Goodman, Alex & Wolhart, Walter D. Experimental Investigation of the Low-Speed Static and Yawing Stability Characteristics of a 45 Degrees Sweptback High-Wing Configuration with Various Twin Vertical Wing Fins, report, November 1, 1951; (https://digital.library.unt.edu/ark:/67531/metadc56210/m1/1/: accessed November 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .