laminar flow, causing rapid melting and rapid transition back to turbulent flow. Maximum achievement of 95% laminar flow over those areas was desired. However, the design effort was canceled due to the plugging problems. Pioneering data was obtained in the X-21 flight program, including the effects of surface irregularities, boundary-layer turbulence induced by three-dimensional span-wise flow effects in the boundary layer (referred to as span-wise contamination) and degrading environmental effects such as ice crystals in the atmosphere. Disposition Both X-21As ended up in storage at Edwards Air Force Base, California, where they gradually became derelicts, used primarily as photo targets. The remains can still be viewed, but no efforts have been made to recover either example for restoration or display. Specifications (X-21A) See also References Notes Bibliography Winchester, Jim. X-Planes and Prototypes. London: Amber Books Ltd., 2005. . "X-Planes Detailed Data – Northrop X-21A" Retrieved: 15 November 2017. External links Globasecurity.org – X-21 Laminar Flow Control aeroweb.brooklyn.cuny.edu – Northrop X-21A Plattner, C. M. X-21 Tests Laminar Flow Control Theory. // Aviation Week & Space Technology, June 24, 1963, v. 78, no. 25, pp. 52–62. Edwards Air Force Base X-21, Northrop X-021 High-wing aircraft Twinjets Aircraft first flown in 1963