Free flight measurements of catastrophic water drop breakup

Results are reported for a free-flight drop breakup and impact experiment conducted in a rain and dust erosion facility in order to verify that the definition of catastrophic water-drop breakup corresponds to the elimination of the drops' potential for erosion in flight. The erosion facility is a ballistic range in which material samples are flown through rain, dust, or ice environments at speeds up to 15,000 ft/sec, suffer multiple-impact erosion, and are subsequently decelerated and recovered to measure erosion damage and crater morphology. Plots are presented which show the predicted minimum initial drop diameter vs. standoff distance from the surface of an aluminum insert in the impact model as well as the predicted number of impacts vs. effective standoff distance. To verify the predictions, twelve test firings were made, and the number of impacts on the recovered model as well as the predicted number of impacts vs. effective standoff distance. To verify the predictions, twelve test firings were made, and the number of impacts on the recovered model was counted after each test. The observed numbers of impacts are plotted against standoff distances, and good agreement is found between the experimental data and the prediction based on the criterion based on the criterion for catastrophic breakup.