In the early period of the Cold War, the US was confronted with a difficult question: how to send bombers into the heart of enemy territory, handle the incoming fast fighter jets as well as long-distance missiles, and still stay alive in a world dominated by nuclear weapons. One method was that of the “penetration fighter” — a long-distance escort capable of clearing the way of danger and bringing its driver home safely.
With the XF-90, the Skunk Works of Lockheed, led by Kelly Johnson and Willis Hawkins, gave a response to that call. The images of the XF-90 seemed quite up-to-date for the time they were made. The team took concepts from the first jets and geometrically calculated the swept wings with an angle of 35 degrees, additionally equipping the aircraft with Fowler flaps, leading-edge slats, and the peculiar combination of afterburners with tip tanks. Even the tail parts were allowed more movements than before — changes that were meant to be beneficial for performance.
However, there was a negative side to every technological advance. The structure was made of 75ST aluminum, which is a more robust alloy than the standard 24ST, and the extra strength came with additional weight. The engines were not up to the same pace: the power of Westinghouse J34 turbojets, consisting of two runs, simply did not meet the airframe demand.
On paper, the figures seemed quite impressive — a theoretically very high speed of 665 mph, a range of 2,300 miles, and a ceiling of 39,000 feet — but practically, the performances of the XF-90 were lower than those of other airplanes the Air Force was expecting and the proposals of the rivals.
Trials of flight made those limitations very clear. The XF-90 was able to exceed Mach 1 speed only when diving; rocket assist was even required at times for take-off. Compared to the likes of McDonnell XF-88 and North American YF-93, it felt clumsy. When the Air Force chose the XF-88 and changed the strategic focus, the penetration-fighter idea lost fairly quickly, without much public attention.
Nevertheless, the reputation of the XF-90 was the one it gained from being a very durable machine. It underwent rigorous structural testing at the National Advisory Committee for Aeronautics with one of the prototypes, and another one was sent to the Nevada Test Site, where nuclear weapons experiments were conducted.
The effects were beyond expectations: fractures less than an eighth of an inch in size were the only damage caused by a one-kiloton explosion; the crushing of the nose stopped short of total failure in the case of a 33-kiloton blast; albeit the detonation that tore off the tail was quite strong at 19 kilotons, it still was not enough to scatter the aircraft in pieces.
After the incident, the staff estimated that the repair of the damaged aircraft to a flying state would take them approximately 106 hours.
Many years later, the staff of the United States Air Force National Museum in Dayton, Ohio, undertook the tireless task of locating, restoring, and putting on display the weathered and radiation-stained remains of the XF-90. Still in position, the exhibit is a physical, though very rare, memory of a design surviving the blasts that pose the greatest threat to most other similar ones.
Moreover, the aircraft, the XF-90, was never allowed to fly in the military, nor did it carry out its initial mission, but it did not leave aviation without a footprint. Its pros and cons were a factor that played in the mindsets of the times after it, one of those teachings that only theoretical trials can bring about.
The story of the XF-90 stands as a prominent example of how humans, by continually pushing the limits of engineering and, in a sense, even when failing, broaden the possibilities of technology.