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Fat Wings XF-91 Thunderceptor Was America’s First Supersonic Rocket Fighter, Never Made It

The years that came immediately after the end of the Second World War have been a time of great transformation for the entire world. With hopes and dreams fueled by the technological advancements achieved during the conflagration, the world’s powers continued an insane race that would eventually end with humans landing on the Moon, and countless advancements in other areas.
Republic XF-91 Thunderceptor 15 photos
Photo: USAF
One field of human activity that benefited from the race is aviation. Having become essential to military operations during the war, airplanes were now seen as wonder weapons that could bring the enemy to its knees in no time, and with very little damage on the friendly side. But to do that, airplanes had to be, above all, fast.

It was just two years after peace settled upon the world that Chuck Yeager climbed on board the Bell X-1, nicknamed Glamorous Glennis, and took off from the underbelly of a B-29 to make the first-ever supersonic level flight, effectively opening the doors to what would become common occurrence in the world of military and, for a brief time, civilian aviation.

It was however since before this historic moment that the military top brass asked for a supersonic fighter planes capable of intercepting Russian aircraft when the Cold War would grow hot. The call to arms was answered by Bell, Vultee, and Republic, among others, and resulted in some insane machines being created and tested on the ground and in the sky.

One of them is the XF-91 Thunderceptor. Designed by Republic Aviation (makers of smash hits like the P-47 Thunderbolt and F-105 Thunderchief), the Thunderceptor was supposed to be a machine powered by a mixed propulsion system, capable of accelerating faster than sound toward its target.

The propulsion system comprised a General Electric afterburner engine capable of delivering 6,700 lbs. thrust, and a Reaction Motors rocket with four combustion chambers capable of boosting that by an extra 6,000 lbs. The firing of the two systems should have allowed the airplane to reach a top speed of 984 mph (1,584 kph), well beyond Mach 1.

But it’s not necessarily the engine combo that made this plane stand out, but the way it is drawn. Its most distinctive feature is the shape of the wings - believe it or not, that was not only intentional, but also functional.

You see, Republic went for a swept wing design on their supersonic fighter concept, and such a configuration comes with dangers that, on account of the aerodynamics of the wing, especially at its tips, could send the aircraft tumbling in extreme cases. To fix that, engineers decided to make the wing surface increasingly larger as they moved toward the tips, a design called reverse tapered. Although effective in achieving the desired goal, it makes this plane one ugly-looking bird.

Republic managed to make two of these, and flew the first one in 1949. Two years later, the Thunderceptor flew past the sound barrier to become “America’s first rocket-powered fighter to fly faster than the speed of sound,” as the National Museum of the United States Air Force calls it.

Crazy as it was, the design was not to the military’s liking (like all the others made during that era), especially since it could only fly for under half an hour at a time, defeating its purpose as an effective interceptor. Shortcomings, the lack of funding, and the arrival of the North American F-100 Super Sabre, the first fighter jet capable of level supersonic flight, killed the Thunderceptor program.

Of the two made, only one remains, sitting inside the aforementioned museum ever since it was transferred from Edwards Air Force Base in 1955.
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About the author: Daniel Patrascu
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Daniel loves writing (or so he claims), and he uses this skill to offer readers a "behind the scenes" look at the automotive industry. He also enjoys talking about space exploration and robots, because in his view the only way forward for humanity is away from this planet, in metal bodies.
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