Drag due to lift: Concepts for prediction and reduction

This article describes some of the fundamental ideas underlying methods for induced-drag prediction and reduction. A review of current analysis and de sign methods, including their development and common approximations, is fol lowed by a survey of several approaches to lift-dependent drag reduction. R ecent concepts for wing planform optimization, highly nonplanar surfaces, a nd various tip devices may lead to incremental but important gains in aircr aft performance. Focusing on relatively high-aspect-ratio subsonic wings, t he review suggests that opportunities for new concepts remain, but the grea test challenge lies in their integration with other aspects of the system.