X-Planes Overview

The "X" designation, originally "XS" for eXperimental Supersonic, applied to a family of experimental aircraft not intended for production beyond a limited number built solely for flight research. The D-558-1 and -2 did not bear the "X" label but were clearly intended for the same purpose. This was also true of the non-X-designated lifting bodies, whereas the XB-70 was originally intended to be a production bomber, and the XF-92A was expected to be a production fighter. Neither of the two latter aircraft actually went into production, and both models became significant research aircraft, hence their inclusion here.