Kuhn, Richard E. & Draper, John W. Investigation of effectiveness of large-chord slotted flaps in deflecting propeller slipstreams downward for vertical take-off and low-speed flight, report, January 1955; (https://digital.library.unt.edu/ark:/67531/metadc56039/m1/1/: accessed October 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .