Communicated by the Principal Director of Scientific Research (air), Ministry of Supply

Imomlbressibte Flow Summary.-The report presents the theoretical calculations of gust alleviation factor made for rigid aircraft and with one degree of freedom only (i.e., vertical motion). It is shown that for average gust lengths and for orthodox (tailed) aircraft the influence of thesecond degree of freedom (i.e., pitching) on the value of the gust alleviation factor is negligibly small, providing the pitching moment of inertia and damping are not unduly small. The influence of aspect ratio, the importance of the mass parameter and the gust shape on the values of the gust alleviation factor are shown. The large influence of the gust shape on the value of the alleviation factor makes the gust analysis by simple measurements of maximum aircraft acceleration inadequate, and the full records of the time-history of the aircraft are necessary. An alternative, more direct method of gust measurements is suggested. The inadequacy of the present gust alleviation curve in Air Publication 970 is pointed out and a suggestion for replacement of this curve by the curves calculated in this report is made.