A Flight Investigation Of The Effects Of Compressibility On Applied Gust Loads

Two jet-propelled airplanes were flow at different speeds in rough air to investigate the effects of compressibility on applied gust loads at Mach numbers up to 0.68. The results indicated that no compressibility correction to the slope of the lift curve was necessary.

Six numerical examples are presented for steady, two-dimensional, compressible, nonviscous flow in centrifugal compressors with straight blades. A seventh example is presented for incompressible flow. The solutions also applye to radial-flow turbines with rotation and flow direction reversed. The effects of variations in following parameters were investigated: (1) flow rate, (2) impeller-tip speed, (3) variation of passage height with radius, and (4) number of blades. The numerical results are presented in plots of the streamlines, constant Mach number lines, and constant pressure-ratio lines. Correlation equations are developed whereby the flow conditions in any impeller with straight blades can be determined for all operating conditions.

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This paper presents the results of an analysis of approximately 100,000 hours of V-G data from one type of four-engine civil transport airplane to determine the magnitude and frequency of occurrence of the gust loads and gusts. The data were obtained during routine operations from 1947 to 1954 on five different routes. The normal accelerations for each of the five operations may be expected to exceed the value corresponding to the limit-gust-load-factor increment, on the average, twice (once positive and once negative) within the range of 5,000,000 to 22,300,000 flight miles. A derived gust velocity of 50 feet per second was exceeded twice within the range of 600,000 to 1,900,000 flight miles. The gust loads of the present operations were less than the loads experienced by other four-engine civil transports previously investigated, but the differences are not significant. The present data indicated only small differences due to seasonal effects and different operational utilization.