Relative frequency of occurrence of different normal accelerations at the centre of gravity of aircraft in turbulence

Abstract

An examination is made of the relative .frequency of occurrence of different normal accelerations, at points near the aircraft centre of gravity of 5 different aircraft, from about 200 hours of research flying sub-divided into about 12 000 time periods mainly of about 1 minute. It is shown that the commonly used assumption of a Rayleigh distribution for vertical gust velocity maxima for each period gives poor estimates of the cumulative totals of all the periods for each aircraft. If, however, it is assumed that (i) the frequency of occurrence of different magnitudes of the maxima of the gust velocity vector is a Rayleigh distribution, (ii) the vector changes direction sufficiently slowly for the maxima of the components to occur at the same time as the maxima of the vector, hold for each period, the estimates of the cumulative totals of all the periods for each aircraft do not differ significantly from the measurements. Nor is there any significant difference between the measurements and the cumulative totals of gust velocity maxima in 36 traverses of severe turbulence encountered in 23 000 flying hours of civil aircraft operations.