THEORY OF THE FLIGHT OF AIRPLANES IN ISOTROPIC TURBULENCE - REVIEW AND EXTENSION
ADVISORY GROUP FOR AERONAUTICAL RESEARCH AND DEVELOPMENT PARIS (FRANCE)
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Recent experimental information on low-level atmospheric turbulence is first reviewed. It is suggested that the assumptions of homogeneity and isotropy customarily adopted for high altitudes are still useful in this regime, and that the integral scale is roughly equal to 910 of the altitude up to about 1000 ft. Next, the previously published theory of the power-series approximation as applied to the vertical component of the gust is extended to include all three velocity components simultaneously. Fourteen different one- dimensional input power spectra and cross spectra are found of which only five are important. Of these five, only one is a cross-spectrum involving two different velocity components u and v. Formulae for them are calculated and curves are presented. The gust derivatives required for calculating airplane response are defined and discussed, and the most important ones are shown to be simply the negatives of classical stability derivatives. Methods of approach for calculating the remaining ones are suggested.
- Fluid Mechanics