Pushing the frontiers of aerospace technology involves imagination and the taking of risks. Many experimental aircraft tested critical new concepts, while many successfully disproved terrible ideas.

WC-135R Constant Phoenix on the runway. - Wikimedia Commons/U.S. Air Force AFCENT by Airman 1st Class Zeeshan Naeem, cropped and resized, Public Domain. There are some aircraft that will forever be ...

The Northrop X-4 Bantam had a tendency to pitch nose-down at high speeds—generally not a desirable condition for a plane. Experimental aircraft—usually designated by “X” markings in U.S. aircraft ...