An investigation of the aerodynamic characteristics of planar and non-planar outboard wing planforms

Abstract

The outboard planforms of wings have been found to be of prime importance in studies of induced drag reduction. This conclusion is based on an experimental and theoretical study of the aerodynamic characteristics of planar and nonplanar outboard wing forms. Seven different configurations; baseline rectangular, elliptical, swept and tapered, swept and tapered wth dihedral, swept and tapered with anhedral, rising arc, and drooping arc were investigated for two different spans. Span efficiencies as much as 20% greater than baseline can be realized with nonplanar wing forms. Optimization studies show that this advantage can be achieved along with a bending moment benefit. However, parasite drag and lateral stability estimations were not included in the analysis. The induced drag benefits are believed to accrue from the movement of vorticity away from the center of span line. Self-induced velocity components from the nonplanar lifting surface could conceivably alter the downwash distribution enough to lower the induced drag. The importance of wake curvature to account for the nonplanar alignment of the vortex sheet is also stressed. Flow surveys show the vortex roll-up. An extensive comparison of the separated flow behaviour of the configurations is also documented with flow visualization photographs.