Bates, William R.; Lovell, Powell M., Jr. & Smith, Charles C., Jr. Additional studies of the stability and controllability of an unswept-wing vertically rising airplane model in hovering flight including studies of various tethered landing techniques, report, November 6, 1951; (https://digital.library.unt.edu/ark:/67531/metadc58981/m1/1/: accessed June 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .