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An improved technique for drag prediction based on the analysis of wake flows is presented and demonstrated. The technique is demonstrated using three-dimensional flow field solutions obtained with several Euler codes. The flow field solutions are obtained for several wing configurations at both lifting and nonlifting conditions for a range of speeds. At subsonic speeds, the induced-drag prediction is shown to be more accurate (and virtually independent of numerical viscosity levels in the Euler flow field solutions) than the prediction obtained by surface pressure integration. At transonic speeds, a separate wave-drag prediction procedure allows the decomposition of the total inviscid drag into wave drag and induced drag. Preliminary results indicate that the drag-prediction technique in a slightly revised form may be applicable to predict induced drag and wave drag at supersonic speeds.

Preliminary results are presented of a study conducted to analyze the effects of several planform modifications on the aerodynamic characteristics of a high-aspect-ratio, natural laminar flow (NLF) wing. The study addresses the potential aerodynamic improvements available at both cruise and high angles of attack by use of swept wing-tip shapes. The swept wing tip appears to offer a viable addition to the lift of wing-tip designs which provide improvements in aerodynamic efficiency, with the added safety benefit of providing high angle-of-attack departure resistance.