Bound typescript (cover title: "Hays Rotor Patents on drop-center rotors, resilient hub structures, automatically unloading blades, variable blade twist, asymmetrical feathering, and tension loaded blade flaps") with drawings and black and white photographs. Compiled March 3, 1947, Box: 7, Folder: 8. Russell Randolph Hays papers, RH MS 564. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/278197 Accessed May 04, 2024.