↑ "Johnson, Clarence Leonard - National Aviation Hall of Fame". nationalaviation.org. Retrieved 12 April 2018. ↑ Area 51 - Black Jets: A History of the Aircraft Developed at Groom Lake, Bill Yenne 2014, p.95 ↑ "The Lockheed X-7". www.456fis.org. Retrieved 12 April 2018. ↑ Goodall and Goodall 2002, p.