Republic XF-91 Thunderceptor - Testing and Evaluation

Testing and Evaluation

The first prototype made its first flight on 9 May 1949, breaking the speed of sound in December 1951. It was later modified with a small radome for gunnery ranging (although not the "full" radome from the second prototype). The second prototype included the full radome and chin-mounted intake, but was otherwise similar. This airframe was later modified to use a V-tail for testing. With both the jet and rockets running, the aircraft could reach Mach 1.71, rather respectable for the early 1950s. Both prototypes completed 192 test flights over the course of five years.

The second prototype, 46-681, had an engine failure during takeoff from Edwards AFB in the summer of 1951. Republic test pilot Carl Bellinger escaped from the aircraft just as the tail melted off - total flight time was a mere 90 seconds. By the time fire apparatus arrived, driving seven miles across the dry lake bed, the tail section had been reduced to ashes. 46-681 was then fitted with a V or "butterfly" tail (more common on Beechcraft of the era) and was flight tested with this configuration. It was later used at Edwards AFB as a crash-crew training simulator, then scrapped.

As an interceptor the Thunderceptor was soon eclipsed by designs from other companies, but like the Thunderceptor none of these would go into production. The United States Air Force decided to wait the short time needed to introduce newer and much more capable designs created as a part of the 1954 interceptor project. The Thunderceptor, like the other interceptor designs of the era, had extremely short flight times on the order of 25 minutes, making them almost useless for protecting an area as large as the United States. The 1954 designs outperformed the XF-91 in speed, range, loiter time, as well as including the radar and fire-control systems needed for night and all-weather operation. The era of the dedicated day fighter-type interceptor was over.