A procedure for evaluating the spacewise variations of continuous turbulence on airplane responses.

Abstract

As airplanes become larger and more flexible, they become more susceptible to dynamic excitation due to spacewise variations in gust loading over the major aerodynamic surfaces. An analytical procedure is derived to account for spacewise variations in gust velocity on airplane dynamic responses. The gust velocity field is assumed to be random in the stationary Gaussian sense, and is described in three orthogonal components by appropriate cross power spectral density functions. The cross power spectral density functions are derived from a standard form of gust velocity autocorrelation function. This assumption implies that the turbulence model is frozen in time, random in space. The autocorrelation function is used to generate a gust spectral matrix for use in airplane dynamic gust analysis. Finally, the procedure for obtaining the gust spectral matrix, which is a matrix of gust cross power spectral density functions, is reduced to use of a single chart and simple arithmetic. This procedure is ideally suited for digital computer look-up and computation. The gust spectral matrix is wholly consistent with the one-dimensional power spectral analysis procedures in current use, and will reduce to identical results when variations in gust velocity normal to direction of flight are ignored. The application of this procedure to airplane continuous turbulence analyses requires the computation of the complex frequency response functions for gust loading on individual aerodynamic panels.