A High Precision Differential Force Balance and Experimental Method to Measure Small Fluid-Dynamic Forces Due to Small Geometry Changes,
DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER BETHESDA MD
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This paper describes the experimental hardware and method developed to measure the effect of fluid-dynamic resistance of placing a small fillet at the juncture of the main body hull or fuselage and the leading edge of an appendage. Since the conventional measurement method, in which total resistance of each configuration is measured separately and then compared, was considered inadequate to accurately measure this effect, a new method was developed, in which the separate configurations were tested at or near the same time under the same test conditions. This was accomplished by using a rotating fillet mechanism that was remotely actuated to change fillet configurations during testing. Thus the bias error that would occur during separate testing was reduced to a minimum. By making multiple measurements of the differential resistance with the high precision differential balance, developed specifically for the experiment, precision error was reduced to an acceptable level. Calibrations of the measurement system under laboratory conditions showed that the balance was able to measure a simulated differential resistance a small weight on the order of 0.4 N with a 95 confidence interval of or 0.015 of the total simulated resistance, large weight on the order of 200 N.