ILASS Americas, 20 th Annual Conference on Liquid Atomization and Spray Systems, Chicago, IL, May 2007 Multiscale Design of Rain Simulator K. Knasiak * , R. J. Schick and W. Kalata Spray Analysis and Research Services Spraying Systems Co. Wheaton, IL 60189-7900 USA. Abstract The United States Army is interested in building a rain test simulator. It must be able to simulate rain rates ranging from 1.07 - 14 mm/min. Furthermore, the drop size shall be in the range of 500 - 4500 µm. The simulator has to be designed to support two types of tests, rain resistance (top spraying) and water integrity (side spraying). The top spraying rain simulator was build and tested for the drop size and rain fall distribution with variable spray heights and rain rates. For each rain rate separate spray nozzle was chosen. The measured drop size fell within the desired size range. The measured rain fall distributions were the most uniform at the highest nozzle heights. * Corresponding author