1880. The Effect of Entrapped Air on Moment of Inertia Measurements


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G Jones: 1880. The Effect of Entrapped Air on Moment of Inertia Measurements. 1989.



At the 1987 International Conference of the Society of Allied Weight Engineers, the point came up that the effect of ambient air on moment of inertia measurements was an area that needed further study. Since China Lake NWC Environmental Engineering Branch, headed by Steven N. Tanner, owns a large vacuum chamber, I undertook to do some moment of inertia measurements with the effect of ambient air removed. This study led to the derivation of a formula for estimating the effect of ambient air on moment measurements. I also discovered some valuable techniques for performing measurements on low mass density items, test items with very small moments of inertia and test items with moments of inertia larger than the advertised maximum measurement capability of the Space Electronics KGR 300. I will state the most important findings right up front: The formula for estimating the moment of inertia contributed by entrapped ambient air is given by Iea = r/45 (L^3.5)(H^l.5) where the test object is a rectangular plane, r is the density of the ambient air, L is the length of the plane, H is the height of the plane. I call this relationship Spike’s rule for determining entrapped air moment of a planar solid.


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