Abstract
The basic fact is recognized that throughout the service life of an airplane there occurs a variety of landing conditions and, consequently, it is subjected to transient dynamic loads of varied time histories. Accordingly, a statistical analysis is proposed. The landing-gear impact load is regarded as a nonstationary random process. In this paper the ensemble means and the correlation functions of landing impacts are defined and their experimental determination from flight or drop tests is illustrated. From these the mean response (displacement, bending moment, shear, or stress), the root mean square deviation from the mean, and higher statistical moments are computed. The results are used to find the most probable maximum stress (at any point in the structure) attained in a given number of landings, or the most probable total number of landings a given aircraft can withstand. A stress envelope can be derived which represents the distribution of the severest stress in the structure for a large number of landings. A design based on such an envelope, statistically, will have a uniform factor of safety over the entire aircraft with respect to landings.
