Kermit G. Pratt, Floyd V. Bennett
Charts are presented for estimating the effects of variations in short-period stability characteristics of a rigid airplane on its root-mean-square vertical-acceleration and pitch-angle response to continuous atmospheric turbulence. From these charts the root -mean-square quantities in dimensionless form can be estimated for values of four other dimensionless parameters which describe the airplane short-period stability characteristics and the scale of atmospheric turbulence. The trends of the root-mean -square responses with each of the four parameters are discussed in terms of two significant combinations of the parameters involved. The charts are best suited for application to rigid unswept-wing airplanes of not more than 200-foot wing span flying at low subsonic speeds. It is believed, however, that useful estimates of first-order effects can be made for airplanes with other wing plan forms flying at high speeds. Analysis of the charts indicates that the variations of the vertical acceleration and pitch angle with the other parameters are largely determined by the damping ratio of the airplane and a relative-turbulence scale. Some examples of the application of these charts show that the vertical-acceleration response of a moderate-speed unswept-wing fighter airplane is increased by a rearward shift in the center of gravity, is not changed significantly with a change in altitude if the equivalent airspeed and true turbulence intensities are constant (effects of changes in Mach number are not included), and is increased by an increase in the geometric scale.
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