The "X"-Planes

The X-planes are a series of experimental United States aircraft (and some rockets) used for testing of new technologies and usually kept highly secret during development.

Below is a listing with relevent documents for each.

The X-5 (Bell Aircraft)

1.  The Bell X-5 Research Aircraft [67 Pages]

The X-20 "Dyna-Soar" (Boeing)

The X-20 Dyna-Soar ("Dynamic Soarer") was a United States Air Force (USAF) program to develop a spaceplane that could be used for a variety of military missions, including reconnaissance, bombing, space rescue, satellite maintenance, and sabotage of enemy satellites. The program ran from 24 October 1957-10 December 1963, cost US$660 million, and was canceled just after spacecraft construction had begun.

1. The Black Vault Encyclopedia Project Reference for the Boeing X-20 Dyna-Soar
2. Strangled Infant: The Boeing X-20A Dyna-Soar by Clarence Geiger