Fluid-dynamics studies were made of simplified model fuel tanks mounted on a mechanism that simulated a wing undergoing torsional oscti-lations of a few degrees. The tanks were mounted as follows: vertically offset (pylon mounted) below the axis of oscillation; inclined to the horizontal as in a climbing or diving attitude; and swept with respect to the axis of oscillation as in a centrally mounted tank on a swept wing undergoing torsional oscillations. The effective moment of inertia of the fluid was determined experimentally for the various tank con¬figurations over a tank-fullness range from empty to full and was es¬sentially unaffected by the oscillation frequency of the spring-inertia dynamic system except when this frequency was near the lowest natural fluid frequency because of its own wave motion. Comparisons of the experimental and theoretical inertia solutions for full pylon-mounted tanks and centrally mounted swept-wing tanks shoved good agreement. Moreover, the theoretical solutions for full centrally mounted swept-wing tanks offer good engineering approximations for partially full conditions because of the small effect of tank fullness on the ratio of the mea tired effective moment of inertia of the fluid to the moment of inertia of the fluid considered as a solid. For partially full pylon-mounted tanks, the ratio of the effective moment of inertia of the fluid to the moment of inertia of the solid was small, and this inertia ratio increased rapidly with tank fullness greater than 75 percent and approached the theoretical values for the 100-percent-full tank.'nStudies of the effect of vertical, horizontal, and diffused baffles in a pylon-mounted tank revealed that the effective moment of inertia of the fluid was increased above that found in the unbaffied partially full tank. It was also found that the diffused baffle distributed throughout the interior of the pylon-mounted tanks produced high damping charac¬teristics for partially full conditions, whereas the use of the diffused baffle in a partially full, centrally mounted tank did not produce high damping characteristics.
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