were published [6], most of them focusing on mass-strength analysis.