7. Boeing X-32
The X-32 and X-35, the Most Exploitatively Named X-Planes, were concept demonstrators in a fierce flyoff to be renamed F for "fighter," as in Joint Strike Fighter. If precedent had been followed, they would have been named the YF-32 and YF-35, like the prototypes YF-16 and YF-17 of the Lightweight Fighter flyoff of the 1970s. But "Battle of the X-Planes" had such a great marketing ring to it. Flying an airplane and buying an airplane are two widely disparate activities. Bob Cunningham of General Dynamics’ pre-design group constantly preached to young engineers the Doctrine of Beauty: If the customer doesn’t like the looks of the thing, regardless of performance, he doesn’t buy. "And if he doesn’t buy at this point," Cunningham said, "it dies; it never makes it into hardware. In short, you can sell a beautiful design a lot easier than an ugly one." Cunningham’s team fielded the winning YF-16.
—J. Campbell Martin
8. Rockwell X-30
The National Aerospace Plane, the Worst Case of Technological Optimism, was an attempt to build a single-stage-to-orbit vehicle powered by a supersonic combustion ramjet. By the early 1980s, scramjet technology, some researchers argued, was ready to power an aircraft. The optimism proved not to be justified. The aircraft’s size, weight, and cost increased, while performance decreased. At the end, the X-30 had a 3,000-feet-per-second velocity deficit that would prevent it from reaching orbit. It was officially cancelled in January 1995, when Air Force participation ceased.
9. Bell X-16
The X-16 was not an experimental or research aircraft. The "X" designation was cover for its real mission: a high-altitude reconnaissance aircraft sponsored by the Air Force. The X-16 had long, swept wings, two jet engines slung under the wings, a bicycle landing gear with outrigger wheels under the wings, and a large payload of cameras and other reconnaissance equipment in the fuselage. Kelly Johnson of Lockheed’s Skunk Works, always ahead of his time, realized an unconventional design was required. This became the U-2, which is still used. The X-16 was cancelled before it ever flew.
10. Northrop XP-79B
Another example of Jack Northrop’s lifelong fascination with flying wings. This was his only attempt at a nearly tailless fighter, and, as usual with Northrop, it was innovative in a number of other ways as well. Jet powered and made largely of magnesium, its unusual configuration led to the widespread myth that it was designed as a "flying ram," blithely lopping off the wings and tails of enemy aircraft with its lethal reinforced wing. This was clearly false; Northrop intended the airplane to be fitted with an armament pack. Besides, any attempt to slice off pieces of an enemy would immediately throw the fighter into a Frisbee-like spin. The XP-79B had that tendency anyway, and promptly demonstrated it some 15 minutes into its first and only flight, spinning in and killing test pilot Harry Crosby. The little airplane’s entire flying career thus consisted of one takeoff and one fatal crash.
—Raymond L. Puffer