Vortex structures and span loadings from alleviated-wake measurements

Abstract

In an effort to find efficient wing designs that shed non-hazardous vortex wakes, an analysis is made of data taken in the wakes of three configurations of a subsonic transport. The study begins with the observation that alleviated-wake configurations often shed vortex wakes that induce about the same rolling-moment coefficient on following aircraft of all sizes. In order to determine the span loadings that correspond to these downstream vortex wakes, the analysis first finds the vortex structures that make up the measured downwash distributions. An inverse Betz method is then used to derive the corresponding span loadings. Analysis of these span loadings, and consideration of the induced drag and the energy in various wakes, yields information on some of the characteristics and penalties associated with the design of wings for less hazardous wakes. It is recommended that tools be developed for an optimization process that includes drag, wing-root bending moment, weight, complexity, etc. and the design of vertical and horizontal lifting surface for vortex wakes that have an acceptable hazard. Nomenclature