A Philosophy of Strength Factors

IN aeronautical work the general engineering outlook in regard to the specification of strength factors has been supplemented by an appreciation of the unusually variable nature of the loads coming upon the aeroplane structure. The two questions have generally been treated as separate ones, and it is only recently that efforts have been made to bring them together by relating both to accident rates. In doing so we have on the one hand to allow for the frequency of occurrence of loads of different magnitudes and on the other hand to allow for the variation in strength among aeroplanes produced to a given design. The purpose of this report is to try, in a preliminary and elementary way, to weld these various aspects of the design of aeroplane structures into a logical and consistent whole—a philosophy of strength factors —and, by so doing, to reduce accident rates, to bring into better perspective some of our past problems, to point to ways of further development, and to prepare for making the fullest use of the speed and acceleration loading statistics now accumulating.