But before he could fly the 4,000-mile-per-hour space plane, Armstrong had to test his skills under extreme G-forces in a giant Navy centrifuge in Johnsville, Pa. He would be strapped in to a working model of the X-15’s cockpit, inside a gondola attached to the end of a 50-foot rotor arm. “An incredibly complicated and ingenious hook-up between gondola, centrifuge and an analog computer enables the pilot in the gondola to put the centrifuge through dizzying maneuvers that simulate the X-15’s expected flight behavior,” Griswold wrote.
(Though Armstrong took the X-15 on seven low-altitude test flights,
pilot Joseph A. Walker was the only person to fly the plane higher than
100 kilometers, the definition of a spaceflight. The X-15, retired in
1970, still holds the record for the fastest manned aircraft.)