NACA-ARR-L4121

Abstract

A number of samples of flight acceleration data taken by the National Advisory Committee for Aeronautics under a variety of operating conditions were evaluated to determine the total frequencies and the frequency distribution of atmospheric gusts. The samples include 1748 hours of operation by several airplanes of the domestic airlines of the United States, a Martin M-130 airplane of the Pacific Division of Pan American Airways System, and the Boeing B-15 airplane of the Arm Air Forces. These data are supplemented by V-G records, so that more than 9,000,000 miles of operation are represented. Samples taken on an Aeronca C-2 airplane at low altitude in the turbulent air of the earth's boundary latter are compared with similar samples taken on the Lockheed XC-35 airplane at high altitude within cumulus-congestus and cumulonimbus clouds. <br>Similar data of German origin have been reanalyzed and included for comparison. <br>It was concluded that the distribution of gusts within turbulent regions of the earth's atmosphere follows a substantially fixed pattern regardless of the source of the turbulence. The total frequencies are therefore governed by the total length of flight path in rough air, and operating conditions determine the total frequencies only by affecting the ratio of the length of flight path in rough air to total length of the path. Gust-load frequencies were found to be inversely proportional to airplane size. <br>It was further concluded that the gust frequencies can be applied with small error to the estimation of stress frequencies in the primary structures of airplanes. The results of the analysis are applicable to the fatigue testing of the primary structure of the airframe and to the estimation of the probability of encountering gusts of excessive intensity within any stated period of operation.