Letter from R. H. Prewitt, Committee S-2, Helicopters, Society of Automotive Engineers, July 14, 1947, Box: 5, Folder: 16. Russell Randolph Hays papers, RH MS 564. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/278168 Accessed October 10, 2024.