X-Planes from the X-1 to the X-60: An Illustrated Historyby Michael H. Gorn, Giuseppe De Chiara English | December 21, 2021 | ISBN: 3030863972 | 183 pages | MOBI | 14 Mb
X-planes: Research Aircraft, 1891-1970: A Unique Pictorial Record of Flying Prototypes, Their Designers and Pilots (Aviation Pioneers 1) By Hugh W. Cowin 1999 | 96 Pages | ISBN: 1855328763 | PDF | 45 MB