The Response of an Airplane to Random Atmospheric Disturbances

Citation

Diederich, Franklin Wolfgang (1954) The Response of an Airplane to Random Atmospheric Disturbances. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/XPKW-QH24. https://resolver.caltech.edu/CaltechETD:etd-12102003-105523

Abstract

The statistical approach to the gust-loads problem is extended by considering the aerodynamic forces due to the lateral and longitudinal variation of instantaneous gust intensity and using them in dynamic analyses of rigid and flexible airplanes free to move vertically, in pitch, and in roll, based on the assumptions of stationarity of the process (in the statistical sense) and of linearity of the forces involved. The effect on the wing stresses of the interaction of longitudinal, vertical and lateral gusts is considered. The method of analyzing the rigid-body motions is similar to that used for analyses of the dynamic stability of airplanes, in that the equations of motion are referred to stability axes and expressed in terms of conventional stability derivatives. The method of analyzing the dynamic effects of structural flexibility consists of an extension of a numerical-integration approach to the static aeroelastic problem and is in a form which offers the possibility of calculating divergence and flutter speeds with relatively little additional effort. The mean-square values, correlation functions and power spectra of some of the aerodynamic forces required in this type of analysis are calculated for certain special correlation functions of the atmospheric turbulence and certain special lift distributions. It is shown, for instance, that the mean-square lift is substantially reduced due to the difference in instantaneous intensity of the turbulent velocity along the span if the span is relatively large compared to the integral scale of turbulence, but that the mean-square pitching moment is substantially increased if the tail length is relatively large. Also, the wing stresses due to vertical, horizontal and side gusts are shown to be statistically independent under certain conditions.

Thesis Files