Göthert & Röber. Systematic Investigations of the Effects of Plan Form and Gap between the Fixed Surface and Control Surface on Simple Flapped Wings, report, May 1949; (https://digital.library.unt.edu/ark:/67531/metadc64486/m1/1/: accessed December 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .